Muscle strength matters most for risk of falling apart from body mass index in older adults: a mediated-moderation analysis

The primary objective of this study was to analyze the moderating effect of body mass index (BMI) on the association between lower body strength, agility, and dynamic balance, considering the mediating influence of lower body flexibility and aerobic endurance in community-dwelling older adults. This study included a sample of 607 community-dwelling older adults (female = 443; male = 164) aged between 60 and 79 years (M = 69.24; SD = 5.12). Participants had a mean body mass index of 28.33kg/m2 (SD = 4.45). In the mediation-moderation model, positive associations were found between lower body strength and lower body flexibility, aerobic endurance, and agility and dynamic balance (p < 0.05). As for the moderation effects and interactions, BMI was found to have a significant interaction with lower body strength on agility and dynamic balance (β = −.04, [−.06, −.03]), representing an R2-change of 0.04 (p <.001). Conditional direct effects were estimated at BMI scores of 23.9 (β = −.09, [−.15, −.03]), 27.7 (β = −.19, [−.24, −.14]), and 32.7 (β = −.33, [−.40, −.26]) kg/m2. Older adults with high levels of muscular strength tended to have shorter timed up-and-go test times, regardless of BMI. Also, individuals with lower levels of lower body strength were found to have longer timed up-and-go test times, and this relationship became more pronounced with increasing BMI.