In many team sports, competition schedules require athletes to perform multiple competitions over several days with limited rest. The stressful demands of competition may induce fatigue and temporarily impair an athlete's performance, with detrimental effects lasting from minutes or hours to days after competition (7). Suggested causes of muscular fatigue include decreases in muscle pH and glycogen with accompanying increases in blood lactate, extracellular potassium, free fatty acids, an increase in core temperature, and inflammation (3,7). If the inflammatory process is not controlled, an athlete's performance may decrease with subsequent activity (7).
This has led to the development of recovery interventions to attenuate the detrimental effects of the inflammatory process that could potentially expedite recovery. Cryotherapy in the form of cold water immersion (CWI) has several proposed physiological effects that may assist in recovery from fatigue, including the ability to decrease cellular need for oxygen by decreasing cellular metabolism (29), decreasing heart rate and blood pressure (27), reducing inflammation (14,24), and decreasing core (4), intramuscular (19), and cutaneous temperatures (19). Cryotherapy is also used to control pain and edema formation (20). Cold water immersion is a common recovery tool used after competition and is often suggested by coaches and medical staff to reduce the believed performance decrements in repeated exercise demands. Despite encouraging anecdotal information from athletes, there is limited and equivocal evidence of the effectiveness of CWI after repeated bouts of intense exercise separated by 48 hours, which is a typical between competition recovery periods (7,33). Cold water immersion has been shown to be beneficial in male cyclists with measures of sprint performance maintained and slightly improved at 24 hours (23) and at 4 and 5 days after immersion (30). When compared with passive recovery, the changes in isometric squat performance and weighted squat jumps after fatigue were significantly less after CWI (31). In contrast, over a 4-day simulated soccer tournament, repeated bouts of CWI were no more beneficial on physical performance measures than thermoneutral water immersion (26). Additionally, a single bout of CWI did not affect exercise circuit performance over 24 hours (18). Differences observed between studies may be related to water temperature, duration of immersion used during CWI, or recovery time between exercise bouts.
In many team sports, such as soccer, the typical recovery period between matches is 48 hours or longer, and the effect of CWI on performance estimates in this setting has not been examined. Because it has been hypothesized that CWI will lower inflammation and maintain or improve performance, many elite soccer players use CWI on a daily basis after practice or matches. Alternatively, one could hypothesize that 48 hours is adequate to allow for full recovery independent of the use of CWI. Therefore, the purpose of the present study was to examine the use of CWI as a recovery modality on the performance estimates typically used in elite soccer players, including the yo-yo intermittent recovery test (YIRT) and the countermovement vertical jump (CMVJ). The YIRT is a test that mimics the repeated sprint demands of a soccer player, whereas the CMVJ can be used to estimate anaerobic power. The secondary aim was to test the effect of CWI on perceived fatigue (PF) in the legs using a visual analog scale (VAS).
Experimental Approach to the Problem
This was a randomized, single-blinded study completed over a 48 h period. All assessors were blinded to group allocation. We hypothesized that 48 h of recovery would allow for adequate physiological recovery and as such, soccer players in the control condition who did not receive CWI would respond similarly to soccer related performance estimates compared with soccer players who used CWI as a recovery modality. Subjects were randomly allocated to either CWI (experimental group) or passive rest (control group) and completed the same intervention (CWI or control) on 2 separate visits separated by 24 h. Subjects were asked to refrain from non-assigned cryotherapy and non-steroidal anti-inflammatory medications throughout the testing period.
Twenty-two Division I collegiate soccer players (13 men and 9 women; age, 19.8 ± 1.1 years; height, 174.0 ± 9.0 cm; mass, 72.1 ± 9.1 kg) volunteered to participate in this study during the spring (noncompetitive) season. All subjects were familiar with CWI and routinely used this procedure as a recovery modality. Athletes were eligible to participate if they were actively practicing and competing with the team at the time of testing. Athletes were excluded if they had a lower extremity injury that prevented full participation within the previous 6 weeks, history of cold sensitivity or decreased skin sensation, or open wounds on the lower extremity. Athletes participating in this study completed similar intensity team training and weight training during the duration of the study. The only changes in the athletes' normal routine were the performance testing and the intervention. The environmental conditions of temperature and relative humidity on test day 1 and test day 2 (separated by 48 hours) were 6.1°C and 62%, and 8.9°C and 96%, respectively. The Institutional Review Board of the University of Virginia approved the study, and all participants provided written informed consent before participation.
