In general, the literature showed that when heavyweight athletes were excluded from the analysis, the prevalence of RWL was approximately 89% [2,5,19,20]. Brito et al. [21] did not observe significant differences in the prevalence of RWL between competitor levels: regional (59.8%), national (72.9%), and international (40%). Conversely, Malliaropoulos et al. [22] found that male international judo athletes had the highest prevalence of RWL (92.9%) compared to national (78.8%), regional (74.1%), and club-level athletes (58.3%). These conflicting results can be attributed to differences in the number of athletes. Brito et al. [21] reported a lower number of international athletes (only four), whereas Malliaropoulos et al. [22] did not report the total number of international-level judo athletes. When examining prevalence across different weight categories, Malliaropoulos et al. [22] reported no significant differences, particularly when heavyweight athletes were excluded. In the context of sex-based comparisons, Artioli et al. [2] found no statistically significant differences between males (84.1%) and females (84.8%). In contrast, senior athletes had the highest prevalence of RWL (73.5%) followed by junior athletes (53.3%) and cadets (52.2%) [17]. Artioli et al. [2] found a difference between competitors using the Rapid Weight Loss Questionnaire. This score indicated the severity of the RWL process (i.e., the higher the value, the more aggressive and dangerous the RWL process). Notably, state- (25 points), national- (28 points), and international-level (31.5 points) judo competitors obtained higher scores than regional-level (17.5 points) competitors. In addition, international competitors obtained higher scores than state-level competitors.

Athletes frequently reduced approximately 5% (ranging between 3 and more than 10%) [2,20,21,24-26] of their body mass close to the competition (i.e., 3-7 days before the competition) [23,26,27]. Moreover, studies indicated that the use of RWL methods increased closer to the day of the competition [21,28,29]. This suggests that most of the body mass reduction occurred in the days before weigh-in. The most utilized methods in this process were increased physical exercise, food and fluid restrictions (especially carbohydrate restriction), and sauna or plastic clothing [2,21,30-33]. Additionally, more aggressive and dangerous methods were reported (e.g., use of laxatives and diuretics) [21].

Regarding comparisons based on sex, Yoshioka et al. [24] indicated that no differences existed between males (3.4%) and females (4.9%) in terms of the magnitude of body mass reduction. However, Escobar-Molina et al. [17] found that males showed a higher frequency (47.1%) of >5% reduction in body mass than females (27.3%). In the context of age groups, Escobar-Molina et al. [17] observed that senior athletes had a higher frequency (47.1%) of >5% reduction in body mass than cadets (28.3%) and junior athletes (30.0%).

Studies that investigated the magnitude of RWL following the 5% tolerance rule established in 2013 demonstrated that athletes reduced their body mass by 5.8-6.8% [34,35]. Therefore, a longer recovery period between the weigh-in and beginning of the competition and/or the tolerance rule may encourage athletes to reduce their body mass by >5 %.

Overall, despite the controversy among the studies, the literature provides valuable results regarding the prevalence and magnitude of RWL practices among judo athletes. These results suggest that RWL is a common strategy employed by athletes across different levels of competition. Recent studies have explored the impact of regulatory measures such as the 5% tolerance rule on RWL practices. These studies reported a higher magnitude of RWL [34,35] than previous results [2], which indicated a body mass reduction of approximately 5%. Further studies are needed to determine the effectiveness of these rules on RWL behavior in athletes.

Table 2 presents the studies that evaluated performance using judo-specific tests. Concerning performance in judo-specific tests, Abedelmalek et al. [36] found that RWL impaired SJFT performance, while Fortes et al. [15] reported a lack of performance increase during training for those in the RWL group compared with the control group [15]. Similar results were found by Ceylan et al. [37], who demonstrated that RWL, at a magnitude of 5%, affects performance in both the SJFT and the judogi grip strength-endurance test. Two tests were conducted: the dynamic strength-endurance test, in which the athlete held the suspended judogi with the elbow fully extended and performed elbow flexion (number of movements), and the isometric strength-endurance test, in which the athlete had to maintain the position with the elbow fully flexed for as long as possible. However, no negative effects were reported when recovery was achieved [38-40]. These varying results are possibly influenced by the distinct time of recovery between the weigh-in and assessment.

