Exercise testing and training with beta-adrenergic blockade: role of the drug washout period in "unmasking" a training effect.

To determine whether or not a training effect can be achieved with beta-adrenergic blockade and whether there is a difference between selective and nonselective therapy, we recruited 40 healthy subjects (16 women, 24 men) to participate in a 9-week exercise training program. After a baseline exercise treadmill test, subjects were randomized to oral therapy groups of atenolol, 50 mg daily (AT 50), atenolol, 100 mg daily (AT 100), propranolol, 80 mg twice a day (Prop), or placebo. Repeat exercise tests were performed at week 1, week 8, and at week 9, with week 8 to 9 being a 1-week drug-free washout period. At week 8, maximal oxygen consumption (Max VO2), when compared with baseline levels, was increased slightly in AT 50 (4.2%) and Prop (2.4%), decreased in AT 100 (5.3%), and increased significantly in the placebo group (12.7%). After washout, Max VO2 increased significantly compared with baseline in AT 50, AT 100, and Prop (9.8%, 10.8%, and 9.8%, respectively). We conclude that there is no significant difference between selective and nonselective beta-blockade therapy in the development of a training effect. This effect, however, may not become apparent until the drug is withdrawn.