Metabolic aspects of maximal exercise performance after slow release metoprolol and after atenolol

Summary Maximal exercise performance by eight healthy male subjects was tested after one week of medication with slow-release metoprolol 200 mg/d (metoprolol-SR), atenolol 200 mg/d or placebo, in a double blind crossover trial. The maximal working capacity was significantly decreased after atenolol and metoprolol-SR. Plasma glucose and FFA concentrations during the exercise test did not change: either after placebo therapy or after beta-blockade. The anaerobic threshold did not change after beta-blockade, but the changes in lactate due to the exercise were less after beta-blockade. Neither beta-blocker affected the exercise-induced alteration in airway resistance. Both drugs caused a small but significant ventilatory depression at rest and at 75% of maximal exercise. It is concluded that the limiting factor in maximal exercise performance after ₁-adrenergic blockade does not lie in oxygen transport to the working muscles via ventilation and the circulation, but is most probably due to anaerobic metabolism.