The reduction in carbohydrate ingestion due to RWL methods can decrease the blood buffering capacity [13,41]. Acidosis due to the combination of RWL and low carbohydrate intake decreases muscle hydrogen ion efflux, which can accelerate fatigue. Furthermore, anaerobic performance can be impaired by low-carbohydrate diets. Low carbohydrate ingestion can decrease glycolysis and, consequently, impair high-intensity exercise performance [13,41]. In the study by Artioli et al. [2], recovery time was provided between weigh-in and performance assessment. During this time, athletes ingested large amounts of carbohydrates, which could partial-ly restore muscle glycogen stores. In contrast, in the studies by Fortes et al. [15] and Abedelmalek et al. [36], carbohydrates were not ingested after weigh-in.

An increase in HR can be partially attributed to increased blood viscosity, which can decrease the cardiac output and HR recovery for a given work output. In addition, RWL possibly negatively affected the aerobic pathway [15,42]. Another important factor is the recovery time. Fortes et al. [15] and Abedelmalek et al. [36] did not include recovery time between weigh-in and performance assessment. In contrast, in the study by Artioli et al. [2], athletes had 4 h to recover between the weigh-in and test. At this point, the athletes could recover their body mass and fluid loss.

Reale et al. [43] analyzed body mass regain after weighing and showed that athletes who had a larger recovery of body mass had the highest percentage of victory. This was initially interpreted as an indication that these athletes had a larger magnitude of RWL before the competition. However, the magnitude of RWL before competition could not be estimated from the body mass regain between the weigh-in and beginning of the competition [8]. Conversely, a study by Nascimento et al. [44] did not find differences in the number of medals between athletes who reported using RWL procedures and those who reported not using these procedures. However, this study only used questionnaires, and athletes reported the number of medals. Further research is needed to determine whether athletes who adopt RWL procedures and regain a higher amount of body mass are more successful than those who do not undergo these procedures or regain less body mass. Furthermore, analyzing additional variables to represent performance is necessary.

These findings highlight the complex relationship between RWL practices and performance in judo athletes. While some studies demonstrated clear negative effects of RWL on performance, others indicated potential mitigating factors, such as recovery time and carbohydrate intake. However, current judo rules provide sufficient recovery time for athletes. Therefore, further studies are needed to standardize the recovery time, as stipulated in official competitions.

Table 3 presents studies that assessed the effects of RWL on maximal isometric strength. These studies provided conflicting data, with negative [13,14] or negligible effects [26,45]. These controversial results can be explained by different methodologies (e.g., dominant or non-dominant hand and competitive level of athletes). Degoutte et al. [13] reported a decrease in maximal isometric left handgrip strength after RWL in national-level judo athletes; however, whether this was the non-dominant or dominant hand remained unclear. Conversely, Filaire et al. [14] measured both hands of national judo athletes. Their results showed that RWL impaired maximal isometric strength of only the left hand. Morales et al. [45] and Coufalová et al. [26] investigated the maximal isometric handgrip strength of national and international athletes for both hands. They found that RWL did not affect the maximal isometric handgrip strength in either hand. Although the studies used different national- and international-level judo athletes and the hand dominance in each group was not clear, their results suggested that RWL is more likely to affect the maximal isometric left handgrip strength in national-level judo athletes. In addition, Morales et al. [45] included two groups: the RWL and Progressive Weight Loss (PWL) groups. The RWL group reduced body mass by >3% during one week, whereas the PWL group decreased body mass by <3% during the same period. In contrast, in the studies by Degoutte et al. [13] and Filaire et al. [14], athletes reduced their body mass by approximately 5%. Therefore, the difference in the percentage of body mass reduction may explain the differences between the results of these studies.

