Journal of Physical Fitness and Sports Medicine
Official journal of the Japanese Society Physical Fitness and Sports Medicine
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The Journal of Physical Fitness and Sports Medicine (JPFSM)
[Volume 16, Number 1 January 25, 2027]
Regular Article
- Received: April 10, 2025 / Accepted: August 18, 2025
Abstract
This study aimed to evaluate a musculoskeletal screening method for elementary school students using ultrasound and lower limb flexibility assessments, with the goal of early detection of Osgood-Schlatter disease during the growth period. A total of 143 boys in the fourth to sixth grades of elementary school from a single prefecture underwent musculoskeletal screening between November 2021 and February 2023. Using a diagnostic ultrasound device, the tibial tuberosity was observed, and its developmental stage was classified based on Ehrenborg’s four-stage classification (Ehrenborg, G and Lagergren, C. (1961). Acta Chir. Scand., 121: 315–327). The presence of Osgood-Schlatter disease was determined based on the presence of irregularities in the ultrasound image. Lower limb flexibility was assessed quantitatively using finger-floor distance (FFD) and heel-hip distance (HHD). The cartilaginous stage (C stage) was the most common developmental stage observed. Osgood-Schlatter disease was identified in eight children (5.6%) and was found only in the epiphyseal (E) and bony (B) stages (P=0.004, φ=0.308). HHD was significantly greater in the Osgood-Schlatter group (P=0.040, r=0.680). In some children without knee pain or tenderness, irregularities in the tibial tuberosity were detected on ultrasound imaging, suggesting that ultrasound imaging may be useful for the early detection of asymptomatic lesions. This screening approach, which combines ultrasound examination and flexibility assessment, is expected to serve as a novel method for the early detection and prevention of musculoskeletal disorders in children during their growth period. Further large-scale studies and continued investigation into methods for assessing flexibility in growing children are warranted.
Regular Article
- Received: May 14, 2025 / Accepted: August 19, 2025
Abstract
While mortality due to spinal cord injuries (SCI) and urinary tract infections has markedly decreased, the incidence of malignant tumors and lifestyle-related diseases is increasing among people with physical disabilities. However, regular assessment of body weight and composition remains challenging in this population. This cross-sectional study aimed to clarify the relationship between waist circumference, trunk fat percentage, and visceral fat level, with a particular focus on waist circumference as an easily measurable indicator. A total of 151 individuals participated, including 42 with SCI, 42 with cerebrovascular disease (CVD), and 67 without disabilities. Waist circumference, trunk fat percentage, and visceral fat level were measured in sitting and supine positions for all participants, and in the standing position for those without disabilities. Position-related differences were analyzed, with statistical significance set at 5%. Waist circumference varied by measurement position, with the highest values observed in the sitting position. For participants with SCI, the average waist circumference was 90.9±13.1 cm in the sitting position and 81.6±10.9 cm in the supine position. In participants with CVD, the respective values were 93.4±9.8 cm and 86.5±8.5 cm. Waist circumference showed significant positive correlations with both trunk fat percentage and visceral fat level. Standard screening values may underestimate adiposity in people with physical disabilities. These findings suggest the necessity of adopting specific reference values and support the utility of waist circumference measurements taken in the sitting and supine positions in this population.
Regular Article
- Received: July 9, 2025 / Accepted: August 27, 2025
Abstract
More research is needed to understand how exercise time and physical fitness relate to body size. In particular, there are no studies that have examined the relationship between physical activity and physical fitness, taking into account both overweight/obesity and thinness, using national samples. This study aimed to analyze exercise time by body size and physical fitness using a Japanese national sample of Japanese children and adolescents. The survey included 19,471 primary and 10,596 secondary schools in Japan. After excluding participants with missing data, the analysis included 878,348 Year 5 primary school students and 757,358 Year 8 secondary school students. Body mass index (BMI) was calculated based on participants’ height and weight, and they were subsequently categorized into four BMI groups: underweight, normal weight, overweight, and obese. Physical fitness was classified as high or low based on the total score from eight physical fitness tests. Exercise time was assessed via a questionnaire and compared between the high- and low-fitness groups within each BMI category. Among the boys and girls in primary and secondary schools, exercise time was greater in the high-fitness group compared with the low-fitness group across all four BMI categories (Underweight, normal-weight, overweight and obesity). In conclusions, this study suggested that exercise time is positively associated with higher physical fitness regardless of whether an individual is obese, underweight, or normal weight. These results may indicate the importance of promoting exercise time among all children, and further longitudinal studies are needed.
