Oxidative capacity and fatigability in run-trained malignant hyperthermia-susceptible mice.

Introduction: The purpose of this study was to test the hypothesis that malignant hyperthermia model mice (RyR1Y522S/wt) are more vulnerable to exercise-induced muscle injury and fatigability and adapt less to run training.

Methods: After 6 weeks of voluntary wheel running, we measured anterior crural muscle fatigability, muscle injury, and cytochrome oxidase (COX) and citrate synthase (CS).

Results: Although RyR1Y522S/wt mice ran without undergoing MH episodes, they ran 42% less distance than wild-type (WT) mice. Muscles from WT mice exhibited increased fatigue resistance and COX content after training. Muscles from RyR1Y522S/wt mice demonstrated no significant change in fatigability or COX and CS after training. However, muscles from RyR1Y522S/wt mice displayed less intrinsic fatigability and greater COX/CS content and muscle damage than WT mice.

Conclusions: RyR1Y522S/wt mice can run without having rhabdomyolysis, and their inability to adapt to training appears to stem from intrinsic enhancement of mitochondrial enzymes and fatigue resistance.