Effects of Cold Water Immersion and Contrast Water Therapy for Recovery From Team Sport: A Systematic Review and Meta-analysis

Abstract

Higgins, TR, Greene, DA, Baker, MK. Effects of cold water immersion and contrast water therapy for recovery from team sport: a systematic review and meta-analysis. J Strength Cond Res 31(5): 1443–1460, 2017—To enhance recovery from sport, cold water immersion (CWI) and contrast water therapy (CWT) have become common practice within high level team sport. Initially, athletes relied solely on anecdotal support. As there has been an increase in the volume of research into recovery including a number of general reviews, an opportunity existed to narrow the focus specifically examining the use of hydrotherapy for recovery in team sport. A Boolean logic [AND] keyword search of databases was conducted: SPORTDiscus; AMED; CINAHL; MEDLINE. Data were extracted and the standardized mean differences were calculated with 95% confidence interval (CI). The analysis of pooled data was conducted using a random-effect model, with heterogeneity assessed using I². Twenty-three peer reviewed articles (n = 606) met the criteria. Meta-analyses results indicated CWI was beneficial for recovery at 24 hours (countermovement jump: p = 0.05, CI: −0.004 to 0.578; All-out sprint: p = 0.02, −0.056 to 0.801) following team sport. The CWI was beneficial for recovery at 72 hours (fatigue: p = 0.03, CI: 0.061–1.418) and CWT was beneficial for recovery at 48 hours (fatigue: p = 0.04, CI: 0.013–0.942) following team sport. The CWI was beneficial for neuromuscular recovery 24 hours following team sport, whereas CWT was not beneficial for recovery following team sport. In addition, when evaluating accumulated sprinting, CWI was not beneficial for recovery following team sports. In evaluating subjective measures, both CWI (72 hours) and CWT (24 hours) were beneficial for recovery of perceptions of fatigue, following team sport. However neither CWI nor CWT was beneficial for recovery, of perceptions of muscle soreness, following team sport.

Introduction

In team sports, habitual activity that consists of multiple training sessions, competition games, and recovery over a week occur each week of the season (⁴⁶). These multiple training sessions can consist of dedicated conditioning sessions incorporating skills and unit practices, resistance training sessions, functional training and team runs involving strategy and game patterns (^7,46). This cycle extracts an ever-increasing physical toll from athletes, impacting muscle contractibility at the point of fatigue, because of metabolic disturbances followed by structural disruptions within the muscle fibers (^2,50,53).

In the context of team sports, during general preparation and specific preparation phases of a periodized program, metabolic disturbances and structural disruptions are essential (²⁸). They are required for the development of adaptation to a given workload and consequently enhancement of athletic performance during these periods of the training program (²⁸). However, during the competition phase of a season, the focus is on the maintenance of a player's physiological condition as opposed to its development (²⁸). Maintenance becomes problematic during the competition phases of team sport as structural disruptions have a recovery period of between 3 and 7 days (²⁸). With time periods of less than 72 hours between games/training sessions, players are exposed to additional training stimuli before they are fully recovered leading to the development and accumulation of fatigue (⁴⁶). As fatigue has been defined as a reduction in physical and or functional performance (⁴⁶), the management of these structural disruptions becomes essential in relation to athletic performance.

To enhance and/or accelerate recovery of the structural disruptions associated with team sport, a number of hydrotherapy protocols have been adopted in the field of professional sport (^4,5,19,35,43). Hydrotherapy is a broad-based term in sport science and includes immersion in hot or cold water, ice massage, hot and/or cold showers, exercise in water, or various combinations of these interventions (^4,5,19,35,43). The professional sporting community in general believes that hydrotherapy accelerates the recovery process of athletes, bringing about a faster return to an optimal functioning state. However, supporting evidence in the sport science literature is inconsistence and despite its popularity, support for hydrotherapy remains equivocal.

A number of factors explaining the inconsistencies between results across the sport science literature have been raised. Halson and Leeder et al. (^19,35) stated that when evaluating recovery from sporting performance a number of factors need to be taken into account (^19,35). Initially, athletes will respond differently to different types of physiological stressor. Non–weight bearing activities such as swimming and cycling will generate different physiological disturbances than weight-bearing activities such as running (^19,35). Furthermore, sports involving collision/impact events would elicit additional physiological disturbances again (^19,35). Therefore, evaluation of recovery modalities should be conducted using physiological stressors similar to the sporting activities for each specific athletic population (^19,35).

Training status of participants also needs consideration. Because of high training status and subsequent adaptation processors, well-trained, professional, elite level athletes may have blunted responses to physiological stressors in comparison with untrained or recreational athletes (^19,35). Results from evaluations of recovery protocols with participants of either high training or untrained cannot be routinely transferred to differing participants (^19,35). Therefore, recovery protocols should be evaluated with participants of an appropriate training status (^19,35).

When evaluating hydrotherapy, biochemical markers, subjective measure of muscle pain and fatigue, neuromuscular performance and sporting performance have routinely been used as measures for recovery from fatigue (^19,35). To date, conflicting findings have been reported across studies providing no clear indications as to the beneficial effect of hydrotherapy toward recovery from biochemical markers, subjective measures, neuromuscular recovery, and sporting performance in team sport.

