A trained athlete at rest has a lower heart rate but normal cardiac output. What must happen?

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Multiple Choice

A trained athlete at rest has a lower heart rate but normal cardiac output. What must happen?

The key idea is that cardiac output equals heart rate times stroke volume. If a trained athlete at rest has a lower heart rate but still a normal cardiac output, the stroke volume must increase to keep the product the same. In other words, the heart pumps more blood with each beat to compensate for the slower beating rate. In athletes, a larger stroke volume at rest often comes from a more compliant, more voluminous ventricle and enhanced filling (preload), which strengthens each contraction via the Frank-Starling mechanism. This higher stroke volume allows the heart to maintain normal total output even though the heart rate is lower. The other options aren’t required by the scenario: heart rate doesn’t have to rise; venous return and preload can contribute to higher stroke volume, but they aren’t strictly necessary to explain why stroke volume must increase to keep CO normal.

The key idea is that cardiac output equals heart rate times stroke volume. If a trained athlete at rest has a lower heart rate but still a normal cardiac output, the stroke volume must increase to keep the product the same. In other words, the heart pumps more blood with each beat to compensate for the slower beating rate.

In athletes, a larger stroke volume at rest often comes from a more compliant, more voluminous ventricle and enhanced filling (preload), which strengthens each contraction via the Frank-Starling mechanism. This higher stroke volume allows the heart to maintain normal total output even though the heart rate is lower.

The other options aren’t required by the scenario: heart rate doesn’t have to rise; venous return and preload can contribute to higher stroke volume, but they aren’t strictly necessary to explain why stroke volume must increase to keep CO normal.

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