The Effect of Pressotherapy on Performance and Recovery in the Management of Delayed Onset Muscle Soreness: A Systematic Review and Meta-Analysis

Background: It has been demonstrated that pressotherapy used post-exercise (Po-E) can influence training performance, recovery, and physiological properties. This study examined the effectiveness of pressotherapy on the following parameters. Methods: The systematic review and meta-analysis were performed according to PRISMA guidelines. A literature search of MEDLINE, PubMed, EBSCO, Web of Science, SPORTDiscus, and ClinicalTrials has been completed up to March 2021. Inclusion criteria were: randomized control trials (RCTs) or cross-over studies, mean participant age between 18 and 65 years, ≥1 exercise mechanical pressotherapy intervention. The risk of bias was assessed by the Cochrane risk-of-bias tool for RCT (RoB 2.0). Results: 12 studies comprised of 322 participants were selected. The mean sample size was n = 25. Pressotherapy significantly reduced muscle soreness (Standard Mean Difference; SMD = −0.33; CI = −0.49, −0.18; p < 0.0001; I2 = 7%). Pressotherapy did not significantly affect jump height (SMD = −0.04; CI = −0.36, −0.29; p = 0.82). Pressotherapy did not significantly affect creatine kinase level 24–96 h after DOMS induction (SMD = 0.41; CI = −0.07, 0.89; p = 0.09; I2 = 63%). Conclusions: Only moderate benefits of using pressotherapy as a recovery intervention were observed (mostly for reduced muscle soreness), although, pressotherapy did not significantly influence exercise performance. Results differed between the type of exercise, study population, and applied treatment protocol. Pressotherapy should only be incorporated as an additional component of a more comprehensive recovery strategy. Study PROSPERO registration number—CRD42020189382.


Introduction
Physical activity, especially at the competitive level, causes a lot of negative changes in the human body [1,2]. Inflammation occurs as a result of damage to muscle cells [3] from which creatine kinase (CK), lactate dehydrogenase, and metabolites are released [1,2]. In such cases, we observe decreased efficiency, faster muscle fatigue, a decrease in the range of motion (ROM), and the appearance of pain in places where they are overloaded [4,5]. This phenomenon is exacerbated especially with eccentric exercises (ECC) [6], in which intense exercise may cause Delayed Onset Muscle Soreness (DOMS) [7].
To increase exercise capacity as well as reduce the risk of injury, the key element is the use of training measures related to biological recovery to reduce metabolites to minimum values and to ensure the right amount of energy substrates, including ATP and phosphocreatine [8].

Materials and Methods
The present review and meta-analysis were reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and follow the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions [23]. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. Systematic Reviews [24].

Search Strategy and Screening Procedures
Searches were carried out on the following electronic databases: MEDLINE (PubMed and EBSCO), Web of Science, SPORT Discus. We did not have any limits and we searched all articles to March 2021 for studies aimed at determining the effect of pressotherapy on the magnitude and time course of Po-E muscle soreness and sports performance and recovery following exercise-induced muscle damage. We also searched current information about registers and reports in ClinicalTrials.gov. Additionally, we carried out a manual search of the bibliography of the included works and tracked their citations in the Scholar database. We head the same keywords as in databases. There were no associated publications, reports, or registers.

Inclusion Criteria
Those studies in which the title and abstract were related to the aim of the present review were included for full-text request. We included studies that (1) were conducted as randomized control trials (RCT) and cross-over designs; (2) included a mean participant age between 18 and 65 years old. (3) Healthy adults with exercise-induced muscle damage regardless of their level of sports activity and performance (4) were based on at least one exercise intervention described as "External assisted mechanical therapy" (machines).

Exclusion Criteria
Studies were excluded if (1) outcome measurements were not reported as DOMS max values, or (2) they were not written in English. A third reviewer (SW) resolved cases of initial reviewer disagreement. Nonrandomized experiments, observational studies, secondary studies (any types of evidence syntheses), and opinion pieces (e.g., narrative reviews, editorials) were excluded too.

Selection Process, Data Collection, Data Extraction, and Management
Two initial reviewers (MJ and MC) independently examined the titles and abstracts of retrieved articles to identify suitable studies and extracted the following information from the included studies: First author's name and year of publication; study design; characteristics of the participants included; mean age; sample size and percentage of female subjects; weekly frequency, period and modality of External assisted mechanical therapy intervention; the reported measurement of Muscle functional capacities (e.g., strength, power), Muscle damage markers (e.g. serum CK levels), Joint ROM, and pain sensation. A third reviewer (SW) resolved cases of author disagreement.

