Final answer:
During muscle fatigue, the force of muscle contraction decreases due to depleted ATP reserves and various biochemical imbalances.
Step-by-step explanation:
During muscle fatigue, the force of contraction decreases. Muscle fatigue is a state when a muscle can no longer sustain its level of contraction due to the depletion of ATP reserves or other factors such as lactic acid buildup, Na+ and K+ imbalances, and potential damage to the sarcoplasmic reticulum (SR) and sarcolemma.
It is notable that during sustained muscle use, the nervous system employs recruitment to prevent complete muscle fatigue by alternating which motor units within the muscle are active, thus allowing some to rest.