Up to 120 hours are required to restore disturbances in metabolic and physical performance markers after soccer match-play (
). We recently reported reduced countermovement jump (CMJ) performance and elevated 19 creatine kinase (CK) concentrations in the 48 hours after professional soccer matches of 90-min ( ) and 120-min ( 21 ) durations. However, professional European soccer teams may play in excess of 60 competitive matches per season ( 23 ) and thus at specific times of the year, multiple matches will be played within a single week ( 6,10 ). Although unclear ( 10 ), injury risk has been observed to increase when less than 96 hours separates games ( 6 ) and the reduced recovery time between matches played in FIFA World Cup competitions is perceived by physicians to be a primary cause of injury in professional soccer players ( 10 ). Therefore, the ability to facilitate postmatch recovery is desirable. 18
A number of interventions have been proposed to facilitate postexercise recovery (
), including nutritional strategies, cold water immersion, active recovery, compression garments, massage, and electrical stimulation. An additional method is whole-body cryotherapy (WBC), which typically involves exposure to very cold and dry air (−110 to −195° C) for a period of 2 to 3 minutes in a temperature-controlled chamber ( 19 ). As summarized in a narrative review ( 2,12,14 ), the therapeutic effects of repeated WBC exposures have been proposed to relate to changes in hematology (i.e., reduced hemolysis), muscular enzyme activity (i.e., reductions in circulating CK and lactate dehydrogenase concentrations), and modified hormonal responses (i.e., stimulated noradrenaline release). The importance of anti-oxidant capacity, inflammation, immunity and cardiac markers ( 2 ) and performance and perceptual indices of recovery have also been highlighted in WBC research ( 2 ). 3
Most studies employing WBC for recovery purposes have implemented multiple cold exposures; either, within a single day or throughout the week(s) after muscle-damaging exercise. In elite Italian rugby players engaged in regular training, Banfi et al. (
) observed reductions relative to baseline values in muscle enzyme concentrations after 5 once-daily sessions of WBC over the course of a week. Similarly, numerous WBC exposures (3 minutes at −140 to −195° C) over a 6-day period improved the recovery of peak torque, rate of torque development, squat jump start power, and reduced muscle soreness at various time points after damaging hamstring exercise ( 1 ). Although multiple WBC sessions administered over the course of a 6- or 7-day period seem advantageous, the feasibility of such practices (i.e., repeated cold exposures) may be limited in soccer players who are competing in congested fixture schedules and thus likely have limited time (i.e., <96 hours) between consecutive matches, and may also have travel commitments associated with away games. 12
Despite the use of WBC in athletic populations, limited studies have profiled the responses to an isolated bout of WBC performed after muscle-damaging exercise. Of those that have, authors have typically examined the short-term (i.e., ≤30 minutes) effects of cold exposure (
). Furthermore, as training status (through habituation to eccentric contractions) has been proposed to modulate the efficacy of WBC ( 25,28 ), there is a need to determine the effects of a single WBC session in professional athletes. In a study examining the optimal duration of cryotherapy exposure, Selfe et al. ( 14 ) recently observed no differences in inflammatory markers between trials of 1, 2, or 3 minutes performed on the day after a competitive Rugby League match. However, in the absence of a noncryotherapy trial to determine the efficacy of the intervention per se, the effects of an isolated bout of WBC in professional athletes recovering from intermittent exercise remain to be determined. Therefore, the aim of this study was to examine the physiological, performance, and perceptual effects (over 24 hours) of a single bout of WBC performed shortly after repeated sprint exercise in professional soccer players. 25 Methods
Experimental Approach to the Problem
To investigate the effects of a single WBC exposure performed after repeated sprint exercise on physiological, performance, and perceptual responses, 14 professional academy soccer players were required to attend the testing venue on 6 occasions throughout a 14-day period. The first 2 of these sessions were preliminary visits that included procedural habituation, whereas both main trials each required a further 2 separate visits.
