A person riding in a 100-mile bicycle race relies on which energy system to fuel her long ride?

A 100-mile ride lasts a long time, so the rider needs a sustained supply of energy. Aerobic respiration uses oxygen to break down fuels and make ATP over extended periods, making it the main energy system for endurance exercise. Anaerobic respiration and ATP already stored in muscle cells can support brief, intense efforts but cannot fuel the whole ride.

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