Key result
Contrary to expectations, mice selectively bred for high voluntary wheel running were not more resistant to muscle injury caused by either contusion or wheel running compared to control mice.
Why the study?
It was hypothesized that populations selected for high locomotor activity may possess evolutionary adaptations that resist exercise-induced muscle injury and/or enhance recovery.
Mice selectively bred for high voluntary exercise do not possess evolutionary adaptations that confer resistance to or enhanced recovery from muscle injury.
High-runner mice lack expected muscle injury resistance; leaves open whether activity selection confers protection in translational models.
Muscle injury can be caused by strenuous exercise, repetitive tasks or external forces. Populations that have experienced selection for high locomotor activity may have evolutionary adaptations that resist exercise-induced injury and/or enhance the ability to cope with injury. We tested this hypothesis with an experiment in which mice are bred for high voluntary wheel running. Mice from four high runner lines run ~three times more daily distance than those from four non-selected control lines. To test recovery from injury by external forces, mice experienced contusion via weight drop on the calf. After injury, running distance and speed were reduced in high runner but not control lines, suggesting that the ability of control mice to run exceeds their motivation. To test effects of injury from exercise, mice were housed with/without wheels for six days, then trunk blood was collected and muscles evaluated for injury and regeneration. Both high runner and control mice with wheels had increased histological indicators of injury in the soleus, and increased indicators of regeneration in the plantaris. High runner mice had relatively more central nuclei (regeneration indicator) than control in the soleus, regardless of wheel access. The subset of high runner mice with the mini-muscle phenotype (characterized by greatly reduced muscle mass and type IIb fibers) had lower plasma creatine kinase (indicator of muscle injury), more markers of injury in the deep gastrocnemius, and more markers of regeneration in the deep and superficial gastrocnemius than normal-muscled individuals. Contrary to our expectations, high runner mice were not more resistant to either type of injury.
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Kay et al. (2022) studied Muscle injury (n=158). Selective breeding for high voluntary wheel running vs. Non-selected control lines was evaluated on Resistance to muscle injury (measured by wheel running after contusion, and histological indicators/creatine kinase after wheel running). Contrary to expectations, mice selectively bred for high voluntary wheel running were not more resistant to muscle injury caused by either contusion or wheel running compared to control mice.
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