Combat sports are a group of regulated contact activities and martial arts in which athletes engage in one-on-one physical contests. Depending on the specific rule sets for competition, athletes may strike, kick, hit, throw, punch, or grapple with their opponent, with the aim of scoring more points or disabling their rival and preventing the continuation of the match.1 A common feature across all combat sports is the use of weight categories for competition where athletes are paired with opponents of similar anthropometrical characteristics to promote safety and physical equality between participants.2 However, in an attempt to gain a competitive advantage many combat sport athletes manipulate their body mass through weight cutting so they are paired with an opponent of lesser body mass.3 Weight cutting is a process involving rapid weight loss (RWL) so combat sport athletes can qualify for a lower competition weight category, followed by rapid weight gain (RWG) where they attempt to recover body mass losses before the start of competition. Up to 80% of athletes across numerous combat sports partake in some form of weight cutting before competition where the magnitude of RWL and RWG reportedly ranges from 3% to 10% of pre-RWL body mass.4,5
Although weight cutting procedures vary among combat sport athletes, the process is typically performed over 2 to 7 days6,7 with target body mass losses achieved immediately before the official weigh-in where event organizers officially register the athlete’s body mass to confirm they comply with weight category requirements. After weigh-in, athletes then have approximately 3 to 24 hours for RWG before their match commences, depending on the specific combat sport.8 Strategies used by combat sport athletes to facilitate RWL in the days before weigh-in may include various combinations of restricting total caloric intake, reducing carbohydrate intake, manipulating fecal bulk and gastrointestinal content, increasing energy expenditure and reducing glycogen bound body fluid through exercise, and/or water loading.9 Although the magnitude of body mass losses associated with these methods are poorly reported, one controlled study observed a body mass reduction using a water loading technique applied over 5 days of approximately 3% of pre-RWL body mass.10
During the hours leading up to competition, combat sport athletes may achieve additional losses in body mass of up to 5% or more by inducing acute dehydration through fluid restriction combined with exercise, and/or sauna or steam room use to facilitate sweating.5,11 Following weigh-in, strategies for RWG generally involve regularly ingesting large volumes of fluids and food consumption.12 The abrupt changes in body mass that occur with weight cutting are associated with numerous physiological effects. Specifically, RWL may result in decreased plasma volume, increased submaximal heart rates, impaired thermoregulation, electrolyte disturbances, muscle glycogen depletion, reduced muscle buffering capacity, altered metabolic profiles, and changes in serum hormone concentrations.2,13,14 Furthermore, it has been reported that following RWG, athletes may remain dehydrated based on urine osmolarity and urine specific gravity measurements despite recovering almost all body mass losses.15–17 Additionally, total hemoglobin mass, blood volume, and blood glucose concentrations may be impaired before competing.18,19 As such, the RWL and RWG associated with weight cutting may impact exercise capacity and have consequences for match performance.
Results from studies examining the effects of RWL on exercise performance in combat sports athletes are conflicting.20–22 For instance, Barley et al23 found reduced upper body maximal power and repeated high-intensity effort performance measured via medicine ball throw distance and a novel sled pushing task, respectively, in mixed martial arts athletes following RWL. However, no changes were observed in handgrip strength or vertical jump height. Conversely, Barbas et al24 reported that parameters of upper body strength (handgrip strength, bear hug strength, and hip and back strength) in a cohort of elite Greco-Roman wrestlers were unchanged following RWL. Fewer studies have investigated the effects of RWG on exercise performance. Pallarés et al17 observed increases in upper body strength (handgrip strength) and upper and lower body power (bench press velocity and countermovement jump) in Olympic combat sports athletes who were dehydrated from RWL following RWG. Alternatively, Alves et al25 found that handgrip strength remained compromised after 24 hours of RWG in their cohort of mixed martial artists. Furthermore, Barley et al23 reported that the decrements in performance associated with RWL were shown to persist following a 24-hour RWG period.
Given the inconsistencies across individual studies, a quantitative assessment of the current literature examining the effects of weight cutting on exercise performance in combat sports athletes is warranted. Therefore, the purpose of this investigation was to systematically search the literature for rigorous studies examining the effects of RWL and RWG associated with weight cutting of ≥3% total body mass on exercise performance in combat sports athletes and evaluate the strength of the combined evidence using a meta-analytic procedure.
Methods
Study Protocol
The research study was designed in accordance with the specifications outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols, and the recommended elaboration and explanation document.26,27
Eligibility Criteria
Studies were required to meet the following criteria to be eligible for possible inclusion in the meta-analyses: (1) participants were restricted to athletes with amateur and/or professional competitive experience in appropriately governed combat sports (eg, boxing, kick boxing/muay thai, mixed martial arts, wrestling, karate, taekwondo, Brazilian jiu jitsu, and/or judo); (2) participants were a minimum of 18 years of age; (3) studies employed either a within or between participant design; (4) RWL was achieved within a maximum of 7 days and/or RWG was achieved within a maximum of 36 hours; (5) participants achieved RWL of ≥3% using caloric restriction, increased energy expenditure, and/or total body fluid manipulation procedures only; (6) data were collected at a minimum of 2 of the following time points: pre-RWL, post-RWL, and/or following RWG; (7) body mass changes in RWL and RWG were verified by the investigators; and (8) outcome measures included discernible tests of exercise performance. Studies using research designs where exercise performance data may have been influenced by confounding variables (eg, thermal strain at time of testing, data collected immediately postcompetition or bout, or experimentally controlled nutritional interventions) were excluded.
Systematic Search Strategy
The systematic literature search strategy and study eligibility process is described in Figure 1. The search was conducted on March 31, 2020 by systematically exploring PubMed (MEDLINE), Scopus, SPORTDiscus (EBSCO), Web of Science (via Thomas Reuters) and Sports Medicine and Education (PROQUEST) databases using the search terms (“Combat sport” OR “Mixed martial arts” OR “MMA” OR “Box*” OR “Judo” OR “Judoka” OR “Karate” OR “Taekwondo” OR “Wrestling”) AND (“Weight cut*” OR “Weight loss” OR “Rapid weight loss” OR “Rapid weight gain” OR “Weight cycl*”). Citations were limited to complete texts written in English using human participants. A total of 15,009 studies were captured from the initial search and imported to bibliographic management software (EndNote, version X8.2, Clarivate). Following the removal of duplicates, 11,920 studies remained. An extensive manual search of the identified literature was then undertaken where article titles and abstracts were screened for relevance. Following this, 518 articles were assessed against the eligibility criteria where their reference lists were screened for additional literature pertinent to this study that may not have been captured through the search (n = 0) where a total of 25 eligible studies were identified for possible inclusion in this investigation.
—Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram outlining the implemented search strategy and eligibility process.
Citation: International Journal of Sports Physiology and Performance 17, 7; 10.1123/ijspp.2021-0104
Methodological Quality and Risk-of-Bias Assessment
All 25 studies eligible for possible inclusion were assessed for methodological quality and risk of bias using the Rosendal scale, which is suitable for evaluating exercise studies.28 Due to the nature of the research, blinding participants and/or investigators from experimental conditions is not possible. Therefore, questions related to blinding were removed from the scale as per the instrument instructions and as performed by others.29,30 Two authors (Brechney and Goodman) independently reviewed all citations that were considered for inclusion in this study with any discrepancies settled by consensus. Only studies scoring ≥50% on the scale were accepted for data extraction as per scale instructions.28 Following this, 8 studies were excluded based on low quality, and 17 studies were accepted for final inclusion in this investigation (Figure 1; Supplementary Table S1 [available online]).
Data Extraction
All exercise performance tests administered in the 17 included studies were closely scrutinized where the underlying exercise capacity assessed in each test was determined by consenus of all authors. Individual tests were then collated for homogeneity to create subgroups based on convergent validity, which is defined as the extent to which the test protocols evaluated the same exercise capacity construct and tests results would likely be highly correlated.31 Four test subgroups were identified where the tests included within each subgroup were considered to be sufficiently similar to justify combining for further analysis. The exercise capacity test subgroups identified were: (1) tests of anaerobic capacity, which measured performance during tasks requiring participants to generate maximal mechanical work during a single repetition of a short duration activity (eg, 10–30 s)32; (2) tests of repeated high-intensity effort performance, which measured performance during tasks requiring participants to repetitively generate maximal mechanical work during short duration activity (eg, 5–30 s) across trials that are each separated by a brief recovery period33; (3) tests of explosive power, which measured performance during tasks requiring participants to rapidly exert maximal muscular force for a single repetition of an activity34; and (4) tests of maximal muscular strength, which measured performance during tasks requiring participants to produce maximal muscular force without reference to time for a single repetition of an activity.34 The exercise capacity test subgroups and associated outcome measurements combined for analysis are described in Table 1.
Exercise Capacities and Tests
| Exercise capacities tested | Administered tests | No. of studies |
|---|---|---|
| Anaerobic capacity | Wingate test (bike ergometer/arm crank) | 5 |
| Maximal strength | Handgrip strength | 7 |
| Bear hug strength | 1 | |
| Arm, trunk, knee, hip, and back flexion/extension strength | 1 | |
| Power | Bench press velocity and power | 2 |
| Maximal voluntary isometric contraction (knee extension) | 3 | |
| Vertical jump height | 1 | |
| Countermovement jump power | 1 | |
| High-intensity repeat-effort performance | Special judo fitness test | 1 |
| Repeated isokinetic knee extension | 1 | |
| Intermittent arm crank sprint | 1 |
Statistical Analysis
Outcome data were transferred into Comprehensive Meta-analysis (version 3, BioStat) and analyzed using a generic inverse variance, random effects model with 95% confidence intervals (CIs). A random effects model was used to account for differences in research designs and participant characteristics between studies. Significance was investigated through examination of P values where alpha was set at ≤.05. Standardized effect sizes were calculated and reported as Hedges (g).35 The magnitude of such effects was determined using standardized conventions and represented as trivial (<0.20), small (0.20–0.49), moderate (0.50–0.79), and large (≥0.80).36 Heterogeneity between studies was evaluated using Cochrane Q where alpha was set at P ≤ .10. The magnitude of heterogeneity was stratified using the I2 statistic, where 0% to 40%, 30% to 60%, 50% to 90%, and ≥75% denote low, moderate, substantial, and considerable, respectively.37 Subgroup analyses were performed for each exercise capacity test type across the following time points: pre-RWL, post-RWL, and post-RWG. A leave-one-out sensitivity analysis was performed when heterogeneity was statistically significant to determine the robustness of the findings. Some studies reported both absolute and/or relative exercise performance data. Given that relative data were expressed with respect to body mass, sensitivity analyses using only absolute performance data were also completed. Publication bias was investigated statistically through the Begg and Mazumdar’s rank correlation test and Eggers linear regression method,35 which were applied to all analyses. Where publication bias was detected, Duval and Tweedie’s trim and fill correction was applied and the resultant effects on Hedges g and the 95% CI were explored.
Results
Study and Participant Characteristics
Seventeen studies were accepted for inclusion in this analysis (Figure 1). Separate data sets were identified in Mendes et al,22 Finn et al,38 Rankin et al39 and treated independently. Both Finn et al38 and Rankin et al39 asked participants to engage in ad libitum RWL (pre-RWL to post-RWL) and this data were incorporated into the analysis. However, controlled nutritional RWG (post-RWL to post-RWG) was adopted, thus, this data were excluded. Ööpik et al40 used a similar approach, however, as participant samples were not independent for each condition, data were combined between pre-RWL and post-RWL. The assessment of vertical jump in the study by Camarço et al21 was also removed from this analysis due to extreme outlying results. Among the studies included, 7 combat sports were identified: Wrestling (9 studies n = 162), Taekwondo (1 study, n = 62), Judo (5 studies; n = 56), mixed martial arts (4 studies, n = 33), Boxing (1 study, n = 25), Karate (1 study, n = 5), and Brazilian jiu jitsu (1 study, n = 2). One study41 did not specify the combat sport (n = 14). For RWL (pre-RWL to post-RWL), 15 datasets contributed to the exercise performance capacities. Three studies examined exercise performance during RWG (post-RWL to post-RWG). Eight contributions informed how weight cutting (pre-RWL to post-RWG) influences exercise performances. Artioli et al42 expressed performance data relative to body mass, while Timpmann et al43 provided both relative and absolute values. The remaining studies used absolute values only. Exercise performance data were found for anaerobic capacity (n = 4), repeated high-intensity efforts (n = 4), power (n = 4), and maximal muscular strength (n = 9). Barbas et al24 examined vertical jump height in their cohort at baseline, before, and following 5 wrestling bouts. Given the probable confounding of the matches on exercise performance, comparisons were made between baseline and prior to the first match only (Table 2). Three studies17,24,44 tested participants throughout a real competitive period, while all other studies were conducted in controlled laboratory settings.