Although the popularity of hydrotherapy for recovery has increased in team sport, a number of questions have been raised with regard to its suitability (^10,54). Initial concerns have included heat applied in contrast therapy increasing inflammation and edema (¹⁰). The initial impact of heat may have a detrimental effect on recovery with increased inflammation and edema (¹⁰). However, the authors speculated the initial heat would be offset by the subsequent application of cold, although the benefits of a single continuous immersion would exceed those of intermittent immersions (¹⁰).

In addition, Versey et al. (⁵⁴) speculated that hydrotherapy may blunt the chronic adaptation processes. It was theorized that hydrotherapy could disrupt mechanisms of fatigue, which may be a prerequisite for adaptation, sought by athletes and training staff, in the development of fitness (⁵⁴). However, benefits associated with recovery in the acute stages, specifically increases in frequency, intensity, or duration of training could offset the potential detrimental effects through a blunted adaptation response (⁵⁴).

In an attempt to clarify the efficacy of recovery methods, a number of reviews/meta-analyses have subsequently been conducted (^5,35,43). Authors from these reviews have drawn to the reader's attention limitations that currently exist in recovery research, in particular, the practice of comparing results from trained and untrained participants. It was highlighted that interpretation and transfer of both data and results between untrained and trained participants are difficult (⁴³). In addition to limitations associated with varying training status of participants, the variation between different exercise stressors was also raised. The nature of physiological stress will vary considerably between different types of exercise stressors (³⁵). Further to this, the potential for reduced performance will vary depending on the exact exercise stressor that an athlete is recovering from (^19,35). Furthermore, it was identified that weight-bearing activities, including running and weight training respond differently, in physiological stress and recovery response, to non–weight bearing activities such as cycling and swimming (¹⁹).

Despite raising these issues, the reviews included articles encompassing both a range of participants and a range of exercise stressors. With the increase in research into recovery, the opportunity prevails to extend the work initiated by these reviews, and to narrow the focus on specific methods and athletic populations. It has been identified that team sport comprises a number of high-intensity repeat efforts, including a multitude of directional changes, jumping efforts, and physical impacts/collisions (^9,52), and that each event adds to the physiological stress confronting the athletes' ability to recover (^9,52). Therefore, limiting studies to those evaluating recovery in team sport is essential to be able to evaluate the true beneficial effect of recovery interventions in team sport.

Furthermore, although there are vast arrays of recovery modalities, actively used, including stretching, massage, electrical stimulation, active recovery, and compression garments, the implementation of hydrotherapy for recovery has grown in popularity in team sport, without clear scientific support (¹). Therefore, the purpose of this article was to systematically review the available research evaluating hydrotherapy for recovery in team sport. This critical appraisal of recovery methods is necessary to inform the translation of this evidence base into guidelines for enhancing recovery in team sport athletes, currently absent from the sport science literature.

Methods

Design

The systematic review was carried out following the recommendations outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement (³⁷). A computerized literature search of online databases was undertaken by one author (T.R.H.), between September 9, 2014 and September 20, 2014. Before excluding papers, all authors (T.R.H., D.A.G., and M.K.B.) met to review the papers. Papers were excluded immediately when each author agreed. If there was a disagreement on the suitability of an article, a meeting was called with authors presenting arguments, either for or against a paper's inclusion/exclusion. If agreement was still absent, the decision with most authors in support was adopted. Capture dates were limited to individual databases dates for online availability. Databases searched included: SPORTDiscus with Full Text (1998–2014); AMED–The Allied and Complementary Medicine Database (1995–2014); CINAHL Complete (1998–2014); MEDLINE Complete (1997–2014). Search strategy included a combination of Boolean logic [AND] keyword search (Interventions, recovery, team sport) (Figure 1). A hand search was also conducted by one author (T.R.H.). The hand search included searching through the reference lists of articles identified in the database search. Papers included in the hand search were the articles identified to be included in this systematic review and published reviews on recovery.

Figure 1.: Flowchart of outcomes of search strategy.

Studies were excluded if they were not evaluating recovery, evaluated performance without a recovery intervention, adaptation to a training protocol, assessing recovery of acute or chronic injury.

Interventions

To be included, studies were required to use a physiological stressor associated with team sport. This could include competitive games, simulated competitive games, team training, or combinations of the above. Studies were to include comparison between postexercise recovery modalities associated with hydrotherapy and at least one other group, and examined a time period of no less than 24-hour postphysiological stressor.

Studies that used general or non–sporting specific physiological stressors, evaluated a single limb/body section, evaluated the immediate response (<24 hours), without extending to 24 hours or beyond, and following hydrotherapy were excluded (^6,8).

Study Populations

Studies comprised of male participants, female participants, or both were included. Participants were required to be reported as free from injury or illness and further classified as either/or well-trained, athletic, elite/semi-elite, professional/semiprofessional, and academy/institute team athletes. Studies evaluating untrained, recreational athletes or athletic status not disclosed were excluded.

