Longitudinal characterization of functional, morphologic, and biochemical adaptations in mouse skeletal muscle with hindlimb suspension

ABSTRACT Introduction Hindlimb unloading‐induced muscle atrophy is often assessed after a homeostatic state is established, thus overlooking the early adaptations that are critical to developing this pattern of atrophy. Methods Muscle function and physiology were characterized at 0, 1, 3, 7, and 14 days of hindlimb suspension (HS). Results Reductions in muscle mass were maximal by Day 14 of HS. Functional strength and isolated muscle strength were reduced. MyHC‐I and ‐IIa expressing fibers were reduced in size by Day 7 in the soleus and by Day 14 in the gastrocnemius (MyHC‐I fibers only). Atrogin‐1 and MuRF1 expression was increased by Day 1 in both the calf and tibialis anterior while IGF‐1 expression was significantly reduced on Day 3. Phosphorylation of Akt was reduced on Day 14. Conclusions Insight into these early changes in response to HS improves understanding of the molecular and functional changes that lead to muscle atrophy. Muscle Nerve 48 : 393–402, 2013