Effect of the FIFA 11+ soccer specific warm up programme on the incidence of injuries: A cluster-randomised controlled trial.

BACKGROUND: Soccer players incur injuries that typically affect their performance. Injuries are caused by intrinsic and extrinsic factors that call for multifactorial preventive interventions. The study examines the impact of the FIFA 11+ warm up programme on the incidence and severity of injuries in second division soccer players in Rwanda.
METHODS: Twelve teams (309 players) were randomised in the intervention group and 12 teams (317 players) in the control group using a cluster randomized controlled trial with teams as the unit of randomization. Intervention group teams implemented the FIFA 11+ soccer specific warm-up programme during training and matches at least three times a week over seven months of the Rwandan soccer season. Control group teams continued with usual warm up exercises. The primary outcome of this study was the overall incidence of training and match injuries. Injuries, training and match exposure as well as severity categories were recorded per the F-MARC guidelines.
RESULTS: A lower proportion of players sustained injuries in the intervention group (52%) compared to the control group (63%) (Odd ratio: 0.7; 95%CI: 0.5-0.9). A significantly lower rate ratio was observed in the intervention group for overall (RR = 0.6; 95%CI: 0.5-0.8) and match (RR = 0.6; 95%CI: 0.5-0.8) injuries. Compliance to the injury prevention programme was 77%. In the intervention group, the incidence of injury was similar across all teams and across the medium and highly compliant teams. There was a statistically significant 55% and 71% reduction of the rate of moderate and severe injuries in the intervention group respectively.
CONCLUSION: The 11+ warm up injury prevention programme resulted in a significant reduction in the odds of sustaining injuries. In addition, injuries sustained were less severe. The programme should be rolled out to all teams in Rwanda and may well result in a decrease in the incidence and severity of injury in similar contexts. TRIAL REGISTRATION: Pan African Clinical Trial Registry (PACTR201505001045388).

RCT Entities:   Population Interventions Outcomes

Introduction

The incidence of injury in soccer players is high at all levels and ranges from 1.2 to 18.8 per 1000 hours [1-3]. For individual soccer players, the loss of income due to injury may have severe consequences as alternative employment possibilities may be decreased, particularly in low-income countries [4]. Effective injury prevention is therefore an important goal for professional teams. Injuries generally occur more frequently during matches than during training and most commonly in the lower extremities [5-7]. Sprains, strains and contusions are the most prominent types of injuries [8-10] resulting in extended periods of absence from training and match participation and lead to medical and rehabilitation expenses [11, 12]. Loss of key players due to injuries may also have an impact on the performance and success of teams [13]. There is therefore a constant need for injury prevention studies to identify the effectiveness of prevention programs on actual incidence of injury using prospective methods.

Studies have examined the effects of several interventions in preventing injuries in soccer using one or more strategies [14-20]. An orthosis have been reported to be supportive after previous ankle injuries but no effect was found for initial injuries [15, 16]. There is also good evidence supporting balance and proprioceptive exercises for preventing recurrent ankle sprains [15, 17, 18] and ACL injuries [19]. In contrast, stretching and flexibility exercises did not reduce the risk of muscle and tendon injuries [20, 21]. Similarly video-based awareness interventions did not have any effect in the reduction of the number of soccer injuries [22]. Reliable evidence is available supporting the impact of Nordic eccentric hamstring exercises to prevent hamstring injuries [20, 23–25], nevertheless strengthening exercises were not found to be effective in preventing other soccer injuries [26].

Due to the complexity of the game and the multi-component aetiology of injuries, multimodal interventions have been recommended [27]; programmes incorporating core strength, balance, coordination and plyometrics have been reported to reduce overall injuries [28, 29]. Encouraged by these studies, the Federation of International Football Associations (FIFA) developed a multi-component soccer specific injury prevention intervention programme [30]. The FIFA 11+ injury prevention programme was developed by the group of experts commissioned by FIFA to reduce perceived intrinsic risk factors for injuries in soccer [30]. The programme is composed of 15 evidence-based exercises targeting strength, balance and coordination performed in sequence during warm up. The three components involve: 1) slow running and dynamic stretching, 2) six sets of exercises targeting the trunk and legs with three progression levels and 3) running drills with increased speed with different complexity of movements. The exercises are recommended to be performed at least three times per week [30]. The FIFA 11+ programme increased general lower limb strength as measured by countermovement and squat jumps [31], increased peak torque of concentric and eccentric hamstring strength [32], leading to improvement of neuromuscular control and the correct alignment of the hip, knee and ankle joints in joints during dynamic activities in young athletes [33]. Therefore the programme may play an important role in preventing lower limb injuries [18, 21, 24–26, 34–36].

At the time of this study, the positive impact of the FIFA 11+ warm up in preventing injuries had been studied with only 4 randomized controlled trials (RCT) available [37-40]. Since this time, others have concluded that the FIFA 11+ programme is effective for soccer players of different ages and levels [41-43]. Among the four RCTs that assessed the effect of the FIFA 11+ programme on the occurrence of injuries, three were conducted among male soccer players. Two of them were conducted among youth [38, 39] while one was conducted among veterans [40]. In Nigeria, a study randomised 20 youth teams into an intervention group that performed the FIFA 11+ warm-up programme (10 teams with 212 players) and a control group instructed to continue with their standard warm-up (10 teams with 204 players) [38]. A significant reduction in incidence of all injuries and lower extremity injuries was observed in the intervention group compared to the control group. However, the study did not find any significant difference in specific injuries such as in the thigh, knee, and ankle. Further, the study did not have any effect on the severity of injuries and did not specifically impact incidence of contact or non-contact injuries [38]. Another RCT of 1525 collegiate male soccer players from the USA demonstrated the protective effects of the FIFA 11+ in reducing injuries [39]. The intervention group players (n = 675) were instructed to perform the intervention three times per week for the full season. The control group players (n = 850) used their standard warm-up routine. The intervention reduced overall injuries by 46% and significantly reduced time loss due to injuries. Although the study shows the effectiveness of the warm- up programme, collegiate level teams had less exposure instances as they only participated in 18 matches and completed 51 practice sessions [39]. In addition, the collegiate-level season was only five months in length, which is shorter compared to most professional seasons lasting eight to ten months [39].

The two studies conducted in youth show that the intervention could reduce the incidence of overall, match [38] and training [39] injuries. Though the studies found a reduction in lower limb injuries, no significant difference was observed in the incidence of specific regional injuries in the thigh, knee and ankle regions. One study reported a reduction in time lost due to injuries while the other one did not find any effect on the severity of injuries.

It was therefore important to examine the intervention programme in a different population. The Rwandan second division youth soccer league is an amateur newly established league with relatively limited competitive experience, potentially predisposing players to more injuries and the FIFA 11+ had not been used in Rwanda. The training context and implementation of the FIFA 11+ programme in a population with limited experience with the warm up and relatively limited intensive soccer experience was of interest. Therefore the aim of this study was to determine the impact of the FIFA 11+ warm up programme on incidence, location, and severity of injuries in amateur second division soccer players in Rwanda.

Methods

Design and ethical approval

A cluster-randomized controlled design was used in this study. The study was approved by the Faculty of Health Sciences Human Research Ethics Committee from the University of Cape Town (HREC/REF: 683/2014) and registered in the Pan African Clinical Trial Registry (PACTR201505001045388). The Federation Rwandaise de Football Associations (FERWAFA) and the clubs gave permission to conduct the study while coaches and players (parents or guardians of the under-18 players) signed consent forms indicating their agreement to participate in the study. Teams were randomized rather than players as implementation of the programme was at the team level.

Participants

Soccer players from all the 24 Rwandan Second Division teams registered in the 2016 season were invited individually to participate in the study. There were 630 players who were eligible for recruitment in their respective teams. Teams registered a mean of 26 (SD = 3) players, ranging between 21 and 37 players per team. The mean age of the players was 20 (SD = 1) years old. Players were relatively inexperienced with a mean of three years playing soccer, while the most experienced player had only six years playing experience. They reported a mean of 2 (SD 1) years in the second division and the same experience in their current team of 2 (SD 1) years. The mean body mass of the players was 65 (SD = 4) kg, mean stature was 169 (SD = 4) cm and mean body mass index (BMI) of the players was 22.6 (SD = 0.9) kg.m-2.

Sample size calculation

Sample size calculation was based on the prevalence study conducted by Twizere [44] who reported that approximately 70% of soccer players in Rwanda sustained injuries in a year. Using this estimate and targeting a 20% reduction of injuries using power of 90% for generalised linear regression model and two-tailed alpha of 5%, a sample size of 125 was required per group. Taking into consideration the design effect of two for cluster randomization, the minimum number of players needed was 217 in each group. The mean number of 20 players per team would be sufficient given the intra-class correlation of 0.03 [45].

Randomisation and allocation of the participants

Random sampling was used to allocate the 24 teams to the study groups. The numbers representing the the 24 teams were placed in sealed envelopes with an equal opportunity of being selected for groups. A research assistant selected the envelope for both groups drawing one by one to achieverandom allocation by team to either the intervention group or the control group. The principal investigator, assisted by the Rwanda soccer technical director, supervised the randomization process.

Inclusion criteria

Players who had contracts and licenses from the teams enrolled to play in the second division were included in the study. Players with pre-existing injury at the beginning of the season were included, however data related to the pre-existing injuries were not included in data analysis. Injury and exposure data were obtained for all the participants.

Demographic data: A self-designed form was developed to gather demographic data and information pertaining to the coaching or playing experience.

Training exposure registration form: Coaches were provided a standardised exposure form developed by FIFA2 to record detailed information related to duration of training and player involvement. Any form of physical activities supervised by the coach was recorded as training exposure time in minutes. The duration of the training was recorded from the start of the warm up to the end of the cool down session [46]. The research team collected the forms every two weeks.

Match exposure form: Match exposure was gathered from the referees’ reports submitted to FERWAFA. Match exposure time was defined as the amount of time the player was involved while the team played against another team.

Injury report form: An injury report form was completed by the team medical personnel to collect data pertaining to the incidence of injuries [47]. Definitions of the type, anatomical location, severity and circumstance of injury were provided at the back page of the form. The form was developed and used during major FIFA tournaments and Olympic games [48] and has been extensively used in other studies [49]. For example an injury is defined as any physical complaint that resulted from soccer participation whether in training or match. It does not necessarily mean that there is a need of medical attention. The severity of injury was classified according to the number of days of absence from full soccer participation due to injury. Injuries that resulted in an absence from training or matches for 1–3, 4–7, 8–21 and more than 21 days were classified as “minimal”, “mild”, “moderate” and “severe” injuries respectively [50].

