Lower Extremity Injuries in Novice Runners: Incidence, Types, Time Patterns, Sociodemographic and Motivational Risk Factors in a Prospective Cohort Study.

The aim was to determine types and incidence of running-related lower extremity injuries and identify sociodemographic and motivational risk factors in novice runners attending an eight-month running school. Between January 2011 and October 2014, 349 novice runners were included. Sociodemographic, anthropometric, and data on running motivation and self-perceived health and fitness were collected. Subjects were screened for lower extremity injuries at regular three-month intervals. The cohort mean age was 35.46±7.31 years, and 271 (79.5%) were female. There were 173 (49.9%) injuries recorded, less frequently among women (42.9% vs. 62.7%, p=0.016; OR 0.878, 95% CI 0.788-0.977). The mean body mass index was 23.89±3.88 kg/m2 at baseline and 22.99±3.35 kg/m2 post-school (p<0.001). Median self-perceived fitness level on a ten-point visual analog scale was 4 (interquartile range (IQR) 3-5) at baseline and 8 (IQR 7-8) post-school (p<0.001). Median self-perceived overall health was 6 (IQR 5-8) at baseline and 8 (IQR 7-9) post-school (p<0.001). The knee had a significantly higher rate of injuries compared to other anatomic regions (p<0.001). Subjects listed improvement of fitness as the most common motivation for entering the school (n=159; 45.7%). In conclusion, novice runners should include strengthening exercises for knee injury prevention into their training routine.

Introduction

Running is one of the simplest, most natural and accessible physical recreation activities for health maintenance and disease prevention. Millions of people worldwide engage in running as a daily recreational activity and take part in organized races, on novice, professional, and elite levels. Data from the United States of America show that in 2013 there were more than 50 million participants in organized running activities, and this number is believed to be an underestimate, considering that a sizeable proportion of participations do not enter the statistics (). In Croatia, there is a lack of organized running for novices, as athletic clubs mostly recruit professionals or young athletes. Aimed at providing a wider-scale boot camp for novice runners, the ‘school for runners’ was introduced in 2011 in Zagreb, the country capital. During an eight-month period, novices with varying physical fitness levels were systematically prepared to complete a half marathon (21.2 km) (). Since 2011, more than thousand participants completed the school and later remained active runners at varying levels.

Although introductory fitness programs have numerous benefits and positive life changing effects, some participants experience medical issues, mostly musculoskeletal injuries. Painful joints, muscles and tendons are the usual complaints among the school participants. There are numerous factors associated with injuries in runners and subsequent pain and the inability to train or complete the course. In general, injuries in novice runners are caused by inappropriate running programs or insufficient conditioning of the musculoskeletal system prior to entering a course, even if the progression in training loads is slow. In more experienced runners, injuries are caused by overtraining and overuse during longer periods (-). The pain is mostly in lower extremities and its origin is musculoskeletal system lesion (-).

Musculoskeletal system related running injuries can be defined as discomfort or pain in any part of the system that is severe enough to cause running activity to be decreased or stopped for longer than seven days (). Most published studies on injuries in runners included experienced novices or elite runners (-). Studies on novice runners are scarce, and most of them with a follow-up of no longer than several weeks (-).

The aim of our research was to determine types and incidence of running related lower extremity injuries and to identify sociodemographic and motivational risk factors in novice runners attending an eight-month running school program. The results of our study would be used to create an injury prevention strategy and implement it into the course of the school for runners.

Subjects and Methods

The school for runners

The eight-month school for runners begins in March and lasts until the end of October, when the annual Zagreb Marathon is held. The majority of the school participants aim at completing the half-marathon event. During the first month of the school, the participants are divided into groups of 20 runners and each group is assigned a coach throughout the course. Three training sessions are held weekly, usually in the duration of 45 to 60 minutes. The session begins with a warm-up period, followed by specific strengthening exercises for runners. The remainder of the training session consists of walk-run intervals starting with one-minute walk one-minute run intervals. Towards the end of the session, the running intervals are progressively prolonged. The session ends with cool-down exercises. After one month, the majority of the participants can run uninterruptedly for at least a kilometer. Based on their one-kilometer results, they are re-allocated to groups of 20 runners. The next milestone is reached at three months of training when participants are given the option to participate in a designated 5-km race; at the race, they are paced by school trainers, according to their best times achieved. After the 5-km race, the training sessions are held four times weekly. The next milestone is reached after five to six months when participants are given the option to participate in a 10-km race. After the 10-km race, the training sessions are held five times weekly. After seven to eight months, the participants reach a level of fitness that enables them to finish a half-marathon, usually at the aforementioned annual Zagreb Marathon. The school is leed and supervised by certified kinesiologists and kinesiology students who provide feedback to a medical doctor with regard to medical issues of the participants.

