Prevalence and associated factors of stress fractures, menstrual dysfunction, and eating disorders in high school athletes
Abstract
Abstract:Objective: Stress fractures (SF), menstrual dysfunction (MD), and eating disorders (ED) in young athletes are important issues. We conducted this study to determine the frequency of SF, MD, and ED experienced by high school track and field athletes in Japan and to understand the factors associated with them. Materials and Methods: A cross-sectional study of 1199 high level high school track and field athletes (608 males and 591 females) who participated in a selective training camp held by the Japan Association of Athletics Federations. Results: Approximately one in four male and female athletes self-reported SF. Moreover, we identified the length of the practice time per week and the event (sprinting, middle-distance, jumping, and combined) as relevant factors. Approximately one in three female athletes self-reported MD history, with those participating in long-distance events experiencing it significantly more frequently than those participants in sprinting, throwing, and jumping events. Furthermore, we identified ED history and long-distance events as MD history-related factors. ED history was self-reported at low frequency without gender difference, and long-distance was significantly more frequently reported than sprinting and jumping. Conclusions: About a quarter of Japanese high school track and field athletes experience SF, and about a third of the females experience MD. The association of these with athletic events, training time, and ED should be considered.
Introduction
Protecting the physical and mental health of athletes is an urgent international issue. The International Olympic Committee has emphasized the need for measures by presenting a consensus statement on mental health in athletes in 2019 [1] and a Mental Health Action Plan in 2023 [2], emphasizing the need for countermeasures.
The triad for female athletes, comprising eating disorders (ED), amenorrhea, and osteoporosis, was postulated as a significant threat to the health of female athletes by Yeager et al [3] and the American College of Sports Medicine in 1997 [4]. Since then, numerous recommendations and statements have been made regarding ED and triad as problems that threaten the life and performance of athletes [4, 5, 6].
The 2007 recommendations of the American College of Sports Medicine redefined the pathological levels of triad as hypothalamic menstrual dysfunction (MD) and bone health disorders with a background of low energy availability (LEA) with or without ED [7]. According to the 2014 statement of the International Olympic Committee, LEA can occur in male and female, leading to relative energy deficiency in sport (REDs) [8]. Since the IOC Consensus on REDs was updated in 2018, there has been a gradual increase in reports targeting male athletes [9]. According to the Consensus Statement on Triad in Male Athletes, 2021, LEA and REDs are important issues for both male and female athletes [10, 11, 12]. The IOC updated the 2023 Consensus Statement on REDs and proposed clinical assessment and research methods [13]. Certain of the preferred or recommended REDs investigation methods presented in the statement include bone stress injury and fracture history, self-reported menstrual history, and eating disorder history.
Globally, countermeasures against EDs in athletes are required, and researchers and national federations (NFs) are requested to conduct fact-finding surveys [1, 2, 8]. Nevertheless, surveys on the actual status of SF, MD, and EDs in athletes in Japan are scarce. In particular, studies on high school athletes in their late teens have been few, and evidence on which athletic events are at high risk is lacking. Male and female high school students are in the process of acquiring peak bone mass [14, 15] and are simultaneously in the prime age for SF and ED [16]. Endurance sports, as well as esthetic sports, weight class sports, and aerial sports, are at high risk for EDs [17, 18, 19, 20], but research is lacking, especially for young athletes.
Although two major factors (i.e., those modifying the load applied to the bones and the load resistance ability of the bones) are reportedly associated with SF in long-distance runners. The former include biomechanical factors, training factors, and training surfaces, while the latter include genetics, nutrition, and endocrine status [21].
Track and field events have various characteristics, including endurance events, sprinting, jumping, throwing, and combined events. Comparisons between events may provide information on the events possessing higher rates of SF, MD, and ED. Furthermore, it may be possible to identify factors associated with SF, MD, and ED in high school track and field athletes.
We designed a cross-sectional survey of high-level high school track and field athletes to answer these clinical questions.
Materials and methods
Data collection
This cross-sectional study used data from a voluntary questionnaire survey. The study included high school students who participated in seven selective training camps held in Japan from 2021 to 2023 by the Japan Association of Athletics Federations (JAAF). All were Japanese nationals. The questionnaire was explained orally and in writing by members of our research group to the group of competitors during the training camps. All athletes were provided the opportunity to privately and confidentially complete the survey. The questionnaire was designed using Microsoft Forms (Microsoft Corporation, One Microsoft Way, Redmond, WA, U.S.A.) and the participants answered the questionnaire by scanning the QR code on the research description document with their smartphones. The information transmitted over Internet was encrypted through a secure server, and data were converted without including personal information.
