There is insufficient evidence to determine whether whole'body cryotherapy (WBC) reduces self'reported muscle soreness, or improves subjective recovery, after exercise compared with passive rest or no WBC in physically active young adult males. There is no evidence on the use of this intervention in females or elite athletes. The lack of evidence on adverse events is important given that the exposure to extreme temperature presents a potential hazard. Further high'quality, well'reported research in this area is required and must provide detailed reporting of adverse events.
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One small cross'over trial involving nine well'trained runners provided very low quality evidence of lower levels of muscle soreness after WBC, when compared with infrared therapy, at 1 hour follow'up, but not at 24 or 48 hours. The same trial found no difference in well'being but less tiredness after WBC at 24 hours post exercise. There was no report of adverse events.
All four trials compared WBC with rest or no WBC. There was very low quality evidence for lower self'reported muscle soreness (pain at rest) scores after WBC at 1 hour (standardised mean difference (SMD) '0.77, 95% confidence interval (CI) '1.42 to '0.12; 20 participants, 2 cross'over trials); 24 hours (SMD '0.57, 95% CI '1.48 to 0.33) and 48 hours (SMD '0.58, 95% CI '1.37 to 0.21), both with 38 participants, 2 cross'over studies, 1 parallel group study; and 72 hours (SMD '0.65, 95% CI '2.54 to 1.24; 29 participants, 1 cross'over study, 1 parallel group study). Of note is that the 95% CIs also included either no between'group differences or a benefit in favour of the control group. One small cross'over trial (9 participants) found no difference in tiredness but better well'being after WBC at 24 hours post exercise. There was no report of adverse events.
Two comparisons were tested: WBC versus control (rest or no WBC), tested in four studies; and WBC versus far'infrared therapy, also tested in one study. No studies compared WBC with other active interventions, such as cold water immersion, or different types and applications of WBC.
Four laboratory'based randomised controlled trials were included. These reported results for 64 physically active predominantly young adults (mean age 23 years). All but four participants were male. Two trials were parallel group trials (44 participants) and two were cross'over trials (20 participants). The trials were heterogeneous, including the type, temperature, duration and frequency of WBC, and the type of preceding exercise. None of the trials reported active surveillance of predefined adverse events. All four trials had design features that carried a high risk of bias, potentially limiting the reliability of their findings. The evidence for all outcomes was classified as 'very low' quality based on the GRADE criteria.
Two review authors independently screened search results, selected studies, assessed risk of bias and extracted and cross'checked data. Where appropriate, we pooled results of comparable trials. The random'effects model was used for pooling where there was substantial heterogeneity. We assessed the quality of the evidence using GRADE.
We aimed to include randomised and quasi'randomised trials that compared the use of whole'body cryotherapy (WBC) versus a passive or control intervention (rest, no treatment or placebo treatment) or active interventions including cold or contrast water immersion, active recovery and infrared therapy for preventing or treating muscle soreness after exercise in adults. We also aimed to include randomised trials that compared different durations or dosages of WBC. Our prespecified primary outcomes were muscle soreness, subjective recovery (e.g. tiredness, well'being) and adverse effects.
We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, CINAHL, the British Nursing Index and the Physiotherapy Evidence Database. We also searched the reference lists of articles, trial registers and conference proceedings, handsearched journals and contacted experts.The searches were run in August .
Recovery strategies are often used with the intention of preventing or minimising muscle soreness after exercise. Whole'body cryotherapy, which involves a single or repeated exposure(s) to extremely cold dry air (below '100 °C) in a specialised chamber or cabin for two to four minutes per exposure, is currently being advocated as an effective intervention to reduce muscle soreness after exercise.
The currently available evidence is insufficient to support the use of WBC for preventing and treating muscle soreness after exercise in adults. Furthermore, the best prescription of WBC and its safety are not known.
All four studies had aspects that could undermine the reliability of their results. We decided that the evidence was of very low quality for all outcomes. Thus, the findings remain very uncertain and further research may provide evidence that could change our conclusions.
All four studies compared WBC with either passive rest or no treatment. These provided some evidence that WBC may reduce muscle soreness (pain at rest) at 1, 24, 48 and 72 hours after exercise. However, the evidence also included the possibility that WBC may not make a difference or may make the pain worse. There was some weak evidence that WBC may improve well'being at 24 hours. There was no report and probably no monitoring of adverse events in these four studies.
We searched medical databases up to August for studies that compared WBC with a control intervention such as passive rest or no treatment; or with another active intervention such as cold water immersion. We found four small studies. These reported results for a total of 64 physically active young adults. All but four participants were male. The studies were very varied such as the type, temperature, duration and frequency of the WBC and the exercises used to induce muscle soreness. There were two comparisons: WBC compared with a control intervention; and WBC compared with far'infrared therapy.
Delayed onset muscle soreness describes the muscular pain, tenderness and stiffness experienced after high'intensity or unaccustomed exercise. Various therapies are in use to prevent or reduce muscle soreness after exercise and to enhance recovery. One more recent therapy that is growing in use is whole'body cryotherapy (WBC). This involves single or repeated exposure(s) to extremely cold dry air (below '100°C) in a specialised chamber or cabin for two to four minutes per exposure. This review aimed to find out whether WBC reduced muscle soreness, improved recovery and was safe for those people for whom it can be used.
This review aimed to examine the effects, both beneficial and harmful, of WBC used for the purpose of preventing or treating muscle soreness after exercise. Currently, no guidelines for a clinically effective or safe WBC protocol are available. Because of the extreme temperatures employed during WBC, the potential for short' and long'term adverse effects needs to be elucidated. A systematic review of the evidence is also important because of the increasing use of WBC by elite and recreational athletes and the potential for long'term use throughout a sporting career in an attempt to alleviate DOMS.