Clarys et al. [46] utilized a test that mainly recruited the biceps and forearm muscles. A curl bar was pulled towards the trunk by flexing the elbows to an angle of 90°. This test was performed with different intensities: (1) fixed at 60% of the maximal isometric strength for 10 s; (2) maximal effort for 3 s; (3) 60% for 7 s; (4) maximal effort for 3 s; (5) 60% for 7 s; and (6) finishing with a maximal effort for 10 s. This test was used to simulate the immobilization technique used in ne-waza (groundwork combat). In addition, this study analyzed two groups: high RWL (≥3% body mass reduction) and low RWL (<3% body mass reduction), without a control group. The low RWL group did not show any isometric strength impairment. In contrast, the high RWL group exhibited decreased isometric strength. This procedure may have an advantage over the measurement of handgrip strength only, given the judo-specific muscle mass involved [46]. Given that grip strength is a crucial determinant of success in judo, further studies with standardized methods are required to assess grip strength. Additionally, reporting of both the non-dominant and dominant hand strengths could be implemented.

During RWL, athletes decreased fat mass and fat-free mass [28,47,48]. A reduction in the fat-free mass can impair muscle strength and power45. A decrease in fat-free mass is frequently achieved through a combination of energy restriction and intense exercise training [48]. Additionally, because of the methods adopted during the process, such as dehydration, a decrease in extracellular or intracellular water concentration can occur [27,49]. Specifically, cellular volume plays a crucial role in orientation of cell metabolism, with cellular swelling promoting anabolism, and cellular shrinkage promotes catabolism. These changes, due to RWL, decrease muscle strength. Furthermore, a decrease in intracellular water can impair magnesium concentration [49]. As magnesium is a potent component of muscle performance, its reduction can decrease maximal strength. Matias et al. [49] found that athletes with decreased intracellular water levels showed decreased isometric strength. Additionally, the indirect effects of RWL on body composition and intracellular water concentration further elucidated the multifaceted nature of its influence on muscle performance.

Studies addressing the effects of RWL on muscle power have used squat jumps, countermovement jumps, or protocols involving intermittent jumps (Table 3) [14,46]. Generally, the RWL does not affect muscle power. Studies have shown that the RWL does not affect anaerobic power [2,50]. Regarding anaerobic capacity, Degoutte et al. [13] and Artioli et al. [2] observed no changes in performance after RWL. However, Ohta et al. [50] found a decrease in the mean power after RWL.

Filaire et al. [14] evaluated vertical jumps using squat jump (SJ) and counter movement jump (CMJ) tests before and after RWL. The athletes also performed successive maximal jumps (CMJ) during periods of 7 s and 30 s. Notably, RWL did not affect SJ or CMJ height or mechanical power during the period of 7 s. However, a significant decrease in work output was observed during the 30-s jumping test. The decrease in work output was possibly associated with the altered acid-base balance after the RWL period. A low-carbohydrate diet may lower the blood’s buffering capacity [41]. When combined with weight loss, reduced carbohydrate intake can decrease the efflux of hydrogen ions from muscles, potentially leading to faster fatigue during muscular contractions [14]. The reason for the lack of a decrease in the 7 s jump test is not clear. However, in the 7 s jump test, the phosphagen stores can be highly important. Furthermore, after 4 days of weight loss achieved by food restriction, ATP and creatine phosphate concentrations were not altered in the muscles [51]. This may explain the lack of alteration in the 7-s jumping test. Furthermore, previous studies have reported that RWL through body fluid loss (diuretic effects) does not impair the maximal strength or neuromuscular system for activating dynamic and static force production [52-54].

Clarys et al. [46], who also investigated the effects of RWL on muscle power, used an intermittent jump test with five series of 20 maximal squat jumps, with 1 min rest between each series. This study analyzed two groups: high RWL (≥3% of body mass reduction) and low RWL (<3% of body mass reduction). They found that the RWL did not affect the average jump height in either group.

