Background: Physical inactivity has many detrimental effects on health, yet the impact of physical inactivity in early life on muscle health in adulthood remains unknown. Early postnatal malnutrition has prolonged effects into adulthood and we propose that early postnatal physical inactivity would have similar effects. Methods: To test this hypothesis we exposed postnatal mice (~P28, C57BL/6J) to 14 days of physical inactivity (shortly after weaning, from ~28 to 42 days of age) in the form of muscle disuse with hindlimb unloading (HU). After this early-life physical inactivity, they were allowed to normally ambulate until 5 months of age (adulthood). They were then tested for physical function (grip strength) and muscle size of the hindlimb plantar flexors and muscles were removed. Immunofluorescence was carried out on soleus, plantaris and gastrocnemius cross-sections for analysis of myofiber cross-sectional area (fCSA). Muscle weights and fCSA and myofiber diameter were used to quantify changes in muscle and fiber size. Results: Compared to age-matched controls, no notable effects of early life physical inactivity (HU) on skeletal muscle size (indicated by muscle weight) or myofiber cross sectional area were observed. However, a significant reduction in adult grip strength was observed in those exposed to HU early in life. Conclusions: Although no significant changes in muscle composition (whole muscle or myofiber size were evident, a distinct decrease in muscular function was observed. Since grip strength is a strong predictor of health status, muscular functionality, and early mortality, these findings of premature dynopenia (muscle weakness) as a result of early life muscle disuse are concerning.
Authors: Jevnikar BE, Smith AD, Doctor A, Williams, R, Kachulkin A, Monnig J, Perlman E, Schmidt R
Advisor: Paul Reidy, Kinesiology
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