Intervention

Control group

Coaches of the teams in the control group were invited to attend a training on basic first aid and emergency procedures for one day. The coaches received training from the researcher on basic first aid and emergency procedures. The training covered topics relating to the occurrence of injuries, field assessments, and phases of rehabilitation. First aid for injuries affecting specific body parts (ankle, knee, hip, groin, hamstring, hand and head) including concussion were also discussed. The discussion focused on specific conditions that affect players on the field such as nosebleeds, eye and dental injuries. They were requested to continue with the way they usually organise the warm up and practices for their players. There was no specific warm up regime in the control group. None of the control group coaches were familiar with the FIFA 11+ warm up programme. Typically the soccer training started with a warm up, followed by technical and/or tactical drills. However, depending on the period of the season physical training may include specific exercises for cardiovascular endurance, muscle strength, coordination and speed for performance.

Experimental group

Procedure. During the pre-season period, coaches, players and medical personnel of all the second division teams in the experimental group were invited to attend an instructional meeting to present the purpose of the study to clarify roles. An instructor recognized by the Confederation Africaine de Football (CAF) introduced the concepts of injury prevention, the development, and use of the FIFA 11+ injury prevention programme. The FIFA 11+ involves slow speed runs combined with dynamic stretches; followed by exercises designed to strengthen the trunk muscles and balance exercises targeting the lower limbs; and finally running at an increased speed including different drills. A power point presentation and video were used to describe each exercise and in-depth explanations of the appropriate movements and positions were presented (S1 Appendix). Coaches also took part in practical sessions performing each exercise while the instructor provided corrections for flaws in technique. On the third day of the training, the coaches played the roles of both the instructor and the player. Coaches were provided with copies of the FIFA 11+ manual and cards as well as a DVD for further reference. Coaches were requested to organize the FIFA11+ programme as a warm up for the players in their teams at least three times a week. The research team collected completed training exposure and injury forms every two weeks.

Compliance and follow up

The instructor and the principal investigator visited the intervention group coaches once a week for the first month of the season, followed by monthly visits to foster implementation and compliance. Additional instructions were provided where necessary. The research assistants collected the completed forms twice a month. The medical personnel recording the injuries and research assistants were blinded to the group.

Statistical analyses

Descriptive statistics were used to present baseline characteristics. A weighted independent t-test was used to assess the difference in the demographic characteristics of the players between the two groups. The primary outcome with respect to efficacy of the FIFA 11+ warm up programme was the comparison of incidence of overall, training and match injury per 1000 hours of exposure with a 95% confidence interval between the intervention and control groups. Comparison of injury rates (Rate Ratio, RR) by study group was based on a team-adjusted Poisson regression analysis fitting the generalized linear regression model. Compliance was computed based on each team’s implementation of the FIFA 11+ sessions throughout the season as a percentage of total training and match sessions and categorized as high compliance (> 75%), medium compliance (50% to 74%), or low compliance (<50%). The influence of compliance on the injury outcome was also analysed. Additional analyses were conducted for region of injury, lower limb injury location, and the severity of injuries. The categories of the severity of injuries were reflected by days of absence from full soccer participation [50]. Microsoft Excel (Version 2000, Microsoft, Redmond, Wash.) was used to capture the data. Data analysis was carried out using “Statistica” data analysis software, version 13.2, Dell Inc. and the Statistical Package for Social Sciences (SPSS) for Windows, version 21.0, SPSS Inc, Chicago, USA.

Results

Of the 25 teams that participated in the 2016 second division league, 24 (630 players) agreed to participate in the study and were randomised (intervention 12 teams, 312 players; control 12 teams, 318) (Fig 1). Five players (4 intervention, 1 control) were lost to follow up. No player was injured before the start of the season.

Fig 1

Flow chart of participants through trial.

Characteristics of players in the intervention and control group

The independent t-test was conducted after assessing the normality of data and adjusting for clustered teams. There were no statistically significant differences in the demographic characteristics of the players from the intervention group or control groups (Table 1).

Table 1

Demographic characteristics of players in the intervention and control groups.

Characteristics	Intervention Group	Control Group	p-value
	Mean (SD)	Mean (SD)
Age (years)	19.9 (1.5)	19.7 (1.4)	0.089
Soccer experience (years)	2.9 (0.8)	3.0 (0.9)	0.328
Second division experience (years)	1.7 (0.7)	1.9 (1.0)	0.131
Current club experience (years)	1.5 (0.7)	1.7 (1.0)	0.223
Weight (kg)	65.3 (3.5)	64.4 (4.6)	0.206
Height (cm)	169.5 (3.5)	169.2 (4.0)	0.486
Body Mass Index (kg.m-2)	22.7 (0.8)	22.5 (1.0)	0.188

Training and match exposures

Players in the intervention group completed 61043 hours of training and 4290 match hours, with 65333 total exposure hours in the season. The control group players were exposed to 59165 hours of training and 4224 match hours, totaling 63389 hours. Teams in the intervention group had significantly greater total overall and training exposure hours than teams in the control group (p<0.001). however, there was no significant difference in match exposure between the two groups (p = 0.367).

Compliance with the injury prevention programme and injuries

The teams in the intervention group implemented the injury prevention programme in approximately 75% of combined training sessions and matches (range 60–97%, mean 3.6 times/week, range 2.8–4.9/ week). Teams in the intervention group demonstrated moderate to high compliance. No difference was found in either the overall injuries or any other subtype of injuries according to the levels of compliance.

Effects of the FIFA 11+ injury prevention intervention injury incidence

There were 420 time loss injuries (intervention n = 168,40%, control n = 252,60%). Taking exposure into consideration, the incidence of injuries in the intervention group was 2.6 (95%CI: 2.2–3.0) injuries/ 1000 hours of exposure and 4.0 (95%CI: 3.5–4.5) injuries/ 1000 hours of exposure in the control group. Statistically significant lower incidence was observed in the intervention group compared to the control group for overall (p<0.001), training (p<0.05) and match (p<0.001) injuries (Table 2).

Table 2

Effect of the intervention on the incidence of overall, training and match injuries.

Injuries	Study group	Number of injuries	Exposure (hours)	Incidence (95%CI)	Rate ratio (95%CI)	p-value
Overall	Intervention	168	65333	2.6 (2.2–3.0)	0.6 (0.5–0.8)	<0.001
	Control	252	63389	4.0 (3.5–4.5)
Training	Intervention	64	61043	1.0 (0.8–1.3)	0.7 (0.5–0.9)	0.028
	Control	89	59165	1.5 (1.2–1.9)
Match	Intervention	104	4290	24.2 (20.0–29.3)	0.6 (0.5–0.8)	<0.001
	Control	163	4224	38.6 (33.2–44.8)

Effect of the FIFA 11+ injury prevention on injury risk

Out of a total 312 players in the intervention group, 163 (52%) players sustained injuries while in the control group, 200 out of 318 (63%) players incurred injuries. Of those players who sustained injuries, the majority sustained only a single injury. Although the frequency of players sustaining one injury in either group was similar (109 in the intervention group compared to 98 in the control group), the control group had more than twice the number of multiple injuries per player over the season. The odds of sustaining injuries were significantly lower in the intervention group for overall (OR: 0.65; 95%CI: 0.47–0.89) and match (OR: 0.71; 95%CI: 0.50–0.99) injuries. The reduction in the risk of training injuries did not reach significance in the intervention group (OR: 0.73; 95%CI: 0.50–1.09). There were 116 (37%) players that sustained lower limb injuries in the intervention group and 144 (45%) in the control group. The risk of sustaining lower extremity injuries was significantly lower in the intervention group (OR: 0.72; 95%CI: 0.52–0.98), with a strong trend for the reduction in the risk of ankle injuries (OR: 0.52; 95%CI: 0.32–0.86). The odds of contact and non-contact injuries were also significantly lower in the intervention group compared to the control group with a significantly lower risk of traumatic injuries observed in the intervention group (OR: 0.70; 95%CI: 0.51–0.96) (Table 3).

Table 3

Effect of the intervention on the risk of injuries between study groups.

		Intervention group (n = 312)	Control group (n = 318)	Odds ratio (95%CI)	p-value
Injuries		n (%)	n (%)
	Overall	163 (52)	200 (63)	0.65 (0.47–0.89)	0.009
	Training	57 (18)	74 (23)	0.73 (0.50–1.09)	0.122
	Match	85 (27)	110 (35)	0.71 (0.50–0.99)	0.046
Location of injury
	Lower extremities	116 (37)	144 (45)	0.72 (0.52–0.98)	0.047
	Thigh & groin	20 (6)	33 (10)	0.65 (0.37–1.17)	0.194
	Knee	38 (12)	43 (14)	0.89 (0.56–1.42)	0.701
	Ankle	27 (9)	49 (15)	0.52 (0.32–0.86)	0.013
Mechanism of injury
	Contact	126 (40)	172 (54)	0.56 (0.42–0.79)	0.001
	Non-contact	42 (13)	80 (25)	0.46 (0.31–0.70)	<0.001
Aetiology of injury
	Overuse	8 (2.5)	15 (4.7)	0.53 (0.22–1.27)	0.219
	Trauma	160 (51)	191 (60)	0.70 (0.51–0.96)	0.033

Effect of the FIFA 11+ injury prevention intervention on injury severity

Players in the intervention group lost 40% less days due to injuries (median 6, interquartile range, IQR: 6; range 1–84 days) compared to the control group (median 8, IQR = 11; range 1–153 days) (p < 0.001). There was a statistically significant reduction of the rate of moderate (55%) and severe (71%) injuries in the intervention group respectively (Table 4).

Table 4

Effectiveness of the intervention on the severity of injuries.

Severity of injury	Intervention group (n = 168)		Control group (n = 252)		Rate ratio (95%CI)	p-value
	n (%)	Incidence (95%CI)	n (%)	Incidence (95%CI)
Minimal (1–3 days)	44 (26)	0.7 (0.5–0.9)	40 (16)	0.6 (0.5–0.9)	1.07 (0.70–1.64)	0.850
Mild (4–7 days)	63 (38)	1.0 (0.8–1.2)	69 (27)	1.1 (0.9–1.4)	0.89 (0.63–1.25)	0.543
Moderate (8–28 days)	52 (31)	0.8 (0.6–1.0)	113 (45)	1.8 (1.5–2.1)	0.45 (0.32–0.62)	<0.001
Severe (>28 days)	9 (5)	0.1 (0.1–0.3)	30 (12)	0.5 (0.3–0.7)	0.29 (0.14–0.61)	0.001

Discussion

To our knowledge, this is the second RCT examining the effect of the FIFA 11+ injury prevention programme among male amateur soccer players in an African population. The study population had relatively limited overall soccer experience and the FIFA 11+ was not used prior to this study, providing a unique context for studying the effect of the warm-up programme. This study showed that the introduction of the FIFA 11+ programme with moderate to high compliance in training and competition decreased the incidence of injuries compared to a control group using their usual warm up. Along with significantly lower overall, training and match incidence rates, the severity of injuries was lower in the intervention group and fewer days were lost due to injury. The programme was implemented in at least three quarters of all sessions, rising to 91% prior to matches. The levels of compliance did not have any impact in the incidence of injuries in the control group. Of importance there were no injuries or adverse side effects while performing the 11+ programme. Only one previous study reported on the side effects of the intervention, as players reported muscle soreness and one hamstring strain during the 11+ warm up programme [39].

