After completing a 60-second all-out cycling sprint, a subject continues breathing room air while seated at rest. His oxygen consumption remains elevated above resting levels for several minutes before returning to baseline. The rapid early component of this excess post-exercise oxygen consumption is chiefly explained by:
- A Resynthesis of depleted phosphocreatine and ATP stores in muscle ✓
- B Removal of accumulated blood lactate by gluconeogenesis in the liver
- C Persistently elevated circulating catecholamines maintaining thermogenesis
- D Replenishment of myoglobin-bound oxygen in muscle fibres
Correct answer: A. Resynthesis of depleted phosphocreatine and ATP stores in muscle
Explanation
The classic oxygen debt has two phases. The fast alactic component, roughly the first 2 to 3 minutes, represents oxidative resynthesis of ATP and phosphocreatine consumed during the sprint. The slow component covers lactate clearance via gluconeogenesis and oxidation, plus the cost of elevated cardiorespiratory function and temperature. Myoglobin recharging requires trivial oxygen and cannot account for litres of extra consumption, so option D is the tempting but quantitatively inadequate distractor.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
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