Cardinal Health and Fitness
The stroke volume response to exercise is vital, since cardiac output increase descends on an increase in stroke volume and heart rate. The physiological adaptations of the heart due
to training and its capacity to increase the stroke volume in response to training are discussed below:
a) The stroke volume of trained endurance athletes are
considerably larger both at rest and during exercise
than the untrained individuals.
b) The greatest increase in stroke volume occurs during
transition from rest to moderate exercise. As the
intensity of exercise increases the increase in stroke
volume are negligible. This response is similar for both
the trained and untrained individuals.
c) A maximal stroke volume is attained at the heart rate
of about 110 to 120 beats per minute. Further increase
in exercise intensity and in heart rate does not affect
the stroke volume, and
d) For untrained individuals the cardiac output is
increased by an increase in heart rate during the
transition from rest to exercise, with only a small
increase in stroke volume. However, for trained athletes
increase in cardiac output is initiated by the
augmentation of both heart rate and stroke volume.
At rest and in the supine position the stroke volume of an untrained individual ranges between 70 to 120 ml per beat depending upon the body size. In trained endurance athletes the stroke volume ranges between 120 to 200 ml per beat. Trained endurance athletes generally have low resting heart rate and a relatively large stroke volume, which indicates an efficient circulatory system. Because of the smaller size of the heart in women compared to men, their maximal stroke volume is usually 25 percent lower to that of men.
Changes in Heart Size (Cardiac Hypertrophy)
Acute (temporary) and chronic (permanent) adaptations take place in the muscles of the heart due to endurance training.
Due to training the size (volume) of the heart increases (Hypertrophy).
The cardiac hypertrophy of endurance athletes is characterized by a normal thickness in the ventricular wall and a large ventricular cavity. Hence a greater volume of blood can be accommodated in the ventricular cavity. A normal size ventricular cavity and a thicker ventricular wall characterize the cardiac hypertrophy of wrestlers and throwers. Hence their stroke volume response will be similar to that of untrained individual.
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