Athletes were categorized into six groups of athletic specialties – 1) sprinting: ≤ 400 m, including hurdles; 2) middle-distance (800-1500 m); 3) long-distance (3000–5000 m, including steeplechase and racewalking); 4) jumping events: long jump, triple jump, high jump, and pole vault; 5) throwing events: javelin throw, hammer throw, shot put, and discus throw; and 6) combined events: male octathlon and female heptathlon. Those competing in more than one event were requested to select the one in which they specialize the most to avoid duplication. Those specializing in road racing, such as EKIDEN, were not included in this study.
The survey included data on height, weight, post-high school athletic level, history of EDs, history of stress fractures, history of MDs (menstruation for > 3 months and delayed menarche without menstruation), and hours of practice per week. Data on bone health were obtained from a questionnaire. Bone health was examined in terms of stress fracture history instead of bone density, because determining bone density by questionnaire is a challenge. Because we did not directly measure low bone mass, we determined probable triad as a case where all three histories (SF, ED, and MD) were present.
Statistical analysis
Statistical analysis was performed using JMP Pro version 17 software for Windows (SAS Institute Inc., Cary, NC, U.S.A.). Descriptive statistics were employed to summarize collected data. Means and standard deviations were used to present findings. Student’s t-test was used when continuous variables were equally distributed, and Welch’s t-test was used when unequally distributed. Fisher’s exact test (two-sided) for contingency tables was used to test the relationship between categorical variables, with a significance level of P < 0.05 for comparisons between the two groups. To examine data equivalence in the six athletic specialties, we used Fisher’s exact test (two-sided test) to analyze the differences between categorical variables. For continuous variables, we used the Kruskal-Wallis test, a nonparametric method, as the variances were unequal. The significance level was set at P < 0.05.
Pairwise comparison tests were performed for items that showed no equivalence among the six disciplines. Pairwise comparisons were corrected for Bonferroni’s P-value, using P < 0.0033 as the significance level, because the 6 groups contained 15 combinations. The Wilcoxon test was used for continuous variables. Fisher’s exact (two-sided) test was used for categorical variables. Univariate and multivariate logistic regression analyses were used to analyze factors associated with SF and MD. For factors that were significant (P < 0.05) in univariate logistic regression analysis, we adjusted for potential confounders using multivariate logistic regression analysis.
Results
Participant selection
A flowchart of the cases included in this study is shown in Figure 1. The study included 1,712 participants. After excluding nonparticipants and cases with missing data, 1199 (70.0%) participants were included (608 males and 591 females).
Participant characteristics
Table 1 shows participant characteristics. Differences in age, practice hours per week, days for rest per week, history of SF, or history of ED between men and women were insignificant. Body mass index (BMI), weight, and height were significantly different. MD among female competitors was 201 (34.0%), including 10 (1.7%) with delayed menarche who had not yet experienced menstruation. The average age of menarche in Japan is 12.2 years [22], and the definition of delayed menarche has been used since 2017 for those aged 15–17 years who have not yet experienced menarche [23]. The proportion of delayed menarche in the general population is unavailable.
Specialty and competition level of the athletes
Table 2 shows the specialty and competition level of the athletes who participated in the study.
The competition level of the athletes who cooperated in the survey was as follows: national competition (29.6% male, 39.4% female; P = 0.0004), regional competition (52.3% male, 46.7% female; P = 0.057), prefectural competition (male: 15.3%, female: 11.7%; P = 0.076), and city competition (male: 2.8%, female: 2.2%; P = 0.059).
According to the number of registered members of the All Japan High School Athletic Federation in 2022, 3.6% were national competition-level competitors, and 35.4% were regional competition-level competitors [24]. Most study participants (81.9% male and 86.1% female) were either at the national or regional level, indicating that the study targeted high level national competitors. More females than males were at the national level. Differences in the overall sex ratio of the participants (608:591) (P = 1.00) were absent, and differences in the ratio of athlete number per specialty were insignificant (P = 0.22).
Characteristics by event specialty
Characteristics of all athletes by event specialty
Table 3 shows the characteristics of athletes by event specialty. The history of SF was significantly greater in sprinting than throwing. The history of ED was significantly greater in long-distance than sprinting and jumping. BMI was significantly higher in the case of throwing than that of the other events. BMI was significantly higher in the case of sprinting than that of long- and middle-distance events. BMI was significantly higher in the case of combined events than long- and middle-distance events. BMI was significantly higher in the case of jumping than long- and middle-distance events. The training hours were significantly longer for throwing than for long-distance, middle-distance, sprinting, and jumping.
