Objectives This study aims to investigate the association between skeletal muscle mass index (SMI) and physical activity among female university students who had exercise habituation in junior and high school. Methods The body composition of 120 Japanese female students was measured using the bioelectrical impedance analysis (BIA) method, and their physical activity level (PAL) was measured using a factorial method. Based on the ‘Dietary Reference Intakes for Japanese’ (DRIs-J), according to the Ministry of Health, Labour and Welfare, PAL (24-h energy consumption/basal metabolic rate) classifications were defined as low-PAL (PAL < 1.6), moderate-PAL (1.6 ≤ PAL < 1.9), and high-PAL (1.9 ≤ PAL < 2.2), respectively. Results Individuals with low-PAL had a significantly lower SMI, especially for the lower limb muscles, than individuals with moderate-PAL or higher. More than 50% of the individuals with currently low-PAL corresponded or tended to correspond to the SMI cut-off value defined by the Asian Working Group for Sarcopenia or the 2017 National Health and Nutrition Survey of Japan. Therefore, more than half of the female students with currently low-PAL, even those with an exercise habituation in the past, corresponded to the cut-off value for muscle loss in sarcopenia diagnosis, particularly in the lower limbs. Conclusions These results suggest that it is important to maintain a moderate or higher level of physical activity in the DRIs-J classification, even for young women who used to exercise in the past, to maintain muscle mass accordingly.

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This study investigated the relationship between normal weight obesity (NW-O) and skeletal muscle mass index (SMI) in 120 female university students who participated in sporting activities during junior and senior high school. The current physical activity level (PAL) was estimated by a factorial method using 24-h physical activity recall. The body mass index (BMI) of the participants ranged from 18.5 to 24.9 kg/m2; their body fat (BF) was classified as NW-O if above the 75th percentile (28.9% BF), normal weight and lean (NW-L) if below the 25th percentile value (21.0%BF), and all others were normal weight (NW). PAL was significantly lower in NW-O than in NW-L. SMI was significantly lower in NW-O than in NW and NW-L, and 60% of NW-O had Low-SMI (<6.3 kg/m2). Although lower limb muscle mass was significantly lower in NW-O than in NW and NW-L, no significant differences were found in the upper limbs. These results suggest that the current PAL is associated with NW-O, and NW-O is associated with a lower SMI, even in young females with past exercise habits. Therefore, the prevention of NW-O in young females is important for the prevention of not only lifestyle-related diseases, but also future sarcopenia.

This study investigated the association between nutritional intake and indices of muscle mass or strength in 104 female Japanese university students who participated in sports activities during their junior and senior high school periods and had a high current physical activity level (PAL). Body composition was measured by the bioelectrical impedance method, and appendicular muscle mass (AMM) and skeletal muscle mass index (SMI) were evaluated as muscle mass. PAL was estimated using a factorial method and nutritional intake status was investigated using a food frequency questionnaire based on food groups (FFQg). Grip strength was measured as an index of muscle strength. According to the criteria for diagnosis of sarcopenia, four of the participants had low muscle mass and one also had low grip strength. Although there were no significant differences in body size or grip strength between participants with a high versus low SMI, participants with a low SMI had a significantly higher percentage of body fat (27.7 ± 4.7% vs. 23.3 ± 4.1%), and significantly lower AMM (16.0 ± 1.4 kg vs. 20.6 ± 1.5 kg), total energy intake (1770.4 ± 386.5 kcal/d vs. 2017.1 ± 389.9 kcal/d), and protein intake (57.3 ± 15.0 g/d vs. 67.0 ± 14.2 g/d), as well as a tendency to have a significantly lower carbohydrate intake (239.6 ± 49.3 g/d vs. 268.1 ± 54.4 g/d), than those with a high SMI. These results indicate that even some female university students with a high PAL have a lower muscle mass and might have a low dietary intake, mainly protein and carbohydrate. The results of multiple regression analysis of AMM, SMI, or grip strength with PAL and nutrient intake revealed that PAL and total energy intake or protein intake were significantly and positively associated with muscle mass and strength. These results suggest that a high PAL as well as total energy intake and protein intake among the macronutrients contribute to high muscle mass and muscle strength in young women.

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