[Volume 16, Number 2 March 25, 2027]
Regular Article
- Received: July 24, 2025 / Accepted: September 10, 2025
Abstract
Lateral ankle sprains (LAS) account for a substantial proportion of ankle injuries in rugby union and are associated with a high recurrence rate. A history of LAS is known to increase future injury risk, yet few studies have quantitatively examined this relationship. This study aimed to investigate the epidemiological characteristics of LAS among male collegiate rugby players based on the presence or absence of prior injury history. A total of 146 players were prospectively followed over seven seasons and divided into two groups according to their LAS history. Group-specific exposure time was used to calculate injury incidence, severity, and mechanism-specific burden. A total of 131 LAS cases were recorded. The History group showed a significantly higher incidence rate (1.22/1,000 PHs) than the No History group (0.72/1,000 PHs), while no significant difference in severity was observed. Contact-related mechanisms, including other player collisions and lineout landings, were more frequent and burdensome in the History group. These findings suggest that injury history is not merely a contextual factor, but a key determinant of future injury risk and characteristics. Prevention and rehabilitation strategies should be tailored accordingly. Mechanism-specific training and history-informed return-to-play protocols are essential to reduce the burden of LAS in athletes with prior injuries.
Regular Article
- Received: February 22, 2025 / Accepted: September 10, 2025
Abstract
This study aimed to develop and conduct a preliminary validation of the hitoe system, a novel smartphone application and wearable device designed to tailor exercise loads to individual exercise tolerance, with the goal of supporting personalized cardiac rehabilitation. A preliminary validation study was conducted involving 28 healthy adults (26 males, mean age 42.3 ± 11.2 years). Participants used the hitoe system to perform 13 activities, including sedentary tasks, household chores, walking, and cycle ergometer. Exercise intensity was measured in metabolic equivalents (METs) and compared with values obtained using a standard gas analyzer. Statistical analyses, including intraclass correlation coefficients (ICCs) and Bland-Altman analyses, were applied to assess the accuracy and reliability of the device. The hitoe system demonstrated satisfactory agreement with gas analyzer measurements across most activities. Bland-Altman analyses revealed that the majority of data points fell within ±2.0 METs, indicating limits of agreement. High ICCs were observed for activities such as cycle ergometer (ICC = 0.797), vacuuming the floor (ICC = 0.693), and lifting a 5 kg weight (ICC = 0.614), reflecting strong reliability. In contrast, sedentary activities such as sitting (ICC = 0.033) and desk work (ICC = 0.144) showed lower ICCs, although the absolute differences between the two methods remained within approximately 1 MET. The preliminary findings suggest that the hitoe system may be useful for assessing physical activity intensity, particularly during higher-intensity activities. The system may offer a promising tool for real-time feedback and tailored exercise prescription in cardiac rehabilitation. Further studies involving patients with cardiovascular diseases are warranted to validate these preliminary results and enhance the system’s precision in clinical settings.
Regular Article
- Received: June 20, 2025 / Accepted: September 22, 2025
Abstract
This longitudinal study aimed to determine the performance-related knee injury risk factors in male university rugby union players. Baseline performance measurements were taken in the pre-season and included: (1) strength tests–maximal isometric voluntary contraction (MVC) and single-limb hop test; (2) balance tests–Balance Error Scoring System and Y Balance Test–Lower Quarter; and (3) movement quality–Landing Error Scoring System. The Limb Symmetry Index (LSI) was calculated using strength tests. Knee injury surveillance data, including incidence, severity, and burden, were tracked and analyzed over 1 year. Of the 79 candidate players, 64 completed the test set, and 58 were included in the analysis. We observed 15 knee injuries in 13 players. The injury incidence was 0.4 injuries/1000 player-hours (1000 h) (95% confidence interval [CI], 0.2–0.5); severity was 51 days (95% CI, 0–104); and the burden was 19 days/1000 h (95% CI, 11–31). High LSI of hip internal rotation (odds ratio [OR], 1.09; 95% CI, 1.02–1.16) and MVC of hip extension (OR, 1.10; 95% CI, 1.00–1.20) were identified as significant factors associated with the occurrence of knee injury. In conclusion, the present study suggests that knee injuries are associated with the LSI of hip internal rotation and MVC of hip extension. Players with high performance levels are more exposed to higher injury risks during matches. Given that performance test results may predict knee injury incidence, regular monitoring of such tests may help prevent knee injuries.