Study Characteristics and Key Findings
| Study citation | Δ body mass (absolute, kg; relative, %) | Recovery duration, h | Exercise test(s) administered | Results Mean (SD) and/or g (95% CI) |
|---|---|---|---|---|
| Abedelmalek et al47 | Pre-RWLvs post-RWL: NR; −4.2% (NR%) | NA | Special judo fitness test | Pre-RWL = 31 (3) (number of throws) |
| Post-RWL = 26 (3) (number of throws) | ||||
| Pre-RWL vs post-RWL = −1.64 (−2.52 to −0.76) | ||||
| Alves et al25 | Pre-RWL vs post-RWL: −7.4 (2.7) kg; −9.9% (NR%) | 24 | Maximal handgrip strength | Pre-RWL = 51.7 (5.4) kg |
| Post-RWL = 47.8 (5.8) kg | ||||
| Post-RWG = 49.3 (5.1) kg | ||||
| Post-RWL vs post-RWG: 4.6 (2.2) kg; 6.9% (NR%) | Pre-RWL vs post-RWL = −0.67 (−1.43 to 0.08) | |||
| Post-RWL vs post-RWG = 0.27 (−0.47 to 1.00) | ||||
| Pre-RWL vs post-RWG = −0.44 (−1.18 to 0.30) | ||||
| Artioli et al42 | Pre-RWL vs post-RWL: −3.8 (NR) kg; −4.8% (1.1%) | 4 | 30-s upper-body Wingate test | Pre-RWL = 299.0 (34.1) W/kg |
| Post-RWL vs post-RWG: NR; 2.5% (0.1%) | Post-RWG = 322.7 (38.5) W/kg | |||
| Pre-RWL vs post-RWG = 0.61 (−0.30 to 1.52) | ||||
| Barbas et al24 | Pre-RWL vs post-RWL: NR; −6.0% (NR%) | 12 | Handgrip strength | Pre-RWL = 52.9 (2.4) kg |
| Post-RWG = 55.1 (2.6) kg | ||||
| Pre-RWL vs post-RWG = 0.26 (−1.48 to 0.99) | ||||
| Post-RWL vs post-RWG: NR; 1.2% (NR%) | Bear hug strength | Pre-RWL = 119.4 (4.1) kg | ||
| Post-RWG = 120.8 (5.0) kg | ||||
| Pre-RWL vs post-RWG = 0.09 (−0.64 to 0.82) | ||||
| Vertical jump height | Pre-RWL = 40.1 (2.2) cm | |||
| Post-RWG = 41.7 (1.9) cm | ||||
| Pre-RWL vs post-RWG = 0.23 (−0.51 to 0.96) | ||||
| Hip and back strength | Pre-RWL = 209.9 (6.8) kg | |||
| Post-RWG = 217.5 (7.2) kg | ||||
| Pre-RWL vs post-RWG = 0.32 (−0.42 to 1.05) | ||||
| Barley et al41 | Pre-RWL vs post-RWL: −3.0 (NR) kg; −3.2% (1.1%) | 3 | Knee extension MVIC | Pre-RWL = 295 (48) N·m |
| Post-RWL vs post-RWG: 2.0 (NR) kg; 2.6% (1.1%) | Post-RWG = 297 (49) N·m | |||
| Pre-RWL vs post-RWG = 0.04 (−0.65 to 0.73) | ||||
| Camarço et al21 | Pre-RWL vs post-RWL: −5.6 (1.6) kg; −7.2% (1.9%) | 36 | Handgrip strength: Right hand | Pre-RWL = 53.0 (2.4) kg |
| Post-RWL = 53.5 (3.5) kg | ||||
| Post-RWG = 52.6 (2.0) kg | ||||
| Post-RWL vs post-RWG: 6.1 (1.0) kg; 6.5% (1.1%) | Pre- vs post-RWL = 0.105 (−0.41 to 0.62) | |||
| Post-RWL vs post-RWG = −0.18 (−0.69 to 0.33) | ||||
| Pre-RWL vs post-RWG = −0.09 (−0.60 to 0.42) | ||||
| Left hand | Pre-RWL = 50.3 (5.7) kg | |||
| Post-RWL = 51.8 (4.8) kg | ||||
| Post-RWG = 50.6 (2.0) kg | ||||
| Pre- vs post-RWL = 0.16 (−0.35 to 0.68) | ||||
| Post-RWL vs post-RWG = −0.19 (−0.70 to 0.33) | ||||
| Pre-RWL vs post-RWG = 0.04 (−0.65 to 0.73) | ||||
| Bench press power | Pre-RWL = 251.8 (12.1) W | |||
| Post-RWL = 251.0 (22.3) W | ||||
| Post-RWG = 257.1 (21.1) W | ||||
| Pre-RWL vs post-RWL = −0.03 (−0.49 to 0.54) | ||||
| Post-RWL vs post-RWG = 0.21 (−0.31 to 0.72) | ||||
| Pre-RWL vs post-RWG = 0.47 (−0.06 to 1.00) | ||||
| Coufalová et al45 | Pre-RWL vs post-RWL: −3.4 (NR) kg; −4.6% (NR%) | NA | Maximal handgrip strength: Right hand | Pre-RWL = 48.3 (7.5) kg |
| Post-RWL = 49.9 (7.6) kg | ||||
| Pre-RWL vs post-RWL = 0.20 (−0.62 to 1.02) | ||||
| Left hand | Pre-RWL = 48.8 (7.1) kg | |||
| Post-RWL = 49.2 (7.7) kg | ||||
| Pre-RWL vs post-RWL = 0.05 (−0.76 to 0.87) | ||||
| Maximal arm flexion strength: Right arm | Pre-RWL = 31.4 (3.7) kg | |||
| Post-RWL = 31.7 (6.1) kg | ||||
| Pre-RWL vs post-RWL = 0.05 (−0.76 to 0.87) | ||||
| Left arm | Pre-RWL = 29.3 (3.4) kg | |||
| Post-RWL = 30.6 (5.9) kg | ||||
| Pre-RWL vs post-RWL = 0.27 (−0.55 to 1.08) | ||||
| Maximal arm extension strength: Right arm | Pre-RWL = 28.2 (5.1) kg | |||
| Post-RWL = 27.1 (3.8) kg | ||||
| Pre-RWL vs post-RWL = −0.24 (−1.06 to 0.58) | ||||
| Left arm | Pre-RWL = 29.2 (5.4) kg | |||
| Post-RWL = 26.5 (3.8) kg | ||||
| Pre-RWL vs post-RWL = −0.55 (−1.38 to 0.28) | ||||
| Maximal trunk flexion strength | Pre-RWL = 78.1 (16.6) kg | |||
| Post-RWL = 68.9 (17.1) kg | ||||
| Pre-RWL vs post-RWL = −0.52 (−1.35 to 0.31) | ||||
