Motor Function And Muscle Mass Are Reduced In Hindlimbs After Short Term Immobilization In Young Mice

Prolonged periods of skeletal muscle inactivity or mechanical unloading (e.g., bed rest, spaceflight, or immobilization) can result in a significant loss of musculoskeletal mass, size, and strength which ultimately leads to muscle atrophy. Despite the previous information, the effect of short-term immobilization on muscle contractility torque, muscle strength, and muscle wet weight at a young age has not been previously investigated. PURPOSE: To investigate the effect of 6 days of hindlimb immobilization (HLI) on muscle contractility torque, grip strength, and muscle wet weight in young mice. METHODS: Six C57BL/6 mice in the same group composed of 3 females and 3 males of 3 months of age were immobilized on their right hindlimb for 6 days with regular chow and water ad libitum. Baseline measures and 6 days later were performed: body mass (bm) in grams (g), muscle contractility in right gastrocnemius tetanic torque (mN-m), and grip strength (right hindlimb in grams). Endpoint, dissection of gastrocnemius and soleus for wet weight. Mean, Standard Deviation, R-squared (n2), and Unpaired t-tests were performed as statistical tests. RESULTS: There were no significant differences in body mass during the 6 days of HLI in 3-month-old C57BL/6 mice (n2 = 0.0002, p = 0.9602). Tetanic torque tracings during a 1-second train of stimuli at 90 Hz from a young 6 mice showing loss of torque after 6 days of right HLI [18.85 + 3.48 (mN-m) versus 11.48 + 1.66 (mN-m), n2 = 0.6861, p = 0.0009]. In vivo, absolute right hindlimb grip demonstrated significant reduction after 6 days of HLI [35.90 + 7.86 (g) versus 17.40 + 2.78 (g), n2 = 0.7469, p = 0.0003]. Normalized soleus wet weight to body mass was significantly reduced in right HLI versus left hindlimb [0.0030 + 0.0001 (g/bm) versus 0.0032 + 0.0001 (g/bm), n2 = 0.4523, p = 0.0166]. Similarly, absolute gastrocnemius wet weight was significantly reduced in right HLI [0.0133 + 0.0011 (g) versus 0.0154 + 0.0012 (g), n2 = 0.4637, p = 0.0148]. CONCLUSION: These preliminary results suggest that HLI in young mice (3-month-old C57BL/6 mice-18 years in humans approx.) may have a negative impact on muscle contractile function, right hindlimb strength, and gastrocnemius and soleus wet weight. Short periods of immobilization could be catastrophic for the maintenance of motor function and muscle mass at a younger age.