Relationship between the amount of daily activities and muscular development in preschool and school children

本研究旨在探讨年龄和性别对学龄前儿童肌肉大小和功能及运动适能的影响，并阐明日常活动的数量和强度如何成为解释肌肉发育和运动适能的个体差异的因素。作为本研究的主要发现之一，在学龄前和学龄期，男孩和女孩在肌肉厚度、肌肉力量和随年龄变化方面没有显著差异，但男孩即使在学龄前也表现出比女孩更好的运动表现。回归分析表明，用于预测运动成绩的因素在男孩和女孩之间是不同的，这可能是导致运动成绩性别差异的原因之一。肌肉的大小与全身的自然生长更密切相关，而不是日常活动的数量和强度。另一方面，学龄前儿童的脂肪量与日常活动的平均强度呈负相关，这表明日常活动的强度将是学龄前儿童肥胖程度的决定因素。此外，运动能力与日常活动的强度有关，而与日常活动的数量无关，因此，经常参加超出正常步行水平的中到高强度的体育活动可能是促进学龄前儿童肌肉功能发展的一个因素。

The present study aimed to investigate the influences of age and sex on the muscle size and function and motor fitness in preschool and school children, and to clarify how the amount and intensity of daily activities become factors explaining the individual differences in muscular development and motor fitness. As one of the major findings of the present study, three were no significant differences between boys and girls in muscle thickness, muscle strength and their age-related changes in preschool and school ages, but boys showed better motor performances than girls even in preschool age. A regression analysis showed that factors selected for predicting motor performances differed between boys and girls, which might be assumed to be involved as a reason for the sex-related differences in motor performances. Muscle size was more closely related to the natural growth of the whole body rather than the amount and intensity of daily activities. On the other hand, fat mass for preschool children was negatively related to the mean intensity of daily activities, suggesting that the intensity of daily activities will be a determinant factor for the magnitude of fatness in preschool age. In addition, motor performances were related to the intensity but not to the amount of daily activities, and so frequent participation in physical activities with moderate to high intensity beyond the level of normal walking may be assumed to be a factor promoting development in muscle function in preschool and school children.