Which type of energy system does glycogen primarily fuel during high-intensity exercise?

Glycogen primarily fuels both the aerobic and lactic systems during high-intensity exercise due to its role as a readily available source of glucose. When engaging in strenuous activities, the body looks to glycogen stored in the muscles and liver for energy.

In the absence of sufficient oxygen, especially during short bursts of very high-intensity exercise, the body relies on the lactic system, which converts glycogen to glucose anaerobically, producing lactic acid as a byproduct. This pathway can generate energy quickly but is limited in duration due to lactate accumulation.

Conversely, during slightly less intense exercise or as intensity moderates, the aerobic system begins to engage, utilizing glycogen in the presence of oxygen to produce energy more sustainably over a longer duration. Glycogen continues to be a key energy source under aerobic conditions, allowing for sustained exercise performance.

This dual capability illustrates why glycogen is integral to both the lactic and aerobic systems during high-intensity exertion, making the correct response encompass both energy pathways.