Outcome Measures

Studies were required to measure the effect recovery interventions on one or more outcome measures. Measures could include biochemical markers, physical performance, and subjective measures of performance, and/or muscle soreness, power, acceleration, fitness tests, neuromuscular performance, or passive assessments.

Data Extraction

Data relating to types of interventions (cold water immersion [CWI], contrast water therapy [CWT], thermal-neutral water immersion), physiological stressor (competitive game, simulated game, team training), data collection time points, mean totals, and SDs, were extracted by one author (T.H.). Where insufficient information was provided, attempts to contact the authors through e-mails were made to obtain the missing data.

Assessment of Methodological Quality

To be included, studies were to meet the minimum quality threshold, defined as having met all the inclusion criteria. Further quality assessment was conducted using a modified Delphi Scale (^11,26) and Jadad Scale (³⁶).

Meta-analysis

All meta-analysis calculations were conducted with the Comprehensive Meta-Analysis software (Version 2.2.057; Biostat Inc., Englewood, New Jersey, USA). A p-value of <0.05 was considered statistically significant for all analyses. Statistical heterogeneity was assessed using the I², which describes the percentage of variability in effect estimates that is due to heterogeneity rather than chance (³⁵). To assess for the presence of publication bias, visual inspection of funnel plots was used to investigate the relationship between effect size and sample size.

The standardized mean differences (mean difference between recovery intervention and control groups divided by pooled SD) were calculated across variables including neuromuscular performance (jump performance, sprint times, agility), subjective measures of fatigue and muscle soreness, biochemical markers, repeat effort tests, and game performance markers, with a 95% confidence interval (CI) (³⁵). For the purposes of meta-analysis, the direction of change for some studies was reversed to ensure consistency of directionality between the tests; reduced times in sprints indicated improvement in recovery, whereas increased subjective values of fatigue or muscle soreness indicated improvement in recovery. The analysis of pooled data was conducted using a random-effect model allowing for the calculation of the direct probability of a treatment effect.

Results

Identification and Selection of Studies

The original search produced 10,276 articles. After reviewing the titles and abstracts as well as conducting a hand search through the reference lists of manuscripts, the total number of articles was reduced to 396. Further elimination of papers based on the eligibility criteria provided the final total of papers at 23 (Figure 1).

Cohort Characteristics

Across the included studies a combined total of 606 participants (506 men; 47 women; 53 not reported) participated in the trials. Three studies evaluated both male and female participants, 2 studies evaluated female participants only, and 19 studies evaluated male participants only. A further 2 studies did not report the gender of the participants. Participants were recruited from 8 different team sports (AFL [n = 2], American Football [n = 1], Basketball [n = 4], Netball [n = 2], Football [n = 5], Futsal [n = 1], Rugby Union [n = 10], Rugby League [n = 3], Volleyball [n = 2]), with one study describing participants as team sport athletes. Four of the included studies recruited participants from multiple sports, whereas the rest of the studies recruited participants from only one of the above-mentioned team sports (Table 1). Thirteen of the studies were conducted during the competition phase of the sporting calendar. Five studies were carried out during the preseason phase of the sporting calendar and 2 studies were conducted during the off-season phase of the sporting calendar. Six studies did not report the phase of the sporting calendar in which they were conducted (Table 1).

Table 1.: Participant characteristics.*

Physiological Stressor

Seven studies incorporated team training sessions as their physiological stressor with 11 studies incorporating competition games as the physiological stressor. Six studies incorporated both competition games and team training sessions as the physiological stressors and 6 studies incorporated simulated team sport games as the physiological stressor (Table 2). Hydrotherapy interventions applied included CWI (n = 21), contrast water therapy (n = 13) and showers (n = 2). Several studies included additional recovery interventions that included compression garments (n = 4), saunas (n = 1), massage (n = 2) and active recovery (n = 5). Control protocols included seated rest (n = 20), thermoneutral water immersion (n = 3), nutritional intake (n = 1), placebo (n = 1), stretching (n = 3), and several groups evaluating response of more than one recovery intervention without a control group.

Table 2.: Study protocols.*

Table 2-A.: Study protocols.*

Table 2-B.: Study protocols.*

Studies used a range of times for immersion when applying CWI including a total time immersed of 10 minutes (n = 12), which included 7 studies applying 2 cycles of 5-minute immersions and 1 study applying 5 cycles of 2-minute immersions. Additional immersion times included a single 15-minute immersion (n = 2), 5-minute immersion (n = 7) either as a single 5-minute immersion (n = 3) or 5 cycles of 1-minute immersion (n = 4). Temperatures for cold water ranged between 5 and 15° C with most studies applying cold water between 10 and 12° C (n = 20). Hot/warm water temperatures ranged between 38 and 42° C in most studies (n = 13) applying CWT with immersion times of between 1 and 3 minutes (Table 2).

Data collection time points included baseline, within 1 hour (n = 18), 24 hours (n = 18), 48 hours (n = 8), 72 hours (n = 1), 96 hours (n = 2) and 7 days (n = 3), postexercise stressor. Six studies included other data collection points.