After ethical approval from the Swansea University Ethics Committee, 14 male academy soccer players recruited from an English Premier League club (age: 18 ± 2 years, range 17–21 years; mass: 74.5 ± 5.5 kg, stature: 1.78 ± 0.05 m) provided written informed consent (and parental consent where players <18 years) before study involvement.
Two main trials (Cryo: Whole-body cryotherapy, Con: Control), separated by 7 days, were completed in a randomized, counterbalanced, and crossover design. Main trials were performed in an enclosed sports hall that housed a 3G surface and was maintained at a temperature of ∼25° C. To minimize the effects of circadian variation, the timing of measurements were consistent between trials. A light tactical training session, abstention from caffeine and replication of dietary intake was required in the 24 hours before the first visit of each trial.
On arrival, resting capillary blood and saliva samples were taken before perceived muscle soreness and recovery was assessed. After a short warm-up (∼5 minutes), players performed 2 CMJ attempts (separated by 30 seconds) on a portable force platform (Type 92866AA, Kistler, Germany). A standardized 10-min warm-up (consisting of channel drills, dynamic stretches, and progressive intensity sprinting) and 5-min passive rest then preceded 15 × 30 m timed (Brower timing system, Salt Lake City, UT, USA) sprints that were each separated by 60-second rest (
). Each sprint required deceleration to a standstill within a 10-m zone, which contributes to the muscle-damaging properties of the protocol ( 16 ). The protocol elicits similar distances covered at high intensity to those observed in a similar age group of professional players during match-play ( 16 ). Blood and saliva samples, perceived muscle soreness and recovery, and CMJ performance were assessed immediately, 2 hours and 24 hours after the repeated sprint protocol, and these measurements took ∼10 minutes to complete on each occasion. 22
After providing blood and saliva samples and having completed the perceived recovery and soreness scales and CMJ testing, players commenced the WBC treatment in a purpose-built temperature-controlled portable cryotherapy unit (BOC Cryotherapy Chamber, Linde, Surrey, United Kingdom) within 20 minutes of completing the repeated sprint protocol. Before entering the liquid nitrogen cooled chamber, players towel-dried themselves (to remove sweat) and wore minimal clothing (wearing shorts, socks, clogs, mask, gloves, and a hat covering the auricles to avoid frostbite; (
)); processes which were completed within 10 minutes. Players entered the first precooling chamber (−60° C) for 30 seconds before moving into the second chamber (−135° C) for a further 120 seconds; a duration considered optimal when using a chamber of −135° C ( 28 ). Minimal deviations from the target temperature were observed when players moved between the precooling and main chambers. Players were instructed to gently move fingers and legs to avoid tension, and to take slow, shallow breaths while in the chamber ( 25 ). On leaving the chamber, players dressed in enough training attire to attenuate subjective feelings of cold and remained seated for ∼95 minutes in the same room as used in the Con trial. In Con, players remained seated in a temperate environment (∼25° C) for ∼110 minutes. All players remained seated until the 2-hour postexercise assessments before being provided with a meal from a standardized menu and then leaving the laboratory. Players were requested to replicate their postvisit dietary intake between trials, and no structured training was scheduled in the time between the 2-hour and 24-hour measurements. Verbal questioning of players on arrival for the 24-hour postexercise assessment supported adherence to these requests. 28,30
Peak power output was determined according to previously described methods ( ). Briefly, the instantaneous velocity and displacement of the player's center of gravity was derived from the vertical component of the ground reaction force (GRF) elicited during the CMJ and the participants' body mass. Instantaneous power output was determined using 20,29 Equation 1, and the highest value produced from the 2 attempts performed at each time point was deemed the peak power output.
