Physical Activity Related to Body Muscle Mass Index and Stiffness Index in 7-to-10-Year-Old Girls.

The relationship between moderate-to-vigorous physical activity (MVPA) performance time and body muscle mass and stiffness index in pre-puberty school-aged girls has not been fully elucidated. The effect of sexual maturity on bone mass is more pronounced in girls. This study aimed to clarify the relationship between MVPA performance time and the above-mentioned factors. This was a prospective, population-based cohort study of 111 girls aged 7-10 years. Data were collected via medical examination, clinical measurements, and questionnaires. Spearman's ρ analysis was used to determine the association between skeletal muscle mass index (SMI) and stiffness index, muscle strength, and MVPA performance time. Participants who met the recommended MVPA level accounted for only 24.3% ( n = 27) of all participating girls ( n = 111). The following factors were significantly positively correlated with MVPA level at spearman's ρ analysis: SMI ( r = 0.303, p = 0.001), stiffness index ( r = 0.229, p = 0.015), grip strength ( r = 0.283, p = 0.003), back muscle strength ( r = 0.197, p = 0.038), and standing long jump distance ( r = 0.288, p = 0.002). Multiple regression analysis's results revealed that SMI ( β = 0.237; p = 0.024) was associated with MVPA performance time. These results can help school-aged girls to pay adequate attention to having healthy physical activity habits to prevent the decline of skeletal muscle mass, stiffness index, and body muscle strength.