Bradycardia that develops in response to regular aerobic exercise is the result of which physiologic adaptation?

Bradycardia that develops in response to regular aerobic exercise is the result of which physiologic adaptation?

• A. Increased stroke volume
• B. Decreased respiratory rate
• C. Decreased stroke volume
• D. Increased heart rate

Answer: (A)

Endurance training makes the heart pump more efficiently, with a larger stroke volume driven by increased ventricular size, greater venous return, and improved contractility. Because cardiac output at rest stays roughly the same, a higher stroke volume allows the heart to beat fewer times per minute, producing the resting bradycardia seen in trained athletes. In other words, the heart’s efficiency improves enough that it doesn’t need to pump as often to meet the body’s needs. The relationship CO = HR × SV explains this: as SV increases, HR can decrease to maintain CO. The autonomic system also shifts toward more vagal (parasympathetic) influence, which supports a lower resting heart rate, but the primary functional change linked to bradycardia here is the increased stroke volume.

Endurance training makes the heart pump more efficiently, with a larger stroke volume driven by increased ventricular size, greater venous return, and improved contractility. Because cardiac output at rest stays roughly the same, a higher stroke volume allows the heart to beat fewer times per minute, producing the resting bradycardia seen in trained athletes. In other words, the heart’s efficiency improves enough that it doesn’t need to pump as often to meet the body’s needs. The relationship CO = HR × SV explains this: as SV increases, HR can decrease to maintain CO. The autonomic system also shifts toward more vagal (parasympathetic) influence, which supports a lower resting heart rate, but the primary functional change linked to bradycardia here is the increased stroke volume.