Heat stress treatment is a classic physical therapy, which is employed in the orthopedic field. In the field of physical fitness/sports science, morphological changes of skeletal muscle by heat stress have been well studied. In recent years, energy metabolic adaptations by heat stress have also been actively studied. In this review, we provide an overview of recent findings on heat stress-induced mitochondrial adaptations in skeletal muscles, and further discuss our unpublished data and recent findings in related research fields. First, we summarized heat stress-induced positive regulation of mitochondrial content and its underlying molecular mechanisms from perspectives of mitochondrial biogenesis and degradation. Consequently, we reviewed beneficial effects of heat stress on mitochondrial health in disused and aged muscles, focusing on mitochondrial stress response at the organelle level (mitochondrial selective autophagy; mitophagy) and molecular level (mitochondrial unfolded protein response). Finally, we overviewed future directions to better understand heat stress-induced mitochondrial adaptations in skeletal muscle.