Subjects

Participants having enrolled in the school for runners between 2011 and 2014 were included in the study. Lower age limit was set at 18 years and participants were screened for running contraindications by a medical doctor before the first session. A medical doctor was present at all training sessions and participants were encouraged to communicate their health concerns. All participants gave their consent to participate in the study.

Data collection

Upon entry, sociodemographic (age and sex) and anthropometric (height and weight) data were collected on a predefined form. From the anthropometric data, the body mass index (BMI) was calculated using the formula: weight in kilograms divided by height in meters squared. BMI was re-calculated at the final session of the course. Apart from these data, a questionnaire was administered to the participants upon entry to assess for: (i) past injuries, (ii) past sports engagements, (iii) self-perceived overall health, (iv) level of fitness (on a 10-point scale), (v) motivation for enrollment in the school, and (vi) whether or not they were planning to complete a marathon. At the final session, a questionnaire was administered to assess: (i) whether during the course an injury occurred (injury was defined as pain in lower extremities, originating from the musculoskeletal system), (ii) anatomic region of the injury, (iii) duration of the injury, (iv) whether the injury caused the participant to abandon the school, (v) which type of training session they found to be easiest/most difficult, (vi) 5-km and half-marathon time (if successfully completed), (vii) whether or not they used additional counseling from sources other than ones provided in the school, and (viii) regularity of session attendance. After collecting all questionnaires, data were copied into an Excel spreadsheet.

Statistical analysis

Shapiro-Wilk test was used to test normality. Continuous variables were summarized as mean (standard deviation, SD), differences between two groups were assessed using t-test and differences among more than two groups using ANOVA. Ordinal variables were summarized as median (interquartile range, IQR), differences between two groups using Mann-Whitney U-test, and differences among more than two groups using Kruskal-Wallis test. Dichotomous variables were summarized as absolute (relative) frequency, and differences were assessed using χ2-test. All tests were two-sided and the level of significance was set at 0.05, with adjusted p values for multiple comparisons. The SPSS ver. 17.0 (Chicago, IL, USA) and Graphpad Prism ver. 6.0 (Graphpad Software, San Diego, CA, USA) were used on analyses.

Results

In the observed period, 349 participants were enrolled. Their mean age was 35.46±7.31 years and 271 (79.50%) were women. Injuries were reported by 173 (49.90%) participants. The mean BMI was 23.89±3.88 kg/m2 at baseline and 22.99±3.35 kg/m2 after the school (p<0.001). The 5-km race was completed by 234 (67.10%) participants in the mean time of 30.50±6.44 min. The half-marathon (21.097 km) was completed by 214 (61.30%) participants in the mean time of 129.96±30.85 min. One hundred and ninety-eight (55.30%) participants were planning to complete a marathon (42.2 km). Median self-perceived level of fitness was 4.00 (3.00-5.00) at baseline and 8.00 (3.00-5.00) after the school (p<0.001). Median self-perceived overall health status was 6.00 (5.00-8.00) at baseline and 8.00 (7.00-9.00) after the school (p<0.001). The majority of participants (76.90%) had a history of sports activity engagement (p<0.001 for theoretical distribution). Also, the majority (82.60%) of participants did not use additional counseling from sources other than those provided in the school (p<0.001 for theoretical distribution). The knee was the anatomic region most frequently injured, significantly more often compared to other regions (p<0.001). The long slow distance was perceived as the easiest training session by 141 (40.40%) participants and fartlek as the most difficult one by 103 (29.50%) participants (p<0.001). As the main motivation for enrollment, the participants reported improvement of fitness (n=159, 45.70%). Detailed subject characteristics are listed in Table 1.