Countermovement Jump

The results showing the effect of hydrotherapy as a recovery modality, on countermovement jumps (CMJ), are displayed in Figures 2 and 3. Overall, results for CMJ indicated that CWI was beneficial for recovery of neuromuscular recovery 24 hours following the exercise stressor (p = 0.05, CI: −0.004 to 0.578). However, at all other time points, CWI did not enhance neuromuscular recovery (1 hour: p = 0.39, CI: −0.202 to 0.514; 48 hours: p = 0.56, CI: −0.244 to 0.451; 72 hours: p = 0.38, CI: −0.360 to 0.954). Furthermore, results for CMJ indicated CWT did not enhance neuromuscular recovery at any time points following the exercise stressor (1 hour: p = 0.07, CI: −0.004 to 0.863; 24 hours: p = 0.46 CI: −0.227 to 0.498; 48 hours: p = 0.39, CI: −0.191 to 0.489).

Figure 2.: Forest plot for cold water immersion vs. control in countermovement jumps.

Figure 3.: Forest plot for contrast water therapy vs. control in countermovement jumps.

Best Sprint

The results showing the effect of hydrotherapy as a recovery modality, on a one all-out maximal sprint test, are displayed in Figure 4. When evaluating performance of all-out sprint performance, CWI enhanced recovery 24 hours following the exercise stressor (p = 0.02, CI: −0.056 to 0.801). However, overall results for one all-out maximal sprints indicated that CWI had minimal effect on enhancing recovery as measured in one all-out sprint performance 1 hour, 48 hours, and beyond 90 hours following the exercise stressor (1 hour: p = 0.07, CI: −0.039 to 0.873; 48 hours: p = 0.15, CI: −0.159 to 1.068; >90 hours: p = 0.15, CI: −0.093 to 0.591). When evaluating the effect of CWT as a recovery modality with a one all-out maximal sprint test, data from only one study at each time point was available; therefore, a meta-analysis was unable to be conducted.

Figure 4.: Forest plot for cold water immersion vs. control in one all-out sprint.

Accumulated Sprint Time

The results showing the effect of hydrotherapy as a recovery modality, on accumulated sprint time, are displayed in Figure 5. Overall, results indicated that at 24, 48, and 72 hours following the exercise stressor, CWI was not beneficial in enhancing recovery when evaluated with accumulated sprinting (24 hours: p = 0.29, CI: −0.189 to 0.637; 48 hours: p = 0.44, CI: −0.171 to 0.392; 72 hours: p = 0.07, CI: −0.062 to 1.209). No studies examining accumulated sprinting evaluated the effects of CWT.

Figure 5.: Forest plot for cold water immersion vs. control in accumulated sprinting.

Muscle Soreness

The results showing the effect of hydrotherapy as a recovery modality, on muscle soreness, are displayed in Figures 6 and 7. Combined results for perceptions of muscle soreness, indicated that CWI did not enhance participants perception of muscle soreness (1 hour: p = 0.20, CI: −0.192 to 0.920; 24 hours: p = 0.08, CI: −0.092 to 1.936; 48 hours: p = 0.41, CI: −1.632 to 4.011; 72 hours: p = 0.09, CI: −0.121 to 1.555). Furthermore, as with the findings with CWI, CWT did not enhance perceptions of muscle soreness, following exercise stressor (24 hours: p = 0.12, CI: −0.233 to 2.082; 48 hours: p = 0.25, CI: −0.999 to 3.803).

Figure 6.: Forest plot for cold water immersion vs. control in muscle soreness.

Figure 7.: Forest plot for contrast water therapy vs. control in muscle soreness.

Subjective Measures of Fatigue and Effort

The results showing the effect of hydrotherapy as a recovery modality, on participants' subjective measures of fatigue and effort are displayed in Figures 8 and 9. Combined results for perceptions of fatigue indicated that CWI enhanced athletes' perception of fatigue and recovery 72 hours following the exercise stressor (p = 0.03, CI: 0.061–1.418). However, in contrast, CWI did not enhance athletes' perception of fatigue and recovery at all other time points (24 hours: p = 0.44, CI: −0.264 to 0.611; 48 hours: p = 0.28, CI: −0.309 to 1.063; >90 hours: p = 0.16, CI: −0.240 to 1.422). As with CWI at 72 hours, at 48 hours CWT enhanced athletes perceptions of fatigue and recovery following exercise stressor (p = 0.04, CI: 0.013–0.942) but did not enhance perceptions of fatigue and recovery 24 hours or 72 hours following exercise stressor (24 hours: p = 0.59, CI: −0.373 to 0.661; 72 hours: p = 0.08, CI: −0.082 to 1.408).

Figure 8.: Forest plot for cold water immersion vs. control in measures of fatigue.

Figure 9.: Forest plot for contrast water therapy vs. control in measures of fatigue.

Flexibility/Range of Motion

Although flexibility and/or range of motion has anecdotal support to indicate recovery, there was lack of studies to conduct a meta-analysis. Data from only 2 studies were available for evaluation of each hydrotherapy intervention.

