SUMMARY 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 maximal treadmill tests were performed before starting drugs or training, and were repeated 3-5 days after completing 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 maximal 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.ENDURANCE EXERCISE results in adaptive changes in the cardiovascular system known as training or conditioning effects. In normal subjects performing near-maximal exercise, the conditioning process results in greater physical work capacity, total body oxygen consumption, cardiac output, stroke volume and arteriovenous oxygen difference.1 ' At submaximal work loads, conditioning results in diminished myocardial oxygen consumption, lower heart rate and higher stroke volume.2 S Similar changes occur with exercise training in many patients with coronary artery disease.4 6-11 The potentially favorable nature of these changes is the physiologic basis for the use of aerobic exercise programs in rehabilitating patients with coronary artery disease. coronary artery disease, and aerobic exercise is often prescribed in cardiac rehabilitation programs. If ,B-adrenergic stimulation is needed for exercise conditioning, then fi blockade might be expected to interfere with this process. To test this hypothesis, we studied 17 healthy, sedentary men before, during and after an intensive 5-week aerobic exercise program. Using a double-blind protocol, eight subjects received placebo and nine propranolol during the training period. Conditioning effects were compared in the two groups by evaluating maximal treadmill performance while the subjects were not taking drugs before and aft...

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The response to isometric handgrip exercise (IHE) and isometric quadriceps exercise (IQE) (30% maximum voluntary contraction held 3 min) was studied before and after 5 wk of aerobic training. Training exercises involved only the lower extremities. Seventeen healthy unconditioned males aged 21--35 yr were subjects. During training nine subjects received propranolol in doses that provided a high degree of beta-adrenergic blockade; eight received a placebo. All subjects were tested before training or drug and after training, 3--5 days off drug. With IGE after training, the placebo group had lower maximum heart rate (91 +/- 4 to 79 +/- 5 beats/min, P less than 0.05), systolic blood pressure (151 +/- 5 to 139 +/- 4 mmHg, P less than 0.05), and double product (heart rate x systolic blood pressure) (138 +/- 10 x 10(2) to 110 +/- 7 x 10(2), P less than 0.05). The response to IQE in the propranolol group was unchanged after training. Heart rate, systolic blood pressure, and double product with IHE was unchanged in either group after training. Aerobic conditioning can modify the hemodynamic response to isometric exercise. This effect is specific for the trained muscle group and is prevented by beta-adrenergic blockade.