Using the approach described by Anderson , we developed a logic model to capture the wide range of potential effects of WBC exposure ( Figure 1 ). This model is divided into two sections: (1) potential recovery benefits and (2) potential adverse effects. Missing from this model is any appraisal of the logistical, environmental and financial costs associated with WBC.
Only a few studies have sought to examine the physiological effects ( Fonda ; Hammond ; Selfe ) of different WBC protocols on different population. Selfe studied the effects of a 1, 2 and 3 minutes exposure of WBC at '135°C on changes in the inflammatory cytokine interleukin'six (IL'6), tissue oxygenation, skin and core temperature, thermal sensation and comfort in professional rugby league players, and concluded that two minutes was the optimum exposure length that should be applied as the basis for future studies. Fonda , employing '130 to '170°C partial'body (head out) cryotherapy, supported these findings and demonstrated that longer durations do not substantially affect thermal and cardiovascular response, but do increase thermal discomfort in healthy young male adults.
Although the research examining WBC is typically limited in terms of quality and statistical power ( Costello a ; Costello b ), some studies have described a reduction in creatine kinase activity after training ( Wozniak ), increases in parasympathetic activation ( Hausswirth ; Zalewski ) and an increase in anti'inflammatory cytokines (proteins that serve to regulate the inflammatory response) ( Ferreira'Junior b ; Lubkowska ; Lubkowska ) after WBC exposure. A reduction in the severity of muscle damage after exercise and an increase in anti'inflammatory cytokines post'treatment may help to reduce both the initial damage and the secondary inflammatory damage associated with EIMD. However, from a mechanistic perspective, very little is known about the physiological and biochemical rationale for using WBC in the management of DOMS.
Reductions in muscle and skin tissue temperature after WBC exposure ( Costello b ; Costello c ; Costello a ) may stimulate cutaneous receptors and excite the sympathetic adrenergic fibres, causing constriction of local arterioles and venules ( Costello d ; Savic ). Consequently, WBC may be effective in relieving soreness through reduced muscle metabolism, skin microcirculation, receptor sensitivity and nerve conduction velocity. In addition, both Bleakley and Cochrane describe the potential psychological benefits of using other modalities of cold exposure (e.g. cold water immersion) to reduce the subjective feeling of DOMS following exercise.
In the field of athletic training, a new method of exposing people to these extreme temperatures, called partial'body cryotherapy (PBC), using a portable cryo'cabin, has recently been developed. This system has an open tank and exposes the body, except the head and neck, to temperatures below '100°C. Recently, recreational athletes have started to emulate elite athletes in using these treatments after exercise.
Whole'body cryotherapy (WBC) is increasingly used in sports medicine as treatment for muscle soreness after exercise. This treatment involves exposing individuals to extremely cold dry air (below '100°C) for two to four minutes. To achieve the subzero temperatures required for WBC, two methods are typically used: liquid nitrogen and refrigerated cold air. During these exposures, individuals wear minimal clothing, which usually consists of shorts for males and shorts and a crop top for females. Gloves, a woollen headband covering the ears, and a nose and mouth mask, in addition to dry shoes and socks, are commonly worn to reduce the risk of cold'related injury.
Symptoms associated with DOMS typically dissipate within five to seven days post exercise with adequate rest ( Cheung ). Nevertheless, various interventions have been advocated to prevent or treat, or both prevent and treat, EIMD and associated DOMS. Interventions include cool'down, stretching, nutritional supplements, massage, hydrotherapy, compression, electrotherapy and non'steroidal anti'inflammatory medications ( Bieuzen ; Bleakley ; Herbert ). Despite their widespread popularity ( Nédélec ), empirical support for the use of these interventions for DOMS remains tenuous ( Bleakley ; Herbert ).
DOMS is a broad term used to describe the muscular pain, tenderness and stiffness experienced after high'intensity, eccentric (when the muscle is forcibly stretched when active) or unaccustomed exercise ( Cheung ; Ebbeling ; Howatson ; Newham ). Clinically associated with EIMD, DOMS is proposed to result from mechanical disturbances of the muscle membrane that evoke secondary inflammation, swelling and free radical proliferation ( Connolly ). These events typically peak 24 to 96 hours post exercise ( Cheung ) and may reduce physical capacity via alterations in muscle length, maximal force and range of motion ( Prasartwuth ; Saxton ). Although damage to the exercised musculature is linked to the biochemical expression of intracellular enzymes, compensatory neuromuscular recruitment patterns may contribute both central and peripheral factors to DOMS aetiology ( Byrne ).
Elite'level athletic participation necessitates recovery from many physiological stressors, including fatigue to the musculoskeletal, nervous and metabolic systems ( Nédélec ). Athletic participation may also result in exercise'induced muscle damage (EIMD), which may lead to delayed'onset muscle soreness (DOMS) and decrements in subsequent performance ( Howatson ). Various therapeutic modalities of recovery are currently used by athletes in an attempt to offset the negative effects of strenuous exercise ( Bieuzen ; Bleakley ; Costello b ; Minett ; Nédélec ).
We prepared a 'Summary of findings' table for the main comparison (WBC versus rest, no or a placebo intervention) using the GRADE profiler ( Schünemann ). We summarised the quality of evidence by applying the principles of the GRADE framework and following the recommendations and worksheets of the Cochrane Effective Practice and Organisation of Care Group for creating 'Summary of findings' tables ( EPOC ). We assessed the quality of the evidence according to four levels (high, moderate, low and very low). We presented the evidence for primary outcomes only. We selected muscle soreness assessed for pain at rest at 1, 24, 48 and 72 hours; well'being and tiredness at 24 hours and adverse events as the 7 outcomes for presenting in a 'Summary of findings' table.