Subjects were familiar with testing procedures before beginning the study. These trained soccer players routinely perform both the YIRT and CMVJ in fitness evaluations. Members of the research team supervised all tests performed.
Before each YIRT, subjects completed a maximal CMVJ using a vertical jump stand (Vertec; Sports Imports, Columbus, OH, USA), as described by Wikstrom et al. (32) for a baseline estimate of anaerobic power. Subjects stood next to the vertical jump stand and were instructed to reach up and tap the highest vane possible while keeping both feet firmly on the ground. The subject's standing reach height was recorded, and each subject was asked to perform a maximal CMVJ to touch the highest vane possible; the highest value of 3 trials was recorded. Maximum vertical jump was determined to be the difference between the maximum height reached during the CMVJ and the standing reach height.
All subjects completed the YIRT (5,6) on 2 separate occasions separated by 48 hours. The YIRT is considered a gold standard for evaluating soccer performance and is routinely used by high-level soccer teams. This test has high reproducibility, and the test performance is highly related to match performance in soccer (21,22). Biopsy of the quadriceps muscle group and blood chemical analysis indicate that the YIRT results in significant changes in water content, muscle creatine phosphate, lactate, pH, and glycogen, as well as blood lactate immediately after the YIRT (21). The YIRT is a highly intense exercise test that stresses both the aerobic and anaerobic energy systems, and the physiological demands involved in the test protocol are similar to the demands of a soccer match (10,21). This test has been reported to be sensitive and appropriate to distinguish differences between players and seasonal changes in soccer performance (21). Additionally, performance on the YIRT has been positively correlated with V[Combining Dot Above]O2max (r = 0.46) and CMVJ (r = 0.50) (10).
The test protocol was completed by multiple 2 × 20 m shuttles defined by 2 separate markers according to the timing on an audiotape (5,6). Subjects were required to touch the first marker as closely as possible to the time that the first sound was emitted from the audiotape, then turn around and return to the end marker before a second sound was emitted. The frequency of the sound signals on the recording was increased so that running speed increased 0.5 km per hour (km·h−1) each minute from an initial starting speed of 8.5 km·h−1. When the subject missed 2 nonconsecutive shuttles signaled by the beeps, the test was concluded and the maximum level achieved was recorded. At the completion of the test, rating of perceived exertion (RPE) using the Borg scale (8) was recorded to assess the level of volitional fatigue.
Within 5 minutes of completing each YIRT, each subject was reassessed in CMVJ. Immediately after CMVJ measurements, subjects were instructed to shower and begin their allocated intervention condition. Immediately before beginning the intervention, the subjects were provided a VAS and were asked to mark their PF in their legs. The VAS (15) used was a 10-cm horizontal line with a left anchor of “not tired at all” and a right anchor of “very tired” with no other markings. Subjects were asked to make a vertical mark on the line to indicate their perceived level of fatigue.
Group Assignment and Cold Water Immersion
Subjects were randomly allocated into the control (passive rest) or experimental (CWI) group via sealed envelope allocation. Subjects were aware of their group assignment, but investigators performing all assessments were blinded to the intervention.
The CWI group (n = 12) immersed the lower extremity up to the umbilicus into a cold tub at a temperature of 12°C for 15 minutes. No jets were turned on, but water was circulated by a built-in filtration system. Parameters of CWI were chosen based on recent literature using water immersion in trained subjects. Multiple authors reported water immersion times of 12–15 minutes, with temperatures ranging from 10–15°C (13,16,23,27,30,34). The control group (n = 10) sat quietly at room temperature for 15 minutes. After the intervention was complete, subjects were asked to go about normal activities of daily living for the remainder of the day and before repeated testing.
At 24-hour postimmersion, the subjects returned and were reassessed on the VAS for PF and CMVJ, then completed a second 15-minute intervention (CWI or control) as assigned from the previous session. At 48-hour postimmersion, subjects were reassessed on CMVJ, YIRT, and VAS for PF as described above.