| Maximal trunk extension strength | Pre-RWL = 79.5 (20.2) kg | |||
| Post-RWL = 70.4 (19.1) kg | ||||
| Pre-RWL vs post-RWL = −0.44 (−1.26 to 0.39) | ||||
| Maximal knee flexion strength: Right knee | Pre-RWL = 27.1 (5.6) kg | |||
| Post-RWL = 29.3 (6.4) kg | ||||
| Pre-RWL vs post-RWL = 0.35 (−0.48 to 1.17) | ||||
| Left knee | Pre-RWL = 26.7 (6.1) kg | |||
| Post-RWL = 28.6 (8.4) kg | ||||
| Pre-RWL vs post-RWL = 0.25 (−0.57 to 1.07) | ||||
| Maximal knee extension strength: Right knee | Pre-RWL = 60.1 (12.2) kg | |||
| Post-RWL = 64.6 (12.0) kg | ||||
| Pre-RWL vs post-RWL = 0.36 (−0.47 to 1.18) | ||||
| Left knee | Pre-RWL = 57.9 (9.6) kg | |||
| Post-RWL = 59.2 (13.8) kg | ||||
| Pre-RWL vs post-RWL = 0.11 (−0.70 to 0.92) | ||||
| Degoutte et al49 | Pre-RWL vs post-RWL: −3.8 (NR) kg; −5.0% (NR%) | NA | Handgrip strength | Pre-RWL = 53.6 (2.7) kg |
| Post-RWL = 50.4 (2.5) kg | ||||
| Pre-RWL vs post-RWL = −1.18 (−2.03 to −0.32) | ||||
| Finn et al38 A | Pre-RWL vs post-RWL: −3.4 (NR); −4.6% (NR%) | 2 | Arm crank Wingate test | Pre-RWL = 36.9 (5.2) kJ |
| Post-RWL = 37.8 (6.0) kJ | ||||
| Pre-RWL vs post-RWL = 0.16 (−0.69 to 1.01) | ||||
| Finn et al38 B | Pre-RWL vs post-RWL: −3.5 (NR); −4.6% (NR%) | 2 | Arm crank Wingate test | Pre-RWL = 37.2 (6.8) kJ |
| Post-RWL = 35.4 (6.2) kJ | ||||
| Pre-RWL vs post-RWL = −0.26 (−1.15 to 0.63) | ||||
| McKenna et al48 | Pre-RWL vs post-RWL: NR; −3.0% (0.3%) | 1 | 30-s lower body Wingate test | Pre-RWL = 656.0 (82.5) W |
| Post-RWL = 651.1 (70.2) W | ||||
| Pre-RWL vs post-RWL = −0.06 (−0.94 to 0.82) | ||||
| Mendes et al22 A | Post-RWL vs post-RWG: −4.0 (NR) kg; −5.2% (1.3%) | 4 | Arm crank Wingate test: Mean power | Pre-RWL = 235.3 (33.5) W |
| Post-RWG = 224.1 (29.0) W | ||||
| Pre-RWL vs post-RWG = −0.34 (−1.13 to 0.45) | ||||
| Peak power | Pre-RWL = 451.4 (40.5) W | |||
| Post-RWG = 446.9 (49.6) W | ||||
| Pre-RWL vs post-RWG = −0.10 (−0.88 to 0.69) | ||||
| Total work | Pre-RWL = 27.7 (3.4) kJ | |||
| Post-RWG = 26.4 (3.1) kJ | ||||
| Pre-RWL vs post-RWG = −0.39 (−1.18 to 0.41) | ||||
| Mendes et al22 B | Post-RWL vs post-RWG: −4.0 (NR) kg; −5.3% (1.0%) | 4 | Arm crank Wingate test: Mean power | Pre-RWL = 226.3 (42.4) W |
| Post-RWG = 217.4 (38.0) W | ||||
| Pre-RWL vs post-RWG = −0.21 (−1.06 to 0.64) | ||||
| Peak power | Pre-RWL = 433.3 (90.1) W | |||
| Post-RWG = 433.3 (81.1) W | ||||
| Pre-RWL vs post-RWG = −0.00 (−0.85 to 0.85) | ||||
| Total work | Pre-RWL = 26.7 (4.4) kJ | |||
| Post-RWG = 25.4 (3.9) kJ | ||||
| Pre-RWL vs post-RWG = −0.29 (−1.15 to 0.56) | ||||
| Ööpik et al40 | Pre-RWL vs post-RWL: −4.0 (0.9) kg; −4.9% (0.9%) | 17 | Glucose only Knee extensions: Submaximal work | Pre-RWL = 2973 (579) J |
| Post-RWL = 2894 (811) J | ||||
| Pre-RWL vs post-RWL = −0.10 (−1.05 to 0.85) | ||||
| Maximal work | Pre-RWL = 5790 (3164) J | |||
| Post-RWL = 4746 (1814) J | ||||
| Pre-RWL vs post-RWL = −0.37 (−1.33 to 0.60) | ||||
| Total work | Pre-RWL = 8684 (2662) J | |||
| Post-RWL = 7563 (2354) J | ||||
| Pre-RWL vs post-RWL = −0.40 (−1.37 to 0.56) | ||||
| Glucose and creatine Knee extensions: Submaximal work | ||||
| Pre-RWL = 3050 (695) J | ||||
| Post-RWL = 2585 (656) J | ||||
| Pre-RWL vs post-RWL = −0.62 (−1.60 to 0.36) | ||||
| Maximal work | Pre-RWL = 5520 (2315) J | |||
| Post-RWL = 4515 (1428) J | ||||
| Pre-RWL vs post-RWL = −0.47 (−1.44 to 0.50) | ||||
| Total work | Pre-RWL = 8452 (2855) J | |||
| Post-RWL = 7023 (2006) J | ||||
| Pre-RWL vs post-RWL = −0.52 (−1.49 to 0.45) | ||||
| Pallarés et al17 | Post-RWL vs post-RWG: NR; 3.1% (1.4%) | 16 | Bench press velocity | Post-RWL = 0.527 (0.2) m/sa |
| Post-RWG = 0.566 (0.2) m/sa | ||||
| Post-RWL vs post-RWG = 0.26 (−0.13 to 0.64) | ||||
| Countermovement jump power | Post-RWL = 1646 (367) Wa | |||
| Post-RWG = 1691 (360) Wa | ||||
| Post-RWL vs post-RWG = 0.12 (−0.26 to 0.51) | ||||
| Maximal handgrip strength: Dominant hand | Post-RWL = 40.9 (12.4) kga | |||
| Post-RWG = 40.7 (12.4) kga | ||||
| Post-RWL vs post-RWG = −0.02 (−0.40 to 0.37) | ||||