If some of the included trials were at high risk of bias for one or more domains, we intended to perform sensitivity analysis to determine whether inclusion of such trials significantly influenced the effect size. We planned to consider trials at high risk of bias in sensitivity analysis if allocation concealment was unclear or at high risk of bias, or if attrition was greater than 20%. We performed sensitivity analysis to explore the effects of using fixed'effect or random'effects analyses for outcomes with statistical heterogeneity.
We investigated whether the results of subgroups were significantly different by inspecting the overlap of CIs and by performing the test for determining subgroup differences that is available in Review Manager ( RevMan ).
We conducted an exploratory subgroup analysis based on study design: parallel group versus cross'over. As well as issues relating to potential carry'over effects and suboptimal analysis of cross'over trials, they are likely to be at increased risk of serious bias where there is lack of blinding and subjective assessment of outcome.
We chose these subgroup analyses because gender, type of athletic activity and training status may impact the severity of DOMS experienced after exercise ( Howatson ; McGinley ). In particular, DOMS may be augmented in untrained males after eccentric exercise when compared with trained females performing concentric exercise. Moreover, reductions in tissue temperature may be more pronounced after repeated, or longer, WBC exposures ( Costello c ).
Results of comparable groups of trials were pooled using either fixed'effect or random'effects models. The choice of the model to report was guided by careful consideration of the extent of heterogeneity and whether it could be explained, in addition to other factors, such as the number and size of included studies. Ninety'five per cent CIs were used throughout. We considered not pooling data when considerable heterogeneity (I² > 75%) could not be explained by the diversity of methodological or clinical features observed among trials. When it was inappropriate to pool data, we presented trial data in the analyses or tables for illustrative purposes and reported them in the text.
We planned to use funnel plots to assess for publication bias; however, there were insufficient studies. Should sufficient trials become available in future, we plan to use funnel plots to assess for publication bias based on the effect estimates (horizontal scale) against standard error (on a reversed scale, vertical) using Review Manager software, with continuous data represented as SMDs, and dichotomous data represented as risk ratios on a logarithmic scale.
Assessment of heterogeneity between comparable trials was evaluated visually with the use of forest plots, as well as Chi² tests and I² statistics. The level of significance for the Chi² test was set at P = 0.1 ( Deeks ): a P value for Chi² < 0.1 was considered to indicate statistically significant heterogeneity between studies. Values of I² were interpreted as follows: 0% to 40% might not be important; 30% to 60% may represent moderate heterogeneity; 50% to 90% may represent substantial heterogeneity; and 75% to 100% may represent considerable heterogeneity.
In cases where data were missing, we considered why they were missing. We contacted study authors to request missing data or to ask for an explanation as to why data were missing. Unless missing standard deviations were derived from CIs, standard errors or exact P values, we did not assume or impute values for these in order to present results in the analyses.
We extracted data at clinically relevant time points. When available, data were extracted for, and separate analyses conducted at, the following time points: up to 1 hour after the exercise and then at 24'hour intervals (1 to 24 hours, 25 to 48 hours, 49 to 72 hours, 73 to 96 hours and over 96 hours). In studies using a randomised cross'over design, and where a carry'over effect was not thought to be a problem, we aimed to undertake paired analysis when sufficient data were available; otherwise, data were analysed as if these studies used a parallel group design.
For each study, we calculated risk ratios and 95% confidence intervals (CIs) for dichotomous outcomes, and mean differences and 95% CIs for continuous outcomes. For continuous outcomes that were pooled on different scales, we used standardised mean differences (SMDs). Where possible, follow'up scores were used in preference to change scores. An exception was made for strength outcomes, where recovery to baseline is arguably of most interest to athletes and researchers.
Each study was graded for risk of bias in each of the following domains: sequence generation, allocation concealment, blinding (participants and intervention providers; outcome assessment), incomplete outcome data and selective outcome reporting. Two other sources of bias were also considered on the basis of the following questions: (1) 'Was the exercise protocol clear and consistent between groups?', and (2) 'Were co'interventions used, and if so, were they standardised across groups?'. For each study, the information pertaining to each of the domains was described as reported in the published study report (or, if appropriate, based on information from related protocols or published comments, or after discussion with the relevant authors) and the associated risk of bias judged by the review authors. Studies were assigned 'high risk', 'low risk', or 'unclear risk' when there was uncertainty or when information was insufficient to allow review authors to make a judgement. Disagreements between review authors regarding the 'Risk of bias' assessment were resolved by consensus.
Two review authors (JTC, GMM) independently assessed risk of bias using the tool described (and the criteria outlined) in the Cochrane Handbook for Systematic Reviews of Interventions ( Higgins ). To minimise bias in the interpretation of this scale, two review authors (JTC, GMM) initially assessed 10 unrelated studies (not included in the current review); disparities in 'Risk of bias' judgements were reviewed and discussed before any of the included studies were evaluated.
Two review authors (JTC, GMM) used a customised form to independently extract relevant data on methodology, eligibility criteria, interventions (including detailed characteristics of the exercise protocols and the WBC protocol employed), comparisons and outcome measures. Details of the characteristics of trial participants such as training status, age, sex and health status were also recorded. When available, we extracted data on participant subgroups, including any equity considerations such as ethnicity and socioeconomic status. Any included study written by one of the current review authors was reviewed by review authors who did not participate in the original study. Any disagreement was resolved by consensus or by third party adjudication (IBS, PRAB). We contacted primary authors to clarify any omitted data or study characteristics. For intention'to'treat analysis, data were extracted according to the original allocation groups, and losses to follow'up were noted where possible.
