Which statement correctly defines oxygen debt and describes the lactate shuttle?

• A. Oxygen debt is the extra oxygen required after exercise to restore ATP and clear lactate; the lactate shuttle transports lactate to the bloodstream for excretion.
• B. Oxygen debt is the immediate oxygen deficit at the start of exercise; the lactate shuttle channels pyruvate away from glycolysis.
• C. Oxygen debt refers to the total oxygen consumed during exercise; lactate shuttle is unrelated to energy metabolism.
• D. Oxygen debt refers to excess post-exercise oxygen consumption; the lactate shuttle transfers lactate between tissues and reconverts it to pyruvate for oxidation.

Answer: (D)