Abstract
Endurance during prolonged exercise decreases more markedly with nonselective than beta 1-selective beta-blockade. Because both types of blockers exert comparable effects on cardiac performance, oxygen supply to the working muscle, and extramuscular substrate mobilization, the difference in exercise capacity is apparently due to other factors. The available information in the literature along with experimental results from our laboratory suggests that inhibition of intramuscular lipolysis only occurs with nonselective beta-blockade and may partly account for this difference. In addition, alterations in potassium fluxes are particularly induced by nonselective beta-blockade and result in more pronounced decreases in the intracellular-extracellular potassium ratio during exercise than caused by placebo or beta 1-selective blockade. In contrast to what was initially proposed, intramuscular glycogenolysis appears not to be affected by either type of beta-blockade, and a decrease is unlikely to be involved in the reduced exercise capacity.
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