Introduction

Ischemic preconditioning (IPC) is a procedure that induces tissue ischemia via circumferential compression of limb(s) followed by reperfusion in a repeated, cyclic manner 18 30 . This occlusive practice has generated considerable interest recently, with IPC reported to enhance exercise performance 18 . The mechanisms for IPC as an ergogenic aid are unclear, but may be related to local hyperemia inducing greater tissue oxygenation 24 , enhanced mitochondrial function 1 and acceleration of muscle deoxygenation dynamics during moderate-intensity exercise 23 . Despite these potential beneficial effects during exercise, there are doubts about the efficacy of IPC for human performance 30 , and due to the high heterogeneity of results (i.e., IPC responders and non-responders), authors suggest investigating the individual phenotype 18 .

Several authors have attempted to demonstrate the beneficial effects of IPC on exercise performance 7 10 15 20 30 . For example, 10 strength-trained men who performed 5 sets of 5 maximal voluntary knee extensions of the right leg on an isokinetic dynamometer, preceded by either IPC of the right lower limb (3×5 min compression/5 min reperfusion cycles at 200 mm Hg) or sham (20 mm Hg), increased muscle perfusion and O 2 uptake, conducive to higher repeated force capacity 31 . In a randomized, crossover study, 13 healthy men improved their 5 km running time trial performance after IPC, compared with a control intervention, accompanied by lower blood lactate concentrations at submaximal exercise workloads 2 .

On the other hand, some authors suggest that IPC does not exceed the placebo effect and others that CPI has no effect on performance improvement 33 36 .

Despite some studies that report beneficial effects of IPC on simple actions and discrete exercise (e.g., running, swimming and cycling) 18 30 , little attention has been given to IPC use for team sport participants, and even less for IPC as a recovery modality. Proper recovery interventions are crucial for human performance and studies have attempted to find them 11 34 . To our knowledge, only 2 studies have investigated the effectiveness of IPC as a recovery intervention 3 5 . One study demonstrated no positive effects from IPC after a strenuous bout of eccentric exercise (3 sets of 100 repetitions), at 24, 48 and 72 h post-exercise compared with a non-IPC (control) recovery period 5 . The other reported a beneficial effect of IPC on repeated sprint ability and jump height performances but only at 24 h after the intervention 3 . Although these study designs were interesting, the exercise bout examined was atypical in practical terms (i.e., involved a high volume of eccentric actions) with the recovery period also potentially too long for some athletes during sporting competition. For instance, during an amateur “sevens” rugby union tournament, matches commonly occur over a period of 2 to 3 d with only ~1 h of rest between matches. Consequently, implementation of treatment between matches to improve recovery and enhance performance would be highly advantageous. Given that IPC induces local hyperemia, potentially higher tissue oxygenation 24 , and enhanced mitochondrial function 1 , IPC may provide a novel means to enhance recovery and subsequent performance within a short timeframe (i.e., ~1 h), similar to that during competitive tournaments. Thus, the aim of this study was to evaluate the effectiveness of IPC on acute recovery and performance in rugby union players.

Materials and Methods

Participants

Eight male, amateur rugby union players (24±4 yrs; 179±5 cm; 88±9 kg) competing at the state level, participated as volunteers. All participants were informed about the experimental procedures and gave written informed consent prior to participation in accordance with approval by the local Ethical Committee for Human Experiments and meet ethical standards in sport and exercise science research 16 . Prior to the study, all players had undergone at least 6 months of rugby-specific training, with the study taking place during the pre-competition phase of the season. None of the players reported any cardiovascular, pulmonary, metabolic diseases, musculoskeletal injuries, skin or gastrointestinal infections. Further, none reported to have used anabolic steroids or drugs that may have affected physical performance, and none were taking any anti-inflammatory drugs for at least one week before the study.

All players were nonsmokers and were instructed to avoid any consumption of food or drinks in the 3 h prior to testing and to refrain from alcohol consumption and exercise in the 24 h prior to the testing session. Caffeine ingestion was limited to coffee at 06:30–09:00 with the rugby-specific exercise protocol and performance tests beginning at 16:00.

