Exercise modality-dependent mitochondrial respiratory capacity in satellite cells and conditioned serum-induced responses in cultured myotubes.

Exercise-induced mitochondrial adaptations contribute to muscle function and metabolic health. We aimed to investigate the association of moderate-intensity swimming (MOD) and high-intensity interval training (HIIT) with mitochondrial function in skeletal muscle cells treated with exercise-conditioned serum. Male ICR mice (7-8 weeks old) were assigned to the Sedentary, MOD or HIIT group. The MOD group underwent five sessions of 60 min. The HIIT group performed weighted high-intensity swimming intervals. This study assessed mitochondrial enzyme activity in the plantaris muscle, mitochondrial respiratory capacity in isolated satellite cells, and mitochondrial function in C2C12 myotubes treated with exercise-derived serum. Serum was obtained immediately and 24 h postexercise to assess acute effects and chronic adaptations, respectively. The MOD and HIIT groups demonstrated significantly increased muscle citrate synthase and cytochrome c oxidase activities compared with the Sedentary group, but with no significant differences between the MOD and HIIT groups. Satellite cells exhibited higher basal respiration, ATP production and maximal respiratory capacity in the MOD group than in the Sedentary and HIIT groups. Acute serum notably improved maximal mitochondrial respiration in cultured C2C12 myotubes in the HIIT group, whereas serum from chronic training improved those parameters but demonstrated no modality-specific effects. MOD enhances mitochondrial respiratory function in satellite cells, probably owing to sustained aerobic metabolic signalling, whereas HIIT produces a potent but transient systemic response that acutely boosts mitochondrial function in muscle cells. The differential effects of exercise modalities emphasize the importance of timing and exercise modality in driving specific mitochondrial adaptations, thereby providing valuable insights for tailored exercise prescriptions for optimizing metabolic health.