[Volume 16, Number 3 May 25, 2027]
Regular Article
- Received: July 7, 2025 / Accepted: September 29, 2025
Abstract
In Japan, research on how specific types of sedentary behavior are associated with academic performance among school-aged children remains limited. This cross-sectional study investigated the relationship between various sedentary behaviors and academic performance among Japanese children and adolescents. Data were collected in 2023 from 342 primary and 456 junior high school students in Unnan City, Shimane Prefecture. Academic performance was categorized as high or low based on median scores in Japanese and mathematics. Sedentary behaviors were assessed using a questionnaire—including time spent on reading books and newspapers and total recreational screen time, which was calculated from the time spent playing TV games, watching videos or using social networking services (SNS), and using educational tablets at home. Multiple linear regression analyses were conducted, adjusting for factors, such as gender, grade, breakfast habits, sleep duration, sports club participation, and cram school attendance. Spending < 2 hours on TV, games, watching videos, or SNS use was significantly associated with higher academic performance across school levels. Conversely, spending < 2 hours on total recreational screen time and using educational tablets at home was linked to higher scores among primary students. Reading books was positively associated with Japanese language scores in both groups. Thus, the type of sedentary activity plays a crucial role in the academic outcomes. A shorter duration of recreational screen time and educational and literacy-related behaviors were associated with higher academic performance. This study highlights the need for further longitudinal research considering household socioeconomic factors to better understand these associations.
Regular Article
- Received: May 27, 2025 / Accepted: October 2, 2025
Abstract
We aimed to develop regression models for estimating oxygen consumption (VO₂, ml·kg⁻¹·min⁻¹) during treadmill walking based on accelerations of the upper and lower limbs and walking velocity, quantitatively assess the contribution of each sensor location, and validate the accuracy and practicality of a simplified model. Eighteen healthy adults with regular exercise habits (nine men, nine women) participated in treadmill walking trials at varying speeds (3–6 km·h⁻¹; up to 5.5 km·h⁻¹ for women). Vector magnitude (VM) from triaxial accelerometers attached to both wrists and both ankles was recorded simultaneously with VO₂ measurements from a portable breath-by-breath gas analyzer. Multiple regression models were constructed using FootVM (ankle VM), HandVM (wrist VM), and walking velocity as predictors. FootVM alone showed a moderate correlation with VO₂ (R² = 0.464), but adding walking velocity substantially improved the model’s accuracy (Model 2: R² = 0.810, standard error of estimate = 1.25 ml·kg⁻¹·min⁻¹). Incorporating HandVM yielded only a minimal, non-significant model fit improvement (R² = 0.815, ΔAIC = +18.4, βstd = −0.06), with no meaningful statistical contribution. Bland–Altman analysis indicated 95% limits of agreement for estimation error within ±2.46 ml·kg⁻¹·min⁻¹, corresponding to < 1 MET (3.5 ml·kg⁻¹·min⁻¹). These findings support the rational selection of a simplified model using only FootVM and walking velocity, which achieved a balance between high accuracy and practicality. The ability to estimate VO₂ precisely using only ankle-mounted accelerometers highlights its potential for use in clinical and home-based physical activity assessment.
Regular Article
- Received: July 2, 2025 / Accepted: October 8, 2025
Abstract
For busy individuals seeking to establish an exercise habit, weight-bearing exercise-based high-intensity interval training (HIIT) is a time-efficient option. Although single sessions have been shown to improve postprandial blood glucose, whether unsupervised HIIT supports long-term adherence remains unclear. Therefore, this study compared the effects of eight weeks of supervised HIIT and moderate-intensity continuous training (MICT) on adherence and blood glucose indicators. We recruited 46 healthy young adults with no exercise habits, and low to moderate physical activity. After a two-week pre-measurement period, participants were randomly assigned to a HIIT group that performed weight-bearing exercise-based HIIT three times a week for eight weeks without supervision, an MICT group that performed running three times a week for eight weeks without supervision, or a control group that did not change their lifestyle. The intervention period was followed by a two-week post-measurement period for between-group and pre- and post-intervention comparisons. The primary outcome was exercise adherence, assessed based on a self-report and supplemented with a tri-axial accelerometer and glycemic index. Adherence was significantly higher in the HIIT group (60.6 ± 25.7%) than in the MICT group (27.9 ± 22.3%). No significant differences in glycemic index were observed either pre- to post-intervention or between groups. Overall, unsupervised HIIT produced greater adherence than comparable running but did not alter blood glucose levels in healthy young adults.
