High-intensity aerobic, but not resistance or combined, exercise training improves both cardiometabolic health and skeletal muscle mitochondrial dynamics

We assessed the effects of 12 wk of supervised high-intensity interval training (HIIT), resistance training, and combined training (CT) on skeletal muscle mitochondrial abundance and markers of fission and fusion. HIIT increased mitochondrial area and size and promoted protein changes indicative of increased mitochondrial fusion, whereas lessor effects were observed after CT and no changes were observed after RT. Furthermore, increased mitochondrial area and size after HIIT associated with improved mitochondrial respiration, cardiorespiratory fitness, and insulin sensitivity.