In judo, since the competition performance is likely to depend on the body weight (1), a weight class system is adopted to avoid such inequality, and athletes are required to weigh in and clear a delimited weight range before a match. It is known that the majority of senior judo athletes prefer to compete in a lower weight class than their normal weight and adjust their weight prior to competition by weight loss using gradual or rapid methods (2, 3). Gradual weight loss is achieved by dropping body fat by creating a negative energy balance through increased physical activity and decreased energy intake from food. Rapid weight loss is a weight loss technique in which water and carbohydrates are severely restricted or consumed, and extremely short-term, drastic weight loss is implemented in an attempt to temporarily clear the prescribed weight only at the weigh-in. In particular, rapid weight loss is of concern in terms of its safety aspects, psychological (4–6), decreased immune capacity (7), increased muscle damage (8), and impaired performance (9, 10). Despite all the health risks, rapid weight loss is very prevalent because of the potential for competitive advantage in cases of adequate recovery from post-weigh-in to competition (11). Furthermore, numerous athletes find themselves compelled to rapid lose weight in order to avoid being at a competitive disadvantage (12).

On the other hand, judo is now a sport that is popular among people of all ages (13), and international competitions for juniors are held every year. In most cases, weight limits are set for junior competitions as well, and, like senior judo athletes, they must weigh in and clear the weight limits prior to competition. Berkovich et al. reported that many (74%) of junior athletes experienced rapid weight loss before the age of 13 (14), indicating that even juniors practice weight adjustment for competition as a common practice it can be seen that. In addition, since losing a moderate amount of body fat in preparation for competition improves instantaneous force and other aspects of judo performance (15), weight adjustment is a fundamental aspect of athleticism, but junior athletes differ greatly from senior athletes in both mental and physical aspects. Weight loss (pressure to lose weight), such as weight manipulation and food restriction, is a risk factor for eating disorders (16, 17) and is also known to increase the risk of injury occurrence (18) Normally, children are at a time when nutritional accumulation is important for tissue growth. Even if it is gradual weight loss, going through weight loss with an immature body and mind is not only a transitory increase in burden, but also a risk to lifelong health.

Specific discussions and actions have been slow to address this widespread manipulation of junior athletes' body weight to compete. This may be due to the lack of research to elucidate the circumstances surrounding junior judo athletes and the accumulation of scientific evidence for the effects of subsequent health conditions. Little is known about the current status of weight loss and its effects specifically on female junior athletes (19). For female athletes, adequate hormone production during the growth period is important for the acquisition of sufficient bone mass and subsequent reduction of health risks (20). And the higher incidence of eating disorders compared to males should also be fully noted (21–23).

Therefore, this study was conducted with the aim of understanding the status of weight loss among Japanese junior female judo athletes during their developmental stages (elementary school, junior high school, and high school), and to clarify their past weight loss experiences and the effects of weight loss on their current development.

The aim of this study was to ascertain the weight loss status of Japanese junior female judo athletes during their developmental stages (elementary school, junior high school, and high school), and to elucidate the effects of weight loss on their development. The survey results revealed that the majority of first- through third-year high school students who participated in the study had experience weight loss during their junior high school years. Furthermore, the findings suggested that weight loss during junior high school, a period characterized by the onset of growth spurts and critical nutritional requirements, may adversely affect bone development. This represents a novel discovery, as no previous reports have addressed the reality of weight loss among junior judo athletes in Japan. And it is imperative that appropriate measures be implemented to address these findings.

In aesthetic sports for females, among many other sports, previous studies have demonstrated that intense exercise and lack of energy during adolescence inhibit bone growth and prevent full height gain (28, 29). The present study indicates that a similar phenomenon was observed with weight loss in judo athletes. First, in subjects belonging to the 48 kg, 52 kg, 57 kg, and 63 kg weight classes, which are lightweight to medium weight classes, the current height was significantly shorter in the group that had experienced weight loss compared to the group that had not experienced weight loss in junior high school (Figure 3). In general, weight loss in martial arts is often achieved by maintaining a negative energy balance (2, 30). On the other hand, normal development in humans is achieved by adequate nutritional supplementation (31, 32). In particular, with regard to height growth, it is known that adequate nutrition and accompanying adequate hormone secretion are essential during the period before height growth stops due to complete fusion of the epiphyseal line, roughly around age 15 in females (31). The results of this study suggest that the one-month or shorter weight loss for judo competitions in junior high school, or the awareness and behavior of trying to maintain weight on a daily basis despite the growth period, were factors that inhibited satisfactory bone growth for these females.