Two review authors (JTC, GMM) independently selected trials for inclusion. First, we screened titles and abstracts of publications obtained by the search strategy and removed only those that were obviously outside the scope of the review. We were over'inclusive at this stage and obtained the full text of any papers that potentially met the review inclusion criteria. We checked for multiple publications and reports of the same study. The same two review authors then independently selected trials using a standardised form to record their choices. We were not blinded during this process with respect to study authors' names, journal or date of publication. When possible, translation of non'English language studies was undertaken. We contacted primary authors when necessary to ask for clarification of study characteristics. Disagreement between the review authors was resolved by consensus or by third party adjudication (CB, PRAB, IBS).
Experts and colleagues working in the subject area were also asked to notify us on the existence of new or ongoing studies, which we also considered for inclusion.
We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (5 August ), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 7), MEDLINE ( to July Week 4 ), MEDLINE In'Process & Other Non'Indexed Citations (5 August ), EMBASE ( to Week 31), the Cumulative Index to Nursing and Allied Health (CINAHL) ( to 5 August ), the British Nursing Index (BNI) ( to 5 August ) and the Physiotherapy Evidence Database (PEDro) ( to 7 August ).
We also aimed to include randomised trials that compared different durations or dosages of WBC. We excluded trials in which the same WBC protocol was used in both arms as a co'intervention. Comparisons with pharmacological interventions were also excluded.
We aimed to include trials that compared the use of WBC versus a passive or control intervention (rest, no treatment or placebo treatment) or active interventions designed to prevent or treat delayed'onset muscle soreness (DOMS), including, but not limited to, cold water immersion (immersion in water colder than 15°C), warm water immersion (immersion in water warmer than 15°C), contrast water immersion (alternating hot and cold water immersion), cool'down, stretching, massage and compression garments.
We included trials in which at least one group in the trial comprised participants treated with whole'body cryotherapy (WBC) before or after exercise. WBC was defined as exposure of the body (trunk, arms and legs) to extremely cold dry air (below '100°C). These exposures are typically administered as a once'off treatment, or repeated several times on the same days or over several days.
No restrictions were placed on gender or on type or level of exercise. All field' and laboratory'based (including eccentric) exercise modalities were included. We excluded studies focusing on children (< 18 years of age) or on injured participants. As anticipated, people with vascular problems, such as Raynaud's disease, who are contraindicated for cryotherapy, were excluded from trials.
We included randomised and quasi'randomised (method of allocating participants to a treatment that is not strictly random, e.g. by date of birth) controlled clinical trials evaluating whole'body cryotherapy for prevention and treatment of muscle soreness after exercise in adults. This included randomised cross'over trials and trials carried out in laboratory or field settings.
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Knee extensors' isometric strength was slightly lower after the WBC intervention at 48 hours (MD '4.50%, 95% CI '8.34 to '0.66; see Analysis 2.4 ). No other significant differences were observed at the 4 other follow'up points (1, 24, 72, and 96 hours). Notably, strength was slightly greater (> 100%) than baseline in 6 of the 10 results presented in Analysis 2.4 .
Aside from exploratory subgroup analysis based on study design, there were insufficient data to carry out our planned subgroup analyses (see Subgroup analysis and investigation of heterogeneity ). Notably, only one study included a sample of female participants ( Costello ), and there was significant heterogeneity in the dosage of WBC and the type of exercise performed in the studies. Additionally, we performed very limited sensitivity analysis; this being limited to the inspection of the results of using fixed'effect versus random'effects models for pooling.
The results of statistical tests for heterogeneity for the pooled data together with the visual inspection of the CIs showed little important heterogeneity in the results. An exploratory subgroup analysis by study design was conducted for the 72 hour follow'up as this had the greatest heterogeneity (Chi² = 4.30, df = 3 (P = 0.23); I² = 30%). This found no statistically significant differences between the pooled results of cross'over trials and parallel group trials (test for subgroup differences: Chi² = 0.01, df = 1 (P = 0.91); I² = 0%; see Analysis 1.8 ).
Although there was some variation in the measurement device and contraction type, all four studies tested lower limb strength. Pooled results over six follow'ups are displayed in Analysis 1.7 . At all follow'up times the best estimates favoured the WBC group but the mean differences were very small and the 95% CI included the line of no effect at 1 hour (MD 1.76%, 95% CI '4.50 to 8.01%; 3 trials) and at 48 hours (MD 2.69%, 95% CI '2.21 to 7.60%; 4 trials) post exercise. The pooled results showed modest strength increases in the WBC group at 24 hours (MD 5.16%, 95% CI 0.66 to 9.65%; 3 trials), 72 hours (MD 6.92%, 95% CI 2.32 to 11.52%; 4 trials) and 96 hours (MD 6.73%, 95% CI 1.87 to 10.87%; 4 trials). Only Fonda reported results at 120 hours; also finding a significant difference in favour of WBC (MD 12.60%, 95% CI 0.48 to 24.72%).
Maximal strength, which was reported in all four studies, was assessed over a range of time points post intervention. In order to complete a meta'analysis on strength as a percentage of baseline, raw data were sought from all four studies. Despite not being included in the report of the original study, Hausswirth provided additional raw data for follow'ups at 72 and 96 hour post intervention and these data are subsequently included in the analysis of this review.
None of the included studies recorded or reported adverse events or complications relating to the interventions. Moreover, no study examined the effects of the chronic use of WBC. It was unclear whether any study actively monitored specific adverse effects as part of its outcomes.