Biochemical Markers

A number of markers were used across studies including creatine kinase (CK), interleukin-6 (IL-6), aspartate aminotransferase (AST), C-reactive protein (CRP), lactate dehydrogenase (LDH), and lactate and pH. With the exception of CK, a dearth of studies evaluating IL-6, AST, CRP, and LDH were available for meta-analyses to be conducted. The results showing the effect of hydrotherapy as a recovery modality on CK are displayed in Figure 10. Overall, results for CK indicated that CWI did not enhance clearance levels of CK 24 hours following the exercise stressor (p = 0.06, CI: −0.009 to 0.658). There were insufficient data available at additional time points to conduct a meta-analysis beyond 24 hours with CWI. Furthermore, there was insufficient data on CWT to conduct a meta-analysis at any time point (^27,38,48).

Figure 10.: Forest plot for cold water immersion vs. control in measures of creatine kinase.

Discussion

This is the first systematic review with meta-analyses to specifically investigate hydrotherapy as a recovery protocol with well-trained, team sport athletes. Although a number of reviews have been conducted on hydrotherapy and recovery, all have included considerable variation between training status and physiological stressors of participants. Overall, results indicated that in enhancing neuromuscular recovery following team sport, only CWI (24 hours) enhanced neuromuscular recovery. However, benefits in neuromuscular recovery identified at 24 hours were not evident at any other time point. In evaluating subjective measures, CWI (72 hours) and CWT (24 hours) enhanced perceptions of fatigue, following team sport. However, neither CWI nor CWT was identified as enhancing recovery of perceived muscle soreness following team sport.

This systematic review with meta-analyses identified 23 articles from the sport science literature that investigated hydrotherapy for recovery in team sport. Reflecting the increasing amount of research into recovery, 15 of these articles were published after 2011. However, despite this increase a paucity of scientific research into team sport recovery still exists. Previously, the need to extend the period of research in team sport recovery to beyond 48 hours was identified (⁸). Despite this recommendation, only 6 of the 23 studies evaluated periods longer than the 48-hour period. As team sport predominantly involves a cyclic week of competition and multiple training sessions, the effect of common recovery interventions, specifically hydrotherapy, needs to be evaluated beyond 48 hours.

Most studies evaluated the effect of hydrotherapy 24 hours following physiological stressor; only 3 studies extended the research to 72 hours following; and only 3 studies extended research to 90 hours or beyond. In addition, a number of studies evaluated extended time periods. Extended time periods included the compounding effect of 3 and 4-day tournaments (^38,48,39,47). Extending time points included evaluating a number of interventions over an AFL season (¹), evaluating a 4-week period of a rugby union competition and a weekly cycle of simulated rugby union inclusive of training (²³), and finally, an investigation over several weeks of an NRL competition (⁵⁵).

Limitations in study designs were also identified. Blinding of participants in research is problematic, particularly with hydrotherapy, leaving participants open to the placebo effect. Unfortunately, blinding of participants from different interventions is not possible. A randomized, crossover design may aide against the placebo effect in some cases but not all, specifically subjective measures of pain or fatigue (^1,52).

The CMJ and one all-out sprint running performance are routinely used as indices of neuromuscular performance (⁵²). It has been suggested that after exercise-induced muscle damage, a decline in CMJ and sprinting performance is a result of compromised neuromuscular function and neuromuscular efficiency (⁵²). Across studies in this review, the reliability of these tests was reported. However, validity of the tests, to reflect recovery with well-trained team sport athletes, was not.

Compromised neuromuscular function has been associated with a number of factors. These factors include muscle activation and muscle coordination, as the nervous system may facilitate changes in recruitment patterns (^3,45). With myofibrillar damage or disruption (²⁵) the nervous system would bypass the more severely damaged muscle fibers, specifically fast twitch (⁴⁵). This would then bring about changes in recruitment patterns and the coordination of muscle activation (²⁵). With the change in muscle activation and coordination, a slowing of peak velocity would result (²⁹).

It has been proposed that the CMJ may not be sensitive enough to evaluate recovery of power in well-trained athletes (^8,23,47). Authors speculated that well-trained athletes may have sufficient motivational drive to record near maximal efforts in one off all-out tests (⁶). Others postulated that the level of exercise-induced muscle damage would be less with well-trained athletes because of adaptation processes (^23,47). Well-trained athletes would therefore have a larger portion of functioning motor units and intact muscle fibers allowing for near maximal efforts (⁴⁷).

Although results indicated that CWI was beneficial for recovery, it should be noted that at 1 hour and 24 hours following team sport activity, irrespective of recovery intervention, the power of athletes as measured by a CMJ was still compromised. Athletes recorded below baseline scores of 5–15% at 1 hour and 3–10% at 24 hours following team sport activity. The benefits in recovery from both CWI and CWT, during the first 24 hours, appear to be attenuating the detrimental effects of team sport. However, by 48 hours, irrespective of recovery intervention, control and hydrotherapy intervention groups had returned to within 2% of baseline scores for CMJ. Only 2 studies evaluated the effectiveness of CWI and CWT in CMJ performance beyond 48 hours. In both studies, results were unclear as to whether CWI or CWT provided any beneficial effect in restoring CMJ performance (^23,48).

