Attenuation of exercise conditioning by beta-adrenergic blockade.

Abstract

High levels of .beta.-adrenergic stimulation evidently accompany strenuous exercise, but the possibility that .beta.-adrenergic blockade might prevent exercise conditioning has not been adequately investigated. Normal, sedentary men, ages 21-35 yr, before and after 5 wk of intensive aerobic conditioning were studied. On a double-blind protocol, 8 received placebo and 9 propranolol throughout the conditioning period. A high level of .beta.-adrenergic blockade was documented in all subjects receiving propranolol; individual mean plasma propranolol concentrations were 100-292 ng/ml. Both groups trained at comparable intensities. Graded maximal treadmill tests were performed before starting drugs or training and were repeated 3-5 days after completing the conditioning period, when .beta.-adrenergic blockade was no longer present. In subjects who received placebo training increased exercise duration (16.4 .+-. 1.3 to 21.2 .+-. 1.5 minutes [.+-. SEM (standard error of the mean)], P < 0.01) and maximal O2 uptake (43.6 .+-. 2.9 to 52.7 .+-. 3.2 ml/kg per min, P < 0.05). Subjects who received propranolol had only modest improvement in exercise duration (16.0 .+-. 0.6 to 17.3 .+-. 0.9 minutes, P < 0.05) and no significant change in maximal O2 uptake (40.4 .+-. 1.4 to 40.9 .+-. 0.9 ml/kg per min). With training, diastolic pressure at maximal exercise decreased in subjects who received placebo (63 .+-. 3 to 48 .+-. 3 mm Hg, P < 0.05) but was unchanged in subjects who received propranolol. Training did not alter maximal heart rate in either group. High levels of .beta.-adrenergic blockage apparently attenuated aerobic conditioning in these normal subjects. .beta.-Adrenergic stimulation was apparently essential in exercise conditioning.