Early Life Muscle Disuse Causes Premature Dynapenia In Adulthood

Abstract

Muscle power is critical for older people to independently and safely perform the activities of daily living. Physical activity in general and resistance training, in particular, are essential for the prevention of muscle power loss with ageing. PURPOSE: To analyze the associations between moderate-vigorous intensity physical activity (MVPA) and functional fitness in older women, including the role of muscle power in mediating these associations. METHODS: Participants were 54 older women with a mean age 73.5±6.8yrs. MVPA (min day−) was measured by accelerometry. Lower limb peak muscle power (W/kg) was assessed using a mechanography ground reaction force platform. Functional fitness (lower body strength, agility/dynamic balance, and aerobic endurance) was objectively assessed through physical fitness tests from the Senior Fitness Battery, respectively: 30s chair stand (repetitions), 8-foot up-and-go (s), and 6-minute walk test (m). Functional fitness was also subjectively evaluated via the 12item Composite Physical Function Scale Questionnaire which gives a global score of physical function (points). Direct and indirect mediation model effects were estimated using the PROCESS macro developed by Preacher and Hayes, and 95% bootstrap confidence intervals were constructed to test the hypothesis that muscle power mediated associations. Age was examined as a covariate. RESULTS: A significant portion (40-78%) of the total effect of MVPA on functional fitness in older women was explained by muscle power. The indirect effects were observed on physical function global score (β=0.040 95% CI [0.010, 0.099]) and in each of the functional fitness parameters: lower body strength (β=0.048, 95% CI [0.013, 0.117]), agility/dynamic (β=-0.009, 95% CI [-0.024, 0.002]) and aerobic endurance (β=0.656, 95% CI [0.146, 1.694]). There were no direct effects of MVPA on functional fitness. CONCLUSION: To improve functional fitness in older women, physical activity interventions should consider the mediating role of muscle power and include activities that require force to be rapidly generated.