In this study, we aimed to investigate the effects of long-term voluntary running exercise and caloric restriction during development on the skeletal muscle mass and intracellular signaling in female rats. Four-week-old female Wistar rats (n = 23) were randomly divided into the sedentary (SED) and voluntary running exercise (EX) groups, and then acclimated to a new environment. At 5 weeks of age, the rats in both groups were further divided into the ad libitum (AD+SED or AD+EX, n = 6) and calorie-restricted (CR+SED or CR+EX, n = 5-6) groups. EX group underwent 12 weeks of voluntary running exercise. CR group was only fed 70% of the food fed to the AD + SED group. After 12 weeks of intervention, soleus and plantaris muscles were removed, and the levels of intracellular signal transduction proteins involved in protein synthesis and degradation were measured by Western blotting. Significant diet × condition interactions were observed in the body, soleus muscle, and plantaris muscle weights. Specifically, plantaris muscle weight in the CR + EX group was significantly lower than that in the other groups; however, their soleus muscle weight was similar to that in the CR + SED group. In the plantaris muscles, significant diet × condition interactions were observed in the phosphorylation levels of 4E-binding protein 1, UNC-51-like autophagy-activating kinase-1, and light chain 3-II/I. Moreover, these factors were significantly altered in the CR + EX group than in the other groups. Notably, no significant interactions were observed in the soleus muscles. Our data suggest that long-term voluntary running exercise and caloric restriction exacerbate skeletal muscle loss, possibly mediated by muscle type-specific intracellular signaling mechanisms involved in protein synthesis and degradation.

Given that the long head of the biceps femoris (BFlh), semitendinosus (ST), and semimembranosus (SM) have hip adduction moment arm, this study aimed to clarify the influence of hip abduction angle on their shear modulus, measured by using shear wave elastography, to determine an effective stretching position where these muscles are more elongated and demonstrate higher passive tension. Twelve healthy young men participated in the study. The shear modulus of BFlh, ST, and SM at the middle point was measured using shear wave elastography. The shear modulus was measured at hip abduction angles of 0°, 15°, 30°, and 45°, with the hip and knee joint held at 70° and 0° flexion, respectively. The effects of hip abduction angle on the muscle shear modulus were analyzed using a Friedman test, followed by Wilcoxon signed-rank tests with Benjamini-Hochberg procedure for post-hoc analysis. Effect sizes were calculated using r. Significant differences in shear modulus were found between hip abduction angles for all muscles (p < 0.05). Post-hoc analysis showed that the shear modulus of the SM at 45° was significantly higher compared to 0° (p < 0.05, r = 0.62) and 15° (p < 0.05, r = 0.54). For ST, the shear modulus at 45° was significantly higher compared to 0° (p < 0.05, r = 0.58). The shear modulus in BFlh at 15° was higher than 0° (p < 0.05, r = 0.53). Adding to hip abduction in a position of hip flexion and knee extension increases the shear modulus of the medial hamstrings, particularly the SM.

N-challenge is an enjoyable agility test for children that incorporates straight running, hurdle running, slalom running, and left and right turns, necessitating multiple physical fitness components. In Japan, children’s physical fitness is assessed using the New Physical Fitness Test (NPFT), comprising eight fitness test items. However, the association between agility, as assessed by the N-challenge, and physical fitness, as evaluated by the NPFT, remains unexplored. This study seeks to investigate the relationship between physical fitness as measured by the NPFT and performance in the N-challenge among elementary school children. The study involved 460 students from grades 3 to 6, including 230 boys and 230 girls. N-challenge running times were measured using a photoelectric tube system originally developed and interfaced with a personal computer. The NPFT was administered following established guidelines. Correlation analysis, controlling for age and sex, examined the relationship between N-challenge outcomes and the eight NPFT items. The results revealed weak to moderate significant correlations (|rs_p| = 0.182-0.648, all p<0.01) between N-challenge running time and seven of the fitness test items and total NPFT scores, except for the sit-and-reach test. Furthermore, a moderate correlation (rs_p = -0.546) was observed between the side-step test and N-challenge performance. Notably, the highest correlation coefficient (rs_p = 0.648) was found between N-challenge and the 50-m sprint test. The results suggest that agility performance assessed by N-challenge test, which consists of multiple motor components, was associated not only with side-step test performance but also with multiple physical fitness components, especially sprinting ability, in elementary school children.