Final answer:
After intense physical activity, elevated oxygen intake helps the body to repay the oxygen debt incurred during exercise by producing ATP to restore energy levels and convert by-products of anaerobic metabolism back into their resting state.
Step-by-step explanation:
The amount of oxygen intake required after strenuous activity is indeed for the production of ATP necessary to restore normal, pre-exertion conditions in the body. This is because intense muscle activity incurs an oxygen debt, which signals the need for additional oxygen post-exercise to recompense for the anaerobic production of ATP during periods of muscle contraction. Oxygen is crucial for the replenishment of ATP and creatine phosphate, the conversion of lactic acid into pyruvic acid and eventually glucose or glycogen in the liver, and other metabolic recovery processes. Post-exercise, the body's oxygen intake remains escalated until this oxygen debt is settled, leading to the increased breathing rate that is commonly observed after intense physical exertion.