Answer:
Explanation:
Interval training works both the aerobic and the anaerobic system. During the high-intensity efforts, the anaerobic system uses the energy stored in the muscles (glycogen) for short bursts of activity. Anaerobic metabolism works without oxygen, but the by-product is lactic acid. As lactic acid builds, the athlete enters oxygen debt, and it is during the recovery phase that the heart and lungs work together to "pay back" this oxygen debt and break down the lactic acid. It is in this phase that the aerobic system is using oxygen to convert stored carbohydrates into energy.
It's thought that by performing high-intensity intervals that produce lactic acid during practice, the body adapts and burns lactic acid more efficiently during exercise. This means athletes can exercise at a higher intensity for a longer period of time before fatigue or pain slows them down.
