Aerobic high-intensity interval training increased mitochondrial capacity in younger people by 49% and 69% in older people after 3 weeks.

It also improved insulin sensitivity and increased mitochondrial proteins and ribosomes (which make new proteins) in muscle cells. The volunteers engaged in aerobic high-intensity interval training (cycling at >90% of peak oxygen consumption) for 3 days and 2 days per week of treadmill walking (45 min at 70% of VO2 peak) or strength training. Those individuals that did strength training increased muscle strength and improved insulin sensitivity. Good reason to mix up the exercise routine with aerobic high-intensity interval training and strength training.