| Nondominant hand | Post-RWL = 41.7 (10.7) kga | |||
| Post-RWG = 41.6 (11.5) kga | ||||
| Post-RWL vs post-RWG = −0.01 (−0.39 to 0.38) | ||||
| Rankin et al39 A | Pre-RWL vs post-RWL: NR; −3.3% (NR%) | 5 | Modified arm crank Wingate test: Average power | Pre-RWL = 204.2 (17.7) W |
| Post-RWL = 189.2 (20.4) W | ||||
| Pre-RWL vs post-RWL = −0.33 (−1.25 to 0.60) | ||||
| Peak power | Pre-RWL = 321.1 (31.4) W | |||
| Post-RWL = 310.7 (27.0) W | ||||
| Pre-RWL vs post-RWL = −0.15 (−1.07 to 0.77) | ||||
| Total work | Pre-RWL = 24.3 (2.2) kJ | |||
| Post-RWL = 22.7 (2.4) kJ | ||||
| Pre-RWL vs post-RWL = −0.29 (−1.22 to 0.63) | ||||
| Rankin et al39 B | Pre-RWL vs post-RWL: NR; −3.3% (NR%) | 5 | Modified arm crank Wingate test: Average power | Pre-RWL = 190.7 (14.8) W |
| Post-RWL = 175.4 (15.6) W | ||||
| Pre-RWL vs post-RWL = −0.15 (−1.35 to 0.51) | ||||
| Peak power | Pre-RWL = 278.7 (27.6) W | |||
| Post-RWL = 255.5 (29.2) W | ||||
| Pre-RWL vs post-RWL = −0.34 (−1.26 to 0.59) | ||||
| Total work | Pre-RWL = 22.8 (1.7) kJ | |||
| Post-RWL = 21.1 (1.7) kJ | ||||
| Pre-RWL vs post-RWL = −0.39 (−1.32 to 0.54) | ||||
| Ribas et al44 | Pre-RWL vs post-RWL: NR; −8.5% (1.3%) | NA | Maximal handgrip strength: Right hand | Pre-RWL = 47.4 (9.9) kg |
| Post-RWL = 40.9 (9.4) kg | ||||
| Post-RWL vs post-RWG: NR; 5.4% (0.8%) | Pre-RWL vs post-RWL = −0.66 (−1.27 to −0.06) | |||
| Left hand | Pre-RWL = 43.9 (8.7) kg | |||
| Post-RWL = 37.9 (8.5) kg | ||||
| Pre-RWL vs post-RWL = −0.68 (−1.29 to −0.08) | ||||
| Timpmann et al43 | Pre-RWL vs post-RWL: −4.4 (NR) kg; −5.4% (0.5%) | 16 | Intermittent arm crank sprint | Pre-RWL = 192.6 (37.9) W |
| Post-RWL = 177.9 (34.2) W | ||||
| Pre-RWL vs post-RWL = −0.40 (−1.05 to 0.26) | ||||
| Timpmann et al46 | Pre-RWL vs post-RWL: −3.7 (NR) kg; −5.1% (1.1%) | NA | MVIC peak torque: 1.57 rads/s | Pre-RWL = 233.9 (41.5) N·m |
| Post-RWL = 218.5 (41.5) N·m | ||||
| Pre-RWL vs post-RWL = −0.36 (−1.00 to 0.28) | ||||
| 3.14 rads/s | Pre-RWL = 110.8 (26.2) N·m | |||
| Post-RWL = 98.5 (47.7) N·m | ||||
| Pre-RWL vs post-RWL = −0.31 (−0.95 to 0.32) | ||||
| 4.17 rads/s | Pre-RWL = 46.2 (10.8) N·m | |||
| Post-RWL = 41.5 (10.8) N·m | ||||
| Pre-RWL vs post-RWL = −0.42 (−1.06 to 0.22) | ||||
| MVIC relative peak torque: 1.57 rads/s | Pre-RWL = 3.12 (0.5) N·m/kg | |||
| Post-RWL = 3.12 (0.5) N·m/kg | ||||
| Pre-RWL vs post-RWL = 0.00 (−0.63 to 0.63) | ||||
| 3.14 rads/s | Pre-RWL = 1.50 (0.3) N·m/kg | |||
| Post-RWL = 1.40 (0.4) N·m/kg | ||||
| Pre-RWL vs post-RWL = −0.27 (−0.90 to 0.37) | ||||
| 4.14 rads/s | Pre-RWL = 0.62 (0.1) N·m/kg | |||
| Post-RWL = 0.62 (0.1) N·m/kg | ||||
| Pre-RWL vs post-RWL = 0.00 (−0.63 to 0.63) | ||||
| Muscle endurance test absolute data: Submaximal work | Pre-RWL = 3018 (1962) J | |||
| Post-RWL = 2339 (1132) J | ||||
| Pre-RWL vs post-RWL = −0.41 (−1.05 to 0.23) | ||||
| Maximal work | Pre-RWL = 4452 (2037) J | |||
| Post-RWL = 4000 (1584) J | ||||
| Pre-RWL vs post-RWL = −0.24 (−0.88 to 0.39) | ||||
| Total work | Pre-RWL = 7471 (3018) J | |||
| Post-RWL = 6415 (2188) J | ||||
| Pre-RWL vs post-RWL = −0.39 (−1.03 to 0.25) | ||||
| Muscle endurance test relative data: Submaximal work | Pre-RWL = 39.8 (26.2) J/kg | |||
| Post-RWL = 33.0 (16.5) J/kg | ||||
| Pre-RWL vs post-RWL = −0.30 (−0.94 to 0.33) | ||||
| Maximal work | Pre-RWL = 59.2 (23.3) J/kg | |||
| Post-RWL = 57.2 (20.4) J/kg | ||||
| Pre-RWL vs post-RWL = −0.09 (−0.72 to 0.55) | ||||
| Total work | Pre-RWL = 98.9 (36.9) J/kg | |||
| Post-RWL = 90.2 (29.1) J/kg | ||||
| Pre-RWL vs post-RWL = −0.26 (−0.89 to 0.38) |
Abbreviations: Finn A, treatment group; Finn B, placebo group; Mendes A, weight cyclers; Mendes B, non-weight cyclers; MVIC, maximal voluntary isokinetic/metric contraction; NA, not assessed; NR, not reported; Rankin A, high carbohydrate; Rankin B, moderate carbohydrate; RWG, rapid weight gain; RWL, rapid weight loss. Note: Data are mean (SD) unless otherwise stated. Recovery duration refers to the hours between the real or simulated weigh-in and competition time points (post-RWL and post-RWG).