The recruitment of all eligible players in the second division and the follow-up over a full season implies that these results might be generalisable to amateur youth players at a similar level of soccer participation. In addition, the satisfactory level of team compliance achieved in the present study provides support for feasibility of implementation. Strengths of this study included adequate sample size, longitudinal data collection andhigh compliance in the intervention group, allowing conclusions on impact of the warm-up. The randomization supports internal validity as there were no significant differences in the demographic variables of the players between the two study groups. The differences in the training exposure could be an external factor influencing the incidence of training injuries especially in the intervention group. The players in the intervention group had significantly higher training exposure hours due to two teams reaching the final stage of the competition with extra training exposure.

There may be several factors contributing to the high compliance levels and ultimately a reduction in injuries. The length of the training was three days, in contrast to previous studies where the duration of training ranged between 1.5 hours [51] and 8 hours [52, 53]. The longer training programme allowed for both theoretical and practical training within a real world context, and enabled coaches to assimilate and master the correct instruction of exercises. Emphasis was placed on the appropriate instructions and corrections of body alignment and execution of the movements. In addition, follow-up visits were made to the teams and contact was maintained with coaches throughout the season.

The motivation of the coaches to improve their practice is an important element of successful training [54]. The use of accredited FIFA training material and careful instruction regarding the correct application of the exercises may have provided the coaches with confidence in the potential of the programme to reduce injuries. A number of studies provided instructional videos to coaches, together with training manuals, posters [27, 55, 56] or a book describing the exercises [52]. Similarly, coaches were provided with DVDs that included descriptions of the exercises, a complete programme of instructions, a booklet and the FIFA link for references. It is possible that the limited training opportunities in the low- to middle-income country setting contributed to the perceived importance of the opportunity and to the full implementation of the acquired skills.

Impact of the FIFA 11+ programme on injuries

The overall, training and match incidence rates were all significantly lower in the intervention group, with an 11% reduction in the overall number of injured players and a mean reduction of time off play by six days, compared to the control group.

The intervention significantly decreased the risk of injuries in the intervention group by 35%; and the odds of sustaining injury in the intervention group were comparatively lower (27% and 29% for training and matches respectively). This reinforces the results from previous studies that demonstrated the efficacy of the FIFA 11+ warm up programme in preventing injuries in general [38-40]. A similar positive impact of the FIFA11+ programme on overall or training incidence was reported in two of the three studies that tested the intervention using RCTs [38, 39]. The impact in terms of absolute reduction varied from -11% (current study) to -49% [39] with substantial variability in incidence of injuries among studies. Only one previous study had a population containing the age bracket of the present study but had a greater sample size [39].

In the present study, the warm-up intervention resulted in significantly lower incidence of match injuries. Any reduction in match injuries would be considered beneficial, as match injury incidences are consistently higher than those sustained during training [1, 3, 6, 7, 57, 58]. The intervention resulted in less contact injuries, that can potentially be attributed to the neuromuscular effects of the FIFA 11+ programme. In other studies, the completion of the FIFA 11+ programme twice per week improved the general physical fitness of young players participating in indoor soccer [59], whereas performing the programme three times per week improved neuromuscular control in amateur soccer players in Italy [33]. While it is not possible to make definitive conclusions from the data collection in this study, improvements in neuromuscular control and fitness may have prepared players to withstand contacts that would otherwise have resulted in injuries. However, we were not able to record the types and mechanisms of contact injuries that could be prevented by the programme as contact injuries are often multifactorial. The results of this study are in contrast with the studies conducted by Owoeye et al. [38] and Hammes et al. [34], where the FIFA 11+ programme did not impact contact injuries. However, these studies [34, 38] reported poor compliance rates and it is possible that the neuromuscular benefits of the programme may not have been achieved. The same studies [34, 38] did not find significant reductions in training injury occurrences [34, 38]. Further studies would be important to investigate the level of compliance required to prevent training injuries.

Significantly lower incidences were observed in the intervention group for moderate and severe injuries, which is in accordance with the studies conducted by Silvers-Granelli et al. [39] and Hammes et al. [34]. Reducing severe injuries has a major impact on the total time lost due to injuries. Not only were the players in the intervention group less likely to suffer severe injury, injured players in the intervention group returned to play sooner than players in the control group.

The intervention significantly reduced the incidence of lower extremity and ankle injuries, comparable with the other studies [38, 39]. This is in line with the aspiration of the FIFA Medical Assessment and Research Centre that designed a programme targeting the reduction of lower limb injuries by including exercises to improve neuromuscular control with good posture and correct alignment of lower limb joints [37]. An experimental study conducted in 20 young athletes found that performing the FIFA 11+ warm up programme over a nine-week period resulted in increased general lower limb strength as measured by countermovement and squat jumps [31]. Analysing muscle activation, Nakase et al. [60] found an increased core muscle activation, specifically the rectus abdominis and the gluteus medius and minimus when performing the FIFA 11+ exercises. Additionally, the rectus abdominis and hip adductor muscles were more active when performing part two of the programme [60]. The increase in abdominal, hip extensor and adductor neuromuscular control may assist with force distribution and proximal control while supporting optimal biomechanical alignment of the hip, knee and ankle joints [33]. However, we were not able to measure changes in specific intrinsic physical factors. We were therefore not able assess the contribution of intrinsic factors in preventing injuries.

The results of the present study complements the existing body of knowledge by providing evidence of the positive effects of the FIFA 11+ prevention programme. The increase in dynamic balance suitable soccer skill performance could lead to the physiological preparedness of the players that subsequently reduce the risk of injuries [61]. It is therefore important to investigate the possibility of extending the use of the preventive programmes to the wider soccer community in Rwanda.

Compliance with the programme

The mean team compliance level in the present study was 77% for all training sessions and matches. The compliance level is somewhat similar to previous studies ranging between 30% [39] and 77% [62]. Therefore, the recommended implementation rate of twice per week [63] was not only met, but exceeded with teams using the mean of 3.6 times the programme, and a minimum of 2.8 times per week. The high compliance rate may be partially attributed to the motivation levels of the coaches observed during training and follow up. Moreover, the training stimuli comprised of various didactic materials, and the extended practical sessions and regular team visits may have contributed to the conformity to the programme. Coaches may have held beliefs that performing the programme as many times as possible would provide a greater increase in neuromuscular strength increased their motivation. However, further investigation, and perhaps qualitative studies are needed to obtain an in-depth understanding of coaches’ motivations for compliance with the injury prevention programme.

Limitations of the study

The nature of the study required close monitoring and supervision of the coaches for compliance and therefore, it was not possible to blind the researcher or coaches to the group allocations. However, the medical personnel and research assistants were blinded as to which team was allocated to the intervention or control groups as well as nature, type and organisation of the intervention, from training to follow-up.

Further, the study relied on the injury reports from the medical personnel of the teams using subjective and physical examination due to limited funding. It would be interesting to explore barriers and facilitators to the use of standardised injury reporting methods within this context; and to identify how acceptability of injury reporting methods and training loads could be improved.

Future studies may benefit from investigation of individual player compliance. Prior to this study there was no systematic recording of injuries and exposure in Rwanda, therefore recording this type of data was also new to both the coaches and medical personnel. This process placed an additional load to their usual work activities. As a result, coaches were not willing to provide player compliance information as this was too time consuming. Further investigation of the perception of players and coaches could be performed for in-depth analysis of the awareness and opinion about injury prevention. More studies are also needed to assess the content of the usual warm up done by teams in the control group for further comparison.

Conclusion and recommendations

This study is the fourth RCT examining the effect of the FIFA 11+ injury prevention programme among male soccer players and the second conducted in an African population. The teams allocated to the intervention group completed the injury prevention programme with the mean of 77% of all training sessions and matches and a mean of 3.6 times per week indicating an acceptable level of compliance with the programme. The intention-to-treat results indicated that the FIFA 11+ programme significantly decreased the incidence of overall, training and match injuries, more specifically lower extremity injury among second division soccer players. Positive effects of the programme on contact and severe injuries are encouraging for reducing serious soccer injuries with consistent implementation. There is therefore a need to incorporate the FIFA 11+ programme in the wider soccer community in Rwanda and similar settings to reduce the burden of injuries.

CONSORT checklist.

(PDF)

Click here for additional data file.

Study protocol.

(PDF)

Click here for additional data file.

Dataset.

(XLSX)

Click here for additional data file.

Appendix.

(DOCX)

Click here for additional data file.

18 Nov 2020

PONE-D-20-09354

Effect of the FIFA 11+ soccer specific warm up programme on the reduction of injuries: a cluster-randomised controlled Trial

PLOS ONE

Dear Dr. Nuhu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The manuscript has been evaluated by several reviewers, and their comments are available below.

The reviewers have raised a number of concerns that need attention. They request additional information on methodological aspects of the study, and revisions to the statistical analyses.

Could you please revise the manuscript to carefully address the concerns raised?

Please submit your revised manuscript by Jan 02 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Carmen Melatti

Associate Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

Reviewer #6: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

Reviewer #4: Yes

Reviewer #5: N/A

Reviewer #6: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

Reviewer #6: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

Reviewer #6: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: A cluster randomized controlled clinical trial was conducted to examine the impact of the FIFA 11+ warm-up on incidence and severity of injuries. The odds of sustaining injuries were lower in the intervention group compared to the control group.

Minor revisions:

1- Abstract: Provide the proportions that correspond to the number of sustained injuries in the following sentence. To improve clarity, replace “fewer” with “a lower proportion of.” “Fewer players sustained injuries in the intervention group (163 players) compared to the control group (200 players)...”

2- Double check that 20% is correct in the following statement. “A 20% reduction in the risk of sustaining moderate/severe injuries was observed in the intervention group (OR: 2.3, 95% C.L: 1.56-3.40).”