In the 70 kg, 78 kg, and 78 kg + weight classes, no height difference was observed between with and without weight loss. These results corroborate our previously stated hypothesis. Examining the age of menarche among respondents in this study by weight class revealed differences in the age of menarche across classes, with heavier weight classes associated with lower ages of menarche (Table 2). In general, women experience a rapid increase in the secretion of female hormones from around 8–9 years of age to 17–18 years of age, the appearance of secondary sexual characteristics, and rapid growth in height, followed by menarche. Menarche occurs 6 months after reaching “maximum height velocity (PHV),” when bone formation proceeds rapidly (33). Participants in this study experienced menarche approximately between the ages of 12 and 13 in the 48 kg, 52 kg, 57 kg, and 63 kg weight classes, while menarche occurred approximately between the ages of 11 and 12 in the 70 kg, 78 kg, and 78 kg + weight classes (Table 2). This difference in age at menarche is considered to represent a difference in the timing of rapid height growth. Among the heavyweight class athletes, most of them had already passed the period of maximum height velocity (PHV) even if they experienced weight loss within the age of 12∼15, which is the age of Japanese junior high school students, and it is possible that this did not have a significant effect on their current height. In addition, heavyweight class athletes generally have more body fat mass compared to lightweight and middleweight athletes (34, 35). Thus, it is possible that weight class athletes have a large amount of body fat reserves and that even if they reduced their food intake for weight loss, they were able to achieve weight loss while ensuring that they had enough nutrients for growth and did not have a significant impact on their growth. While we were unable to examine weight class changes from junior high school to high school in this study, junior high school students belong to the 40 kg, 44 kg, 48 kg, 52 kg, 57 kg, 63 kg, 70 kg, and 70kg + weight classes, while high school students belong to the 48 kg, 52 kg, 57 kg, 63 kg, 70 kg, 78 kg, and 78kg + weight classes. Considering the positive correlation between weight class and height for both junior high school students (34) and high school students, it is thought that the weight class an individual belonged to in junior high school and high school was generally similar, possibly dependent on the skeletal structure they were born with.

This is not to say that weight loss is acceptable for junior athletes based on their individual physique and growth level. The underlying reason for weight loss is to increase the probability of winning a tournament. However, when evaluating their best competition results in junior high school, there was no discernible difference in tournament outcomes between those who underwent weight loss and those who did not (Table 3). The results of this study suggest that the subjects’ weight loss in junior high school may not have been strategic, scientific, and well-considered. In the present study, the menstrual cycle and menstrual symptoms, which are influenced by the nutritional intake, did not differ depending on whether the subjects had experienced weight loss in junior high school or not, suggesting that the intensity of symptoms may be influenced by current lifestyle habits. However, our data revealed a tendency toward delayed onset of menarche among individuals who had participated in judo during junior high school (Table 2). Notably, both women who had not experienced menarche by the time they reached high school were affiliated with the group that had engaged in judo during junior high school. The phenomenon of female athletes exhibiting delayed menarche compared to the general female population has been underscored in numerous studies (36, 37). For female's bodies, strenuous exercise is considered to have no small effect on the maintenance of reproductive development. Adding to this the burden of intentional undernutrition is undesirable. To begin with, it is important that children enjoy sports and compete in a healthy development (38, 39). The way they spend their growing years and their diet have a significant impact on future reproductive function, bone, muscle, and brain development (40–42). Therefore, weight manipulation strategies such as weight loss warrant special attention. Repeated weight loss can cause a decrease in basal metabolism and increase the likelihood of obesity in the future (43–46). And bone formation during school age and young adulthood is crucial for maintaining healthy bones throughout adulthood and beyond (47). Hence, it is very important that strengthening of children with promising futures also be done carefully and appropriately based on their stage of growth.

Note that because the questionnaire was designed to be answered from past memory, we did not use a detailed question focusing only on rapid weight loss, such as a weight loss of 5% or more in one week. The combat sports-specific rapid weight loss techniques that have been noted as generous health risks in senior athletes are probably prevalent in juniors (14), and special effects could also be observed if the number of experiences and actual weight loss ranges were closely examined and investigated.

Suggestions for addressing the current situation were derived from the data of this study. A diverse intake of food groups is typically essential to achieve adequate nutritional balance (48, 49). Scores indicating such food intake diversity were lower in the group that experienced weight loss during junior high school in this study compared to the group that did not undergo weight loss (Table 3). This suggests that the group that experienced weight loss during junior school may have previously lacked opportunities for nutrition education and environmental preparation in meal settings. In addition, it was found that the majority of the subjects would rely on family members and supervision, with very few relying on a nutrition specialist, a dietitian, as an advisor for diet and weight management (Figure 4). Therefore, addressing this issue may necessitate nutrition education aimed at promoting healthy eating habits, as well as education on the concept of appropriate weight class selection and weight control for children. This education should involve not only the individuals themselves but also their family members and supervisors.

In Japan, a measure was taken to abolish national judo tournaments for elementary school students in 2022, due to concerns about excessive coaching of children, such as prioritizing victory (50). However, before this problem becomes more serious, another comprehensive action/policy is needed by the association to address the problem. In terms of Japanese junior high school girls, weight gain of about 3–4 kg per year is usually desirable (51). Therefore, for athletes, especially those in the lightweight to middleweight classes whose height growth was affected this time, to compete in the same class for three years in junior high school would mean that they are competing against normal growth. Children should eat according to their appetites without fear of weight gain. It is not in our budget to have a dietitian on every team in the country. However, nutrition education, which has been limited to top athletes, could be improved by creating new materials and disseminating information widely, or by incorporating lectures on the concept of weight loss and other topics into leadership training sessions. Another possible measure would be to require athletes to submit a plot of their growth curves at the time of competition.

This study has limitations. First, this study was based on data that relied on the recall of survey respondents, not actual measurements. Also, because it is a cross-sectional study, it is not possible to distinguish whether the exposures occurred before or after the observed results. Nonetheless, our study's strength lies in obtaining over 500 responses (Figure 1). However, the population was not randomly selected from the 3,667 registered female high school student athletes of the All Japan Judo Federation in 2022 (52) which is considered the population size, using a rigorous methodology.