If a marathon runner experiences a sudden inability to maintain pace despite adequate glycogen stores, which failure mode primarily explains this phenomenon, considering peripheral fatigue mechanisms?

💡 Explanation

Muscle fatigue during prolonged exertion often leads to reduced cross-bridge cycling because intracellular accumulation of inorganic phosphate and hydrogen ions inhibits myosin ATPase activity, impairing the power stroke; therefore, cycling rates diminish, rather than a central drive deficit being the primary issue.

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