3- Paragraph beginning at line 117: The statistical power calculation should also indicate if the alpha level was one- or two-sided and statistical testing method which archives 90% power.

4- Line 124: Indicate the mechanism used to implement random allocation sequence (such as sequentially numbered containers), describe any steps taken to conceal the sequence until interventions were assigned.

5- Line 180: State the statistical method used to estimate the 95% confidence interval.

6- Table 1: The F and t values can be removed from Table 1. As a table footnote, indicate that p-values were calculated from t-test. Indicate if the distribution of the data was checked for normality prior to applying t-tests. Clarify the statistical method used to estimate the coefficient and its robust standard error.

7- Line 229: The statistical term for average is mean.

8- Table 2: Explain F-ratio variances and p-value variances.

9- Throughout the manuscript: Since the sample sizes of the control and intervention arms are not the same be sure to summarize the data as the proportion affected in addition to the frequency.

10- Table 3: Explain “Row %” and “Design Effect.”

11- Table 4: Consider removing columns of data for t-value and DF. Explain F-ratio variances, p-value variances, Mean Rank Intervention, Mean Rank Control, Sum of Ranks Intervention and Sum of Ranks Control. Possibly simplifying this table could improve clarity.

12- Table 5: Indicate if “Count” refers to sample size.

13- Indicate if any adverse events occurred during the course of the study.

14- Cite the statistical software used for the analysis.

15- An objective of the study was to address the severity of injuries; however, results for severity have not been presented.

Reviewer #2: Thank you for the opportunity to review this article, which bridges the gap between training theory/rehabilitation theory and its impact upon performance measures. Importantly, it addresses these issues as they apply to the topic of the FIFA 11+, which is an area of the sport science literature needing more attention.

I see this manuscript as generally well-written and clearly laid out. The authors have done a nice job of laying out the need for such a study with the Introduction, clearly describing the Methods and Results, and tying the present findings to related studies within the Discussion. Given the interventional nature of this study, in which the members of the research team trained the coaches of the intervention group, and then regularly traveled to conduct follow up meetings with the respective teams, a LOT of work went into this study.

My suggestions for improving this manuscript are largely related to “cleaning up” some English-usage issues, such as the omission of an article within some sentences, a few awkwardly written sentences that may present a lack of clarity for many readers, the lack of use of the Oxford comma, and so on.

In summary, the aim of this project has merit. I recommend the authors address the issues noted below prior to this manuscript appearing in this peer-reviewed journal. Thanks once again for the opportunity to review this paper.

Specific comments:

Line 21: suggest replacing “typically” for “mostly”

Line 26: suggest inserting “the” between “as” and “unit”

Line 60: the statement of “ranges from 18.8 to 1.2” does not seem correct to me. Is this a typo? Logic and conventional practice for stating ranges of numbers suggests these numbers may transposed, the second number may be missing a digit, etc.

Lines 63-64: Suggest revising as follows: “Injuries generally occur more frequently during matches…”

Line 85: Suggest revising as follows: “…was developed by the group of experts commissioned by FIFA to reduce perceived intrinsic risk factors…”

Line 92: Suggest adding a comma after “eccentric hamstring strength56,

Line 93: Suggest revising as follows: “…correct alignment of the hip, knee, and ankle joints during dynamic activity in young athletes.”

Line 95: Suggest revising as follows: “However, the positive impact of the ….”

Lines 128-129. This sentence is awkwardly written. Here is a suggested revision: The principal investigator, assisted by the Rwanda soccer technical director, governed the randomization process.

Line 131: It states “three” but 4 forms are listed. Revise for greater clarity.

Lines 156-157: Revise as follows for greater clarity: “…all the second division teams in the experimental group were invited…”

Line 159: While throughout this manuscript, the Oxford comma is not generally used, its absence here in particularly creates unnecessary confusion. Thus, I recommended revising as follows: “prevention, the development, and use…”

Line 165: Recommend revising: “corrections to flaws in technique.”

Line 191: Recommend revising: “…sessions were defined as medium compliance…”

Line 194: Recommend revising: “…were done for lower limb, such as location of ….”

Line 198: Add “the” after “in” and before “2016”

Line 209: Add a comma after “coaches”

Line 212: Revise to (Table 1).

Lines 224-225: It appears that the intervention group was the group that was significantly greater, but it is not clear as written. Revise this slightly, making this a bit more apparent to the typical reader.

Line 235: Add a comma after “control group”

Line 255: Revise to (Table 3).

Line 272: Revise to (Table 4).

Line 280: Revise as follows: “lost 40% less days; they exhibited a mean of …”

Line 282: Revise to (Table 5).

Line 295: Add comma after “training”. Again, use of the Oxford comma throughout this manuscript would help a bit for the overall presentation.

Line 296: Add a comma after “rates”

Line 297: Revise to: “rising to 91% prior to matches”.

Line 300: Add “previous” between “one” and “study”

Line 339: Add “previous” between “one” and “study”

Line 379: This is an incomplete sentence. Revise for greater clarity.

Line 396: This is another incomplete sentence. Revise for greater clarity.

Reviewer #3: Complements to the authors on this very nicely conducted trial. I have a number of comments regarding the statistical analysis and presentation of results, but the trial design is sound and the results seem quite optimistic and useful.

Comments:

1. Is there a typo in the introduction, paragraph one, first sentence: “… ranges from 18.8 to 1.2 per 1000 hours” or was it intentional to specify the range from high to low? I would expect to see the range specified from low to high, but I supposed either way is acceptable.

2. Specification of sample size in a cluster-randomized trial should address both the number of clusters and the number of participants per cluster. In other words, given that the number of clusters was fixed at 12 per arm, the sample size calculation should specify the number of individuals needed per cluster, given an assumed value for the intra-class correlation (ICC). The source and justification for the ICC, and the corresponding design effect, should be stated.

3. Statistical methods should be clearer about what methods are used to account for clustering. Logistic regression is not appropriate here given the large prevalence rates. Poisson regression is probably the best option for incidence rates. Linear regression for risk differences.

4. In the statistical analysis section, the software package used should be specified (in addition to the “Epi-info complex tables function”.)

5. In the “Characteristics…” section, group means for coach experience should be stated, along with the p-value; the U and Z statistics are not necessary in the text.

6. There is far too much information in Table 1. At the very most this table should show two columns (Intervention and Control Group means) and the p-value. The p-value column is not necessary, but OK to include it this journal requires it.

7. In the “Compliance…” section, the first sentence should start with “The teams in the intervention group…”, for clarity.

8. Delete the first sentence in the “Injuries” section about player-level injuries. This is summarized in the Effects of the intervention at the level of the individual players” section. Instead, overall incidence rates (Table 2) and relative risks should be summarized here.

9. Table 2 should be restructured to show the following information for overall/training/match injuries (three rows):

a. The numbers of injuries in each study arm

b. The numbers of exposure hours in each study arm

c. The incidence rate in each arm, and 95% confidence interval

d. The relative risk of injury comparing arms

e. The p-value

f. (Remove all other extraneous statistical content from this table)

10. Table 3 should be reduced substantially and take a similar format as Table 2, with just three rows (overall, training, match) and the following four columns:

a. Number of players with 1+ injuries in the intervention arm / number of participants in the intervention arm and percent: (n/N %)

b. Same for the control arm (n/N %)

c. The risk difference and 95% CI (Odds ratios are not appropriate with such high prevalence rates, and the relative risk is better calculated using incidence rates which is already done in Table 2)

d. P-value

e. (remove everything else from this table)

11. Revise the text in the “Effects of the intervention at the level of the players” section to provide a simple verbal summary of the new Table 3.

12. Revise Table 4 similarly by adding 95% CIs for the incidence rates and removing all statistical columns except the p-value which should be computed using clustered-date methods.

13. The section “Effect of the intervention on the severity of injuries” really combines two concepts: severity and impact on lost hours. Suggest separating them into:

a. Tabulation of injury severity categories in each study arm, counts and percentages (denominator for percentages being the total of the number of injuries in each arm.)

b. Comparison of days of lost play. (As in Table 5). Show means and ranges for this, not CIs, as there will be interest in the distribution of days lost, not just inference about the mean. And, define the mean: mean per player? per injured player? mean per team?

14. Once Tables 2-5 have been simplified and reformatted, it may be possible to combine them into one single, concise table of results.

15. Would be nice to include an appendix with more detail regarding the intervention. Nothing too long, e.g. just a page, but enough to give a reader a good sense for what is involved and how long it takes.

16. Discussion is generally good but it could be more concise and there are a few typos.

Reviewer #4: The study analyses the effect of a specific warm-up protocol for the prevention of injuries in soccer players. The manuscript is well written and the methodology of the study is appropriate according to the objective of the research. The main limitation of this paper is that it´s not clear whether this research adds anything new to the literature. The gaps in the literature need to be better described in order to justify what this paper adds to the field of knowledge.

Introduction:

It does not give a complete picture of what still needs to be studied about the effectiveness of the FIFA 11+ protocol. With a quick search you can find a systematic review of Baredo et al. (2014) where they include 12 articles analysing the effects of this protocol for injury prevention in soccer players, the narrative review of Bizzini and Dvorak (2015), or even a meta-analysis conducted by Thorborg et al. (2017). All these reviews conclude that the FIFA 11+ injury prevention programme is effective for soccer players of different levels and ages. Thus, the statement made by the authors at the end of the introduction “The positive impact of the FIFA 11+ warm up in preventing injuries has not yet been fully established, with poor compliance to the programme limiting conclusions drawn in several studies” needs to be clarified as it is difficult to sustain based on previous reviews. Without giving a complete picture of the state of the art it is not possible to determine how the submitted manuscript adds new knowledge or insights into this field of knowledge. The authors need better justify the need of this research.

The reference numbers are chaotic. In page 4 line 90 we go from the reference 29 to the number 507?? and next to the 56,…. Then in line 96 this numbers with no order at all are listed as references (30;17;31;23;24;20;32;33;25)

Methodology:

There is a lack of details about the intervention, the warm-up protocol. Although the programme is accessible for the FIFA web page it is not clear how exactly they implemented the warm-up protocol. For example the original programme includes three levels. Furthermore, the reference given for accessing the protocol does not lead to the programme itself (FIFA, F-Marc. The “11+” Manual: A complete warm-up programme to prevent injuries. 2007:1-76. http://www.yrsa.ca/pdf/Fifa11/11plus_workbook_e.pdf.) Thus, more details about the exact intervention are needed as it is key for practical applications and replication.

Discussion: similar to the introduction section, there is a need for better discussing the already existing literature about the effects of the FIFA 11+ programme for preventing injuries.

