Objective . The physical condition of athletes can be assessed easily and quantitatively using objective indicators. Bioelectrical impedance measures the phase angle (PA), representing hydration and cell function, and is a potential clinical indicator of physical condition. This study aimed to investigate the association between PA and physical performance in adolescent athletes. Approach . Overall, 170 adolescent athletes underwent a sports medical check-up, including body composition measurements and physical performance tests. Whole-body and segmental PAs (arm and leg) were determined based on body composition values. Isometric grip power and knee isokinetic muscle strength were measured as parameters of muscle strength. Counter movement jump height and squat jump height were measured as jump parameters. Associations between PA and each muscle strength or jump parameters were analysed using Pearson product-moment correlation coefficient or Spearman’s rank correlation coefficient. Main results . Whole-body and upper limb PAs were highly correlated with grip power ( r = 0.70–0.80). Whole-body and lower limb PAs were correlated with knee isokinetic muscle strength ( r = 0.43–0.59). Whole and all segmental PAs were correlated with counter movement jump height ( r = 0.46–0.57) and squat jump height ( r = 0.42–0.52). Significance . PA can be used to monitor physical condition and sports performance in adolescent athletes. Segmental PAs can help assess the condition of the corresponding body part.

Background: Foot malalignment can augment the risk of lower-extremity injuries and lead to musculoskeletal disorders. This study aimed to clarify the contribution of rearfoot alignment to plantar pressure distribution and spatiotemporal parameters during gait in healthy adolescent athletes. Methods: This retrospective study included 39 adolescent athletes who were divided into the rearfoot eversion and control groups according to a leg heel angle of 7°. A total of 78 legs were analyzed (45 and 33 legs in the rearfoot eversion [women, 53.3%] and control groups [women, 48.5%], respectively). Gait was assessed using an in-shoe plantar pressure measuring system and a wearable inertial sensor. Results: The foot plantar pressure distribution in the hallux was higher in the rearfoot eversion group than that in the control group (p = 0.034). Spatiotemporal parameters showed that the foot pitch angle at heel strike was significantly larger in the rearfoot eversion group than that in the control group (24.5° vs. 21.7°; p = 0.015). Total sagittal range of motion of the ankle during the stance phase of gait was significantly larger in the rearfoot eversion group than that in the control group (102.5 ± 7.1° vs. 95.6 ± 15.8°; p = 0.020). Logistic regression analysis revealed that plantar pressure at the hallux and medial heel and foot pitch angle at heel strike were significantly associated with rearfoot eversion. Conclusions: Our findings suggest that rearfoot eversion affects the gait patterns of adolescent athletes. Notably, leg heel angle assessment, which is a simple and quick procedure, should be considered as an alternative screening tool for estimating plantar pressure and spatiotemporal gait parameters to prevent sports-related and overuse injuries in adolescent athletes.

Decreased muscle-to-fat mass ratio (MFR) is associated with pediatric nonalcoholic fatty liver disease (NAFLD) and may reduce muscular fitness. Regular exercise in sports clubs has not led to reductions in obesity in children and adolescents; they may have decreased MFR. Decreased MFR could cause reduced muscular fitness, which may put them at risk for NAFLD development. We investigated whether MFR is related to muscular fitness and serum alanine aminotransferase (ALT), to determine whether MFR could be used to screen for NAFLD in children and adolescent boys belonging to sports clubs. Altogether, 113 participants (aged 7–17 years) who underwent body composition, laboratory, and muscular fitness measurements during a medical checkup were divided into tertiles according to their MFR. Lower extremity muscular fitness values were significantly decreased in the lowest MFR tertile (p < 0.001); conversely, serum ALT levels were significantly increased (p < 0.01). Decreased MFR significantly increased the risk of elevated ALT, which requires screening for NAFLD, after adjusting for age, obesity, muscular fitness parameters, and metabolic risk factors (odds ratio = 8.53, 95% confidence interval = 1.60–45.6, p = 0.012). Physical fitness and body composition assessments, focusing on MFR, can be useful in improving performance and screening for NAFLD in children and adolescents exercising in sports clubs.

We assessed whether the coronavirus disease 2019 (COVID-19) pandemic-related disruptions impacted the physical fitness of adolescent athletes. We reviewed the age-, sex-, and sports category-matched data of 78 adolescent athletes (divided into two groups: 2019 group = 37; 2020 group = 41) from the clinical database and investigated their height, weight, body composition, flexibility muscle strength, and jump height. We also provided questionnaires to the teams’ coaches to collect data on the duration of practice suspension due to the COVID-19 pandemic; the practice hours per week in August 2019, immediately after the suspension ended, and in August 2020; and the guidelines for the players after resuming their practice. For data analyses, we considered p ≤ 0.05 as statistically significant. The strength of knee flexion and extension was significantly lower in the 2020 group than in the 2019 group; there was no difference in the other physical fitness parameters. The practice duration in August 2019 and August 2020 was the same. COVID-19-related interruptions did not alter the athletes’ jump height, upper-limb strength, and flexibility but reduced lower-limb muscle strength. We recommend that basic strength training protocols be followed to prevent sports-related injuries after such unexpected practice interruptions.