In an endurance-trained athlete at maximal exercise, which factor primarily limits VO2max?

• A Maximal cardiac output (central factor), because oxygen extraction is already near maximal ✓
• B Pulmonary diffusion capacity, because they develop exercise-induced arterial hypoxemia
• C Skeletal muscle mitochondrial density, because oxidative enzyme capacity is the bottleneck
• D Ventilatory muscle fatigue, because they cannot sustain the required minute ventilation

Explanation

In trained endurance athletes, the primary limiting factor for VO2max is maximal cardiac output (central limitation). Their high cardiac output and near-maximal oxygen extraction (~85 percent) make peripheral extraction secondary. Although some elite athletes develop exercise-induced hypoxemia, the consensus central limiting factor remains cardiac output. The muscle mitochondrial option describes a peripheral limitation more relevant in untrained individuals.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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