aData confirmed/provided by corresponding author.
Supplementary Table S2 (available online) shows the participant characteristic data from the studies included in the review. Data were gathered from a total of 255 participants of which 4 studies38,39,45,46 did not disclose participant sex characteristics leaving 120 participants unidentified. The mean (SD) age of all participants was 22.3 (2.4) years. The mean (SD) of body mass reduction between pre-RWL and post-RWL was −4.0 (1.5) kg (absolute value undiscernible in 4 studies39,44,47,48) or 5.4% (2.0%). While between post-RWL and post-RWG, the mean (SD) of body mass recovered was 3.7 (1.1) kg (absolute value undiscernible in 4 studies17,24,42,44) or 4.2% (2.1%) (mean Δ = 1.2%).
Assessment of Study Quality
Supplementary Table S1 (available online) shows the complete assessment of study quality. A total of 8 studies were excluded based on low quality. Mean quality across all 17 studies accepted for inclusion was 62% (12%) with a range of 50% to 100%.
Pre-RWL to Post-RWL
Two contributions in this time point came from the same study.43 In order to minimize bias of detecting a significant finding (by artificially inflating analysis power), the effect demonstrating larger impairment was removed (repeated high-intensity efforts; g = −0.28; 95% CI, −0.53 to −0.03). Consequently, RWL impaired exercise performance to a small extent (g = −0.33; 95% CI, −0.52 to −0.14; P < .01), despite data being substantially heterogeneous (Q13 = 36.21; P < .01; I2 = 64%). This finding remained consistent following the leave-one-out sensitivity analysis (g from −0.27 to −0.39; all P < .01; Supplementary Table S3 [available online]). Additionally, using only absolute performance data in the analysis did not alter this outcome (g = −0.36; 95% CI, −0.55 to −0.16; P < .01; Supplementary Figure S1 [available online]).
Figure 2 shows the effects of RWL on exercise performance subgroups. Only one study48 examined anaerobic capacity in this time point. These authors asked participants to complete a 30-second lower body Wingate test pre-RWL and post-RWL. Data are reported in Table 2, but suggest anaerobic capacity remained unchanged by RWL (g = −0.06; 95% CI, −0.94 to 0.82; P = .89). Repeated high-intensity effort performance declined to a small extent (g = −0.37; 95% CI, −0.59 to −0.16; P < .01) with data demonstrating homogeneity (Q7 = 8.73; P = .12; I2 = 31%). Although small reductions in maximal strength were also found between these time points (g = −0.29; 95% CI, −0.54 to −0.03; P = .03), these data were substantially heterogeneous (Q5 = 19.75; P < .01; I2 = 74%). Furthermore, this finding for maximal strength was not robust as the leave-one-out sensitivity analysis demonstrated nonsignificance when multiple studies were individually removed25,44,49 (all P ≥ .06; Supplementary Table S4 [available online]). When absolute performance data were incorporated into the subgroup analyses, the output for repeated high-intensity effort performance (g = −0.39; 95% CI, −0.61 to −0.05; P < .01; Supplementary Figure S2 [available online]) and maximal strength (g = −0.33; 95% CI, −0.61 to −0.05; P = .02; Supplementary Figure S3 [available online]) was consistent with the main analysis.
—The domain-specific effects of rapid weight loss (pre to post). The size of the squares is proportional to the weight of the study. Negative values reflect impaired exercise performance.
Citation: International Journal of Sports Physiology and Performance 17, 7; 10.1123/ijspp.2021-0104
Post-RWL to Post-RWG
Pallarés et al17 quantified measures of explosive strength/power, while all other studies in this time point performed assessments of maximal strength.21,25 Standardized mean differences between these time points are summarized in Table 2, however, none indicate a change in exercise performance as a product of regaining reduced mass (g ranging from −0.19 to 0.27; all P ≥ .17).
Pre-RWL to Post-RWG
Given multiple contributions from24 in this time point, the data set yielding the most outlying effect was removed from the analysis (power; g = 0.22; 95% CI, −0.18 to 0.62). Consequently, weight cutting procedures did not change exercise performance (g = 0.01; 95% CI, −0.18 to 0.20; P = .88). These data were homogenous (Q6 = 7.70; P = .26; I2 = 22%). Removing the one study42 that reported only relative exercise performance data did not alter this finding (g = −0.00; 95% CI, −0.19 to 0.18; P = .96; Supplementary Figure S4 [available online]).
Figure 3 shows the effects of weight cutting procedures on the exercise performance subgroups. Anaerobic capacity remained unchanged between pre-RWL and post-RWG (g = −0.10; 95% CI, −0.48 to 0.29; P = .62). Similarly, maximal strength also remained unchanged (g = 0.09; 95% CI, −0.13 to 0.32; P = .42). Both findings were homogenous (Q2 = 3.03 and 2.29 respectively; both P = .22 and I2 ≤ 34%). The main finding for anaerobic capacity did not change when removing Artioli et al42 who only reported relative exercise performance data (g = −0.22; 95% CI, −0.54 to 0.09; P = .16). Weight cutting did not alter measures of power in the data reported by Barbas et al24 (g = 0.22; 95% CI, −0.18 to 0.62; P = .28). Similarly, Barley et al41 quantified maximal isometric knee extension torque pre-RWL and post-RWG. These data are also reported in Table 2 but changes in power were not evident (g = 0.04; 95% CI, −0.65 to 0.73; P = .91).
