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 Hypothesis: When placed under physical inactivity conditions, significant differences will be seen in macrophage inflammation and noncontractile tissue concentration when compared to regular physical activity Methods: Testing 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. Immunofluorescence was carried out on soleus, plantaris and gastrocnemius cross-sections for analysis of myofiber cross-sectional area (fCSA), macrophage density (CD68 cells) and extracellular matrix area. Muscle weights and fCSA and myofiber diameter were used to quantify changes in muscle and fiber size. Results: Compared to age-matched controls, a reduction in adult grip strength was observed in those exposed to HU early life. There is a difference in each of our experimental groups, with statistical significance between the amount of macrophage inflammation when compared to our control group. When all the data is pooled there is statistical significance between the physical inactivity groups and control groups in the soleus muscle. All samples in the Physical Inactivity group indicated a significant difference in B-CHP area percentage. Gastrocnemius indicated the biggest difference when comparing the Physical inactivity group to the control group. Conclusion: The increase in ECM area fraction within muscles in the physical inactivity group indicated a greater concentration of noncontractile tissue, resulting in a decrease of functionality of the muscles. The increase in Macrophage inflammation was prevalent within groups exposed to different forms of loading on their hindlimbs when compared to our control groups which leads us to be unable to refute our hypothesis.
Authors: Ryan Williams, Kinesiology and Premedical Studies Major
Anthony Kachulkin, Kinesiology Major
Advisors: Paul Reidy, Kinesiology, Nutrition and Health
Austin Smith, Kinesiology, Nutrition & Health
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