Fig 5. Hypothetical schema of skeletal muscle adaptation in hibernating bear.

Protein anabolism in skeletal muscle of hibernating bears is potentially activated by mTORC1 activation and down regulation of myostatin expression for counteracting to the corresponding enhancement of protein degradation, which can then lead to a net balance of protein metabolism and prevention of excessive muscle loss. Muscle phenotypes shifting toward slow-oxidative fiber and mitochondrial biogenesis are also induced and likely contribute to the more efficient utilization of energy resources for muscle contraction during winter survival.