Risk of Bias Assessment
The risk of bias of RCTs was assessed using the Cochrane risk-of-bias tool for randomized trials (RoB 2.0) [25], in which five domains were evaluated: Randomization process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result. Each domain was assessed for risk of bias. Studies were graded as (1) "low risk of bias" when a low risk of bias was determined for all domains; (2) "some concerns" if at least one domain was assessed as raising some concerns but not at a high risk of bias for any single domain; or (3) "high risk of bias" when a high risk of bias was reached for at least one domain or the studied judgment included some concerns in multiple domains [24]. Assessment for individual randomized, parallel-group trials is presented in Figure 1. For pre-post studies and non-RCTs we used the Quality Assessment Tool for Quantitative Studies [25], in which seven domains were evaluated: Selection bias, study design, confounders, blinding, data collection methods, withdrawals, and dropouts. Each domain was considered strong, moderate, or weak. Studies were classified as "low risk of bias" if they presented no weak ratings; "moderate risk of bias" when there was at least one weak rating; or "high risk of bias" if there were two or more weak ratings [25]. Assessment for individually randomized, cross-over trials is presented in Figure 2. The risk of bias was independently assessed by two reviewers (MJ and PW). A third reviewer (SW) was consulted in case of disagreement. two or more weak ratings [25]. Assessment for individually randomized, cross-over trials is presented in Figure 2. The risk of bias was independently assessed by two reviewers (MJ and PW). A third reviewer (SW) was consulted in case of disagreement.

Outcome Measures
Objective results of interest for meta-analyses from included baseline to last available follow-up. Data were typically collected immediately and 24 h, 48 h, 72 h, up to 96 h after the intervention.

Primary Outcomes
The primary endpoint was to assess the effect changes in MS and sports performance. two or more weak ratings [25]. Assessment for individually randomized, cross-over trials is presented in Figure 2. The risk of bias was independently assessed by two reviewers (MJ and PW). A third reviewer (SW) was consulted in case of disagreement.

Outcome Measures
Objective results of interest for meta-analyses from included baseline to last available follow-up. Data were typically collected immediately and 24 h, 48 h, 72 h, up to 96 h after the intervention.

Primary Outcomes
The primary endpoint was to assess the effect changes in MS and sports performance.

Outcome Measures
Objective results of interest for meta-analyses from included baseline to last available follow-up. Data were typically collected immediately and 24 h, 48 h, 72 h, up to 96 h after the intervention.

Primary Outcomes
The primary endpoint was to assess the effect changes in MS and sports performance.

Secondary Outcomes
The secondary endpoint was to assess muscle functional capacities (e.g., strength, power), muscle damage markers (e.g., serum CK levels), and joint ROM and pain sensation.

Statistical Considerations
Random-effects meta-analyses were performed using the Revman5.4.1 software [26]. Data was represented by Standardized Mean Difference and 95% Confidence Interval (CI). tau-squared Tau 2 , chi-squared Chi 2 and I 2 were used to investigate the presence of heterogeneity in meta-analysis. A p value < 0.05 was considered statistically significant.

Results of the Search
A total of 693 articles related to the topic were retrieved through a comprehensive database and other sources search, of which, 169 articles were duplicates. After removing all ineligible articles, a total of 12 RCTs were included in the analysis. The detailed screening process is shown in Figure 3. power), muscle damage markers (e.g., serum CK levels), and joint ROM and pain sensation.

Statistical Considerations
Random-effects meta-analyses were performed using the Revman5.4.1 software [26]. Data was represented by Standardized Mean Difference and 95% Confidence Interval (CI). tau-squared Tau 2 , chi-squared Chi 2 and I 2 were used to investigate the presence of heterogeneity in meta-analysis. A p value <0.05 was considered statistically significant.