Table 1

Subject characteristics

Variable	N	Mean	SD	p value
Age (years)	349	35.46	7.31
BMI at baseline (kg/m2)	348	23.89	3.88	<0.001*
BMI after school (kg/m2)	348	22.99	3.35
BMI difference (kg/m2)	348	0.90	1.24
Time at 5 km (min)	234	30.50	6.44
Time at half-marathon (min)	214	129.96	30.85
		Median	IQR
Self-perceived overall fitness at baseline	348	4.00	3.00-5.00	<0.001†
Self-perceived overall fitness after school	346	8.00	7.00-8.00
Self-perceived overall health at baseline	348	6.00	5.00-8.00	<0.001‡
Self-perceived overall health after school	346	8.00	7.00-9.00
Regularity of session attendance	348	8.00	7.00-9.00
		Frequency	%
Sex (female)	349	271	79.50
Injury (yes)	349	173	49.90
Planned marathon (yes)	344	193	55.30
History of sports activity	347
No		80	23.10	<0.001§
Yes		66	19.00
Periodically		201	57.90
Anatomic region of injury	173
Foot		30	8.60
Ankle		30	8.60
Lower leg		19	5.40
KneeUpper legHipLower back		76999	21.802.602.60
Additional counseling	344
No		140	40.60
Yes		60	17.40
Periodically		145	42.00
Easiest session	345
Speed		14	4.00
Intervals		123	35.20
Long distance		141	40.40
Tempo		34	9.70
Fartlek		18	5.20
Other		15	4.30
Most difficult session	344
Speed		61	17.50
Intervals		30	8.60
Long distance		93	26.60
Tempo		49	14.00
Fartlek		103	29.50
Other		8	2.30
Motivation for enrollment	348
Fitness improvement		159	45.70
Health improvement		43	12.40
Stress reduction		72	20.70
Competitive motivation		8	2.30
Reducing weight		33	9.50
Other		33	9.50

SD = standard deviation; BMI = body mass index; IQR = interquartile range; *t-test (baseline vs. post-school BMI); †Mann Whitney U-test (baseline vs. post-school perceived fitness); ‡Mann Whitney U-test (baseline vs. post-school perceived overall health); §χ2-test

When comparing injured and not injured participants, there were significant differences in: (i) median self-perceived overall health status before and after the school (8.00, IQR 7.00-9.00 vs. 8.00, IQR 7.00-9.00, p=0.026), (ii) proportion of women (74.30% injured vs. 84.50% not injured, p=0.023), and (iii) history of sports activity engagement (23.80% injured vs. 14.50% not injured, p=0.048) (Table 2).

Table 2

Difference between injured and not injured runners

	Injury			Without injury
	N	Mean	SD	N	Mean	SD	p value
Age (years)	173	35.77	8.15	174	35.16	6.42	0.432
BMI at baseline (kg/m2)	173	24.19	4.26	174	23.62	3.46	0.171
BMI after school (kg/m2)	173	23.21	3.75	174	22.80	2.89	0.262
BMI difference (kg/m2)	173	0.98	1.31	174	0.82	1.16	0.208
Time at 5 km (min)	123	30.33	5.99	110	30.65	6.96	0.706
Time at half-marathon (min)	117	130.32	26.82	96	129.33	35.38	0.816
		Median	IQR		Median	IQR
Self-perceived overall fitness at baseline	173	4.00	3.00-5.00	174	4.00	2.00-5.50	0.285
Self-perceived overall fitness after school	173	8.00	7.00-8.00	174	8.00	7.00-9.00	0.406
Self-perceived overall health at baseline	173	6.00	5.00-8.00	174	7.00	5.00-8.00	0.158
Self-perceived overall health after school	173	8.00	7.00-9.00	174	8.00	7.00-9.00	0.026*
Regularity of session attendance	173	8.00	7.00-9.00	174	8.00	7.00-9.00	0.562
		Frequency	%		Frequency	%
Sex (female)	171	127	74.30	168	142	84.50	0.023*
Planned marathon (yes)	171	100	58.50	172	92	53.50	0.352
History of sports activity	173			172
No		38	21.90		42	24.40	0.048*
Yes		25	14.50		41	23.80
Periodically		110	63.60		90	52.30
Additional counseling	172			172
No		61	35.50		79	46.00	0.137
Yes		33	19.20		26	15.10
Periodically		78	45.30		67	38.90
Easiest session	172			172
Speed		10	5.80		4	2.30	0.276
Intervals		53	30.80		70	40.70
Long distance		74	43.00		66	38.40
Tempo		18	10.50		16	9.30
Fartlek		8	4.70		10	5.80
Other		9	5.20		6	3.50
Most difficult session	172			171
Speed		34	19.80		26	15.20	0.423
Intervals		17	9.90		13	7.60
Long distance		39	22.70		54	31.60
Tempo		23	13.40		26	15.20
Fartlek		54	31.40		49	28.70
Other		5	2.90		3	1.70
Motivation for enrollment	173			174
Fitness improvement		75	43.30		84	48.30	0.678
Health improvement		19	11.00		23	13.20
Stress reduction		36	20.80		36	20.70
Competitive motivation		5	2.90		3	1.70
Reducing weight		18	10.40		15	8.60
Other		20	11.60		13	7.50