Whole blood (5 μl), sampled from the fingertip (after immersion in warm water necessary for one participant during the Con trial), was analyzed for lactate concentrations (Lactate Pro, Akray, Japan). A further 120 μl of blood (Microvette CB300 EDTA; Sarstedt AG & Co, Hamburg, Germany) was centrifuged at 3,000 revolutions per minute for 10 minutes (Labofuge 400R; Kendro Laboratories, Germany), and plasma samples were stored at −70° C before subsequently being analyzed for CK (Cobas Mira; ABX Diagnostics, Northampton, United Kingdom) concentrations. Samples were measured in duplicate (3% coefficient of variation) and recorded as a mean. Saliva samples were collected into sterile vials (LabServe, New Zealand) through passive drool (∼2 ml over 2 minutes), which were then stored at −80° C. To minimize sample dilution, players were instructed to avoid eating, drinking warm fluids, and brushing of teeth in the 2 hours preceding sampling. Samples were analyzed in duplicate using commercially available enzyme immunoassay kits (Salimetrics LLC; State College, PA, USA). The lowest detection limits for testosterone and cortisol were 0.001 nmol·L
−1 and 0.08 nmol·L −1, respectively, and interassay CV values were <10% in both cases. To eliminate interassay variance, samples for each player were analyzed within the same assay kit ( ). The perception of recovery was assessed using a 10-point Likert scale ( 8 ), whereas a 7-point Likert scale evaluated lower limb muscle soreness ( 17 ). 27 Statistical Analyses
Statistical analyses were performed using SPSS Statistics software (IBM Inc., USA) with significance set at
P ≤ 0.05. Data are reported as mean ± SD. Paired samples t-tests were performed for between-trial comparisons of data expressed over a single time point within a trial (i.e., mean and total sprint times). For data expressed over multiple time points within a trial (i.e., individual sprint times, power output, blood lactate and CK concentrations, salivary testosterone and cortisol concentrations; including testosterone/cortisol ratio, and perceived soreness and recovery), between-trial comparisons were investigated using 2-way repeated-measures analysis of variance (ANOVA; within-participant factors: trial × time). Where significant interaction effects were observed, trial was deemed to have influenced responses and simple main effect analyses were performed. Timing effects represent the main effect of time from the 2-way repeated-measures ANOVA analysis performed. Partial eta-squared (η 2) values were calculated, and Bonferroni-corrected post hoc tests (with 95% CI) were performed to isolate significant differences. Results
A 2-way repeated-measures ANOVA analysis revealed that individual sprint times were similar between trials (time × trial interaction:
F (6,78) = 0.354, P = 0.905, η 2 = 0.026) and did not differ throughout the duration of the 15 × 30 m timed sprints (time effect: F (3,44) = 0.574, P = 0.658, η 2 = 0.042). Paired samples t-tests highlighted that mean (Con: 4.34 ± 0.17 seconds, Cryo: 4.37 ± 0.23 seconds, P = 0.572) and total (Con: 65.08 ± 2.56 seconds, Cryo: 65.56 ± 3.38 seconds, P = 0.572) sprint times were comparable between trials. Peak power output was not influenced by trial (time × trial interaction: F (3,39) = 0.762, P = 0.522, η 2 = 0.055) but did differ according to timing (time effect: F (3,39) = 10.091, P < 0.001, η 2 = 0.437). Peak power output reduced immediately postexercise ( P < 0.001) by 134 ± 100 W (−3.2 ± 2.3%) but subsequently returned to pre-exercise values at 2-hour ( P = 0.052) and 24-hour ( P > 0.99) postexercise ( Table 1). Table 1.:
SD blood lactate, peak power output, creatine kinase (CK), perceived soreness, and perceived recovery responses throughout each trial.*
Blood lactate concentrations were similar between trials (time × trial interaction:
F (2,21) = 1.023, P = 0.361, η 2 = 0.073, Table 1) but were influenced by timing (time effect: F (1,16) = 50.609, P < 0.001, η 2 = 0.796). A 2.18 ± 1.01 mmol·L −1 increase from baseline values occurred immediately postexercise ( P < 0.001), but blood lactate concentrations returned to pre-exercise values thereafter ( P > 0.05).
Concentrations of CK did not differ according to trial (time × trial interaction:
F (2,26) = 0.733, P = 0.491, η 2 = 0.053) but did vary due to timing of sample (time effect: F (1,14) = 243.872, P < 0.001, η 2 = 0.949). Compared with pre-exercise values, CK was elevated by 14 ± 13%, 28 ± 10%, and 253 ± 89% immediately ( P = 0.006), 2-hour ( P < 0.001) and 24-hour ( P < 0.001) postexercise, respectively ( Table 1).
