The present study investigates the laterality of muscle thickness (MT) in athletes who perform throwing and hitting motions. Sixty right-handed college athletes (baseball pitchers group, PG; tennis players group, TG; baseball batters group, BG and controls group, CG; all n = 15) participated in this study. Muscle thickness was measured by B-mode ultrasound at the forearm, anterior and posterior upper arm, subscapula, chest, abdomen, lateral abdomen, anterior and posterior thigh and anterior and posterior lower leg. Muscle thickness in the dominant forearm, subscapula, and chest in PG, forearm, chest, anterior and posterior upper arm in TG and the subscapula and chest in BG were significantly larger than those in the non-dominant side. On the other hand, the MT in the non-dominant lateral abdomen in PG, the abdomen and lateral abdomen in TG, and the posterior upper arm and lateral abdomen in BG were significantly larger than those in the dominant side. The ratio of dominant to non-dominant MT was significantly smaller for the internal oblique muscle and total thickness of lateral abdomen in PG, TG and BG than CG. Laterality of the internal oblique muscle and total thickness of lateral abdomen in the non-dominant side is a common characteristic of athletes who perform throwing and hitting motions.

The purpose of this study was to determine the relationship in prepubertal children between lower limb muscle thickness, a quantitative index of lower limb muscle, and sprint motion, in order to clarify the effects of muscle mass development on sprint motion as well as differences in these effects due to sex and muscle location. Participants comprised 41 children in 8year-old (21 boys, 20 girls) in good health attending an elementary school in the city of Kitakyushu. Muscle thickness of the anterior thigh (MTa), posterior thigh (MTp), and calf (MTC) were measured using B-mode ultrasonography. Sprint abilities (sprint speed, stride length, and step frequency), kinematic indices relating to sprint motion and ground reaction force were also measured. Pearson product-moment correlation coefficients were calculated to determine relationships between measured variables. Effects of height and weight were eliminated, and stepwise multiple linear regression analysis was performed, using stride length and step frequency as dependent variables, and kinematic indices and ground reaction force as independent variables. In boys, posterior thigh muscle thickness and calf muscle thickness showed significant simple correlations with flying time/support time (FT/ST), which was selected as an explanatory variable for step frequency. However, no significant relationship was found between step frequency and sprint speed. The conclusion of these findings is that developing lower limb muscle mass affects sprint motion in 8-year-old boys, but does not directly lead to improved sprint speed. In girls, a significant relationship was found between posterior thigh muscle thickness and maximal leg swing velocity during the support phase (ωL), which was selected as an explanatory variable for step frequency, and a significant relationship was found between step frequency and sprint speed. Unlike boys, developing lower limb muscle mass in 8-year-old girls influences step frequency and is closely connected to sprint speed.

The purpose of this study was to compare age and gender differences of lower limb muscle thickness among healthy young children. Five hundred and sixty-one healthy young children aged 3 to 8 years old (284 boys and 277 girls) participated in this study. Anterior thigh, posterior thigh, and calf muscle thicknesses (MTa, MTp, MC) were determined using a B-mode ultrasound. The thickness of each muscle increased significantly as age increased, except in the MTa in the 5-year-old boys' group. A significantly main effect was found in MTa, and there was a higher value in girls than boys, except in the 4-year-old group. A significant age × gender interaction was also observed in MTa, with higher values found in boys than girls, except in the 3- and 5-year-old groups. There was no significant gender different in MC. In addition to the Mt/Tmt ratio, the ratio of each muscle thickness to the total amount of MTa, MTp, and MC was calculated. As a result, in girls, the Mt/Tmt ratio remained constant as age increased in all muscles. On the other hand, in boys, MTa decreased and MTp increased as age increased. From these results, it was suggested that gender differences exist in lower limb muscles thickness among healthy young children aged between 3 and 8 years old. It was also suggested that the muscle development of MTa and MTp was different in boys, while lower limb muscle development in girls stayed constant.

The purpose of this study was to clarify the effects of lower limb muscle mass growth on sprinting ability in children aged 3 to 8 years. The subjects were 514 unimpaired children (266 boys and 248 girls). We measured their lower limb muscle thickness (anterior thigh: MTa, posterior thigh: MTp, and calf: MTC) and 25 meter sprinting time. Muscle thickness was measured using a B-mode ultrasound diagnostic imaging unit. From the 25 meter sprint, we measured the following characteristics in relation to sprinting ability: results, maximum velocity, stride and pitch. The results revealed that sprinting ability significantly correlated with MTp and MTC in both boys and girls. This suggests that, in addition to morphological development, lower limb muscle mass growth contributes to an increase in stride (m/step) and affects sprinting ability during the period from infancy to early childhood. However, no relationship was seen between sprinting ability and anthropometric characteristics (body height and mass) or lower limb muscle thickness among 8-year-old boys. It is possible that lower limb muscle quality and power as well as improvement in elements such as sprinting movement have a stronger influence on sprinting ability than morphological elements such as physique and muscle mass in boys around that age. In contrast, a significant relationship was seen between lower limb muscle thickness and sprinting ability in girls of all age groups, suggesting that, unlike boys, innate lower limb muscle mass influences sprinting ability for girls.

The aim of the present study was to investigate the consciousness among young people (n = 494) of training body part(s) by showing participants a picture of an exercise, through a questionnaire-based survey. Participants were shown a picture of a Back Squat, and were asked which body part(s) they felt was being trained in the picture. Participants who had no experience of doing squatting exercises (NO-SQUAT group, n = 102) and participants who were experienced in terms of doing squatting exercises and weight training under appropriate supervision (INSTRUCTED group, n = 146) were selected for the analysis. On seeing the picture, more than half of the NO-SQUAT group felt that the Back Squat was to train not only their lower body but also another body part(s); among these participants, approximately 70% felt that a Back Squat was appropriate to train their upper torso and arms too. Further, the NO-SQUAT group had made significantly fewer attempts to consciously train their gluteal and knee flexor muscles, and had made significantly more attempts to consciously train their upper torso and arms during the squatting exercises than the INSTRUCTED group had. These results suggest that to do exercises by referring to only a picture may result in the participants not properly understanding how the body part(s) should be trained during exercise. Therefore, to enhance the benefits of training, individuals need to be instructed, under appropriate supervision, on correct technique as well as knowledge about the exercise.