In evaluating recovery with one all-out maximal sprinting performance, CWI (24 hours) was beneficial. However, as with the CMJ, all participants recorded decrements in scores for sprinting performances irrespective of recovery intervention. The reported benefits of CWI at 24 hours were in attenuating the decrements in all-out maximal sprinting performances. Despite the common use of CWT in team sport recovery, only one study evaluated the effects CWT and one all-out sprinting performance. Meaningful evaluation through meta-analysis of CWT was therefore not possible in this review.

This review noted a dearth of research into recovery of sprinting performance beyond 24 hours was noted. In evaluating hydrotherapy and sprinting performance, there were data from only 2 studies to evaluate the effect of CWI at 48 hours following team sport with unclear results identified. Three studies evaluated the effect of hydrotherapy on sprinting beyond 48 hours following team sport (^23,24,34). However, in each case, different time points were assessed. The additional time points evaluated were 90 hours after (⁴⁸); 96 hours after (^24,48); and 144 hours after (²³), discounting any feasibility of conducting a meaningful meta-analysis.

This systematic review and meta-analyses indicated that within 24 hours following team sport, CWI was beneficial in attenuating the detrimental effects of fatigue on neuromuscular function. However, beyond 24 hours, the beneficial effect of CWI in recovery of neuromuscular function was unclear when evaluated with either a CMJ or one all-out sprint. Several studies evaluated neuromuscular function through electromyographic (EMG) measurements (^41,42). Due to methodological differences, additional meta-analysis evaluation was not possible. However, each study reported that CWI offered greater benefits in recovery of neuromuscular function of the knee extensors (⁴²). However, these results need to be viewed with some level of caution. It has been suggested that functional tests best reflect recovery of performance in team sport (⁸), whereas these studies using EMG used a seated knee extension testing protocol. Furthermore, hip extensors and knee flexors have been previously identified as the primary movers in team sport activities (^13,15). Therefore, further research is required to confirm that a reported recovery of the knee extensors (⁴²) can be duplicated with a similar recovery response of the hip extensors and/or knee flexors. In future research, EMG evaluation of the hip extensors and knee flexors while performing functional exercises may provide a greater insight into the effectiveness of either CWI or CWT in facilitating recovery in neuromuscular function with well-trained team sport athletes.

Finally, results from across the review indicated that, irrespective of the recovery intervention, neuromuscular function returned to near baseline levels within 48 hours of team sport activity. This may suggest that the effectiveness of such intervention strategies in enhancing recovery before the next competition is limited.

Perceptual measures of muscle soreness and fatigue are widely accepted tools in the monitoring of athlete's recovery. It has been proposed that athletes will instinctively regulate intensity (⁹) and govern physical workloads (⁴⁰) according to their perceptions (^9,40). Individually, a number of studies in this review did report CWI and/or CWT to be more beneficial in alleviating perceptions of muscle soreness during the acute response (^{17,22,23,27,39,44,49}). Indications from the meta-analysis were that neither CWI nor CWT was beneficial in attenuating perceived muscle soreness.

The reported beneficial effects of CWI and CWT with muscle soreness can be linked with an acute analgesic affect (¹⁶). The mechanisms associated with the acute analgesic effect of CWI and CWT center primarily on the reduction of muscle soreness through pain inhibition and lower pain sensation (^16,29,44,49). The effect of CWI reduces nerve conduction velocity (^16,29,49), which in turn reduces muscle spindle activity allowing the muscle to relax, and alleviating the perception of pain (^16,49).

There have also been additional mechanisms attributed to lower perceptions of muscle soreness and fatigue after CWI and/or CWT. The effect CWI and CWT has on changes in skin temperature has been associated with enhanced perceptions of recovery (³¹). Authors discussed the relationship between changes in skin temperature and human perception of fatigue and comfort (³¹). They postulated that the perception of recovery after CWI and CWT is a result of an increase in skin temperature postimmersions, and that the sensation of skin warming enhances perceptions of recovery (³¹). Alternatively, immersion therapy was associated with partial weightlessness and hydrostatic pressure, both inducing inhibitory mechanisms toward muscle contractions, which allows muscle to relax, reducing stress on muscle, and subsequently reducing perceptions of muscle soreness (³⁹).

Although it is believed that hydrostatic pressure generated during water immersion will impact on recovery mechanisms (¹⁹), it was not evident when CWI and thermoneutral water immersion (TWI) were evaluated jointly (⁴⁸). As CWI was identified to be more beneficial than TWI in enhancing perceptions of recovery (⁴⁸), this would suggest that the underlying mechanisms enhancing perceptions of recovery are associated with the cold temperature rather than hydrostatic pressure.

