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Aerobic training adaptation — MRCP Part 1 MCQ

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HardExercise PhysiologyAerobic training adaptationMRCP Part 1

During constant-load cycling at a work rate just above an athlete’s critical power, pulmonary oxygen uptake continues to rise and reaches VO2max shortly before exhaustion. Which mechanism best explains the finite exercise tolerance?

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Correct answer: C — Progressive W-prime depletion with declining muscular efficiency

The best answer is “Progressive W-prime depletion with declining muscular efficiency”. Above critical power, a sustainable metabolic steady state cannot be established. The finite work capacity represented by W-prime is progressively expended, metabolites accumulate and recruitment of less efficient fibres contributes to the VO2 slow component until VO2max and task failure are reached. Glycogen depletion is not complete within minutes, oxidative phosphorylation continues, cardiac output does not abruptly plateau at the first threshold, and phosphocreatine falls dynamically rather than disappearing irreversibly at onset.

Reference: Critical power: an important fatigue threshold: https://pmc.ncbi.nlm.nih.gov/articles/PMC5070974/