Characteristics of male athletes by event specialty
The history of SF was significantly higher in sprinting than throwing. There was no significant difference in the history of ED across event specialties. BMI was significantly higher in the case of throwing than that of the other events. BMI was significantly higher in the case of sprinting than that of long- and middle-distance events. BMI was significantly higher in the case of combined events than long- and middle-distance events. BMI was significantly higher in the case of jumping than long- and middle-distance events. The training hours were significantly longer in the case of throwing than that of long- and middle-distance events.
Characteristics of female athletes by event specialty
No significant difference was observed in the history of SF across event specialties. The history of MD was significantly more common long-distance than sprinting, throwing, and jumping. The history of ED was significantly more common long-distance than sprinting, throwing, and jumping. Probable triad was found only in long-distance. BMI was significantly higher in the case of throwing than that of the other events. BMI was significantly higher in the case of sprinting than that of long- and middle-distance events. BMI was significantly higher in the case of combined events than sprinting, long- and middle-distance events. BMI was significantly higher in the case of jumping than long- and middle-distance events. The training hours were similar between disciplines.
Factors associated with SF history in male and female athletes
Table 4 presents the analysis of SF history-associated factors in male and female athletes. Our univariate logistic regression analysis identified the following factors to be significantly associated with SF history: discipline (with throwing as a reference), sprinting (crude odds ratio [OR] 2.56, 95% confidence interval [CI] 1.667–3.928), middle-distance (crude OR 2.08, 95% CI 1.020–4.238), jumping (crude OR 1.91, 95% CI 1.205–3.038), combined (crude OR 2.34, 95% CI 1.158–4.716); training hours per week (per1) (crude OR 1.06, 95% CI 1.026–1.094); and BMI (crude OR 0.95, 95% CI 0.899–0.994).
Gender, rest day/week, ED history, and MD history were not relevant factors.
Our multivariate logistic regression analysis identified the following factors to be associated with SF history: discipline (with throwing as a reference), sprinting (adjusted odds ratio [OR] 3.56, 95% CI 1.939–6.520), middle-distance (adjusted OR 3.10, 95% CI 1.286–7.493), jumping (adjusted OR 2.51, 95% CI 1.335–4.733), combined (adjusted OR 2.88, 95% CI 1.281–6.459) and training hours per week (per1) (adjusted OR 1.08, 95% CI 1.042–1.116). BMI was not identified as a significantly associated factor.
MD history-associated factors in female athletes
Table 5 shows the analysis of MD experience-associated factors in female athletes. Our univariate logistic regression analysis identified the following factors to be significantly associated with MD: athletic discipline (with throwing as a reference), middle-distance (crude OR 2.48, 95% CI 1.084–5.686), long-distance (crude OR 4.78, 95% CI 2.169–10.517); BMI (per1) (crude OR 0.93, 95% CI 0.856–0.998); and ED history (crude OR 3.78, 95% CI 1.485–9.640).
Training hours/week, rest day/week, and SF history were not associated factors.
Our multivariate logistic regression analysis identified the following factors to be associated with MD experience: discipline (with throwing as a reference), long-distance (adjusted OR 2.87, 95% CI 1.082–7.606), and ED history (adjusted OR 2.92, 95% CI 1.015–8.423). Middle-distance and BMI were not identified as significantly associated factors.
Discussion
This study on high school track and field athletes in Japan shows the following three points.
- 1.SF: SF history was self-reported by approximately one in four male and female athletes, establishing the length of weekly training hours and events (sprinting, middle-distance, jumping, and combined) as relevant factors.
- 2.MD: Approximately one in three female athletes reported MD history, being significantly and more frequently experienced in the case of long-distance events than in the case of sprinting, throwing, and jumping. We identified ED history and long-distance events as MD history-related factors.
- 3.ED: ED history was self-reported at low frequency by both genders, being significantly more frequent in the case of long-distance than in the case of sprinting and jumping events.
SF
So far, few studies have focused on the incidence of SF and associated factors in high school track and field athletes in Japan.
Factors modifying the load applied to the bones and the load resistance ability of the bones affect SF occurrence. Factors modifying the load to the bones include ground reaction force magnitude, segment acceleration, impact, training duration, frequency, and intensity. Load resistance ability includes diet, nutrition, endocrine status, hormones, and menstrual status [21].
Bennell et al. conducted a 1-year prospective study of 111 male and female track and field athletes (aged 17–26 years) and described a 21.1% SF incidence coupled with neither gender nor events-related differences, although the sites of occurrence were different [25].