Experimental protocol

A randomized crossover design was used to investigate the effect of IPC on performance during the acute recovery (~1 h) period following a rugby-specific exercise protocol ( Fig. 1 ). Beyond the anthropometric measures and familiarization with all physiological, neuromuscular, and perceptual procedures previously performed, the players performed 2 complete trials with 1-week between trials. The trials differed only in the recovery strategy (i.e., 21 min of IPC or passive rest – control). The rugby-specific exercise protocol and performance tests took place at the same time of day (starting at 16:00) to minimize any confounding effects of daily biorhythms. Players completed a set of performance tests followed by the first exercise protocol and post-exercise assessments. The performance tests (T-test, single vertical countermovement jump and 30 s continuous vertical jumps test), were conducted 6 times during the study: i) at baseline (separate day); ii) immediately after the rugby-specific exercise protocol; and iii) after the intervention (IPC or control) during each of the 2 testing sessions, one week apart ( Fig. 1 ). These tests were previously employed in studies involving rugby union players and reported to exhibit high validity and reliability for rugby union players 9 19 38 .

Fig. 1

Experimental design of the study.

Rugby-specific exercise protocol

In an indoor gymnasium (21–24°C, 50–60% relative humidity), after a 7 min warm-up (i.e., 5 min of slow jogging and 2 min of dynamic and static stretching), the players completed the rugby-specific exercise protocol that simulated the physical and skill demands of a rugby union match 14 35 . The protocol simulated a match half (40 min) and consisted of 8 stations performed in the following order (5 min each with 30 s of passive rest between them): i) jumps; ii) skill passing; iii) position scrum with member alternation; iv) slalom agility sprints; v) rest and hydration; vi) dragon walks; vii) slalom agility sprints; and viii) 20 m sprint. All players received similar verbal encouragement by an independent evaluator, who did not know the experimental condition, and completed the protocol as a rotational circuit (same order of tests, in sequence).

To ensure that the internal intensity was similar across the 2 trials, all players wore a Polar RS800CX ® heart rate (HR) monitor (Polar Electro Oy, Kempele, Finland) during each trial with rating of perceived effort ([RPE], 0–10) 37 obtained at the end of each station. The HR was continuously assessed during the exercise protocol and analyzed as the average for all 8 stations. Similarly, analysis of RPE utilized the mean rating across all stations.

Performance Tests

T-test

T-test was performed at baseline (separate day), 1 min after the rugby-specific exercise protocol and 1 min the intervention (IPC or control). The players performed the agility test as fast as possible twice, separated by 1 min, as per the standardized protocol 32 . Briefly, players ran 9.14 m followed by side stepping to the left (4.57 m), side-stepping to the right (9.14 m), side-stepping to the left (4.57 m) and backward running (9.14 m) to the start/finish line. Time of completion was manually recorded by 3 trained assessors using chronometers (SEIKO S141-300, Japan) and averaged. Assessors were blinded with regards to the recovery interventions, as previously suggested 8 . The T-test has been reported to exhibit high validity and reliability across trials with a reliability coefficient of 0.98 32 . To ensure minimal measurement errors, inter-assessor reliability in the current study was examined using an intra-class correlation coefficient (ICC) with a mean ICC value of 0.878 (95% CI=0.836–0.917; p =0.033) calculated.

Countermovement jump test (CMJ)

All players performed the CMJ on a contact mat system (Just Jump, Probotics, Inc., Huntsville, USA) with their hands kept on their hips for the entire jump 25 after the T-test. 3 standardized jumps (90° knee flexion) were completed with 30 s rest between jumps. Jump flight time was measured via the contact mat and jump height calculated using the participant’s mass 25 . The best CMJ height was considered for analysis. The CMJ has been employed as a practical and commonly used valid test of leg power with good intra-day (coefficient of variation – CV=5.2%) and inter-day (CV=5.0%) jump height reliability 6 .

