6. -Trained marathon runners have heart chambers that are enlarged by about 40%

Question

6. -Trained marathon runners have heart chambers that are enlarged by about 40% over those ofnormal individuals. However, at rest, their mean arterial pressure is not elevated over that of a normal person. The most likely reason for this is that at rest, their A. total peripheral resistance is elevated, leading to a decreased blood flow. B. cardiac output is elevated, leading to a normal total peripheral resistance. C. heart rate is depressed, leading to a normal cardiac output. D. stroke volume is increased, leading to an increased cardiac output.

Explanation / Answer

D. Option D is the correct answer

1. Cardiac output is dependent on two factors STROKE VOLUME and HEART RATE.

2. Sportsmen exhibit physiological HYPERTROPHY of heart which according to Frank starling law cause greater force of contraction and hence greater stroke volume. This leads to increased cardiac output.

3.This increased cardiac output at rest leads to baroreceptor stimulation as a result of which total peripheral resistance is decreased and HEART BEAT is decreased. Thus parasympathetic predominance prevails.

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