Canadian researchers caused a stir when they discovered that short bouts of 30-second high-intensity exercise produced changes similar to prolonged endurance training programs. People achieved fitness improvements in as little as 15 minutes during a two-week period.
New studies found that while interval training increased running performance and maximal oxygen consumption, it did not increase cardiac output (blood pumped by the heart per minute). Interval training appears to stress the metabolic capacity of muscle cells, while higher volume endurance training has more central effects. Both types of training appear necessary for optimal endurance fitness. (Medicine Science Sports Exercise, 43: 115-122, 2011)