[Volume 16, Number 4 July 25, 2027]
Short Communication
- Received: August 4, 2025 / Accepted: October 20, 2025
Abstract
Many women are aware of feeling cold in their daily lives. To elucidate the interrelationships among having a cold constitution, exercise habits, and sleep, we conducted an Internet survey that included 600 women and 600 men aged 15 to 69 years. The items in the survey included sex, age, coldness, practice of exercise, and sleep condition. The participants answered all questions with a "yes" or "no" answer. In all age groups, women reported a significantly higher number of coldness-related items than men; however, no differences were found among the age groups. Men who exercise regularly reported a higher number of applicable coldness-related items than those who did not (p = 0.027), but this was not found in women (p = 0.208). In both men and women, regular exercise was positively associated with falling asleep (p < 0.05) and getting enough rest through sleep (p < 0.01). These findings suggest that regular exercise is beneficial for sleep in men and women of all ages; however, in men, it is also associated with increased cold-related symptoms.
Regular Article
- Received: April 22, 2025 / Accepted: October 28, 2025
Abstract
This study aimed to investigate the relationship between cross-sectional area (CSA) of lower limb muscles and UUS velocity on swimmers. Eighteen male swimmers at the regional to national level participated in this study. Kinematic data during maximum-effort UUS were collected using an underwater motion capture system to determine the mean UUS velocity. T1-weighted cross-sectional magnetic resonance (MR) images of the lower limb muscles were acquired using a 3T MR imaging system to determine the CSA of 17 muscles on the swimmers’ right side. Relationships between UUS velocity and the CSA of lower limb muscles were examined using correlation coefficients. A positive significant correlation was found between CSA of rectus femoris and UUS velocity (absolute value: r = 0.475 p = 0.046, relative value: r = 0.548 p = 0.019). However, UUS velocity was not significantly correlated to CSA of other lower limb muscles (r = - 0.445 ~ 0.469). These results suggest that the CSA of rectus femoris has a moderate relationship between UUS velocity among the lower limb muscles, regardless of the body size. Revealing the relationships between muscle size and UUS velocity can provide an important insight regarding which lower limb muscles should be strengthened to enhance UUS performance for swimmers, coaches and researchers.
Short Communication
- Received: August 21, 2025 / Accepted: November 19, 2025
Abstract
Athletes often use caloric restriction (CR) to manage body weight. However, the effects of post-CR weight maintenance on skeletal muscle and fat mass remain unclear. This study investigated the effects of 60% CR for either 8 (8CR) or 2 (2CR) weeks on skeletal muscle and adipose tissue in mice. In the 8CR group, weight loss slowed after 2 weeks. However, body weight and wet skeletal muscle weight were significantly higher and inguinal white adipose tissue weight was significantly lower in the 2CR group compared with the 8CR group. These findings suggest that 8 weeks of CR, including a weight maintenance phase after initial weight loss, may result in a greater loss of skeletal muscle mass and an increase in fat mass compared to 2 weeks of CR. As this study was performed in 8-week-old male mice, the differences between the 2CR and 8CR groups are likely to reflect not simply the length of CR but rather the influence of conducting CR at different stages of growth.