Reviewer #5: The authors have examining the effect of the FIFA 11+ injury prevention programme among male soccer players in an African population. This study showed that the FIFA 11+ programme with moderate to high compliance in training and match preparation decreased the incidence of injuries.

Line 60-61: ranges from 18.8 to 1.2 per 1000 hours.

Is here the lower number first or not?

Injuries occur

63-65: consistently more often during matches than during training and most commonly in the lower extremities

Is this proven?

Line 214 Players had around 3 years of experience in football? This is really small background. Please explain why only 3 years?

Were the coaches included in the analysis and if yes why?

Please explain the training programs of the control groups. Did they all had the same warm up?

Also explain the other parts of training plan during one week.

Reviewer #6: This manuscript explores the effects of a specific FIFA11+ warm-up intervention in the injury incidence in an important sample of amateur soccer players. In general terms, the manuscript is well organized, the research question is well defined and the results are clearly presented, although the use of English is far to reach the higher standards, and some concerns in methods section, as well as several statements in the discussion should be revised and qualified before more consideration for publication. Finally, authors make a correct use of references in their manuscript, but some references need to be reviewed according the journal's instructions. Below is shown some comments for the authors:

Major concerns:

Title: After reading the manuscript, I suggest that the term reduction should be changed by the more correct term incidence. The reduction is precisely an effect of the intervention.

Introduction.

Is the sample an amateur or profesional sample? I gather that is amateur, so theoretical framework should be more contextualized for amateur soccer players. I suggest that review several recent studies investigating specific warm-up protocols for injury prevention in amateur soccer players, like this study:

García-Luna, M.A.; Cortell-Tormo, J.M.; García-Jaén, M.; Ortega-Navarro, M.; Tortosa-Martínez, J. Acute Effects of ACL Injury-Prevention Warm-Up and Soccer-Specific Fatigue Protocol on Dynamic Knee Valgus in Youth Male Soccer Players. Int. J. Environ. Res. Public Health 2020, 17, 5608.

Methods.

Design and ethical approval: The experimental design and the randomization system of the teams should be explained in more detail in this section.

Participants: Please, add in this section the descriptive data of participants (number of players (total / per group), and mean and SD about age, experience, level of amateur/professionally should appear here in one sentence, apart from the Table 1. Otherwise, you should reference or insert there the Table 1 providing more info about demographic characteristics of players). Also, if randomization was based on teams instead of players, descriptive data of teams and their selection criteria should be explained. Lastly, which inclusion/exlusion criteria for player recruitment within respective teams was followed? What is the total dropout rate along the season? Explain more deitaled, please.

Sample size: This section should be renamed as "sample size calculation", and should specify the total number of selected players, and their distribution (number per group). The power analysis seems right.

Randomization and allocation of the participants: Why did you include the head coaches as participant in the study, if they were not subjects for intervention / control? On the other hand, explain more specifically the randomization criteria.

Instruments: Did you collected the coach's perceptions and/or opinions, or motivations, about different practical issues on the implementation of the FIFA11+ program as a warm-up after intervention? I think that some interviews to coaches could be collected, and a qualitative analysis could be performed. If you do not have these data, you should include this question as possible limitation and/or future research.

Intervention: I have some concern in this section: Firstly, there was no control on the usual warm up applied by the different control group coaches along the season. It can be understood that each one continued their usual warm up, but there is no information about this (what type of exercises, duration, intensity, of each warm up, and what frecuency of the sessions, etc. were performed?). I think that report these data would be necessary to check the heterogeneity -or not- of these different warm-up proposals, seeking for standardized systems, if you want to compare the different control warm-up effects with the experimental warm-up effects. Secondly, how it was controlled that coaches effectively applied the FIFA11+ program as a warm up thorough all trainings and matches of the seasons in each club? (if it was done, you have to include it in the section). Please, explain these regards.

Results:

Lines 198-212, and Figure 1: I think that this information about demographic characteristic of coaches and players should be located in the participant section. Also, I do not understand why the coaches were included as participant, if they did not performed the control or experimental warm-ups. I suggest exclude these data from analyses.

Lines 222-225: As it can be seen in this section, there was a significant difference on the total training exposure, that it could have influenced the injury incidence as external explaining factor of the injury incidence as well. You did not report the total exposure hours of control group (please provide it in this section), and other analysis comparing these data should be performed (if it was performed, please provide the significance p-value). If significant differences resulted, you should interpret your data considering this external factor as well.

Discussion:

Lines 292-301: You should specify that the experimental FIFA11+ program was applied as a warm up, and that the incidence of injuries and their severity decreased, always compared to the control programs (traditional programs?? You should comment this regard, as I was pointed above).

Lines 303-309: When you state about the generalization of results, you have to limite only to the amateur soccer players (or players with similar characteristic). Caution on the generalization of results.

Lines 344-346: Here, you stated: "he intervention resulted in less contact injuries, that can potentially be attributed to the neuromuscular effects of the FIFA 11+ programme". What is the basis to state this? I think that contact injury incidence has a multifactorial component that could not be explained by only one factor.

Lines 362-365: This hypothesis is an overstatement. You cannot attribute the effects of a specific warm-up to the recovery of different injuries. Please, qualify this. This should also be qualified in the Line 383, when you state that the experimental warm up reduced the contact injuries during matches (it seems an overstatement). Lines 390-391: Same concern.

Lines 375-379: The idea is not clear. Please, redact more clearly these sentences.

Compliance with the programme section: Similarly that methods section, how it was controlled that coaches effectively applied the FIFA11+ program as a warm up thorough all trainings and matches of the seasons in each club? Please, explain this essential question.

References: Please, review citations accordingly the journal instructions.

English review: I think that a native English speaker should review the English use throughout the manuscript.

**Minor concerns:

Introduction:

Lines 63-65: Authors talk here about the injury incidence. This sentence requires be referenced.

Line 97: this corresponds to the methods section (in study design).

Methods:

Line 108: Please, spell out the FERWAFA acronym, if it is the first time that appears in the manuscript.

Line 131: Instruments: you stated that three forms were used collecting data, but there is enumerated four different forms. Please, correct this regard.

Line 134: Is this form to control the player's exposure during training sessions? So, please specify this in the name of the form.

Line 138: You spell out FERWAFA here, but it appeared above, in line 108. Please, review this regard.

Lines 147 and 149: Please, provide reference about the definition proposed for injury, and the reference for classifying the severity of the injury, or explain the criteria followed to determine this

Discussion:

Line 292: Please, define RCT (it is the first time that appears in the manuscript).

Line 311: Please, specify that the initial training is referred to the pre-season instructional meeting. It is not clear here.

Lines 334-336: Please, provide references of previous studies that you comment here.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

Reviewer #4: No

Reviewer #5: No

Reviewer #6: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

4 Feb 2021

Response to the editor

Comment #1: Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Response:

Many thanks for your guidance. We have checked the style requirements and determined that our manuscript meets them.

Comment #2: Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information

Response:

We appreciate your comment. We updated accordingly.

Response to reviewers

Reviewer #1

A cluster randomized controlled clinical trial was conducted to examine the impact of the FIFA 11+ warm-up on incidence and severity of injuries. The odds of sustaining injuries were lower in the intervention group compared to the control group.

Minor revisions:

Comment #1

Abstract: Provide the proportions that correspond to the number of sustained injuries in the following sentence. To improve clarity, replace “fewer” with “a lower proportion of.” “Fewer players sustained injuries in the intervention group (163 players) compared to the control group (200 players)...”

Response: Many thanks for the suggestion. The sentence is corrected and now reads “A lower proportion of players sustained injuries in the intervention group (52%) compared to the control group (63%)”. Similar wording has been changed throughout.

Comment #2

Double check that 20% is correct in the following statement. “A 20% reduction in the risk of sustaining moderate/severe injuries was observed in the intervention group (OR: 2.3, 95% C.L: 1.56-3.40).”

Response:

Thank you very much for the observation. The sentence was modified to suit the current updated results as suggested by other reviewers.

Comment #3

Paragraph beginning at line 117: The statistical power calculation should also indicate if the alpha level was one- or two-sided and statistical testing method which archives 90% power.

Response:

Many thanks for this suggestion, The information has been added and the text now reads: “Using this estimate and targeting a 20% reduction of injuries using power of 90% for generalised linear regression model and two-tailed alpha of 5%, a sample size of 125 was required per group.”

Comment #4

Line 124: Indicate the mechanism used to implement random allocation sequence (such as sequentially numbered containers), describe any steps taken to conceal the sequence until interventions were assigned.

Response:

Thank you very much for the suggestion. The following sentences were added for clarity. “The numbers representing the 24 teams were placed in sealed envelopes with an equal opportunity of being selected for groups. A research assistant selected the envelope for both groups drawing one by one to achieve random allocation by team to either the intervention group or the control group.”

Comment #5

Line 180: State the statistical method used to estimate the 95% confidence interval.

Response:

Thank you very much for the comment. The method used to calculate the 95% confidence intervals was inserted.

Comment #6

Table 1: The F and t values can be removed from Table 1. As a table footnote, indicate that p-values were calculated from t-test. Indicate if the distribution of the data was checked for normality prior to applying t-tests. Clarify the statistical method used to estimate the coefficient and its robust standard error.

Response:

We appreciate your valuable observation. Following comment #18 from reviewer #2 and comment #6 from reviewer #3, the content was revised and simplified to remain with only mean and standard deviation from both the intervention and control group and their corresponding p-values.

Comment #7

Line 229: The statistical term for average is mean.

Response:

Many thanks for your comment. We totally agree with you about the synonym of both terms. Following the structure of the sentence, we believe that the term average fits well instead of the term mean.

Comment #8

Table 2: Explain F-ratio variances and p-value variances.

Response:

Many thanks for your comment. In line with the comment #9 from reviewer #3, the F-ratio variances and p-value variances were removed and the remaining variables were the number of injuries, exposure hours, and incidence (95% confidence intervals), with rate ratios and the p-values reported.

Comment #9

Throughout the manuscript: Since the sample sizes of the control and intervention arms are not the same be sure to summarize the data as the proportion affected in addition to the frequency.

Response:

Many thanks for your valuable comment. The suggestion was taken into consideration, the frequency and proportion affected were presented especially in table 3.

Comment #10

Table 3: Explain “Row %” and “Design Effect.”

Response:

We appreciate your comment. Table 3 was amended and combined with the results of table 4 as recommended by reviewer #3, comment #10, 11,14.

Comment #11

Table 4: Consider removing columns of data for t-value and DF. Explain F-ratio variances, p-value variances, Mean Rank Intervention, Mean Rank Control, Sum of Ranks Intervention and Sum of Ranks Control. Possibly simplifying this table could improve clarity.