Bennell et al. conducted a retrospective analysis of women in the same population and reported that athletes experiencing SF were more likely to exhibit an MD history.
Nattiv et al. prospectively followed 211 male and female American college track, field, and cross country athletes and discovered that 34 of them experienced 61 bone stress injuries during the 5-year study period. In addition, 23% of the female athletes experienced oligomenorrhea or amenorrhea during the study period [26].
In Japanese data, Nose et al. studied 390 international competition-level female athletes (103 of them being track and field) in various sports (mean age of 20.9 (±4.0) years) and reported that 36 of them developed new SF within 3 months [27]. In the aforementioned study, based on the age group, teenage athletes were at a higher risk of triad-related SF compared with athletes in their 20 s. In addition, they reported age at menarche, training time, prior SF, and SF cumulative risk score [27]. Osuga et al. surveyed 2321 Japanese female college athletes and revealed that prior SF was associated with endurance events (26.4%), technical events (8.7%), weight classifications (11.3%), ball games (16.5%), power events (21.7%), and aesthetic events (24.5%) [28].
In this study, we registered 23.7% and 23.2% of male and female athletes with an SF history, indicating that nearly a quarter of high level Japanese high school track and field athletes experienced SF. The lack of SF-related gender differences was consistent with the study by Bennell et al. and underpinned that SF could occur independently of gender.
Our finding that training time duration was an SF history-associated factor was consistent with the previous studies of Warden et al. [21] and Nose et al. [27]. Long training time could also be considered an important SF-associated factor for high school track and field athletes. In this study, we showed athletic event-related differences as SF history-associated factors. Compared to throwing, sprinting, middle‐distance, jumping and combined events were significantly associated with SF. – The results of this study indicated that events with higher maximum acceleration and ground impact in competition increased SF experience frequency.
On the other hand, rest day/week, ED history, and MD history were not relevant factors of SF in this study.
Rest days affect the repair of micro-damage in bone. The number of rest days in the study participants was small, approximately 1.4 days per week (standard deviation 0.7), with no difference between males and females, and the participants were equally diligent in training, which may explain why no significant differences were observed.
Although not shown in this study, few Japanese high school track and field athletes concurrently engage in other sports or interests. This may be related to the high experience rate of SF.
The results of the present study, which did not confirm a correlation between ED history and MD history, are inconsistent with the reports of Bennell et al. [25] and Nattiv et al. [26].
There is no doubt that ED and MD are essential factors affecting bone mass and quality. Therefore, we believe that the load applied to a bone had a greater influence than the ability of the bone to resist load in the high school track and field athletes included in this study.
In other disciplines not included in this study (e.g., female rhythmic gymnastics, gymnastics, ballet, and road races such as marathons and EKIDEN), the influence of factors modifying the load resistance ability of the bones may be higher, unlike the present results.
MD
The fact that 34% of all high school female athletes experience MD for ≥ 3 months is a problem which cannot be ignored.
In the survey of Osuga et al. studying Japanese female college athletes (n = 1929), amenorrhea at the time of the survey was observed in athletes participating in endurance events (11.6%) and sprinting events (3.8%) compared with the non-athlete group (1.8%) [28].
Although a simple comparison would not be possible, a high level of MD history was identified compared with these numbers.
The identification of ED history as an MD history-associated factor in female high school athletes is consistent with a mechanism whereby ED induces LEA and LEA triggers MD [29]. LEA suppresses the cyclic secretion of luteinizing hormone, resulting in MD. In addition, it is important to note that competing in long-distance events is reportedly an MD history-associated factor.
Dambacher et al. conducted a study involving 287 female collegiate long-distance runners and reported that 162 (56.5%) had MD and 117 (40.8%) were classified as having disordered eating by the Disordered Eating Screening Assessment (DESA-6), respectively [30]. The detailed mechanism by which competing in long-distance events triggers MD has not been clarified in previous studies.
Training for physical function optimized for long-distance running might potentially increase MD incidence via lighter weight, lower body fat percentage, and longer sustained exercise.
ED
Nichols et al. reported that in 170 female high school athletes adjusted for confounding by competition, the prevalence of menstrual irregularity was 23.5%, low bone mass was 21.8%, disordered eating was 18.2%, and triad was 1.2%. They reported that disordered eating was the most common type of eating. They used the eating disorder examination questionnaire (EDE-Q) to investigate disordered eating [31].
Cobb et al. surveyed 85 recreational-level female runners aged 18–39 years and reported the following: MD history (28%), ED symptoms (18%), and 5 h of training per week [32].
