Key result
Physical training resulted in a significantly lower heart rate during exercise but unaltered catecholamine output, suggesting reduced sensitivity of cardiac beta-receptors.
Why the study?
Does physical training alter the sympathoadrenal response to exercise in healthy male volunteers?
Does physical training alter the sympathoadrenal response to exercise in healthy male volunteers?
Physical training lowers exercise heart rate without altering catecholamine output, suggesting reduced cardiac beta-receptor sensitivity rather than decreased sympathoadrenal activation.
Supports beta-receptor desensitization as training mechanism in healthy men; leaves open relevance to patients with cardiovascular disease.
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.
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Brundin et al. (1975) studied Healthy (n=6). Physical training vs. Before physical training was evaluated on Urinary excretion of catecholamines at rest and during a fixed amount of work. Physical training resulted in a significantly lower heart rate during exercise but unaltered catecholamine output, suggesting reduced sensitivity of cardiac beta-receptors.