Results of the Search
A total of 693 articles related to the topic were retrieved through a comprehensive database and other sources search, of which, 169 articles were duplicates. After removing all ineligible articles, a total of 12 RCTs were included in the analysis. The detailed screening process is shown in Figure 3.
The total study population of all selected articles comprised of 322 healthy volunteers with an unequal distribution of sex (n male = 274; n female = 48). Throughout all the studies, mean sample size ranged from 10 to 72 volunteers.
The average sample size of the pressotherapy group was 14.33 and the control group 13.25. The mean age of the study population was 28.1 years. In two studies the mean age was above 40 years. [1,2].
There was a different time of experimental and control condition; the majority performed therapy post-exercise, and after 24 h. The average therapy session was 30 min. The shortest time was 6 min [30] and the maximum was 1 h [11,27,29]. Total therapeutic exposition time varied from 20 to 30 min. [12,33,34] to longer times of 80 min to 6 h [18,19,31].
Muscle soreness had a heterogeneous direction of changes. Some authors observed decreasing after exercise from 72 h to 144 h and significant changes were measured after 72 h and 120 h [11,31]. The majority observed significantly increasing MS Po-E and after 24 h to 96 h [12]. Velanzuela (2018) observed increasing MS after 24 and 48 h but without any significant changes [32]. Oliver (2021) observed increasing MS Po-E, post-recovery, and after 24 h and also without any significant changes [33]. Cranston (2020) observed increasing Po-E in all four muscle groups, post-recovery decreasing in three groups with significant differences between groups, and after 24 h increasing in all four muscle groups, with significant differences between groups [34].
Hoffman (2016) observed that muscle fatigue increases post-race, post-treatment significantly and reached significant difference between groups post-race 24-168 h [12]. Two other authors analyzed the change of these parameters [31,33] and Heapy (2018) observed changes post-race, 24-168 h, and 336 h after exercise, and post-race, the 24-72 h increase was significant [31]. Furthermore, there was a significant difference between the groups of 72 h, 96 h, and 120 h. In Oliver et al (2021) muscle fatigue Po-E, post-recovery, and 24 h Po-E remained unchanged [33].
Two studies assess muscle flexibility parameters [11,27]. Both observed increasing after 72 h and decreasing after 168 h. Swelling and stiffness were observed by Chleboun et al (1995) after 24-96 h and 120 h [19]. The stiffness increased after 24 and 48 h and then decreased to 120 h.
Two studies measured isometric strength [18,19]. Cochrane (2013) observed decreased peak isometric strength after 24 h and increased after 48 and 72 h-all changes were significant [18]. Chleboun (1995) [12] and 120 h [31], and decreased time after 120 h [12]. Another activity to measure effects was a 6 km run after 168 h Po-E. In a countermovement jump (CM) [28,30,32] heterogenous results were observed: decreased post and increased after 24 h-significant changes between groups [28]. Decreased post, 1 and 24 h post and 1 h showed significant changes [30]. After 24 h, it decreased and after 48 h there were no significant changes [32]. Valenzuela   Subgroup analysis from 24 h to 96 h did not reveal a statistically significant difference (p = 0.98) ( Figure 5). Subgroup analysis from 24 h to 96 h did not reveal a statistically significant difference (p = 0.98) ( Figure 5).

Brief Study Informations: Purposes, Direction, and Possible Main Outcomes
Most of the studies used a one-time protocol to assess the time of post-workout re-

Brief Study Informations: Purposes, Direction, and Possible Main Outcomes
Most of the studies used a one-time protocol to assess the time of post-workout regeneration. The most reliable method would be to use it multiple times under different conditions to maximize result accuracy [35].
The best methods of post-workout recovery are sleep and a proper diet [36,37]. Additional methods can only be supplementary. For the assessment of the credibility of the studies, we recommend that the information on whether pressotherapy was the primary method or an addition to the more comprehensive scheme should be included in the research Methodology section.
Maximizing the efficiency of post-workout adaptation is crucial for athletes to maintain an appropriate performance level throughout the season and during the pre-competition preparation periods [38,39]. This is especially important in sports with a high frequency of competitions (i.e., team sports such as soccer and basketball), as well as in disciplines where the athlete prepares for a long time for one event in which their organism achieves peak performance (i.e., individual disciplines such as sprinting or swimming).
We stipulate that pressotherapy does NS affect post-workout regeneration and can only supplement a complex protocol.

Serum CK Level
The blood level of CK is an indicator of the status of muscle damage and of change in both pathological and normal conditions [40]. An increase in this enzyme may predict a state of microscopic tissue impairment after acute and prolonged injuries. Variables in CK level are also observed under physiological conditions in athletes after demanding training. The highest CK growth is observed after prolonged exercise, i.e., triathlon events and demanding strength exercises, or activities that include an eccentric muscle contraction phase, i.e., downhill running [41,42]. In our study, we saw an improvement in this parameter, which suggests that pressotherapy improves regeneration. However, its impact was not statistically significant in any case except the 96 h Po-E group, which had the lowest number of participants. In addition, a significant result was observed in the longest period after the training was performed, which leaves some ambiguity as CK activity decreases with time and it is a natural process [43]. Not without relevance is also the fact that a significant result was observed by Haun et al., who investigated CK levels on a group of trained high-volume endurance athletes, who underwent over 70 h of exertion per week for 3 months. Although significant results have been observed, previous studies suggest that CK levels naturally decline between days 4 and 10 after exercise [44]. The characteristics of the test group (endurance athletes) and testing protocol could also affect the results, as resting CK levels are higher in the trained population [45,46] and everyday strenuous workouts may cause persistent blood rise of CK [47]. Therefore, the potential outcome of pressotherapy on a different group of people would not be so important. To summarize, in the current state of knowledge, pressotherapy should not be recommended as the basic method of recovery after exercise, because there is a large heterogeneity of previous research results.