—The domain-specific effects of weight cutting (pre–rapid weight loss to post–rapid weight gain). The size of the squares is proportional to weight of the study. Negative values reflect impaired exercise performance.
Citation: International Journal of Sports Physiology and Performance 17, 7; 10.1123/ijspp.2021-0104
Publication Bias
Publication bias was found for the overall effect between pre-RWL and post-RWL (Kendall τ = −.19; P = .17; intercept = −1.90; 95% CI, −3.13 to −0.66; P = .01). Application of Duval and Tweedie’s trim and fill correction indicated that 6 studies were missing to the right of the analysis (implying RWL has a positive effect on exercise performance). These studies ranged from a small to large effect (g = 0.21 to 1.45; Figure 4). The corrected output indicated a trivial negative effect (g = −0.09; 95% CI, −0.22 to −0.01).
—Funnel plot of the overall effect between pre–rapid weight loss to post–rapid weight loss. Included and imputed studies are denoted by white and black circles, respectively. Studies to the right of 0 indicate that weight loss has a positive effect on exercise performance.
Citation: International Journal of Sports Physiology and Performance 17, 7; 10.1123/ijspp.2021-0104
Bias was also found for the maximal strength subgroup between pre-RWL and post-RWL (Kendall τ = −.67; intercept = −3.16; 95% CI, −5.06 to −1.26; both P ≤ .03). The correction suggested 3 missing studies exist with a moderate to large positive effect (g ranging from 0.59 to 1.10; Figure 5). The corrected output indicated a small impairment in maximal strength (g = −0.34; 95% CI, −0.13 to 0.06). The remaining comparisons did not display bias (all P ≥ .06).
—Funnel plot of the strength domain between pre–rapid weight loss to post–rapid weight loss. Included and imputed studies are denoted by white and black circles, respectively. Studies to the right of 0 indicate that weight loss has a positive effect on exercise performance.
Citation: International Journal of Sports Physiology and Performance 17, 7; 10.1123/ijspp.2021-0104
Several studies were not included in this analysis due to low study quality (n = 8), among these studies data at the upper range indicated statistically here was reported, that is, Fogelholm et al9 report large improvements in relative Wingate test performance (g = 1.92; 95% CI, 0.96 to 2.88). We believe it is unlikely the studies indicated statistically here exist, at least those with sufficient methodological rigor such that they could be included in qualitative and/or quantitative synthesis such as this. Therefore, we reject the imputed corrections.
Discussion
This meta-analysis investigated the effects of weight cutting and its components (RWL and RWG) on exercise performance in combat sport athletes. Data were obtained from 17 studies with participants achieving an average RWL of ≈5% and average RWG of ≈4% body mass. The major finding from our quantitative synthesis of the currently available evidence is that weight cutting has no influence on overall exercise performance. However, overall exercise performance and subgroup analyses for repeated high-intensity effort and maximal muscle strength performance demonstrated small to moderate impairments following RWL. It should be noted that heterogeneity was observed among some data sets within several analyses, and numerous data sets were excluded from this investigation due to low study quality. As such, more studies examining the effects of weight cutting, RWL, and RWG on exercise performance using robust research designs and rigorous experimental procedures are needed to further strengthen available literature. Furthermore, coaches and athletes should carefully consider the quality, bias, and limitations of previous investigations when evaluating the available evidence to guide decision making around the use of weight cutting practices in preparation for competition.
Weight Cutting
This meta-analysis revealed that weight cutting had no effect on overall exercise performance over the course of weight cutting, nor did it influence the performance of any exercise capacity subgroups explored. These findings suggest that the substantial physiological stress associated with implementing various acute dehydration strategies to induce RWL followed the use of athlete-driven methods to achieve RWG had a negligible net impact on physical function. If weight cutting is not detrimental to exercise performance, it is plausible that athletes may obtain an advantage from using this precompetition preparation strategy and being matched with a smaller opponent, likely shorter in height and limb length, as it may increase their relative striking range.50 However, these results should be interpreted with caution as only 6 studies compared exercise performance between pre-RWL to following RWG and the only outcome measures assessed were anaerobic performance, power, and maximal strength. Therefore, generalizing these findings across a wider scope of exercise capacities should be restricted until additional evidence is available. Furthermore, the fact that none of these studies assessed repeated high-intensity effort performance between pre-RWL and following RWG is critically important. Time–motion analyses of combat sports competitions, including mixed martial arts, have demonstrated a 1:4 ratio of high- to low-intensity efforts of exercise.51 As such, the ability to perform repeated high-intensity efforts is likely a critical determinant of match performance for combat sports athletes and the use of these task types probably provides a more discriminant assessment for evaluating the influence of weight cutting on exercise performance. This is especially so, given that a previous meta-analysis reported that dehydration only impaired exercise performance in those activities that were greater than 30 seconds in duration.52 Thus, the inclusion of repeated high-intensity effort outcome measures in future weight cutting studies is strongly encouraged.
Rapid Weight Loss
Findings of reduced anaerobic capacity, maximal strength, power, and repeated high-intensity effort performance following acute dehydration associated with RWL have previously been reported in some,17,25,40 but not all studies.22,42,45 This meta-analysis found small to moderate detriments in overall exercise performance and the maximal muscle strength and repeated high-intensity effort performance subgroups between pre-RWL and post-RWL. Previously, Alves et al25 have suggested that extracellular sodium (Na+) and intracellular potassium (K+) concentrations may be reduced by RWL. In turn, such alterations may disrupt electrochemical fluid gradients and subsequently decrease the capacity of nerve impulses to properly stimulate sustained musculoskeletal activity, due to compromised calcium (Ca2+) release from the sarcoplasmic reticulum.25 Interestingly, others41,53 have reported that dehydration may not alter neuromuscular function, as measured using a series of brief maximal isometric contractions following RWL. Further investigations exploring neuromuscular function, and RWL and weight cutting, should be undertaken to better understand this prospective relationship, which may better explain our observation of reduced maximal strength. Additionally, how dehydration may impair aerobic function could also be relevant to the reported decrement of repeated high-intensity effort performance, as in practice (ie, during competition), prolonging combat during the bout will require aerobic metabolism. Previously, Sawka et al54 have provided a comprehensive review of active dehydration processes (ie, heat and/or exercise induced) and aerobic performance. Among the various mechanisms discussed, increased cardiovascular strain (reduced stroke volume and heightened heart rate) may be related to our finding, as this could reduce localized perfusion to musculature responsible for performing repeated high-intensity efforts. However, it is worth noting that others19 have reported that RWL of ≈5.5%, did not compromise aerobic performance (VO2peak); despite also identifying reductions in a range of hematologic and nonhematologic parameters (total hemoglobin, reticulocytes, and erythropoietin).
