Impaired Recovery From Muscle Disuse In Early Life Compared To Young And Mature Adulthood

Abstract

Physical inactivity negatively influences health and wellness, which has been a particular concern with aging. Less is understood regarding the impact of muscle disuse during early stages of postnatal skeletal muscle development. PURPOSE: We propose that exposure to muscle disuse early in life will adversely impact muscle recovery compared to adulthood. METHODS: Postnatal day 30 (Young), mature 5 month (Adult) and aged ~25 month (Old) mice were studied as freely moving (Control) or experienced muscle disuse in the form of hindlimb unloading (HU) for two weeks followed by a 7 day recovery period where they were allowed to freely ambulate or “reload” (RL7). We assessed tissue composition, hindlimb and forelimb muscle size and myofiber diameter and cross-sectional area (CSA). RESULTS: Muscle weight was not recovered in the Young and Old for soleus (absolute, normalized) or plantaris (absolute) (P<0.05). In the soleus, the difference between Control and RL7 was 1.19±0.38, 0.21±0.32, 0.81±0.32 mg for Young, Adult and Old, respectively. There was a trend for the Young to have impaired recovery vs adult (p=0.056). In the plantaris, the difference between Control and RL7 was 1.84±0.77, 0.37±0.65, 1.45±0.64 mg for Young, Adult and Old, respectively. The soleus myofiber CSAs were not recovered in any group and the MHC I myofiber were particularly affected in the Young. The plantaris myofiber CSAs were not recovered in the Young due to an impaired recovery in the MHC IIx+b myofibers. CONCLUSIONS: Postnatal mice are particularly susceptible to muscle disuse as shown by impaired muscle recovery compared to young adult and old adult mice. Supported by NIA R01AG AG050781