All training-induced increases in maximum cardiac output must come from a(n) ______.

• A. Increase in stroke volume
• B. Increase in heart rate
• C. Increase in blood pressure
• D. Increase in blood volume

Answer: (A)

Maximum cardiac output during intense exercise is determined by heart rate times stroke volume. In trained individuals, heart rate at maximal effort changes little, while the heart’s ability to pump blood per beat increases. Endurance training leads to a larger left ventricular chamber, improved filling (preload) partly from expanded plasma volume, and stronger contractility with a more favorable afterload. These adaptations raise stroke volume, so the rise in maximal cardiac output after training is driven mainly by an increase in stroke volume. Blood pressure or blood volume contribute to this process, but the primary limiter and the main driver of the boost in max cardiac output is the increase in stroke volume.