Artioli et al. [2] and Ohta et al. [50] indicated no effect of RWL on anaerobic power. These results may be due to the recovery time provided after RWL (4 h) or the low body mass reduction during the week of competition (i.e., approximately 3%). Similar results were found for anaerobic capacity. Previous studies found no effect of RWL on performance [2,13,49].

Table 4 presents studies that evaluated health-related risks in response to RWL. Four studies focused on the immunological effects of RWL, particularly its effects on upper respiratory tract infections (URTI). Hiraoka et al. [55] examined the effects of RWL on secretory immunoglobulin A (SIgA) and incidence of URTIs. This study investigated two groups: <5% and >5% of RWL. Notably, SIgA decreased close to the competition (3 and 1 days before the competition). SIgA is a potential marker of protection against URTIs [56]. However, these results were found only in the group with >5% of RWL. In addition, in the experimental group, one incidence of URTI was observed, whereas no such incidence was found in the control group. These results suggest that the magnitude of RWL can be a key factor to induce deleterious effects on the immunological status of judo athletes. Shimizu et al. [57] investigated the effect of RWL on URTI symptoms, utilizing 7 days of food restriction. After this period, the participants reduced their body mass by 3.6%. The results showed that RWL increased URTI symptoms. Also utilizing food restriction, Kowatari et al. [58] assessed the leukocyte, neutrophil, lymphocyte, and phagocytic activity. They utilized 20 days for the body mass reduction; however, the assessment was performed only one week prior to the competition. The results showed that the phagocytic activity decreased after the body mass reduction. These studies reveal a consistent pattern of RWL-induced immunosuppression, characterized by decreased levels of SIgA and increased incidence of URTI symptoms. The findings suggest the importance of considering the magnitude of RWL, as more substantial reductions (>5%) appear to pose a greater risk to immune function.

Abedelmalek et al. [36] investigated the effects of RWL on cortisol, testosterone, and proinflammatory cytokines. Both groups performed an exercise protocol with or without caloric restriction. After exercise accompanied by caloric restriction, cortisol and proinflammatory cytokine levels were higher than in the no-caloric restriction condition. Examination of cortisol, testosterone, and proinflammatory cytokines provides valuable information on the hormonal and inflammatory responses associated with RWL. The observed elevations in cortisol and proinflammatory cytokines following exercise accompanied by caloric restriction suggest a potential link between RWL and heightened inflammatory activity, which may further compromise immune function and increase susceptibility to infections. Considering that these RWL methods are adopted near the competition (1-3 days before the competition) [21], athletes may risk their overall performance.

One study investigated the effects of RWL on muscle damage [59]. Biomarkers such as creatine kinase (CK) and aldolase (ALD) were measured in 18 male judo athletes. This study observed changes in muscle damage markers during the weight maintenance (1-4 days) and RWL (5% of RWL in 5-7 days) periods. Muscle damage markers showed no significant changes during the weight maintenance period. In contrast, during the RWL period, CK and ALD levels increased. These results may be associated with the method used for the RWL process (e.g., increased exercise intensity).

One study investigated the effects of weight cycling on the bone metabolic balance. Prouteau et al. [60] evaluated bone markers, including C-terminal telopeptide of type I collagen (CTX), and the uncoupling index (UI) was calculated to determine the relative balance between bone formation and resorption processes during bone remodeling. Before the RWL phase, bone markers were similar between judoists and controls. In addition, the UI showed a positive value, indicating a bone metabolic balance favoring bone formation. During the RWL period, a 4% RWL was accompanied by a 33% increase in CTX levels. Negative values in favor of resorption were reported for the UI. However, in the body mass gain phase, these results were reversed, as body mass gain restored a positive UI in favor of bone formation. In addition, bone mineral density was not altered by weight cycling [60,61]. The mechanisms underlying this increase in resorption have not yet been elucidated. Given that Proteau et al. [60] assessed weight gain 3 weeks after the competition, determining whether these effects on bone metabolic balance remained after the competition was not possible. Further research is required to clarify this and the possible mechanisms underlying these results. The observed increases in CK and ALD during the RWL phase highlight the physiological strain imposed by RWL, particularly on skeletal muscle. Additionally, alterations in bone markers and the (UI suggest a disruption in bone metabolic balance, with implications for bone health and remodeling processes.