SD = standard deviation; BMI = body mass index; IQR = interquartile range; t-test was used for comparison of means, ordinal variables were compared using Mann Whitney U-test, and nominal variables using χ2-test; *statistically significant

With regard to sex, significant differences were recorded in baseline BMI (women 23.20±3.32 kg/m2 vs. men 26.80±4.81 kg/m2, p=0.007) and BMI after the school (women 22.30±2.64 kg/m2 vs. men 25.69±4.35 kg/m2, p=0.002). Also, there was a significant difference in the proportion of injured participants (women 46.70% vs. men 62.90%, relative risk 0.88, 95.00% CI 0.79-0.98), proportion of participants who planned to complete a marathon (women 52.40% vs. men 70.00%, p=0.008), and type of training session perceived to be most difficult (p=0.042).

Discussion

In our study, 173 (49.90%) runners reported injuries. The incidence of injuries was substantially higher compared to previously published research with a shorter and comparable follow-up, and lower compared to research with a longer follow-up. In their meta-analysis on injuries in different populations of runners, Kluitenberg et al. report summary estimates of incidence of injuries among novice runners (). They grouped the studies according to follow-up into three groups: (1) short follow-up (6-15 weeks); (2) one-year follow-up (11-13 months); and (3) follow-up longer than one year. Also, they grouped the studies according to injury definition into: (1) medical attention; (2) time-loss; and (3) pain related. They pooled the results of time-loss injuries during a short follow-up/recall period of four studies, and summary estimate was 26.40% (95.00% CI 14.20, 43.70). For a one-year period, they identified one study, with a proportion of injuries of 27.30% (95.00% CI 24.50, 30.30), and one study for a follow-up longer than one year, with a proportion of injuries of 84.90% (95.00% CI 74.60, 92.20). These results indicate that the incidence of injuries rises with the length of the study (differences between studies might also be attributable to different injury definitions and study populations). Nevertheless, the incidence of injuries in our study (49.90%) was significantly higher than in the study by Nilsen et al. (27.30%), which had a comparable follow-up. Their cohort had a lower proportion of women (49.70%) (). Since we found female sex to be associated with a lower incidence of injuries, this difference could be even bigger if the cohorts were comparable by sex. Age and BMI were similar to that in our study (). The difference that might explain the higher incidence of injuries in our cohort is the running schedule and the goal of the school, i.e. to prepare for a marathon. We believe that the higher incidence of injuries in our study might be attributable to the high mileage, high proportion of runners (55.30%) who entered the school as a preparation for a marathon, and high proportion of runners who completed a half-marathon (61.30%). Namely, both high weekly mileage and participating in a marathon were shown to be associated with an increased risk of a running related injury (). Also, different intercultural pain perception might explain to some extent the difference in the injury reporting prevalence of the authors’ cohort in comparison to other national cohorts ().

In our study, the knee was the most commonly injured anatomic region (21.80%), followed by foot and ankle (8.60% both). Albeit with a somewhat higher proportion (34.70%), it was the most commonly injured region in novice runners in the analysis by Kluitenberg et al. Across published studies, the knee is consistently reported as the predominant site of running related leg injuries (). The exact factors that make the knee most susceptible to injuries are not known, although it is plausible that it is due to the specific anatomy of the knee. Namely, the relative lack of highly adaptive tissues (muscles) makes the knee more sensitive to mechanical load ().

As expected, the mean BMI decreased and self-perceived health and fitness increased post-school as compared to baseline. Hespanhol Junior et al. report on a 3.30-kg reduction in body weight after one year of training. Weight reduction was comparable in our cohort (2.88 kg) (). Running has other beneficial effects on health indices, such as lipid profile improvement and resting heart rate reduction, therefore the subjects in our cohort experienced an overall improvement in self-perceived health.

Long slow distance was perceived as the easiest training session by 141 (40.40%) participants and fartlek as the most difficult one by 103 (29.50%) participants. To the best of our knowledge, there are no published results on training perception in novice runners. We believe that long slow distance training is perceived as being the easiest due to a steady slow tempo. On the other hand, fartlek is perceived as being the most difficult one due to intervals of high-intensity load.

There was a higher proportion of women among the non-injured runners (74.30% injured vs. 84.50% not injured). This finding is also consistent with the results of the previously published research, as females are known to have a lower risk of running related injuries (). Also, a lower proportion of fitness experience in injured versus non-injured runners is consistent with previous research findings (, ).

In conclusion, our results indicate that in order to reduce the incidence of running related injuries, organized running programs should focus less on preparing runners for a specific event, and instead introduce strengthening exercises, with particular focus on the knee.

A limitation of the study was not using objective diagnostic methods to assess injuries.