β‐adrenoceptor blockade and exercise: effects on endurance and physical training

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Abstract
β‐adrenoceptor antagonists influence almost all haemodynamic and metabolic actions in the body. High levels of sympathetic stimulation accompany aerobic exercise and it is known that β‐blockade results in a decreased working capacity. Furthermore it has also been questioned whether β‐blockade inhibits the normal response to physical training. Although adrenergic mechanisms are involved in muscle and liver glycogen breakdown, β‐blockade does not seem to reduce glycogen utilisation during exercise. Both selective and non‐selective β‐blockade inhibit lipolysis and result in less free fatty acids being available for muscle utilisation. Surgical and chemical sympathectomy in animals has been shown to inhibit the responses to physical training but results are now available showing that β‐adrenergic blockade does not prevent the effect of physical conditioning in patients treated with propranolol. It is concluded that β‐blockade during prolonged exercise a) does not reduce oxygen uptake by the working muscles b) decreases fat metabolism, which secondarily increases the use of carbohydrates, resulting in earlier hypoglycaemia and/or depletion of muscle glycogen with reduction in working capacity c) does not inhibit central and peripheral adaptation to physical conditioning.

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