If a marathon runner experiences extreme muscle fatigue toward the end of a race despite adequate hydration, why does muscle force production fail?

💡 Explanation

Muscle fatigue during intense exercise causes anaerobic metabolism to increase hydrogen ion concentration within muscle fibers, decreasing intracellular pH. This inhibits cross-bridge cycling and reduces force production because the acidic environment interferes with protein function. Therefore, reduced pH causes failure, rather than oxygen supply or calcium release directly.

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