Response:

We appreciate your comment. It was addressed together with comment #10.

Comment #12

Table 5: Indicate if “Count” refers to sample size.

Response:

Thank you for your observation. The content of the table was also revised and simplified. The results are presented according to the severity categories. The frequency and percentages are presented as well as the incidence and 95% confidence intervals.

Comment #13

Indicate if any adverse events occurred during the course of the study.

Response:

Thank you very much for your observation. This information was provided in the last two sentences of the first paragraph of the discussion.

Comment #14

Cite the statistical software used for the analysis.

Response:

Thank you for your comment. The information was inserted in the methods section under the statistical analyses subheading.

Comment #15

An objective of the study was to address the severity of injuries; however, results for severity have not been presented.

Response:

Many thanks for your valuable comment. The results about the severity of injuries are now presented in table 4.

Reviewer #2

Thank you for the opportunity to review this article, which bridges the gap between training theory/rehabilitation theory and its impact upon performance measures. Importantly, it addresses these issues as they apply to the topic of the FIFA 11+, which is an area of the sport science literature needing more attention.

I see this manuscript as generally well-written and clearly laid out. The authors have done a nice job of laying out the need for such a study with the Introduction, clearly describing the Methods and Results, and tying the present findings to related studies within the Discussion. Given the interventional nature of this study, in which the members of the research team trained the coaches of the intervention group, and then regularly traveled to conduct follow up meetings with the respective teams, a LOT of work went into this study.

My suggestions for improving this manuscript are largely related to “cleaning up” some English-usage issues, such as the omission of an article within some sentences, a few awkwardly written sentences that may present a lack of clarity for many readers, the lack of use of the Oxford comma, and so on.

Response:

Thank you for this suggestion, we have tried to clean up the sentence structure and hope that the clarity has improved as a result.

In summary, the aim of this project has merit. I recommend the authors address the issues noted below prior to this manuscript appearing in this peer-reviewed journal. Thanks once again for the opportunity to review this paper.

Thank you!

Specific comments:

Comment #1

Line 21: suggest replacing “typically” for “mostly”

Response:

We appreciate your valuable suggestion. We made the changes accordingly.

Comment #2

Line 26: suggest inserting “the” between “as” and “unit”

Response:

We appreciate your comment. We made the changes as suggested.

Comment #3

Line 60: the statement of “ranges from 18.8 to 1.2” does not seem correct to me. Is this a typo? Logic and conventional practice for stating ranges of numbers suggests these numbers may transposed, the second number may be missing a digit, etc.

Response:

Many thanks for the good observation. Another reviewer had also the same comment. We had actually written from highest to lowest. For clarity and understanding for the reader, the sentence now reads “… ranges from 1.2 to 18.8”

Comment #4

Lines 63-64: Suggest revising as follows: “Injuries generally occur more frequently during matches…”

Response:

Many thanks for the suggestion. We corrected it as advised.

Comment #5

Line 85: Suggest revising as follows: “…was developed by the group of experts commissioned by FIFA to reduce perceived intrinsic risk factors…”

Response:

Many thanks for the suggestion. We inserted the content as suggested.

Comment #6

Line 92: Suggest adding a comma after “eccentric hamstring strength56,

Response:

Many thanks for the observation. We inserted the comma as suggested.

Comment #7

Line 93: Suggest revising as follows: “…correct alignment of the hip, knee, and ankle joints during dynamic activity in young athletes.”

Response:

Many thanks for the suggestion. We inserted the content as recommended.

Comment #8

Line 95: Suggest revising as follows: “However, the positive impact of the ….”

Response:

We appreciate your comment. The content of the paragraph was revised and more content was added.

Comment #9

Lines 128-129: This sentence is awkwardly written. Here is a suggested revision: The principal investigator, assisted by the Rwanda soccer technical director, governed the randomization process.

Response:

We appreciate your valuable suggestion. Small change suggested in the text: “The principal investigator, assisted by the Rwanda soccer technical director, supervised the randomization process.”

Comment #10

Line 131: It states “three” but 4 forms are listed. Revise for greater clarity.

Response:

Many thanks for your observation. We revised the title accordingly and it now reads: “Four forms were used to collect data:”

Comment #11

Lines 156-157: Revise as follows for greater clarity: “…all the second division teams in the experimental group were invited…”

Response:

Many thanks for your suggestion. We inserted the content as suggested.

Comment #12

Line 159: While throughout this manuscript, the Oxford comma is not generally used, its absence here in particularly creates unnecessary confusion. Thus, I recommended revising as follows: “prevention, the development, and use…”

Response:

Many thanks for your observation. We inserted the comma as suggested for more clarity.

Comment #13

Line 165: Recommend revising: “corrections to flaws in technique.”

Response:

Many thanks for your suggestion. We inserted the content as suggested.

Comment #14

Line 191: Recommend revising: “…sessions were defined as medium compliance…”

Response:

We appreciate your suggestion. We have adjusted this sentence to read: Compliance was computed based on each team’s implementation of the FIFA 11+ sessions throughout the season as a percentage of total training and match sessions and categorized as high compliance (> 75%), medium compliance (50% to 74%), or low compliance (<50%).

Comment #15

Line 194: Recommend revising: “…were done for lower limb, such as location of ….”

Response:

We appreciate your suggestion. Following your suggestions, it would be understood that the analyses of the location and the severity of injuries will only be for lower limbs; which is not the case in this study. It is the reason why we made other corrections to the sentence to read “Additional analyses were conducted for region of injury, lower limb injury location, and the severity of injuries. The categories of the severity of injuries were reflected by days of absence from full soccer participation45”

Comment #16

Line 198: Add “the” after “in” and before “2016”

Response:

We appreciate your suggestion. We made the corrections as suggested.

Comment #17

Line 209: Add a comma after “coaches”

Response:

Based on the comments from other reviewers, the paragraph related to characteristics of the coaches was deemed not necessary and was therefore removed.

Comment #18

Line 212: Revise to (Table 1).

Response:

Many thanks for your suggestion. Revision done.

Comment #19

Lines 224-225: It appears that the intervention group was the group that was significantly greater, but it is not clear as written. Revise this slightly, making this a bit more apparent to the typical reader.

Response:

Many thanks for your comment. The content was revised for clarity.

Comment #20

Line 235: Add a comma after “control group”

Response:

Thank you very much your comment. We inserted the comma as suggested.

Comment #21

Line 255: Revise to (Table 3).

Response:

Thank you for your suggestion. Revision done.

Comment #22

Line 272: Revise to (Table 4).

Response:

Thank you for your suggestion. Revision done.

Comment #23

Line 280: Revise as follows: “lost 40% less days; they exhibited a mean of …”

Response:

We appreciate your suggestion. We made the corrections as suggested.

Comment #24

Line 282: Revise to (Table 5).

Response:

Thank you for your suggestion. Revision done.

Comment #25

Line 295: Add comma after “training”. Again, use of the Oxford comma throughout this manuscript would help a bit for the overall presentation.

Response:

We appreciate your suggestion. We made the corrections as suggested.

Comment #26

Line 296: Add a comma after “rates”

Response:

We appreciate your suggestion. We made the corrections as suggested. The sentence is now reading “Along with significantly lower overall, training, and match incidence rates, the severity of injuries were lower in the intervention group and fewer days were lost due to injury.”

Comment #27

Line 297: Revise to: “rising to 91% prior to matches”.

Response:

Many thanks for your inputs. We made the corrections as suggested.

Comment #28

Line 300: Add “previous” between “one” and “study”

Response:

We appreciate your suggestion. We made the corrections as suggested.

Comment #29

Line 339: Add “previous” between “one” and “study”

Response:

We appreciate your suggestion. We made the corrections as suggested.

Comment #30

Line 379: This is an incomplete sentence. Revise for greater clarity.

Response:

Many thanks for your comment. The sentence has been revised.

Comment #31

Line 396: This is another incomplete sentence. Revise for greater clarity.

Response:

Many thanks for your comment. We revised the sentence as recommended.

Reviewer #3

Complements to the authors on this very nicely conducted trial. I have a number of comments regarding the statistical analysis and presentation of results, but the trial design is sound and the results seem quite optimistic and useful.

Thank you!

Comments:

Comment #1

Is there a typo in the introduction, paragraph one, first sentence: “… ranges from 18.8 to 1.2 per 1000 hours” or was it intentional to specify the range from high to low? I would expect to see the range specified from low to high, but I supposed either way is acceptable.

Response:

Many thanks for the observation. Another reviewer had also the same comment. For clarity and understanding for the reader the sentence now reads: “… ranges from 1.2 to 18.8 per 100 hours”

Comment #2

Specification of sample size in a cluster-randomized trial should address both the number of clusters and the number of participants per cluster. In other words, given that the number of clusters was fixed at 12 per arm, the sample size calculation should specify the number of individuals needed per cluster, given an assumed value for the intra-class correlation (ICC). The source and justification for the ICC, and the corresponding design effect, should be stated.

Response:

We appreciate your comment. The design effect was mentioned and we added the value of ICC as advised.

Comment #3

Statistical methods should be clearer about what methods are used to account for clustering. Logistic regression is not appropriate here given the large prevalence rates. Poisson regression is probably the best option for incidence rates. Linear regression for risk differences.

Response:

Thank you for your comment. The poisson regression analysis was used to analyse data instead of logistic regression.

Comment #4. In the statistical analysis section, the software package used should be specified (in addition to the “Epi-info complex tables function”.)

Response:

Many thanks for this comment. The content of the other statistical software used in data analyses was inserted. “Microsoft Excel (Version 2000, Microsoft, Redmond, Wash.) was used to capture the data. Data analysis was carried out using “Statistica” data analysis software, version 13.2, Dell Inc. and the Statistical Package for Social Sciences (SPSS) for Windows, version 21.0, SPSS Inc, Chicago, USA. “

Comment #5. In the “Characteristics…” section, group means for coach experience should be stated, along with the p-value; the U and Z statistics are not necessary in the text.

Response:

Many thanks for the good observation. Based on a comment from reviewer#6 (comment#12) who deemed not necessary to include coaches’ data because they did not perform the warm-up exercises, we opted to exclude the presentation of data for the coaches and focus on the data related to the players.

Comment #6. There is far too much information in Table 1. At the very most this table should show two columns (Intervention and Control Group means) and the p-value. The p-value column is not necessary, but OK to include it this journal requires it.

Response:

We appreciate your comment. The table was simplified as suggested. It contains only the mean (SD) values for the intervention and control group and one column for p-values.

Comment #7

In the “Compliance…” section, the first sentence should start with “The teams in the intervention group…”, for clarity.