Regular Article
- Received: August 22, 2025 / Accepted: December 5, 2025
Abstract
Background: Many high school teachers in Japan supervise school sports club activities, which leads to long working hours and elevated stress. However, the relationship between club factors and the health status of coaches remain unclear. Objective: This study examined associations between club factors and the health status of Japanese high school sports club activity coaches. Methods: We conducted a nationwide cross-sectional survey of school sports club activity coaches in all Japanese high schools. Two health outcomes were assessed: self-rated health (SRH; good or poor) and psychological distress using the Kessler 6 scale (K6; high distress or not). Data on seven club factors were collected: sport type, weekday and weekend activity duration and frequency, number of student managers, and club aim. Odds ratios for a favorable health outcome of each factor were calculated. Results: Among 6,045 respondents, weekday activity time ≥ 3 hours was associated with poorer SRH (OR = 0.70; 95% confidence interval: 0.58–0.85) and higher psychological distress (0.67; 0.52–0.86). Coaching ≥ 5 days per week (0.80; 0.68–0.95) and weekend activity ≥ 4 hours (0.83; 0.70–0.98) were also linked to poorer SRH. Aiming for national competitions (1.28; 1.06–1.56) and having ≥ 2 student managers (1.29; 1.07–1.55) were associated with favorable health. Conclusions: Multiple student managers and an emphasis on national competitions were linked to improved coach health, whereas extended weekday and weekend activities were associated with poorer outcomes.
[Volume 16, Number 5 September 25, 2027]
Regular Article
- Received: October 3, 2025 / Accepted: December 16, 2025
Abstract
Since the influence of hypoxia on mitochondrial adaptations in different muscle fiber types remains unclear, this study examined the impacts of hypoxic repeated sprint training (RST) on lactate metabolism and mitochondrial-related protein content, with a special focus on potential differences between different fiber type composition. Eight-week-old ICR mice were randomly divided into five groups: normoxic sedentary control (CON), normoxic 2set-RST (2set-NT), normoxic 4set-RST (4set-NT), hypoxic 2set-RST (2set-HT), and hypoxic 4set-RST (4set-HT). Two or four sets of 5×40-s sprints (recovery: 20-s, inter-set = 5-min) were performed for four weeks (three times/week) under either normoxia (FiO₂ = 20.9%) or hypoxia (FiO₂ = 13%). Skeletal muscle samples were analyzed for mitochondrial and metabolism-related protein content. In the fast-twitch (FT)-dominant plantaris muscle, peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and monocarboxylate transporter 4 (MCT4) were significantly higher in the 4set-NT and 4set-HT compared to the CON (p<0.01). Notably, PGC-1α and MCT4 remained unchanged in the 2set-NT but were significantly elevated in the 2set-HT (p<0.05). Pyruvate dehydrogenase (PDH) E1α subunit was higher in the 2set-HT (p<0.05) and 4set-HT (p<0.01) compared to the CON. Additionally, mitochondrial oxidative phosphorylation (OXPHOS) subunit complex I increased significantly only in the 4set-HT (p<0.05). In contrast, no significant changes were observed in the slow-twitch-dominant soleus muscle. These findings suggest that hypoxic RST selectively increases proteins involved in lactate metabolism and mitochondria, especially in the FT-dominant plantaris. Notably, several proteins (PGC-1α, PDH E1α, and MCT4) were elevated under hypoxia even with lower training loads (2 sets).
Regular Article
- Received: October 23, 2025 / Accepted: December 18, 2025
Abstract
Concussions are a growing concern in youth soccer; yet, detailed information on their mechanisms and grade-specific characteristics remains limited. This study aimed to describe the epidemiological features and mechanisms of soccer-related concussions among middle-school and high-school students in Japan. A retrospective observational analysis was conducted using nationwide insurance data for sports injuries from 2012 to 2022. Concussion cases sustained during soccer were extracted, and their mechanisms were categorized. Sex- and grade-related differences were examined, and incidence rates per 1,000 club members were calculated to account for variations in player population size. Among 696,600 soccer-related injury claims, 3,343 concussion cases met the inclusion criteria. Boys accounted for 3,217 cases (96.2%) and girls for 126 cases (3.8%), with incidence proportion of 0.85 and 0.78 per 1,000 club members, respectively. The most frequent injury mechanism was playing surface-contact with player (39.1%), followed by collisions with other players. Most concussions occurred during competitions rather than practice sessions. As school grade level increased, concussions more often resulted from player-to-player contact during games (middle school: 1st year, 49%; 2nd year, 54%; 3rd year, 63%; high school: 1st year, 57%; 2nd year, 60%; 3rd year, 69%). These findings indicate that most soccer-related concussions among middle- and high-school students occurred after contact and subsequent falls. Even when not directly caused by a collision, loss of balance leading to a fall frequently resulted in concussion. The grade-dependent variation in injury mechanisms highlights the need for tailored prevention strategies focusing on fall dynamics and safe contact techniques.