Attenuation of exercise conditioning by beta-adrenergic blockade.

High levels of ,B-adrenergic stimulation accompany strenuous exercise, but the possibility that #-adrenergic blockade might prevent exercise conditioning has not been adequately investigated.We studied normal, sedentary men, ages 21-35 years, before and after 5 weeks of intensive aerobic conditioning.On a double-blind protocol, eight received placebo and nine propranolol throughout the conditioning period.A high level of ,B-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 maxi- mal treadmill tests were performed before starting drugs or training, and were repeated 3-5 days after com- pleting the conditioning period, when ,B-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 [± SEMI, p < 0.01) and maxi- mal oxygen uptake (43.6 ± 2.9 to 52.7 ± 3.2 ml/kg/min, p < 0.05).Subjects who received propranolol had only modest improvement in exercise duration (16.0 ± 0.6 to 17.3 i 0.9 minutes, p < 0.05), and no significant change in maximal oxygen uptake (40.4 ± 1.4 to 40.9 i 0.9 ml/kg/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.Thus, high levels of f3-adrenergic blockade markedly attenuated aerobic conditioning in these normal subjects.We conclude that ,B-adrenergic stimulation is essential in exercise conditioning.