During muscle fatigue, the body primarily relies on which energy source?

During muscle fatigue, the body primarily relies on glucose for energy production. This is because glucose can be rapidly metabolized through processes such as glycolysis to produce ATP (adenosine triphosphate), which is the immediate energy currency used by muscle cells. As muscle activity increases and fatigue sets in, the demand for ATP rises sharply; thus, glucose metabolism becomes a key pathway for sustaining energy levels in the muscles.

In contrast to glucose, fatty acids and amino acids are not utilized as quickly during short bursts of intense exercise, which is when muscle fatigue typically occurs. Fatty acids require a longer time to break down and cannot provide immediate energy in the same way as glucose. Amino acids can be used for energy but more commonly serve as building blocks for proteins and take longer to metabolize for energy compared to glucose.

Creatine phosphate can help regenerate ATP rapidly for a short duration, but it is more of a temporary energy reservoir rather than a primary energy source during prolonged muscle fatigue. Once creatine phosphate stores are depleted, the body turns to glucose stored as glycogen to continue producing ATP.

Therefore, glucose is the primary energy source during muscle fatigue because it can be quickly mobilized to meet the high energy demands of active muscle tissue.