In adults with obesity, 12 weeks of high-intensity interval training and moderate-intensity continuous training result in similar increases in skeletal muscle mitochondrial proteins involved in respiration and lipid metabolism, despite high-intensity interval training requiring half the exercise time and energy expenditure.

When muscles use up their stored sugar during exercise, it triggers a signal that tells the cell to build more energy-producing factories and improve its ability to burn fat. This signal also turns on proteins that move fat into the factories and manage fat storage, so the muscle can use fat for energy more efficiently. Both short, intense workouts and longer, moderate workouts do this equally well, even though one takes less time.