Required sample size was calculated from previous data in the literature (21) using G*Power version 3.1 (9). An a priori repeated measures between factors design with desired power (1−β) set at 0.80, a large effect size of 0.8, and alpha of 0.05 to yield a total sample size of 16. Post hoc power analysis revealed that this study was adequately powered, with actual power (1−β) > 0.9. Data were analyzed using Statistical Package for Social Sciences (SPSS) Version 17.0 (SPSS, Inc., Chicago, IL, USA). Countermovement vertical jump height was analyzed using a 2 × 4 (group by time) mixed model analysis of variance (ANOVA) with repeated measures over time, whereas total meters covered on the YIRT, final RPE on the YIRT, and VAS for PF were examined using 2 × 2, 2 × 2, and 2 × 3, group by time ANOVAs, respectively. Cohen's d effect sizes were calculated for YIRT and VAS for PF using the pooled SD of the experimental group and the control group (12).
There were no significant differences between the experimental and control groups at any time point, although there was a significant main effect for time (p = 0.02) where subjects increased CMVJ immediately post-YIRT and decreased at 24- and 48-hour post-YIRT (Table 1, Figure 1). Figure 1 shows a plot of each individual subject's CMVJ performance over 48 hours, represented by gray lines. The group mean is represented with a bold line, and the group positive and negative SDs are represented with 2, bold, dashed lines. Tables 2 and 3 and Figures 2 and 3 provide information for YIRT and VAS for PF, respectively. No significant differences were observed between the experimental and control groups for YIRT performance at baseline (p = 0.48, ES = 0.31, confidence interval [CI] = −0.54 to 1.15) or 48-hour post-YIRT (p = 0.35, ES = 0.41, CI = −0.44 to 1.26) (Table 2, Figure 2). Perceived fatigue was similar at baseline and 24 hours within and between conditions (control, 5.6 ± 1.9 cm; CWI, 4.9 ± 2.3 cm; p = 0.47; ES = −0.33; CI = −0.52 to 1.17; and control, 5.7 ± 2.8 cm; CWI, 4.4 ± 1.9 cm; p = 0.22; ES = −0.51; CI = −0.34 to 1.36). Perceived fatigue 48-hour post-YIRT increased similarly between conditions (control, 9.4 ± 0.51 cm; CWI, 9.3 ± 0.6 cm; p = 0.65; ES = −0.18; CI = −0.66 to 1.02) (Table 3, Figure 3). Values of RPE immediately after the YIRT at baseline and 48 hours were 19.7 ± 0.77 and 19.9 ± 0.43, respectively. No significant differences were observed between the experimental and control groups for RPE at baseline (p = 0.49; ES = 0.30; CI = −0.54 to 1.14) and 48 hours after YIRT (p = 0.37; ES = −0.39; CI = −1.24 to 0.46).
The main finding in this study was that CWI immediately and 24 hours after the YIRT in collegiate soccer players did not affect subsequent physical performance estimates or perception of fatigue after 48 hours. Based on the notion that CWI attenuates the inflammatory response, it has been suggested that athletes who receive CWI would have improved performance on the YIRT and decreased lower extremity fatigue over 48 hours, as seen in recently published studies (16,23,30,34). Alternatively, it is possible that 48 hours of recovery would allow for adequate physiological recovery independent of CWI, consistent with recent studies showing that mean sprint time and CMVJ were unaffected by CWI (4,13,18,26).
We chose the YIRT as a valid field test that is closely related to match performance in elite soccer players, with a high reproducibility and sensitivity to detect change on repeated tests (21,22). In the current study, perceived exertion was measured at the end of the YIRT and found to be consistent between the groups during both testing sessions, with values subjectively representing strenuous and maximal exercise on both occasions (8).
It should be noted that in clinical practice, temperatures for CWI range from 0 to 20°C (24) with exposure times ranging from as little as 30 seconds and as long as 30 minutes (33). We chose 12°C based on data suggesting blood flow increases at temperatures below 10°C (14), resulting in treatment below this temperature to be ineffective at diminishing inflammatory effects of exercise. Additionally, it is known that when some tissue temperatures drop below 25°C for long periods, vasodilation in the cutaneous tissues will occur in an attempt to rewarm the tissue to prevent cold injury, again limiting usefulness in diminishing inflammatory responses (14).
