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

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)

Oxygen debt reflects the extra oxygen the body needs after exercise to restore resting conditions—rebuilding ATP and phosphocreatine stores, reloading myoglobin with oxygen, and clearing lactate. After activity ends, the body keeps consuming more O2 to pay back that debt. The lactate shuttle describes how lactate produced in one tissue is transported to other tissues via monocarboxylate transporters, where it can be converted back to pyruvate and then oxidized for energy (or used for gluconeogenesis in the liver). So the best statement links excess post-exercise oxygen consumption to oxygen debt and defines the lactate shuttle as moving lactate between tissues and reconverting it to pyruvate for oxidation.

Oxygen debt reflects the extra oxygen the body needs after exercise to restore resting conditions—rebuilding ATP and phosphocreatine stores, reloading myoglobin with oxygen, and clearing lactate. After activity ends, the body keeps consuming more O2 to pay back that debt. The lactate shuttle describes how lactate produced in one tissue is transported to other tissues via monocarboxylate transporters, where it can be converted back to pyruvate and then oxidized for energy (or used for gluconeogenesis in the liver). So the best statement links excess post-exercise oxygen consumption to oxygen debt and defines the lactate shuttle as moving lactate between tissues and reconverting it to pyruvate for oxidation.