Two studies presented data on muscle soreness during subsequent exercise based on various visual analogue scores ( Ferreira'Junior ; Fonda ). Pooled SMD results are presented for six follow'up times (see Analysis 1.4 ). Though the pooled results for follow'ups at 1, 24, 48, 72 and 96 hours were in favour of WBC, the 95% CIs clipped the line of no effect except at 24 hours (SMD '0.66, 95% CI '1.25 to '0.07; 2 trials). Moreover, the results were moderately to substantially heterogenous for this follow'up. The parallel group trial ( Ferreira'Junior ) showed no difference between the two groups at all five follow'up times, whereas the cross'over trial ( Fonda ) found significant differences at the first four follow'up times but not at 96 hours or 120 hours.
In the 24, 48, 72 and 96 hours analyses, the cross'over trials have been combined with Costello , a parallel group trial. Of note, is that Costello found no difference between the two groups, whereas the two cross'over trials found in favour of WBC. An exploratory subgroup analysis by study design at 24 hours follow'up illustrates this observation, with a highly statistically significant test for subgroup differences (Chi² = 4.98, df = 1 (P = 0.03), I² = 79.9%; see Analysis 1.3 ).
Three studies presented data on muscle soreness at rest based on various visual analogue scores. Results are presented at six follow'up times (see Analysis 1.1 ). The pooled results using the fixed'effect model showed significantly lower levels of soreness in the WBC group at 1 hour (SMD '0.77, 95% CI '1.42 to '0.12; 2 trials); 24 hours (SMD '0.57, 95% CI '1.12 to ' 0.03; 3 trials) and 48 hours (SMD '0.58, 95% CI '1.12 to '0.04; 3 trials). However, there was significant heterogeneity in the analyses at 24 and 72 hours and when applying the random'effects model, the significant findings in favour of WBC were not upheld: 24 hours (SMD '0.57, 95% CI '1.48 to 0.33); 48 hours (SMD '0.58, 95% CI '1.37 to 0.21); see Analysis 1.2 , Figure 5 ). The results for remaining follow'up times also showed no significant differences between groups: 72 hours (SMD '0.65, 95% CI '2.54 to 1.24; 2 trials); 96 hours (SMD '0.33, 95% CI '0.95 to 0.30; 2 trials) and 120 hours (SMD '0.32, 95 CI 1.16 to 0.52; 1 trial).
None of the studies made any reference to a published protocol or trial registration. Therefore, bias from selective reporting of results was difficult to ascertain fully. Hausswirth did not report on measured outcomes (biomarkers of inflammation) within the trial report; however, these data were available from a secondary publication ( Pournot ) based on communication with the authors. Additionally, Hausswirth only reported data up to 48 hours post exercise but upon contact, the authors provided unpublished data on muscle strength for follow'up at 72 and 96 hours following exercise. We thus rated this study at high risk of reporting bias. All studies described outcomes and follow'up times with corresponding results presented by intervention group. In all four studies, additional raw data were provided by corresponding authors in order to calculate percentage change from baseline scores and effect sizes. There was an absence of reporting of adverse events.
In general, the losses to follow'up and missing data were poorly described in the published reports of the included studies. After correspondence, the authors of two trials confirmed no losses to follow'up or violation from the study protocol ( Costello ; Fonda ), whereas the authors of the two other studies confirmed there were missing data ( Ferreira'Junior ; Hausswirth ). Two (of 11) participants were dismissed because of incomplete outcomes in Hausswirth . Ferreira'Junior stated that there were missing data from one individual at two follow'up points. In personal correspondence, Ferreira'Junior indicated that these participants were included in the analysis and that the statistical software, SigmaPlot 11.0, calculated the missing data and automatically decreased the degree of freedom accordingly. The risk of attrition bias for both Hausswirth and Ferreira'Junior was classified as unclear.
Given the type of intervention, it is impractical to blind participants or personnel and thus all four trials were inevitably at high risk of performance bias. We assessed detection bias separately for objective (e.g. strength) and self'reported outcome measures (e.g. DOMS). The risk of detection bias was classified as high for self'reported outcome measures. As it is unclear if the lack of assessor blinding would influence the objective measures (e.g. strength), the risk of bias for the objective measures was classified as unclear.
Allocation concealment was not adequately described in any of the included studies. However, in two studies, there was no clear indication that the investigators would be unable to predict the prospective group ( Fonda ; Hausswirth ), or in the case of cross'over trials, the order of treatments to which participants would be allocated. However, the allocations of the final treatment in the cross'over studies were predictable following knowledge of the first treatment. After personal communication, both Costello and Ferreira'Junior confirmed that an open random allocation schedule was employed. Thus both these trials were rated at high risk of bias for this item.
All corresponding authors of the included trials responded to our requests for any unclear or missing methodological details. Our requests for information were open'ended to avoid any bias resulting from leading questions. Unless an author specifically stated that he or she did not understand our question, we avoided making multiple requests for information. 'Risk of bias' judgements were made by two independent authors, based on information from trial reports and author correspondence; the results are summarised in Figure 3 and Figure 4 . Full details of our 'Risk of bias' assessments for individual trials are given in the Characteristics of included studies .
Details of the four studies in this category are shown in the Characteristics of studies awaiting classification . We have been unable to locate a full report of DRKS , which recruited 24 female football players, or of NCT , which recruited 65 male college students. Additional information is being sought from the authors of Krüger and Ziemann ; these recruited 11 and 18 physically'active young men respectively.
After appraisal of the full study reports, we excluded 17 studies. Ten studies were excluded because they did not include a primary outcome measure of the review (rating of perceived exertion and rating of thermal discomfort/sensation were not considered to be measures of subjective recovery) and six studies because they did not use a relevant WBC intervention. Banfi was a cohort study only. Reasons for exclusion for individual studies can be found in the Characteristics of excluded studies .