The authors also postulated that CWI and CWT benefited perceptions of muscle soreness through the reduction of inflammation after exercise-induced muscle damage (¹). The reduction in inflammation has been attributed to a number of mechanisms. Cold therapy has been reported to reduce edema through vasoconstriction altering lymph evacuation and lymph flow as well as blood flow (^38,49). Reducing edema would result in a reduction in pressure on pain receptors (^9,38,49) and reduced cell necrosis alleviating muscle soreness (²⁷). Furthermore, reduced cellular permeability and cellular diffusion has been associated with vasoconstriction (⁴⁴) reducing both neutrophil migration (²⁷) and inflammation, subsequently inducing inhibitory influences on pain (⁴⁴).

Within this review, it is probable that CWI and CWT only offered an acute analgesic effect on muscle soreness, as the beneficial effects toward muscle soreness were not evident at later time points. Although a number of authors postulated that benefits of either CWI or CWT within 1–2 hours postimmersions could be expected to occur at later time points, these beneficial effects of CWI or CWT were not evident 24 hours following (^38,41,42). A rebound effect in perceptions of muscle soreness from the CWI and CWT groups were identified following a basketball tournament (³⁹). If CWI and CWT had an effect on the reported physiological mechanisms, including reduced edema, reduced cellular metabolism, reduced diffusion, and reduced neutrophil migration, the beneficial effects would be expected at later time points. In addition, the previously discussed link between perceptions of pain and fatigue and intensity regulation was not evident in this review. Individually, a number of articles did report greater beneficial effects of CWI and/or CWT with perceptual measures of recovery; however, no beneficial effects in performance measures were reported (^{1,8,9,23,31,32,48}).

Although it was previously suggested repeat effort testing may be more appropriate in assessing recovery (⁸), there has been a subsequent lack of research. In all, 7 studies were identified in this systematic review that evaluated repeat effort performances, which included actual game performance (^6,47), simulated game performance (^6,21,47), and sprint repeat performance (^9,27,39). A complete meta-analysis could not be conducted due to variations in study protocols, which included variations in running speeds, sprinting distances, recording of results (seconds or meters). Furthermore, as with neuromuscular performance and subjective measures, only 2 studies evaluated beyond 48 hours (^21,48).

Two of the studies did report some notable findings (^6,21). Although reporting differences in overall running distances between groups, the volume of high-intensity running showed no differences (⁶). This may provide an example of players regulating intensity when fatigued, as previously discussed. In attempting to conserve energy for high-intensity activities associated with soccer, players reduced their levels of incidental movement throughout the second game. This led the authors to postulate that hydrotherapy was beneficial for recovery when consecutive games of football were played (⁶).

Additionally, when evaluating performances between 2 simulated games of rugby union, athletes performed all-out maximal sprints in times equal to or improved above baseline scores (²¹). However, when athletes performed multitask rugby-specific actions, performances in the second simulated game were (although not significant) below baseline measures (²¹). This may in itself reflect the complexity of measuring fatigue and recovery with well-trained athletes. The level of exercise-induced muscle damage may not be severe enough, because of adaptations bought about through training. As such, when using well-trained athletes, these athletes may have significant motor units functioning to record near maximal efforts in all-out maximal tests (²¹). As has been previously recommended, repeat effort testing, which reflects actual game requirements may be better suited to assess recovery for well-trained team sport athletes (⁸).

The studies reviewed in this article that evaluating biochemical markers of muscle damage and inflammation indicated that team sports elicit a high level of muscle damage and inflammation, as evident with significant increases in biochemical markers. Although evaluating recovery biochemical markers of both muscle damage and inflammation are routinely assessed, this review highlights the paucity of research evaluating biochemical responses to hydrotherapy and recovery from team field sport. The review identified that CK was the most commonly used biochemical marker evaluated and the only marker with sufficient data to apply a meta-analysis. From the meta-analysis, the overall effect of both CWI and CWT was greater in reducing CK levels at 24 hours after than control groups; no other time points had sufficient data available to conduct meta-analyses. In addition, there were insufficient data across the other biochemical markers, including AST, myoglobin, CRP, IL-6, LDH, and Fatty Acid-Binding Protein (FABP) to conduct meta-analyses.

Despite a large overall effect in reducing CK levels, individual research papers from within the review offered conflicting results. The beneficial effect of CWI and/or CWT in reducing CK levels was reported by several papers (^12,20,32), whereas no beneficial effect of CWI and/or CWT in reducing CK levels was reported in other studies (^3,42,48). The conflicting results may be related to the time course of peak CK levels. Most time course responses evaluated were less than 48 hours, and although 1 study reported peak CK levels at post-24 hours (¹⁸), peak CK levels have been reported to generally occur up to 96 hours postphysiological stressor (³⁴). The conflicting results may reflect the time frames of studies missing peak CK levels. Extended time periods of research would be required to truly evaluate the effect CWI or CWT has on CK levels.