Salivary testosterone concentrations were influenced by trial (trial × treatment interaction:
F (3,39) = 6.231, P = 0.001, η 2 = 0.326) and time of sample (time effect: F (3,39) = 6.275, P = 0.001, η 2 = 0.326). Despite salivary testosterone being similar between trials at pre-exercise and immediately postexercise (both P > 0.05), Cryo elicited a greater salivary testosterone response at 2-hour (+32.5 ± 32.3 pg·ml −1, +21 ± 21%) and 24-hour (+50.4 ± 48.9 pg·ml −1, +28 ± 34%) postexercise (both P = 0.002) compared with Con ( Figure 1). Figure 1.:
SD testosterone (A), cortisol (B), and testosterone/cortisol ratio (C) responses throughout each trial. Con represents control trial, Cryo represents cryotherapy trial. *Significant difference ( P ≤ 0.05) between conditions at the corresponding time point.
Salivary cortisol concentrations did not differ according to trial (time × trial interaction:
F (3,39) = 0.253, P = 0.859, η 2 = 0.019) but did vary due to sampling time (time effect: F (3,39) = 13.998, P < 0.001, η 2 = 0.518). Immediately postexercise, salivary cortisol was similar to pre-exercise values ( P = 0.052), whereas significant reductions were observed at 2-hour postexercise ( P = 0.003). These reductions had dissipated at 24-hour postexercise ( Figure 1). Salivary testosterone/cortisol ratios did not differ due to trial (time × trial interaction: F (3,39) = 0.696, P = 0.560, η 2 = 0.051), but timing did influence the response (time effect: F (2,28) = 8.66, P = 0.001, η 2 = 0.518). Post hoc analyses were unable to isolate these differences relative to pre-exercise values.
Perceived soreness (time × trial interaction:
F (3,39) = 0.700, P = 0.558, η 2 = 0.051) and recovery (time × trial interaction: F (2,22) = 0.245, P = 0.752, η 2 = 0.019) were not influenced by trial, but timing effects were significant ( F (3,39) = 13.010, P < 0.001, η 2 = 0.500, F (3,39) = 27.094, P < 0.001, η 2 = 0.676, respectively). Significant changes were only observed immediately postexercise (both P < 0.001). Discussion
This study aimed to examine the physiological, performance, and perceptual effects of a single bout of WBC administered shortly after repeated sprint exercise in professional soccer players. Based on circulating CK concentrations yielded from capillary blood samples, our findings indicate that perturbations in selected physiological responses were not restored back to baseline values within a 24-hour period. Moreover, a single WBC session increased testosterone concentrations at 2-hour and 24-hour postexercise when compared with a Con trial despite no differences in CMJ performance, blood lactate and CK concentrations, and markers of perceived recovery. Although further investigation is warranted, these findings highlight a potential role for a single WBC exposure in the early stages of recovery from muscle-damaging exercise in professional soccer players.