30 s continuous jump test (CJ30)

The CJ30 test was performed after CJM and consisted of the performance of maximal, continuous vertical jumps during 30 s using the same contact mat system described above. All players were instructed to maintain a standardized jump technique where the torso was as vertical as possible, hands crossed at their chests and a knee joint flexion angle of ~90° at the bottom of the jump. Jump height was calculated as described above with the average jump height of all jumps during the 30 s period used for analysis. The CJ30 has been reported to be a reliable indicator of muscular endurance and performance 9 .

Recovery strategies - ischemic preconditioning (IPC) protocol or control

The 21 min IPC protocol consisted of 3 cycles of 5 min occlusion at 220 mmHg using a 96 cm×13 cm pneumatic cuff applied around the sub-inguinal region of the upper thighs (Komprimeter Riester ® , Jungingen, Germany) alternated with 2 min of reperfusion at 0 mmHg 3 . The applied pressure and cuff width were in accordance with that used in previous studies 28 to ensure that blood flow was occluded during the intervention. The occlusion and reperfusion phases were conducted alternately between the thighs (i.e., each thigh was occluded for 3 cycles of occlusion/reperfusion) with participants remaining seated during the entire 21 min. The effectiveness of occlusion during the IPC session was confirmed by auscultation of the arteries around the ankle 28 during the start of each occlusion/reperfusion phase. No cuff was applied to the thighs during the control protocol and participants sat passively for 21 min.

Rating of recovery

At baseline, before and after the 2 trials of rugby-specific exercise protocol (IPC or control), the players reported their rating of recovery using a total quality recovery scale ranging from 6 (~very, very poor recovery) to 20 (~very, very good recovery) 22 .

Statistical analysis

The Shapiro-Wilk test was employed to verify the normal distribution of the data. Comparisons of data related to the rugby-specific exercise protocol (HR, RPE) were conducted using paired T-tests (normal distribution) or Wilcoxon matched-pairs signed-rank tests (non-normal distribution). Examination of variables between interventions (IPC vs. control) at each time point was carried out via Wilcoxon matched-pairs signed-rank tests with a Bonferroni correction for the number of comparisons. The significance level was set at 0.05 and all analyses were conducted using GraphPad ® (Prism 6.0, San Diego, CA, USA).

Results

During the rugby-specific exercise protocol, mean HR (158.3±18.0 bpm vs. 158.7±16.0 bpm, p=0.96) and RPE (8.2±0.9 vs. 8.0±1.0, p=0.69) were similar prior to the IPC and control interventions, respectively. At baseline, the rating of recovery was similar for the IPC and control trials (18.5±0.5 vs. 18.5±0.8, p>0.05) and similar to the values prior to the rugby-specific exercise protocol (IPC=18.8±0.7; control=18.6±0.5, p>0.05). Following the rugby-specific exercise protocol, the rating of recovery was similar for both trials (IPC=13.9±1.4; control=13.6±1.6, p>0.05).

At each time point (i.e., baseline, post-rugby-specific exercise protocol and post-intervention), T-test and CMJ results were similar for the control and IPC conditions ( Fig. 2a,b ). Likewise, CJ30 performance was comparable (p>0.05) after both the IPC and the control interventions ( Fig. 2c ).

Fig. 2

a T-test (agility), b countermovement jump, CMJ (leg power) and c continuous CMJ during 30-s (muscular endurance) at baseline, immediately after the rugby-specific exercise protocol (Post RSEP) and immediately after the intervention (Post Intervention) for the ischemic preconditioning (IPC) and passive rest (Control) trials. * means p < 0.05 vs. Baseline.

Discussion

Our main finding was that IPC of the thigh muscles (i.e., alternate unilateral occlusion) did not improve the short-term recovery of performance or perceived recovery status for amateur rugby players following a simulated match. During the short intervals of rest (e.g., ~1 h) between matches throughout a competitive tournament (i.e., several matches in the same day), IPC may not be an effective means to enhance athlete recovery and subsequent performance.

Prior studies of IPC and long-term recovery have produced mixed results 3 5 with the only positive effect reported being increased repeated sprint ability and jump height at 24 h after IPC 3 .

