Mediating effect of muscle power on the relationship of physical activity with physical fitness and physical function in older women

Abstract

Objective: This study analyzed if the associations of physical activity with physical fitness and physical function in older women are mediated by muscle power.

Methods: Participants were 54 older women (age 73.5 ± 6.8 yrs). Moderate-to-vigorous intensity physical activity (min day^-1) was measured by accelerometry. Lower limb muscle power (W/kg) was estimated from a single two-leg countermovement jump performed on a force platform. Physical fitness (lower body strength, agility/dynamic balance, and aerobic endurance) was objectively assessed through the Senior Fitness Test Battery, respectively: 30s chair stand (repetitions), 8-ft up-and-go (s), and 6-min walk test (m). Physical function was subjectively evaluated via the 12-item Composite Physical Function Scale Questionnaire (score). Mediation effects were estimated using bootstrapped 95% confidence intervals and were deemed significant if 0 was not included in the intervals.

Results: Mediation analysis controlling to age revealed an indirect effect of moderate-to-vigorous intensity physical activity through muscle power on all physical fitness components, specifically lower body strength (B = 0.048, 95% BootCI [0.013, 0.114]), agility/dynamic balance (B = -0.009, 95% BootCI [-0.024, -0.002]) and aerobic endurance (B = 0.656, 95% BootCI [0.142, 1.597]) and on physical function global score (B = 0.040 95% BootCI [0.009, 0.094]).

Conclusions: These results suggest that physical activity of at least moderate intensity is relevant to daily functional competence, by promoting the maintenance or improvement of muscle power.

Keywords: Ageing; Mobility; Muscle power; Physical activity; Physical function.