Response:

We appreciate your suggestion. We made the corrections as advised.

Comment #8

Delete the first sentence in the “Injuries” section about player-level injuries. This is summarized in the Effects of the intervention at the level of the individual players” section. Instead, overall incidence rates (Table 2) and relative risks should be summarized here.

Response:

We appreciate your comment. The first sentence in the “Injuries” section was deleted. The relevant information was also inserted as suggested.

Comment #9

Table 2 should be restructured to show the following information for overall/training/match injuries (three rows):

a. The numbers of injuries in each study arm

b. The numbers of exposure hours in each study arm

c. The incidence rate in each arm, and 95% confidence interval

d. The relative risk of injury comparing arms

e. The p-value

f. (Remove all other extraneous statistical content from this table)

Response:

Many thanks for your suggestion. We simplified the table 2 as recommended for simplicity and clarity.

Comment #10

Table 3 should be reduced substantially and take a similar format as Table 2, with just three rows (overall, training, match) and the following four columns:

a. Number of players with 1+ injuries in the intervention arm / number of participants in the intervention arm and percent: (n/N %)

b. Same for the control arm (n/N %)

c. The risk difference and 95% CI (Odds ratios are not appropriate with such high prevalence rates, and the relative risk is better calculated using incidence rates which is already done in Table 2)

d. P-value

e. (remove everything else from this table)

Response:

Many thanks for your suggestion. We simplified the content of table 3 and we combined the results with the content of table 4.

Comment #11

Revise the text in the “Effects of the intervention at the level of the players” section to provide a simple verbal summary of the new Table 3.

Response:

We appreciate your suggestion. We revised the content according to the results presented in table 3.

Comment #12

Revise Table 4 similarly by adding 95% CIs for the incidence rates and removing all statistical columns except the p-value which should be computed using clustered-date methods.

Response:

We appreciate your suggestion. The table was removed and its content was presented in table 3.

Comment #13 The section “Effect of the intervention on the severity of injuries” really combines two concepts: severity and impact on lost hours. Suggest separating them into:

a. Tabulation of injury severity categories in each study arm, counts and percentages (denominator for percentages being the total of the number of injuries in each arm.)

b. Comparison of days of lost play. (As in Table 5). Show means and ranges for this, not CIs, as there will be interest in the distribution of days lost, not just inference about the mean. And, define the mean: mean per player? per injured player? mean per team?

Response:

Many thanks for your valuable comments. The table 5, now table 4, was reorganized to present the results according to the injury severity categories. We opted to reserve the results of the other severity measures in the text to avoid having many tables.

Comment #14

Once Tables 2-5 have been simplified and reformatted, it may be possible to combine them into one single, concise table of results.

Response:

Many thanks for your insightful comment. We modified the contents and the design of the tables. We combined the content of table 3 and 4.

Comment #15

Would be nice to include an appendix with more detail regarding the intervention. Nothing too long, e.g. just a page, but enough to give a reader a good sense for what is involved and how long it takes.

Response:

We appreciate your comment. The content was submitted as a supporting document.

Comment #16

Discussion is generally good but it could be more concise and there are a few typos.

Response:

We appreciate your positive comment. We revised and corrected the errors as well as condensing some sentences for flow.

Reviewer #4

The study analyses the effect of a specific warm-up protocol for the prevention of injuries in soccer players. The manuscript is well written and the methodology of the study is appropriate according to the objective of the research. The main limitation of this paper is that it´s not clear whether this research adds anything new to the literature. The gaps in the literature need to be better described in order to justify what this paper adds to the field of knowledge.

Comment #1

Introduction:

It does not give a complete picture of what still needs to be studied about the effectiveness of the FIFA 11+ protocol. With a quick search you can find a systematic review of Baredo et al. (2014) where they include 12 articles analysing the effects of this protocol for injury prevention in soccer players, the narrative review of Bizzini and Dvorak (2015), or even a meta-analysis conducted by Thorborg et al. (2017). All these reviews conclude that the FIFA 11+ injury prevention programme is effective for soccer players of different levels and ages. Thus, the statement made by the authors at the end of the introduction “The positive impact of the FIFA 11+ warm up in preventing injuries has not yet been fully established, with poor compliance to the programme limiting conclusions drawn in several studies” needs to be clarified as it is difficult to sustain based on previous reviews. Without giving a complete picture of the state of the art it is not possible to determine how the submitted manuscript adds new knowledge or insights into this field of knowledge. The authors need better justify the need of this research.

Response:

We appreciate your comment. The purpose of this study was to examine the effectiveness of the warm up programme in a different population group of youth amateurs engaging in competitive football. The setting in an African country where the FIFA 11+ was not used and in a league with relatively novice soccer players adds to the existing literature. We therefore updated the introduction section accordingly.

Comment #2

The reference numbers are chaotic. In page 4 line 90 we go from the reference 29 to the number 507?? and next to the 56,…. Then in line 96 this numbers with no order at all are listed as references (30;17;31;23;24;20;32;33;25)

Response:

Many thanks for your comment. There references were revised.

Comment #3

Methodology:

There is a lack of details about the intervention, the warm-up protocol. Although the programme is accessible for the FIFA web page it is not clear how exactly they implemented the warm-up protocol. For example the original programme includes three levels. Furthermore, the reference given for accessing the protocol does not lead to the programme itself (FIFA, F-Marc. The “11+” Manual: A complete warm-up programme to prevent injuries. 2007:1-76. http://www.yrsa.ca/pdf/Fifa11/11plus_workbook_e.pdf.) Thus, more details about the exact intervention are needed as it is key for practical applications and replication.

Response:

Thank you for your comment. The detailed content was provided in the appendix (S3) submitted separately in the system.

Comment #4

Discussion: similar to the introduction section, there is a need for better discussing the already existing literature about the effects of the FIFA 11+ programme for preventing injuries.

Response:

We appreciate your comment. We reviewed the discussion accordingly.

Reviewer #5

The authors have examining the effect of the FIFA 11+ injury prevention programme among male soccer players in an African population. This study showed that the FIFA 11+ programme with moderate to high compliance in training and match preparation decreased the incidence of injuries.

Comment #1

Line 60-61: ranges from 18.8 to 1.2 per 1000 hours.

Is here the lower number first or not?

Response:

Many thanks for the comment. Two other reviewers pointed this out as well. The sentence now reads, “… ranges from 1.2 to 18.8 per 100 hours”

Comment #2

63-65: Injuries occur consistently more often during matches than during training and most commonly in the lower extremities

Is this proven?

Response:

Many thanks for your observation. It is true that sometimes the occurrence of injuries might not be as described in the sentence above. However taking exposure time into consideration, the incidence of injuries was almost always reported to be higher during matches than training. In line with the suggestion of reviewer#2 comment #4, the sentence now read “Injuries generally occur more frequently during matches than during training and most commonly in the lower extremities”.

Necessary references were inserted.

Comment #3

Line 214 Players had around 3 years of experience in football? This is really small background. Please explain why only 3 years?

Response:

We appreciate your comment. It is true that the experience of the players in playing organized football with clear teams and regular training was around three years. In Rwanda, an African country where football development is not well organized, there are no football academies and structured youth competition except in schools. Many young people play just for fun and the love of the game. In 2004, there was a national programme to develop youth football. A second division league composed of players under the age of 20 years was initiated. We conducted the study when majority of players had the opportunity to play for about 3 years in organized teams.

Comment #4

Were the coaches included in the analysis and if yes why?

Response:

Many thanks for your question. Coached were not included in the analysis. The information about the coaches that was initially presented in the analysis has been removed.

Comment #5

Please explain the training programs of the control groups. Did they all had the same warm up?

Also explain the other parts of training plan during one week.

Response:

We appreciate your comment. We provided more explanation as suggested. Now the paragraph reads: ”Coaches of the teams in the control group were invited to attend a training on basic first aid and emergency procedures for one day. The coaches received training from the researcher on basic first aid and emergency procedures. The training covered topics relating to the occurrence of injuries, field assessments and phases of rehabilitation. First aid for injuries affecting specific body parts (ankle, knee, hip, groin, hamstring, hand and head) including concussion were also discussed. The discussion focused on specific conditions that affect players on the field such as nosebleeds, eye and dental injuries. They were requested to continue with the way they usually organise the warm up and practices for their players. There was no specific warm up regime in the control group. None of the control group coaches were familiar with the FIFA 11+ warm up programme. Typically the soccer training starts with a warm up, followed by technical and/or tactical drills. However, depending on the period of the season, physical training may include specific exercises for cardiovascular endurance, muscle strength, coordination and speed for performance.

Reviewer #6

This manuscript explores the effects of a specific FIFA11+ warm-up intervention in the injury incidence in an important sample of amateur soccer players. In general terms, the manuscript is well organized, the research question is well defined and the results are clearly presented, although the use of English is far to reach the higher standards, and some concerns in methods section, as well as several statements in the discussion should be revised and qualified before more consideration for publication.

Response:

Thank you, the manuscript has been reviewed for language, grammar and sentence structure, we hope that the paper reads clearly. We have responded to the specific comments below.

Finally, authors make a correct use of references in their manuscript, but some references need to be reviewed according the journal's instructions. Below is shown some comments for the authors:

Major concerns:

Comment #1

Title: After reading the manuscript, I suggest that the term reduction should be changed by the more correct term incidence. The reduction is precisely an effect of the intervention.

Response:

We appreciate your comment. Now the title reads: “Effect of the FIFA 11+ soccer specific warm up programme on the incidence of injuries: a Cluster-Randomised Controlled trial”

Introduction.

Comment #2

Is the sample an amateur or profesional sample? I gather that is amateur, so theoretical framework should be more contextualized for amateur soccer players. I suggest that review several recent studies investigating specific warm-up protocols for injury prevention in amateur soccer players, like this study:

García-Luna, M.A.; Cortell-Tormo, J.M.; García-Jaén, M.; Ortega-Navarro, M.; Tortosa-Martínez, J. Acute Effects of ACL Injury-Prevention Warm-Up and Soccer-Specific Fatigue Protocol on Dynamic Knee Valgus in Youth Male Soccer Players. Int. J. Environ. Res. Public Health 2020, 17, 5608.

Response:

Many thanks for your comment. It was taken onto consideration while updating the background of the study as reflected in the last paragraphs of the introduction section.

Methods.

Comment #3

Design and ethical approval: The experimental design and the randomization system of the teams should be explained in more detail in this section.