One of the bases for the efficacy of CWI is related to the purported effects of CWI on inflammation because inflammation has been suggested to limit performance (14,24). The inflammatory process is known to contribute to the etiology of muscle damage and resulting muscle soreness after exercise (2,28). Application of cold draws heat from injured tissues and is therefore able to lower tissue temperature (19). The superficial application of ice results in changes in cutaneous, subcutaneous, intramuscular, and joint temperatures; this decrease in temperature stimulates vasoconstriction in the superficial tissues (11). Cooling of tissues reduces cellular metabolism, thus decreasing the need for oxygen, allowing the involved cells to better survive hypoxia caused by inflammation from the primary injury (25). The use of cold therapy also aids in reducing pain by slowing nerve conduction velocity (24). Muscle spindle activity is decreased and the pain-spasm cycle is interrupted, allowing the muscle to relax and experience less pain (14). Unlike superficial ice, CWI also has the property of hydrostatic pressure, which causes a displacement of fluids in the immersed body, which may assist in the excretion of metabolic substrates from muscles (33). During immersion, a squeezing effect is placed on the body, forcing fluids upward and inward toward nonsubmerged areas of the body (33). This effect is proposed to help shift acute edema and substrates from the fatigued or damaged muscles toward the lymph system to be processed more efficiently, leading to a faster recovery from exercise (33) and maintained or improved subsequent performance.
It has also been reported that CWI decreased blood lactate and peak heart rate in a subsequent exercise bout (13). Cold water immersion has also allowed for the maintenance or improvement of subsequent physical performance measures including cycling power (23,30) and time trial performance (30) and 2-mile race time (34).
In contrast, results of the present study support the notion that when adequate recovery is provided between exhaustive exercise bouts, CWI does not affect estimates of performance. It is likely that 48 hours of recovery is adequate for the resolution of the inflammatory process independent of CWI. In support of this concept, Andersson et al. (1) reported that a 90-minute competitive soccer match transiently increased leukocytes, neutrophils, and proinflammatory cytokines with all levels returning to baseline by 21 hours. In addition, other factors known to affect performance may also adequately recover within 48 hours. For example, with an adequate diet and sensible training approach, 48 hours is adequate to replenish muscle glycogen stores even in activities that involve eccentric loading such as soccer (17). All the soccer players in the present study received regular information regarding appropriate nutrition from the Athletic Department Sports Nutritionist and had daily access to a meal program designed for athletes. In addition, both head soccer coaches work regularly with exercise physiologists, athletic trainers, and strength and conditioning personnel to minimize the risks of overtraining.
We tested elite soccer players to avoid delayed onset muscle soreness, which untrained individuals would have been more likely to experience. We examined a 48-hour period to simulate an in-season soccer schedule, where 2 matches are typically separated by 48 hours. It is possible that in elite athletes, CWI might not be needed to maintain or improve performance if 48-hour recovery is provided between high-intensity exercise bouts. Furthermore, the ambient temperature and humidity were measured and not factors in this experiment and as such, mechanisms related to controlling heat stress, were not a factor. It is possible that CWI may be more beneficial in settings of high temperatures and humidity to reduce body temperature quickly.
We only examined 22 subjects and may be limited by a relatively small sample size. However, we powered the present study based on previous data in the literature, and our statistical power based on our current sample was >0.9. We chose to examine immersion to the umbilicus with time and temperature parameters of 12°C for 15 minutes, modeled after recently published literature with favorable results (13,16,23,27,30,34). It is possible that athletes and clinicians will choose different immersion levels, and time and temperature combinations for their treatment, which may produce different results. It is known that cold temperatures are able to assist in controlling the inflammatory response and reduce metabolic tissue activity quickly after application, so it is reasonable to believe that immersion in cold water will affect these physiological functions, although they were not measured in this study (29). There was no control or recording of dietary intake or hydration status of the participants throughout the study. Although there was a nonsignificant difference of 269 m in YIRT between the groups before intervention, the repeated measures design used in the present study should minimize this potential limitation.
Competitive athletes commonly use CWI after challenging workouts or competitions, in the hope of limiting lower extremity fatigue, as well as preventing decreases in subsequent performance. The results of this study indicate that immersion to the umbilicus in 12°C water for 15 minutes immediately after exhaustive exercise and repeated 24 hours later does not affect the physical performance or PF after 48 hours in collegiate soccer players when compared with passive recovery. The practical implications of the present data for coaches and clinicians suggest that if 48 hours of recovery are available between competitive performance bouts, CWI does not appear to enhance subsequent performance. However, the use of CWI over an entire season cannot be addressed from the present data because we only applied CWI twice over 48 hours.
No funding was received for this study, from the National Institutes of Health, Welcome Trust, Howard Hughes Medical Institute, or other sources. The results of the present study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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