Comparing our study data [MDs (34.0%), SFs (23.2%), EDs (3.4%), and probable triad (0.7%)], the MD-related frequency did not significantly differ from that in previous reports.
However, the low self-reporting rate of ED history is conspicuous; although we cannot deny the possibility that the percentage of ED experienced is actually low, the figures might be low due to avoidance of reporting due to embarrassment or unawareness of ED.
The unawareness of ED may be related to the low awareness of REDs and LEA among athletes in Japan. According to Tsukahara et al. 77.6% of sports physicians in the U.S. tested athletes for REDs, whereas only 17.5% of sports physicians in Japan tested athletes for REDs. Japanese sports physicians do not routinely test athletes for REDs. Tsukahara et al. reported that, compared with 36.7% of Japanese physicians, 98.3% of U.S. physicians suspected LEA and tested for ED [33].
For ED, the following background should be considered. 1, Deliberate underreporting. The athletes may hide ED for fear of being ordered to stop competing or because they feel embarrassed. 2, It is possible that athletes do not have sufficient knowledge of ED and do not use treatment services due to unawareness. 3, Junior athletes may struggle with academic pressures and training during a sensitive developmental period and might be unintentionally under-fuelling. Therefore, information and education about ED and nutrition (including MD as a sign of LEA) for this age group is essential.
Another important finding of our study is the lack of gender difference in self-reported ED history, although the frequency was low. In general, 95% of ED occur in female [34].
Borgen et al. studied 1,620 male and female athletes aged 15–39 years who played various sports and reported a higher risk of ED in female compared with male athletes [17].
Hagmar et al. studied 223 athletes (125 male and 98 female) who participated in the 2002 and 2004 Olympic Games and reported that significantly more female (8.9%) than male (1.7%) athletes had a history of ED [35].
The reasons for the differences between the results of this study and these existing reports are currently unclear.
However, there is growing interest in the presence of ED in male athletes [17, 18].
We believe it is significant to recognize that ED are not limited to females in high school athletics.
The frequency of ED history was significantly higher in long-distance than in sprinting or jumping is also significant in that it identifies a discipline that should be noted.
The Scientific Committee of the National Federations (JAAF) conducted this survey. This allowed us to survey many participants and obtain a high response rate in a high-level athletic population with a uniform background.
Athletics is simple. High school athletes devote the same amount of time in the pursuit of sprinting, running middle or long-distances, throwing, and jumping.
In this study, sampling was limited to high level Japanese high school track and field athletes to examine a homogeneous group of athletes sharing certain relevant conditions (age, lifestyle, among others). Therefore, it is significant that we obtained results related to differences by disciplines. Comparisons between track and field athletes in the same category, rather than those between nonathletes or different sports, reflect the influence of disciplinary characteristics.
The health problems common to each discipline identified in this study and the consideration of discipline characteristics are significant.
Limitations
This study has four main limitations. First, the study’s cross-sectional design makes determining the causality of the results impossible, limiting the results to comparisons between categories and estimates of odds ratios of prevalence in the target population.
Second, because the data are retrospective self-reported, they may be subject to recall and reporting bias, depending on the participants’ interpretation of the questions, sincerity of answers, and ability to accurately recall. Questions about SF, MD and ED may be subject to underreporting because of embarrassment or unawareness of the disease. Thus, actual prevalence may be greater than reported prevalence. However, we believe that the validity of the results will be maintained in the comparisons between genders and disciplines made within this study, as they are subject to the same biases.
Third, we studied the four jumping events (long jump, triple jump, high jump, and pole vault) as one category, which represents a limitation. Long and triple jumps, which are primarily horizontal jumps, exhibit strictly different competition characteristics compared with high jump and pole vault, which are antigravitational jumps. We could not confirm the differences related to these characteristics in this study.
Fourth, few long-distance competitors were present in the target group. Although this study was conducted at the NF training camps held during the study period, few long-distance camps have been held, resulting in a small number of participants. For the same reason, the fact that we could not survey competitors in road disciplines (e.g., EKIDEN) as training camps were not held during the study period, which would have provided a research opportunity, represents a limitation of this study.
Conclusion
This study revealed that about a quarter of Japanese high school track and field athletes experience SF, and about a third of the females experience MD. Our results also indicated that differences among athletic events, training time, and ED history were relevant factors to be considered in these problems.
First, we would like to thank the high school athletes who took the time to participate in this study.
We would also like to express our deepest gratitude to all those involved in athletics who contributed to the implementation of this study.
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