What is a primary role of nitric oxide (NO) in exercise physiology?

What is a primary role of nitric oxide (NO) in exercise physiology?

• A. Mediates vasodilation to increase blood flow to active muscles
• B. Directly increases hematocrit
• C. Inhibits mitochondrial biogenesis
• D. Decreases blood pressure

Answer: (A)

Nitric oxide's primary role in exercise physiology is to rapidly increase blood flow to working muscles by promoting vasodilation. When muscles are active, shear stress on the endothelium and metabolic cues stimulate nitric oxide synthase to produce NO. The NO then diffuses into smooth muscle cells and activates guanylate cyclase, raising cGMP levels, which lowers intracellular calcium and relaxes the muscle around the blood vessels. This relaxation widens the vessels, reducing vascular resistance and delivering more oxygen and nutrients to the exercising muscles to meet their higher metabolic demands. While NO can influence blood pressure systemically, the most important effect in activity is the enhanced, localized blood flow to active tissue. The other options don’t describe NO’s main action: it doesn’t directly increase hematocrit, it doesn’t inhibit mitochondrial biogenesis, and although it can help lower blood pressure, that’s not its primary demonstrated role during exercise.