The included studies did not monitor adverse events or complications relating to the interventions. One study measured tympanic temperature changes associated with WBC and reported that the lowest mean temperature (36.6 ± 0.4°C) was observed eight minutes after WBC ( Costello ).
All four trials reported on muscle soreness, which was assessed using a visual analogue scale (VAS). Three studies measured muscle soreness at rest ( Costello ; Fonda ; Hausswirth ); one during a squat ( Fonda ) and one while performing an isometric knee extension ( Ferreira'Junior ). Fonda assessed the soreness using a 10 cm (0 'no pain' to 10 'severe pain') VAS during the resting and the exercise assessment. Both Hausswirth (0 "no pain" to 100 "maximum possible" on a web interface) and Ferreira'Junior (0 mm "no soreness" to 100mm "severe soreness") used a 100'point visual analogue scale. Costello employed a 10'point (1 'normal, no pain' to 10 "very, very sore") VAS to assess muscle soreness across eight different sites in the lower limb, with the results combined together.
One study compared WBC with far'infrared therapy ( Hausswirth ). During the far'infrared therapy, participants lay supine on the table and the whole body, except the head, was exposed to the treatment for 30 minutes (4 to 14 µm, 45°C). The number of treatments was the same for both interventions (15 minutes, 24, 48, 72 and 96 hours post exercise).
The participants in the control groups of Costello and Ferreira'Junior followed the same procedures as the intervention groups but the chamber or cryo'cabin temperature was set to a temperature of 15°C and 21°C respectively. The control group comprised 'passive rest' in Fonda and seated rest for 30 minutes in a temperate room in Hausswirth .
We found no trials evaluating WBC versus other interventions: cold water immersion (immersion in water colder than 15°C), warm water immersion (immersion in water warmer than 15°C), contrast water immersion (alternating hot and cold water immersion), cool'down, stretching, massage or compression garments. Nor were there trials evaluating the effectiveness of different durations or dosages of WBC.
All four studies exposed participants to the cryotherapy for three minutes. However, before entering the '110°C chamber, Costello included an additional 20 seconds standing in a '60°C chamber and Hausswirth stated that participants traversed through two separate chambers (at '10°C and '60°C respectively). Fonda also stated that the participants were instructed to turn around continuously in the cabin during exposure. The timing of initiating cryotherapy after exercise was not consistent across the studies. Ferreira'Junior and Hausswirth initiated WBC approximately 10 to 15 minutes after exercise, while Fonda and Costello waited until 1 and 24 hours respectively after exercise. Three studies undertook additional WBC interventions after completing the exercise session: Costello (26 hours); Hausswirth (at 24, 48, 72 and 96 hours); and Fonda (at 24, 48, 72, 96 and 120 hours).
the temperature is uniformly distributed in the WBC chamber and not in the cabin (i.e. it is cooler at the bottom of the cabin compared with the top).
Two studies used WBC and exposed participants to a controlled temperature of '110°C in a specialised cryotherapy chamber ( Costello ; Hausswirth ). Two studies used partial'body cryotherapy in a cryo'cabin at temperatures of '110°C ( Ferreira'Junior ) and between '140 to '195°C ( Fonda ). It was noted by Fonda that the temperature was measured on the inner wall of the cabin and not next to the skin. It is likely that the temperature around the skin surface was lower ( Fonda ). Although similar, there are some differences between partial' and whole'body cryotherapy including:
The type, duration and intensity of exercise performed varied across studies. In three studies, the exercise was designed to produce delayed onset muscle soreness (DOMS) under laboratory'controlled conditions ( Costello ; Ferreira'Junior ; Fonda ). The exercise comprised multiple repetitions (100 repetitions) of resistance to lengthening (eccentric exercise) in Costello ; drop jumps (100 jumps) in Ferreira'Junior ; and a combination of drop jumps (50 jumps), bilateral leg curls (50 repetitions) and eccentric leg curls (10 repetitions) in Fonda . The methodology employed by Costello targeted a single muscle group (quadriceps). Athough there was a focus on the hamstring and quadriceps muscles respectively, Fonda and Ferreira'Junior targeted a number of related muscle groups using a jumping protocol. Hausswirth employed a 48 minute simulated trail run (incorporating five 3'minute downhill blocks at a '15% gradient) on a treadmill.
In total, there were data for 64 trial participants of which only 4 (6.3%) were female; all 4 were recruited in 1 trial of 18 participants ( Costello ). The mean age of participants in individual trials was 21 years in Costello , 20 years in Ferreira'Junior , 27 years in Fonda and 32 years in Hausswirth . The largest trial included 26 participants ( Ferreira'Junior ).
We screened a total of records from the following databases: Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (2 records); Cochrane Central Register of Controlled Trials (388), MEDLINE (332), EMBASE (463), CINAHL (286), BNI (5), PEDro (87), the WHO International Clinical Trials Registry Platform (63) and Current Controlled Trials (70). We also found 52 potentially'eligible studies from ongoing searches and through contacting experts and colleagues working in the subject area.
This review examined the effectiveness of whole'body cryotherapy (WBC) for preventing and treating muscle soreness after exercise. Four small laboratory'based randomised controlled trials, reporting on a total of 64 physically'active adults (60 male; 4 female; mean age 23 years), were included. The trials were clinically and methodologically heterogeneous with considerable variation such as in: study design (two were parallel group studies and two were cross'over studies); the type and application of WBC, including modality (whole chamber versus cryo'cabin), timing (WBC undertaken immediately after exercise or 24 hours after exercise), and the temperature and frequency of WBC; and the type of exercise (simulation trial run/drop jumps versus 100 eccentric contractions).
