If a marathon runner experiences muscle fatigue primarily in their quadriceps toward the end of a race despite adequate hydration, which process is most likely responsible?

💡 Explanation

Muscle fatigue often stems from an accumulation of inorganic phosphate, because ATP hydrolysis increases during intense exercise. This buildup interferes with the power stroke of myosin cross-bridges, therefore reducing muscle force production, rather than glycogen preventing contraction or myoglobin enhancing oxygen supply.

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