What happens to glucose stored as glycogen during exercise?

During exercise, glycogen, which is a stored form of glucose found mainly in the liver and muscles, is primarily utilized to provide energy. As the body begins to exert itself, it relies on glycogen stores to maintain adequate glucose levels in the bloodstream and supply energy to working muscles. The process involves breaking down glycogen into glucose through a series of biochemical reactions.

This conversion is crucial because during physical activity, the demand for energy increases, and glycogen serves as a readily accessible source. The glucose released from glycogen is then used to produce ATP (adenosine triphosphate), the energy currency of the cell, which fuels various bodily functions and assists in sustaining performance during exercise.

The other choices do not accurately reflect the biochemical processes involved. Glycogen does not become protein during exercise, nor is it lost as heat directly; instead, energy is released, some of which may be dissipated as heat. Moreover, while some substances may be expelled through urine, glycogen breakdown does not involve expulsion in this way; it is primarily converted to glucose for energy needs. Thus, the correct answer highlights the essential role of glycogen in energy metabolism during exercise.