The authors attributed the IPC-induced improvement to increased blood flow (i.e., reperfusion) and muscular oxygen utilization for a faster recovery of muscular function. However, blood flow and oxygen consumption were not assessed in that study and their mechanistic statements were speculative. In the current study, no measure of performance was different between IPC and control trials immediately and 1 h following a simulated match. This lack of IPC effect was similar to that reported following a strenuous bout of eccentric exercise over 72 h 5 and provides further inconclusive evidence of the recovery benefits of IPC.

Because several matches in a single day are common during amateur rugby sevens tournaments and IPC has been reported to improve performance in exercise of predominantly lactic anaerobic and aerobic capacity 18 , there is evidence suggesting a time-dependent effect of ischemic preconditioning, with the time window of the beneficial effect starting after about 2 h and lasting for at least 8 h after ischemic preconditioning 27 . However, the current results demonstrated no differences between IPC and control. Considering the time, logistics and pain involved with the IPC maneuver 26 , passive recovery may be a more suitable recovery for these athletes during tournaments.

Importantly, the similar IPC and control results in the current study confirmed that IPC did not incur further decrements in performance. Despite not being beneficial for athletes in the short term, IPC did not harm athletes and/or reduce performance in the current study. Whether multiple applications of recovery IPC after many matches have the same, greater, or diminished effect has yet to be examined. With potentially increased muscular damage and fatigue occurring during repeated matches over a short time span such as a competitive tournament 21 , the potential benefits of IPC may become more apparent. Whether these benefits involve improvement in muscle blood flow and oxygenation has yet to be validated with future studies encouraged to examine these parameters during tournament conditions. To our knowledge, no other study has examined recovery with IPC after a team sports simulated match within a short (~1 h) or longer post-exercise time. Therefore, our study was unique in examining the post-exercise use of IPC for team sports and included a very controlled and robust design (i.e., counterbalanced crossover and randomized) that should be followed for future studies.

As indicated previously, similar performances were noted following IPC and control recovery procedures. These similarities were not due to altered performances of rugby-specific exercise protocol because the current HR responses and RPE were comparable between the 2 rugby-specific exercise protocols performed. Further, perception of recovery using the total quality recovery scale was equally lower after the simulated match for both interventions (IPC and control). Therefore, the 2 trials of rugby-specific exercise protocol were equally stressful, resulting in similar states for the recovery strategies. The cardiovascular response imposed on athletes (HR of 158 bpm, ~80% HR peak ) was similar to that experienced by amateur rugby players 13 and elite youth rugby league players (78.8–83% HR peak ) 37 . Additionally, the rating of perceived effort (RPE) imposed on athletes (~8 out of 10) was in line with comparable studies of rugby athletes 37 . Therefore, the current responses of HR, in absolute and relative terms, as well as RPE, were in accordance with prior studies of rugby 35 and further highlight the ecological validity of the rugby-specific exercise protocol.

It is important that some limitations of the present study be documented. The absence of a sham/placebo trial could have affected results, because a potential placebo effect of IPC has been reported for some performance variables 29 30 . A placebo effect may result from the interaction between psychological and physiological variables 4 , however, this was unlikely given that no positive effects of IPC on performance were identified in the current study and the rate of recovery (i.e., a subjective measure that involves psychological factors) was also unaffected by IPC.

Secondly, the current study was limited to a small sample size. Previous studies examining IPC have reported beneficial effects of IPC with a similar sample size 12 . Further, we incorporated non-parametric analyses in the current study to minimize any impact of sample size. Finally, sub-elite players were examined in the current study with results possibly not translatable to elite athletes. However, IPC interventions have promoted similar effects in both amateur 12 and highly trained cyclists 17 with future studies needed to identify possible unique IPC responses based on training status.

Conclusions

IPC does not improve recovery of performance acutely (within 1 h) for sub-elite rugby players following a rugby-specific exercise protocol. The use of IPC between closely scheduled matches performed on the same day may therefore be of minimal benefit with other recovery strategies likely to be more advantageous for enhancing performance. The match and recovery benefits of IPC use during tournaments with greater between-match intervals (~3 h) remains to be clarified.