Maintenance of skeletal muscle function following reduced daily physical activity in healthy older adults: a pilot trial
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INTRODUCTION: Older adults can experience periods of inactivity related to disease or illness, which can hasten the development of physical disability, in part, through reductions in skeletal muscle strength and power. To date no study has characterized adaptations in skeletal muscle physical function in response to reduced daily physical activity. METHODS: Participants (15 men, 69±2 years, 15 women, 68±4 years) restricted their daily steps (<750steps/d, SR) while being energy restricted (ER, -500kcal/d) for 2wks before returning to normal activity levels during recovery (RC, 1wk). Before and after each phase, measures of knee extensor isometric maximum voluntary contraction (MVC), time-to-peak torque (TTPT), and physical function were performed and muscle biopsies were taken from a subset of participants. RESULTS: Following the energy restriction and step-reduction phase (ER+SR), MVC was reduced by 9.1 and 6.1 Nm in men and women respectively (p = 0.02), which returned to baseline after RC in men, but not women (p = 0.046). Tmax (maximum isometric tension) in MHC IIA fibres (p<0.01) and Pmax (maximum power production) in MHC I and IIA (p = 0.05) were increased by 14%, 25%, and 10% respectively following ER+SR. Reductions in muscle strength could not be explained by changes in single muscle fibre function in a sub-sample (n=9 men) of volunteers. DISCUSSION: These data highlight the resilience of physical function in healthy older men in the face of an acute period of ER+SR and demonstrate sex-based differences in the ability to recover muscle strength upon resumption of physical activity.
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