The included studies made two comparisons: WBC versus control (rest or no WBC), tested in four studies; and WBC versus far'infrared therapy, also tested in one study.The results for the primary outcomes of muscle soreness (pain at rest at 1, 24, 48 and 72 hours), subjective recovery (tiredness at 24 hours; well'being at 24 hours) and adverse events are summarised here. The very poor quality of the available evidence for both comparisons means that we are very uncertain about these results.
A summary of the evidence available for the primary outcomes for this comparison is presented in Table 1. Pooled standardised mean difference (SMD) results for muscle soreness (pain at rest) favoured WBC after delayed'onset muscle soreness (DOMS)'inducing exercise at all four follow'ups: 1 hour (20 participants, 2 cross'over studies); 24 and 48 hours (38 participants, 2 cross'over studies, 1 parallel group study); 72 hours (29 participants, 1 cross'over study, 1 parallel group study). However, the 95% confidence intervals (CIs) also included either no between'group differences or a benefit in favour of the control group. The trials were heterogeneous, including in terms of the 'control group' where that of the two cross'over studies was passive rest and that of the parallel group study was standing in the chamber with the temperature set at 15°C. There was statistical heterogeneity, also shown by the statistically significant results of the subgroup analysis by study design, where the data from the cross'over studies were in favour of WBC but those from the parallel group study showed no difference between the two groups. One small cross'over trial found no difference in tiredness but better well'being after WBC at 24 hours post exercise. There was no report and probably no monitoring of adverse events.
One small cross'over trial involving 9 well'trained runners provided very low quality evidence of lower levels of muscle soreness after WBC at 1 hour follow'up, but not at 24 hours or 48 hours. The same trial found no difference in well'being but less tiredness after WBC at 24 hours post exercise. There was no report and probably no monitoring of adverse events.
We included four laboratory'based studies with a total of 64 participants; but substantially fewer participants were available for pooling in several primary and secondary outcomes. The majority of participants were young (mean ages between 20.2 and 31.8 years); we suspect that this probably reflects the current WBC user population. However, only four (6.25%) were female. This finding tallies with our findings of low participation by females in research relating to other recovery interventions (Costello c). It is possible that the results may not be applicable to females. For example, a recent study demonstrated that skin temperature following WBC depends upon anthropometric variables and sex, with females and individuals with a higher adiposity cooling more (Hammond ). It has also been demonstrated that the severity of muscle damage, and subsequent levels of inflammation and muscle soreness, is related to the gender of the participants (Costello c; Enns ) as well as to the exercise performed (Paulsen ).
Only two comparisons were tested by the included studies. Notably, these studies did not allow a comprehensive review of the relative effectiveness of different methods of WBC in comparison with other interventions (e.g. cold water immersion) in treating DOMS post exercise or in elite athletes.
There was also no evidence on different types and timings of WBC. Of particular note on timing is that three studies (Ferreira'Junior ; Fonda ; Hausswirth ) both attempted to 'prevent' DOMS by treating participants immediately after WBC, while Costello attempted to 'treat' soreness by utilising WBC at 24'hour post exercise when inflammation and DOMS are suggested to peak.
The clinical relevance of any differences in DOMS may be dependent on several factors such as the time of the outcome, the capacity for natural recovery after exercise, and the time and costs associated with treatment (Bennett ; Bleakley ; Herbert ). Bleakley has suggested that a 13% to 22% difference in muscle soreness would be important for athletes, particularly those in an elite sporting environment. In the current review, a reduction in muscle soreness of between ˜7% to ˜20% was observed in three studies (Ferreira'Junior ; Fonda ; Hausswirth ), demonstrating a potential positive effect after WBC at 1, 24 and 48 hour follow'ups. This suggests that if WBC is utilised immediately after exercise, reductions in DOMS may be clinically relevant. Due to the limitations of the current evidence base, further research is required to support these findings.
Increases in muscle strength that exceed baseline (> 100%) occurred at several follow'up times in Fonda and Hausswirth . Such increases are unlikely to be observed in a highly'trained group of athletes and, aside from statistical variation, may reflect the training status ('physically active') of the participants.
Although we could not find any reports of adverse events, given the absence of active surveillance these findings do not preclude their existence (Figure 1). Recently, Selfe , examining the optimal duration of WBC exposure in 14 professional rugby league players, reported a case of mild superficial skin burn bilaterally on a mid'portion of the anterior thigh in one athlete. The investigators described the skin damage as consisting of 'erythema and minor blistering which appeared in a horizontal strip approximately 2 cm high and 10 cm wide the day following WBC'. The athlete was a Samoan player with an intolerance to ice packs who did not disclose his cold intolerance to the study team or personnel. It is well established that cold injuries are more prevalent in individuals of African descent compared with their Caucasian counterparts (Golden ; Imray ). This greater sensitivity to cold may be explained by a more intense protracted vasoconstriction in the peripheries during cold exposure (Iampietro ; Maley ). However, as the studies included in this review did not undertake active surveillance for predefined adverse events, the short' and long'term safety of WBC remains unknown.
As with most recovery interventions, trained or elite athletes are most likely to use WBC on a regular basis. Although DOMS is most prevalent in novice athletes, we acknowledge that it may also occur in elite sport: e.g. at the beginning of the season (when returning to training following a period of reduced activity), after injury or after the introduction of a new movement or training method, especially if eccentric in nature. WBC has also been advocated in a clinical and rehabilitative setting as a way to reduce pain and inflammation (symptoms also associated with DOMS); however, our findings are less applicable to these settings.