DOMS
DOMS is a regular experience for advanced or beginner athletes. Its manifestations can range from muscle stiffness to severe excruciating pain [48]. DOMS is most prevalent at the beginning of the sporting season when athletes are returning to training following a period of reduced activity [49]. DOMS is also common when athletes are first introduced to certain types of activities regardless of the time of year. DOMS can negatively attenuate athletic performance [50]. Possible mechanisms include a reduction in joint ROM, peak torque, and a feeling of pain [48]. Compensation methods may raise the probability of further injury [51,52] when participants try to return to activity too early without completing the full recovery process. Therefore, it is of high importance to search for new methods of the most effective regeneration and reduction of MS. Commonly described in the literature are pressotherapy [48], stretching [53], cryotherapy [54], and massage, mainly considered as self-foam rolling. It has been the most often assessed parameter in selected studies. Although pressotherapy is one of the methods of DOMS reduction, our results indicate that its use for this purpose remains questionable. Only when MS was measured after 48 h, was a a significant effect of pressotherapy observed. This method also significantly alleviates DOMS when considering the whole population and all protocols. On the other hand, no significant reduction in MS was found in the remaining groups. Taking into account the previously mentioned methods of therapy, which are easily available (stretching or foam-rolling), as well as low-cost (cryotherapy and water immersion) or self-applicable and physiologic (i.e., rest), there are few arguments in favor of the wide use of pressotherapy in the current state of knowledge. High prices and limited availability suggest other forms as a method of choice and first-line treatment strategy. However, pressotherapy has shown some positive effects, mainly limited to the 48 h Po-E period, so while the above-mentioned factors are not a barrier, it can be used in some circumstances [55] (e.g., in professional athletes as a supplemental method).

Jump Performance
The level of muscle power in the lower limbs is a vital factor in numerous disciplines, such as sprinting [56,57] or in decisive moments of team sports [58,59]. In a widespread view, the research has demonstrated that jump heigh is an applicable index to characterize power output, mainly described by the association found between them [60]. It is meaningful that upright jump may be easily evaluated and hereafter used by team staff and physical trainers to categorize the level of athletes' muscle power within a wider group of participants [61,62]. Due to the great practical importance of jump performance in the overall assessment of an athlete's fitness and the development of motor skills, it is crucial to properly place this type of activity in the training plan and the microcycle [63,64]. Effective recovery after jumping efforts would be of key importance, hence the influence of pressotherapy on jump performance was also assessed in this meta-analysis. In our review, we did not observe any significant effect of pressotherapy on jump ability performed at various intervals from the previous exercise. Further investigation is needed to specify whether and in what population this method will be an effective approach for improving jump performance and overall power generation.

Practical Implications
This study has several practical implications and contributes significantly to the actual state of knowledge in this research area. It can be used by motor preparation specialists and physiotherapy professionals in the prescription of individualized, advanced recovery strategies. This is especially important when maximizing the effectiveness of post-exercise regeneration is necessary (e.g., for elite athletes during the beginning of the season or directly before competitive event).

Conclusions
The conducted systematic review and meta-analysis assessed 12 randomized controlled studies investigating the outcome of pressotherapy on the recovery of absolute (i.e., physiological), and subjective (i.e., perceptual) outcomes. The findings indicate only moderate benefits of using pressotherapy as a recovery intervention, dependent on the type of exercise and used protocol. A reduction in DOMS, changes in CK level, and improvements in perceived recovery were observed after pressotherapy, although they were usually not significant. Dose-response relationships emerged for several variables indicating that different duration protocols may improve the efficacy of pressotherapy if applied after exercise. We recommend further, and continuing, research on various populations and broadening tested protocols to obtain the highest possible homogeneity of results and to facilitate the creation of a consensus statement on whether pressotherapy seems to be an effective method in minimizing exercise-induced negative effects.

Limitations
Although, this paper has a few limitations. Firstly, we performed a comprehensive literature investigation, where we excluded articles that were not published in English. However, from an actual point of view, we suppose this will have a minor effect on our outcomes [65]. Nevertheless, we conducted a reasonable attitude to overwhelm these barriers and attempted to stick to principles of open science. Secondly, the protocols used and the study groups differed between the selected articles. Third, the time of outcome evaluation from the preliminary endpoint was not identical in all trials. Fourth, the particular subgroup analyses were conceivably underpowered due to their small participant number and should be interpreted carefully. To enhance the validity of results in similar research, future randomized studies should concentrate on better conducting and reporting of applied protocol and methodology, intention-to-treat examination, assessor blinding, random sequence generation, control group observation, and reporting of adverse events or the possible other influencing factors. Moreover, not all databases (i.e., EMBASE) were searched.