Rapid Weight Gain
Few studies of sufficient quality have investigated the influence of RWG following weight reduction. As such, we were unable to perform a meta-analysis between post-RWL and post-RWG due to insufficient data sets, while several exercise outcome domains (power and repeated high-intensity effort performance) were also not interpretable due to insufficient data. Thus, only qualitative synthesis was performed. Although a limited number of studies featured in this portion of the analysis,17,21,25 outcomes were aligned to indices of power and maximal strength. However, none of these studies reported improvements to any respective performance outcomes, despite RWG ≈ 5.8%, and recovery durations that correspond and exceed (16–36 h) many professional or high-level combat sport competitions such as mixed martial arts and Boxing.1 Although our data are insufficient, maximal strength is unlikely to be enhanced following RWG. This may be attributable to an acute reduction in energy intake reducing muscle glycogen stores, which have been linked to a compromised excitation–contraction coupling in skeletal muscle cells.1,14 Furthermore, a longer period of time (≥48 h)55 may be required to completely recover from the RWL phase of weight cutting. Indeed, others15–17,25 have shown significant cellular dehydration in combat sport athletes post-RWG between 24 and 36 hours. This may be due to a possible discrepancy between regain of body mass and complete cellular rehydration following RWL.55
Limitations and Future Research
The following should be considered when interpreting the findings of our analysis. First, heterogeneity was present among several findings despite the use of a random effects model and remained following the leave-on-out sensitivity analyses. Meta-analyses using a random effects model that have a high degree of heterogeneity may present challenges for interpretation as studies are weighted almost equally, irrespective of sample sizes, yielding results similar to the mean of the individual studies. However, it is argued that such findings are not fatally flawed and that a more cautious approach to their interpretation should be used.56 This is particularly relevant for meta-analytic analyses performed using a small number of studies, which is typical of most exercise-related clinical trials and intervention studies.56 In addition to the small number of studies identified for possible inclusion in this investigation, a relatively large number of papers were excluded due to insufficient methodological quality and an unacceptable risk of bias, which may have further exacerbated the heterogeneity we observed among data sets. As such, it is strongly recommended that researchers refer to methodological quality and risk of bias assessment criteria when planning and designing future weight cutting studies.
Factors contributing to heterogeneity among those included studies are likely related to differences in research design and data obtained including participant characteristics, strategies used to induce dehydration and facilitate weight recovery, the magnitude of RWL and RWG achieved, measurement timing, measurement types, analytical procedures, and/or the risk of bias.57 Although our approach to combining outcome measurements between studies for quantitative analyses may have contributed to heterogeneity, the largest contributor to the variance observed is likely to be differences in studies designs, specifically differences related to RWL and RWG experimental procedures and measurement timing. Specifically, a wide range of RWL and RWG strategies and timelines were observed between the studies included in this investigation. Of specific note is the frequent use of participant driven approaches to weight cutting among citations. While such methods do provide greater ecological validity for the study of weight cutting, the approach offers less experimental control and may reduce consistency between studies. Thus, we recommend future research be conducted using more consistent procedures and measurement periods for assessing RWL and RWG that better reflect the timelines related to combat sports competition. Furthermore, where athlete driven strategies are used for RWL and/or RWG, studies should attempt to monitor and report participant physical activity levels, diet, and fluid intake during the initial trial and replicate these behaviors in subsequent treatments.
Additionally, we recommend that future researchers report absolute exercise performance data. Weight cutting is likely to produce greater losses in mass than recovery affords.11,15 Indeed, we report this imbalance to be ≈1% across the studies included in this investigation. However, within the context of performance, relative data are likely to provide a biased estimate. For instance, Table 2 shows Timpmann et al43 report both absolute and relative strength performance. Interestingly, the former indicates a small to moderate impairment in maximal peak isokinetic torque (g ranging from −0.32 to −0.43), while the same data when expressed relative to body mass, which declined by ≈4% from baseline, gives the appearance that weight cutting is less detrimental (g ranging from 0 to −0.27). Although we accounted for this using a sensitivity analysis (which did not alter our findings), we would encourage authors to eliminate this from a methodological perspective, as changes in absolute performance are likely to be of greater importance to combat sport athletes.
Practical Applications and Conclusions
To our knowledge, this study presents the first meta-analytical investigation of the effects of weight cutting used by combat sport athletes on overall exercise performance and several underlying exercise capacity subgroups. The data obtained from this analysis suggest that overall exercise performance, maximal strength, and repeated high-intensity effort performance are impaired to a small to moderate extent following RWL. As such, it is recommended that combat sport athletes avoid engaging in RWL where complete RWG cannot be achieved before competition commences. Furthermore, our findings also indicate that the entire weight cutting process (RWL to RWG) may not influence overall exercise performance, anaerobic capacity, or maximal strength. Therefore, there may be no performance benefit derived from this process. However, more high-quality studies examining these issues are needed to reduce the heterogeneity between studies so that more accurate conclusions can be drawn.
Acknowledgments
The authors of this paper would like to thank the contacted authors of the studies who were considered for inclusion in this analysis who took the time to respond to our queries. Your responses made literature selection and data extraction go much smoother for us. Thank you to Professor Frank Marino who assisted with complex conceptual debates among the authors in the design of this study. This study was designed by all authors. Data extraction and analysis were undertaken by Brechney and Goodman, with conceptual and writing assistance by Cannon. Manuscript preparation was conducted by all authors. The leading author is the recipient of an Australian Research Training Program—Higher Degree of Research scholarship. There are no additional conflicts of interest to declare.
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