Final answer:
Free radicals contribute to muscle fatigue by damaging contractile proteins and hindering the ability of muscles to contract effectively, which is prominent during prolonged physical activity.
Step-by-step explanation:
Free radicals can promote muscle fatigue in events lasting longer than 30 minutes by damaging contractile proteins and limiting the number of cross-bridges that can form between myosin and actin. Free radicals are reactive molecules that can alter cellular structures and lead to a decrease in muscle performance. During extended periods of physical exertion, free radicals are produced, which can attack various components of the muscle cell, including lipids, DNA, and proteins.
One of the proteins that can be affected by free radicals is troponin, a key protein that regulates the interaction between actin and myosin, which are necessary for muscle contraction. The interference with this interaction by free radicals can reduce the muscle's ability to contract, contributing to muscle fatigue. This is distinct from ATP production cessation, action potential blocking at neuromuscular junctions, or lactate accumulation, which may play roles in muscle fatigue under different circumstances.