What energy source MUST account for most of the energy produced in the muscle cell during the performance of immediate, heavy, and intense resistance?

Muscle glycogen is the primary energy source for immediate and intense physical activities, such as heavy resistance training, due to its rapid availability and the efficiency with which it can be metabolized. When muscles are engaged in high-intensity exercise, they require a quick source of energy to sustain performance. Muscle glycogen, which is stored within the muscle cells themselves, can be broken down swiftly through anaerobic glycolysis to provide ATP—the energy currency needed for muscle contractions.

This is particularly crucial during short bursts of activity where oxygen delivery to muscles may not meet the demand, making anaerobic processes essential. The breakdown of muscle glycogen produces lactate along with ATP. Its availability directly influences muscle performance during heavy and immediate exertions, allowing athletes to maintain strength and power output.

In contrast, other energy sources like liver glycogen or fatty acids are not as readily accessible for immediate energy needs during high-intensity exercise. Liver glycogen must be converted to glucose and transported to muscles, which takes more time. Fatty acids primarily serve as a fuel for longer-duration, moderate-intensity activities since their oxidation requires oxygen. Chylomicrons, which transport dietary lipids, are also not a direct source of energy during intense physical exertion.

Therefore, muscle