Contrary to previous authors (
), Cryo did not influence blood CK concentrations when compared with Con ( 1,31 Table 1). Conversely, and despite torque loss being limited in the 48 hours after trail running ( ), Hausswirth et al. observed similar CK concentrations to that observed during a passive recovery trial after a single WBC exposure ( 14 ). Therefore, it has been proposed that repeated WBC sessions (a minimum of 5–10) are required before muscle membrane breakdown or exercise-induced cell permeability is modified to such an extent that the significant reductions in CK concentrations seen by previous authors ( 14 ) become evident ( 1,31 ). Moreover, the elevated baseline CK concentrations of soccer players observed in this study and previously ( 14 ) may afford another explanation as to the lack of differences observed between trials in this variable and is likely attributable to residual levels of 21,23,26 muscle damage still present from previous regular training ( ). 26
Testosterone has been suggested to be a primary anabolic hormone involved in protein synthesis and protection against skeletal muscle degradation (
). Notwithstanding the debated role of endogenous hormones in the muscle hypertrophic and strength response ( 15 ), the 21% and 28% increases in testosterone at 2-hour and 24-hour postexercise in Cryo versus Con, respectively, indicate a potentially favorable hormonal profile following a single exposure to WBC after soccer-specific exercise. Such findings corroborate observations of elevated testosterone concentrations following multiple WBC sessions ( 24 ) but are the first to be reported following a single bout of WBC that followed muscle-damaging exercise in professional athletes. As testosterone concentrations influence training motivation ( 13 ), this finding may have important implications for practitioners during congested periods of competition. 7
The anti-inflammatory effects of WBC are a key factor purported to explain its efficacy (
). As opposed to changes in lysosomal membrane stabilization which are apparent after multiple cryotherapy exposures ( 1,2 ), reductions in serum soluble intercellular adhesion molecule-1 (mediator of the leukocyte response at the damaged tissue, resulting in a lower pro-inflammatory response, less reactive oxygen species, and an increase in anti-inflammatory markers) have been proposed to explain the anti-inflammatory response to a single WBC session ( 31 ). Notably, low serum testosterone concentrations are significantly associated with elevated levels of inflammation ( 11 ). Speculatively, and given its role as a potential mediator of the inflammatory response in both healthy and clinical populations, the increases in testosterone observed at 2-hour and 24-hour postexercise versus Con in this study may reflect reduced levels of inflammation after WBC. However, in the absence of inflammation data, these proposed mechanisms should be interpreted with caution. 4
The increased testosterone concentrations observed against Con at 24-hour postexercise in Cryo may also reflect an increased sleep quality that has been reported previously (
). When compared with a previous night's sleep that did not follow a cryotherapy intervention, sleep quality was improved the night after WBC exposure ( 5 ). As sleep deprivation/restriction reduces testosterone concentrations ( 5 ), WBC may be beneficial for players experiencing disrupted sleeping patterns; perhaps resulting from travel or factors associated with evening kick-offs. Unfortunately, records of sleep quality were unavailable to support this supposition and warrants further investigation. 9
In contrast to previous studies that have implemented muscle-damaging exercises that demonstrate low levels of ecological validity to soccer, such as drop jumps combined with eccentric lower-body exercise (
) and isokinetic unilateral knee extensor exercises ( 12 ), we used a repeated sprint protocol ( 28 ) that represents the high-intensity distance covered in soccer match-play ( 16 ) and is also typical of some soccer training sessions. Although physiological measurements were not collected during exercise, players reported increased perceptions of soreness and a reduced recovery state immediately postexercise ( 22 Table 1) while blood lactate concentrations reflected those observed after a soccer match and peak power output demonstrated a soccer-specific fatigue-related profile ( ). Furthermore, we observed increases in CK concentrations that were similar in magnitude to those reported after soccer match-play ( 21,23 ). The reductions in cortisol concentrations observed 2-hour postexercise are likely explained by circadian rhythmicity given the nonsignificant effects of exercise on salivary cortisol when assessed immediately postexercise and the subsequent restoration at 24 hours. Therefore, our data highlight a potential role for WBC as a method of maintaining salivary testosterone concentrations in professional soccer players for up to 24 hours after intense exercise. 21,23 Practical Applications
A single session of WBC elicited greater testosterone concentrations for 24 hours after repeated sprint exercise when compared with a passive recovery protocol despite selected physiological, performance, and perceptual markers being unaffected. Although unclear, such findings may link to an attenuated inflammatory response to exercise, an enhanced sleep quality in the 24 hours after cold exposure, and possibly have implications for subsequent training motivation. Consequently, WBC administered shortly after intermittent exercise may offer an ergogenic strategy for soccer players involved in a congested fixture or training period. A secondary finding of this study was that professional soccer players performing 15 × 30 m sprints (each followed by a forced deceleration within a 10-m zone) experienced a short-term (up to 2 hours) transient reduction in postexercise muscle function (i.e., CMJ performance) and perturbations in circulating CK concentrations that required more than 24 hours to return to baseline.
None to declare. No external financial support received. The results of this study do not constitute endorsement by the NSCA.
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