On the basis of GRADE (Grades of Recommendation, Assessment, Development and Evaluation) criteria, the quality of evidence for the primary outcomes, muscle soreness and subjective recovery, was classified as 'very low' across all follow'up times. The reasons for downgrading the evidence were study limitations (especially lack of blinding) resulting in a high risk of bias, imprecision reflecting the very small sample sizes, and, where pooling was possible, inconsistency reflecting substantial heterogeneity. The reasons for downgrading for individual outcomes for the WBC versus control comparison are detailed in Table 1. Although there were no complications or side effects reported within any of the individual studies, it was unclear whether any study actively monitored specific adverse effects. For similar reasons, the quality of evidence was also judged as 'very low' for all other outcomes including strength. Reflecting serious study limitations and serious imprecision, the evidence for the second comparison, WBC versus far'infrared therapy, was classified as 'very low'.
There is a high degree of inter'individual differences in the level and duration of muscle soreness experienced after exercise. Cross'over designs are therefore popular in this area of research, with two such studies included in this review (Fonda ; Hausswirth ). The two other studies in the review employed a parallel group design (Costello ; Ferreira'Junior ). Bleakley and Bleakley have previously described how cross'over designs can risk certain carry'over effects between exercise and treatment periods, which are not present in parallel group designs. Insufficient recovery from the first exercise bout is a likely carry'over effect, particularly when studies induce DOMS on an untrained population. Secondly, during subsequent exercise bouts patients may experience reduced levels of muscle soreness or muscle damage. This repeated bout effect has been demonstrated to last for several months in humans (Howatson ; McHugh ; McHugh ; Nosaka ; Nosaka ). The two cross'over studies in this review used a time frame of 3 weeks (Hausswirth ) and 10 weeks (Fonda ) between treatment periods. However, it is still possible that the timeframe used by Hausswirth may be appropriate as the trialists used well'trained individuals completing familiar running exercises, who were likely to recover faster.
In this review, we undertook an extensive search of electronic databases and grey literature sources. Although we think this is likely to have identified all relevant published studies, it is possible that some unpublished studies have been missed and we cannot, in addition, rule out publication bias. To the best of our knowledge, the first randomised controlled trial conducted in this area was accepted for publication in December (Costello ). This appears to be the first study which sought to examine the effectiveness of WBC as a post exercise recovery intervention to reduce DOMS. We anticipate that the effectiveness of this intervention on treating or preventing DOMS post exercise is likely to be the focus of more research in the near future. We have not, however, identified any ongoing trials.
One potential source of bias is the post'hoc exclusion of trials not reporting our primary outcomes (seeTypes of outcome measures). However, none of the excluded studies were aimed at the treatment of DOMS.
As none of the included studies had a registered protocol, bias from selective reporting of results was difficult to fully ascertain. However, we made a concerted attempt to retrieve missing summary and raw data, and were able to contact all of the authors.
Two of the included studies used a randomised cross'over design. However, we were unable to perform any paired analysis and data were analysed as if these studies used a parallel group design. Cross'over studies were also combined with parallel group trials in the same meta'analysis. Although this approach gives rise to bias through unit of analysis error, this is expected to be conservative as cross'over studies analysed in this way tend to be under'weighted (Deeks ). Other Cochrane reviews (Bleakley ; Herbert ) have used a similar approach when assessing interventions to ameliorate DOMS. Inspection of the findings for muscle soreness of the two cross'over studies, and our exploratory subgroup analysis based on study design, showed that cross'over designs had a more positive effect on the primary outcome (muscle soreness at rest), compared with the parallel group trial reporting these data (Costello ). The reasons for this are not clear and the sample size is inadequate to speculate. Of note, however, is that a similar finding applied in Bleakley . We suggest that parallel studies represent the better methodological design for future research in this area.
A recent review, conducted by several authors of the current review, that includes a more general perspective has also noted the limited evidence base supporting the use of WBC in an athletic or rehabilitative setting (Bleakley ). Bleakley included 10 controlled trials, of which 3 randomised controlled trials (RCTs) appear in this review (Costello ; Fonda ; Hausswirth ). It did not include data from the latest published RCT (Ferreira'Junior ) included in the current review. Bleakley demonstrated that WBC induces tissue'temperature reductions that are comparable to, or less significant than, traditional forms of cryotherapy such as cold water immersion and ice pack application. Although WBC was reported to have a positive influence on inflammatory mediators, antioxidant capacity, and autonomic function during sporting recovery, the findings were based on weak evidence from controlled studies (Bleakley ). Bleakley concluded that there is some weak evidence that WBC improves the perception of recovery and soreness after exercise but that this does not translate into enhanced functional recovery or performance. None of the 10 trials reported adverse events associated with WBC; but as found in our review, none of the studies appeared to undertake active surveillance of predefined adverse events.
Of the three other Cochrane reviews examining the effectiveness of cold water immersion, stretching, and hyperbaric oxygen therapy for treating muscle soreness after exercise, only that for cold water immersion found some evidence of benefit (Bleakley ). Bleakley found some evidence that cold water immersion reduces delayed onset muscle soreness after exercise compared with passive interventions involving rest or no intervention; however, there was insufficient evidence to draw conclusions on other outcomes or for other comparisons in this review. Herbert concluded that available evidence suggests that muscle stretching does not produce clinically important reductions in DOMS in healthy adults. Bennett also found little evidence to support the use of hyperbaric oxygen therapy to reduce DOMS after exercise, but also noted some evidence that this intervention may increase interim pain. The finding of benefit from cold water immersion, which is a cheaper intervention than WBC, provides an important context in which to view the results of our review.
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