In aerobic exercise, muscles draw on oxygen in the blood as well as fats and glucose. These are used to produce adenosine triphosphate, the basic fuel for all cells. In order for an exercise to be aerobic, it must be maintained for enough time to burn off the cell's stored fuel, left there for periods of brief but intense activity characterized by the fight or flight response. Aerobic exercises are those like running, cycling and long distance swimming, as well as a number of more "modern" (although "trendy" is more accurate) exercises performed at gyms.

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