The effect of physical training on the sympathoadrenal response to exercise

The urinary excretion of catecholamines was measured in six healthy male volunteers at rest and during a fixed amount of work before and after physical training. It was found that, although training resulted in a significantly lower heart rate during exercise, the output of catecholamines was unaltered, indicating that the total activation of the sympathoadrenal system by exercise was similar before and after training. A similar heart rate study before and after training was also made during beta-adrenergic receptor blockade. Under these conditions the heart rate during exercise was not significantly changed by training. It is suggested that physical training reduces the sensitivity of the beta-receptors of the heart.