In addition to the conflicting results into the efficacy of CWI and/or CWT in enhancing clearance of biochemical markers discussed, conflicting positions have been raised by a number of authors. Initially it was stated that enhanced clearance of CK after rugby union reflected enhanced recovery (¹⁸), in contrast, changes in intracellular proteins in venous blood were merely a reflection of increased CK clearance without indicating recovery (⁴⁴). Importantly, opposing positions were identified in relation to biochemical markers and performance. Authors stated that there was no significant correlation between either muscle soreness or performance capabilities and plasma concentrations of either CK or CRP (²⁷), whereas in contrast it was reported that reduced CK levels indicated recovery (¹⁸). It has also been postulated that the acute elevations of myoglobin and FABP compared with the sustained elevation of CK made them a more effective marker (³⁸).

This systematic review identified that team sport does elicit high levels of muscle damage and inflammation, whether in a contact or noncontact sport. In addition, when multiple days of team sport competition and/or training are conducted, levels of muscle damage and inflammation will be compounded (^38,48). Therefore, the importance of recovery after competition and training cannot be overstated. However, there is still a dearth of research evaluating CWI and CWT and biochemical markers, specifically beyond 48 hours, and therefore the efficacy and utility of such therapies remains unclear. The conflicting results discussed above fail to provide a definitive answer in relation to the beneficial effects of either CWI and/or CWT on the subsequent clearance of biochemical markers and enhanced recovery.

In response to previous commentary (¹⁹), this review focused on highly trained team sport athletes. Despite narrowing the focus of the review to well-trained athletes, it is accepted that different team sports still have variations to physical and psychological strains. Although most team sports include contact/collisions, the 2 rugby codes have a higher incidence of contact, eliciting higher degrees of muscle trauma (^14,15,18,52), Whereas both football and AFL have greater physiological and biochemical loads placed on athletes as a result of the greater distances covered in running in competition games (^6,8,27,48). With small court games such as basketball and netball, athletes are required to perform a higher number of high explosive jumps and rapid changes in directions, again eliciting variations in physiological loads (^9,31,38). As postulated by authors within this review, responses to recovery may be highly individualized between athletes and between sports (¹⁹).

Conclusions

This systematic review with meta-analysis has confirmed well-trained team sport athletes undergo high levels of physiological, psychological, and mechanical strain, leading to fatigue, through competition and training. In addition, that when competition and/or training occurs on successive days, there is a compounding effect of the physiological, psychological, and mechanical strain, indicating the presence of residual fatigue (^21,38,48). Therefore, the importance placed on appropriate recovery is not misplaced. Although CWI and CWT were beneficial in attenuating decrements in neuromuscular performance 24 hours following team sport, the indications of this systematic review are that those benefits were not evident 48 hours following team sport.

However, the beneficial effects of CWI and CWT and the athlete's improved perceptions of fatigue were supported with the meta-analysis conducted within this review. The authors postulated that greater perceptions of recovery may extend beyond the timeframes evaluated. Those greater perceptions of recovery may provide athletes with a better frame of mind enhancing the athlete's physical performance at training and competitions. However, at present, supporting evidence that improved the athlete's perceptions of muscle soreness and fatigue will enhance performance at training is not available, or was it supported by the pooled evidence within this review.

Recommendations

From this review, hydrotherapy interventions to attenuate the detrimental effects of team sport activity should use the following protocols. The CWI should incorporate 2 × 5 minute immersions of 10° C with 2-minute seated rest in ambient temperature between immersions. The CWT would be advised to use a protocol incorporating CWI with 10° C, and warm/hot water immersions at 38–40° C. Total immersion times for CWT should total not less than 10 minutes with similar immersion times for both cold and warm/hot used. Recommendations for immersion of whole body (¹⁹) (head out) should be used, or ensure as much body is immersed as facilities allow.

As a scarcity of research into recovery from team sport and hydrotherapy still exists, further research evaluating hydrotherapy for recovery from team sport is required. Research encompassing team sports should be directed toward various sports, including, but not limited to, AFL, basketball, football, netball, and both codes of rugby. It is paramount that future research incorporates both competition and training and that research focuses on the period 48 hours following team sport activity. Only by extending the research beyond the initial 48 hours can the compounding effects of residual fatigue, and subsequent benefits of hydrotherapy be fully evaluated. In addition, hydrostatic pressure generated with hydrotherapy and its effect on recovery should be evaluated with the use of thermoneutral water immersion. Although temperatures for TWI have been previously defined as 34–36° C (⁵¹), authors who have used TWI in this review have used temperatures of approximately 25° C. Investigations of the 2 different temperature ranges for TWI is required to clarify the optimal temperature for TWI.

Physical performance measurements including either game or simulated game performances and functional performance tests should be used. Furthermore, functional tests need to be specific to the sport being investigated. It may provide greater insight into neuromuscular function recovery to incorporate the use of EMG while performing functional performance tests. The use of EMG may aide in the identification of altered motor unit recruitment with well-trained athletes.

Perceptual measures continue to be an important tool in monitoring an athlete's response to games, training, fatigue, and recovery. With this in mind, the association between perceived recovery and enhanced performance in games and/or training needs additional exploration. Future research should include the monitoring of athlete's perceptions of fatigue/recovery and the athlete's physical performance in competition games and at successive training sessions.