Regarding dehydration, which can occur due to methods used during RWL, Bialowas et al. [62] demonstrated that athletes were in a state of dehydration from 5 days before the competition to the day of the competition. Although the authors did not find an association between dehydration and performance in competitions, dehydration can be detrimental to athletes. In addition, future studies should investigate the effects of dehydration on other parameters, such as psychological aspects. The chronic effects of RWL on health status also need to be investigated as athletes frequently reduce their body mass several times during a season.

Two studies investigated the relationships among RWL, eating disorders, and emotional aspects (Table 4). Filaire et al. [16] assessed psychological parameters, lifestyle (e.g., historic weight reduction), eating attitudes, and emotional intelligence. A 70% prevalence of was found in athletes using RWL procedures. Furthermore, 30% of the athletes presented with disordered eating habits. In addition, judo athletes with disordered eating habits had lower scores on happiness, empathy, and emotional self-awareness subscales (emotional intelligence test). Additionally, the study highlighted the pervasive nature of disordered eating habits within the judo community, warranting further investigation into their underlying causes. Escobar-Molina et al. [17] investigated eating disorders and added anxiety ratings. Their research revealed intriguing sex-based disparities, with female athletes exhibiting higher levels of anxiety and greater susceptibility to eating disorders than their male counterparts. Despite the prevalence of RWL practices among senior athletes, this study noted their adeptness in managing the associated psychological stressors, suggesting the presence of coping mechanisms or resilience factors within this demographic. Interestingly, the prevalence of RWL was lower in females than in males.

Further studies investigating the relationship between RWL and eating disorders are necessary, especially among female athletes. The prevalence of eating disorders in female athletes is higher than that in male athletes [17], and this population may be at risk of developing the female athlete triad [63]. In judo, when athletes repeatedly reduce their body mass during the season through low-energy diets, future studies should investigate whether those who engage in weight cycling are at a higher risk of developing eating disorders. In addition, further studies could explore the longitudinal effects of RWL on the mental health of athletes by tracking changes in eating behaviors and emotional resilience over time. Moreover, investigating the efficacy of intervention strategies, such as mental health support programs, in mitigating the adverse effects of RWL could offer valuable insights into athlete well-being and performance optimization.

Table 5 presents studies that reported the effects of RWL on psychological well-being. Regarding the psychological well-being of judokas, three studies investigated the effects of RWL on this parameter. All studies utilized the Profile of Mood States (POMS). Only one study provided a recovery period between the weigh-in and assessment; however, the results were not different. In general, RWL increased several negative aspects (including tension, depression, anger, and fatigue) and decreased one positive aspect (vigor) [13-15]. Isacco et al. [64] investigated the effects of RWL in five successive simulated bouts. This study found that POMS was affected in matches 4 and 5 in athletes who reduced their body mass. Furthermore, these athletes reported a higher rate of perceived exertion. Pinto et al. [6] showed that athletes reported fatigue (34%), irritability (29%), and anxiety (29%) during the RWL process, as well as a perception of a decrease in performance

Fortes et al. [65] investigated the effect of RWL on decision-making abilities by employing a game performance assessment instrument (GPAI) to evaluate judo-specific movements. Although the control group exhibited improvements in GPAI scores, no discernible changes were observed in the RWL group, underscoring the potential cognitive ramifications of RWL in judo athletes.

These findings highlight the profound influence of RWL on psychological well-being, as evidenced by alterations in mood states, decision-making capabilities, and subjective experiences of athletes. However, gaps in the current literature necessitate further exploration to elucidate the extent to which these psychological effects affect the success of athletes in official competitions. Future studies should incorporate recovery periods between weigh-in and competition to provide a more nuanced understanding of the interplay between RWL, psychological well-being, and athletic performance.