Response:

We appreciate your comment. The overall design is included in this section. We felt that the description of the randomization process warranted a separate paragraph under the subheading “Randomisation and allocation of the participants”

Comment #4

Participants: Please, add in this section the descriptive data of participants (number of players (total / per group), and mean and SD about age, experience, level of amateur/professionally should appear here in one sentence, apart from the Table 1. Otherwise, you should reference or insert there the Table 1 providing more info about demographic characteristics of players).

Response:

Thank you very much for your comment. We added the content as requested.

Comment #5

Also, if randomization was based on teams instead of players, descriptive data of teams and their selection criteria should be explained.

Response:

Thank you for your comment. In line with revewer#1 comment #4, More content was added to provide more description on the randomization process of the teams.

Comment #6

Lastly, which inclusion/exclusion criteria for player recruitment within respective teams was followed? What is the total dropout rate along the season? Explain more deitaled, please.

Response:

We appreciate your comment. We inserted a subheading and content describing the inclusion criteria of the players. In the introduction of the results section we mentioned the participants that dropped out and this was also reflected in the corresponding figure.

Comment #7

Sample size: This section should be renamed as "sample size calculation", and should specify the total number of selected players, and their distribution (number per group). The power analysis seems right.

Response:

We appreciate your comment. We renamed the section as suggested. The information about the number of selected players from each group was provided in the introduction of the results section.

Comment #8

Randomization and allocation of the participants: Why did you include the head coaches as participant in the study, if they were not subjects for intervention / control? On the other hand, explain more specifically the randomization criteria.

Response:

We appreciate your comment. In line with revewer#2 comment #9, we provided more explanations about the randomization process.

Similar to the comment #4&5 from reviewer#5, the coaches were not included in the analysis. The information about the coaches that was initially presented in the methods and analysis sections was removed.

Comment #9

Instruments: Did you collected the coach's perceptions and/or opinions, or motivations, about different practical issues on the implementation of the FIFA11+ program as a warm-up after intervention? I think that some interviews to coaches could be collected, and a qualitative analysis could be performed. If you do not have these data, you should include this question as possible limitation and/or future research.

Response:

Many thanks for the observation. This study was part of the research project. The inquiry about coaches’ perception about injury prevention and the 11+ programme was gathered. We are preparing a separate manuscript on related specific results. We initially mentioned this in the discussion section under “compliance with the programme”. However, this information was also inserted in the limitations section.

Comment #10

Intervention: I have some concern in this section: Firstly, there was no control on the usual warm up applied by the different control group coaches along the season. It can be understood that each one continued their usual warm up, but there is no information about this (what type of exercises, duration, intensity, of each warm up, and what frecuency of the sessions, etc. were performed?). I think that report these data would be necessary to check the heterogeneity -or not- of these different warm-up proposals, seeking for standardized systems, if you want to compare the different control warm-up effects with the experimental warm-up effects.

Response:

Many thanks for your comment. This was also noted by reviewer#5 comment#5. One of the advantages of the FIFA 11+ programme is the organization of multiple elements designed to address all components needed for optimal warm-up. The control group was not asked to change what they considered normal practice to provide a pragmatic comparison. This was especially relevant in this context where the soccer league is relatively new, players do not have as much experience and there is no current “control” protocol in the literature. While documenting the type of exercises, duration and intensity would be interesting, this would require different methods and aims, which were beyond the scope of this project.

We have provided more general explanation about the warm up conducted in the control group teams. Now the paragraph reads: ”… They were requested to continue with the way they usually organise the warm up and practices for their players. There was no specific warm up regime organised by the coaches in the control group. None of the control group coaches were familiar with the FIFA 11+ warm up programme.

Typically the soccer training starts with a warm up, followed by technical and/or tactical drills. However, depending on the period of the season physical training may include specific exercises for cardiovascular endurance, muscle strength, coordination and speed for performance.”

In addition we included the need for further research to assess the content of the control teams’ warm up content for comparison with the intervention teams.

Comment #11

Secondly, how it was controlled that coaches effectively applied the FIFA11+ program as a warm up thorough all trainings and matches of the seasons in each club? (if it was done, you have to include it in the section). Please, explain these regards.

Response:

We appreciate your comment. We had initially planned to collect data pertaining to the use of the warm up programme each time it was conducted. However, coaches were did not always record the information. This was also reported in the limitations section. We therefore had to rely only on the frequency that they used the warm-up. This was also mentioned in the limitations sections.

Results:

Comment #12

Lines 198-212, and Figure 1: I think that this information about demographic characteristic of coaches and players should be located in the participant section. Also, I do not understand why the coaches were included as participant, if they did not performed the control or experimental warm-ups. I suggest exclude these data from analyses.

Response:

Many thanks for your valuable comment. We excluded the data for the coaches based on comments from multiple reviewers. Following the CONSORT checklist, participant demographics and the corresponding figure are strongly recommended to be presented at the beginning of the results section.

Comment #13

Lines 222-225: As it can be seen in this section, there was a significant difference on the total training exposure, that it could have influenced the injury incidence as external explaining factor of the injury incidence as well. You did not report the total exposure hours of control group (please provide it in this section), and other analysis comparing these data should be performed (if it was performed, please provide the significance p-value). If significant differences resulted, you should interpret your data considering this external factor as well.

Response:

Many thanks for your valuable comment. The total exposure hours for the control group were added. The comment is well noted and was taken into consideration in the revision of the discussion.

Discussion:

Comment #14

Lines 292-301: You should specify that the experimental FIFA11+ program was applied as a warm up, and that the incidence of injuries and their severity decreased, always compared to the control programs (traditional programs?? You should comment this regard, as I was pointed above).

Response:

Many thanks for your valuable comment. The content about the traditional/usual warm up was inserted.

Comment #15

Lines 303-309: When you state about the generalization of results, you have to limite only to the amateur soccer players (or players with similar characteristic). Caution on the generalization of results.

Response:

Many thanks for your valuable comment. The discussion about the difference between the training exposure and its possible contribution to injury reduction was added.

Comment #16

Lines 344-346: Here, you stated: "he intervention resulted in less contact injuries, that can potentially be attributed to the neuromuscular effects of the FIFA 11+ programme". What is the basis to state this? I think that contact injury incidence has a multifactorial component that could not be explained by only one factor.

Response:

We appreciate your comment. The discussion about the multifactorial nature of contact injuries was inserted.

Comment #17

Lines 362-365: This hypothesis is an overstatement. You cannot attribute the effects of a specific warm-up to the recovery of different injuries. Please, qualify this. This should also be qualified in the Line 383, when you state that the experimental warm up reduced the contact injuries during matches (it seems an overstatement). Lines 390-391: Same concern.

Response:

We appreciate your comment. The referred sentences were removed for clarity.

Comment #18

Lines 375-379: The idea is not clear. Please, redact more clearly these sentences.

Response:

Thank you for your comment. The sentence was revised for clarity.

Comment #19

Compliance with the programme section: Similarly that methods section, how it was controlled that coaches effectively applied the FIFA11+ program as a warm up thorough all trainings and matches of the seasons in each club? Please, explain this essential question.

Response:

We appreciate your comment. Practically we could not fully supervise and control what the coaches are organizing and what the teams are doing on daily basis. However, we mentioned in the compliance section under the methodology: “The instructor and the principal investigator visited the intervention group coaches once a week for the first month of the season, followed by monthly visits to foster implementation and compliance. Additional instructions were provided where necessary.” In addition coaches submitted the records of the frequency of the implementation of the programme along with the exposure forms every two weeks.

Comment #20

References: Please, review citations accordingly the journal instructions.

Response:

Thank you very much for the comment. We revised the in-text references and updated the reference list accordingly..

Comment #21

English review: I think that a native English speaker should review the English use throughout the manuscript.

Response:

Many thanks for the comment. Other than the first author, the other authors are all native English speakers. They have reviewed the manuscript and made changes to wording, sentence structure and grammar.

**Minor concerns:

Introduction:

Comment #22

Lines 63-65: Authors talk here about the injury incidence. This sentence requires be referenced.

Response:

Many thanks for the comment. The references were inserted.

Comment #23

Line 97: this corresponds to the methods section (in study design).

Response:

Many thanks for the comment. The sentence was revised.

Methods:

Comment #24

Line 108: Please, spell out the FERWAFA acronym, if it is the first time that appears in the manuscript.

Response:

Many thanks for the comment. It was spelled out as recommended.

Comment #25

Line 131: Instruments: you stated that three forms were used collecting data, but there is enumerated four different forms. Please, correct this regard.

Response:

Many thanks for the comment. The subheading was corrected.

Comment #26

Line 134: Is this form to control the player's exposure during training sessions? So, please specify this in the name of the form.

Response:

Many thanks for the comment. The content was corrected.

Comment #27

Line 138: You spell out FERWAFA here, but it appeared above, in line 108. Please, review this regard.

Response:

Many thanks for the comment. The content was corrected accordingly.

Comment #28

Lines 147 and 149: Please, provide reference about the definition proposed for injury, and the reference for classifying the severity of the injury, or explain the criteria followed to determine this

Response:

Many thanks for the comment. The reference was inserted.

Discussion:

Comment #29

Line 292: Please, define RCT (it is the first time that appears in the manuscript).

Response:

Many thanks for the comment. The definition was provided.

Comment #30

Line 311: Please, specify that the initial training is referred to the pre-season instructional meeting. It is not clear here.

Response:

Many thanks for the comment. The section was reviewed for clarity. It now reads “The length of the training was three days, …”

Comment #31

Lines 334-336: Please, provide references of previous studies that you comment here.

Response:

Many thanks for the comment. The references were inserted.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

5 May 2021

Effect of the FIFA 11+ soccer specific warm up programme on the incidence of injuries: a cluster-randomised controlled Trial

PONE-D-20-09354R1

Dear Dr. Nuhu,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Don Hoover

Guest Editor

PLOS ONE

Additional Editor Comments (optional):

See suggestion of Reviewer 1, which is to replace "average" with "mean" throughout the final version of the manuscript.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

Reviewer #4: All comments have been addressed

Reviewer #5: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Throughout the manuscript: Replace the term "average" with "mean."

Reviewer #2: The authors have addressed all of my previous comments/suggestions. I personally see this as a valuable study which effectively assessed the efficacy of the FIFA 11+ regimen on a broad basis.

Reviewer #4: The authors have nicely addressed the questions raiesed by the reviewers. Only two minor details:

- Line 330 hadsignificantly (separate the words)

- In the the first reference, the title is in capital letters.

Reviewer #5: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #4: No

Reviewer #5: No

14 May 2021

PONE-D-20-09354R1

Effect of the FIFA 11+ soccer specific warm up programme on the incidence of injuries: a Cluster-Randomised Controlled trial

Dear Dr. Nuhu:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Don Hoover

Guest Editor

PLOS ONE