CHANGES IN STROKE VOLUME WITH BETA-BLOCKADE BEFORE AND AFTER 10 DAYS OF EXERCISE TRAINING IN MEN AND WOMEN

We sought to determine whether 10 days of training would be a sufficie nt stimulus for cardiac adaptations that would allow a greater compens atory stroke volume during beta-blockade. We also sought to determine whether men and women had a similar cardiac reserve capacity for incre asing stroke volume with beta-blockade during submaximal exercise. Eig ht men (age 29 +/- 2 yr, mean +/- SE) and eight women (25 +/- 2 yr) cy cled at 65% of peak O-2 consumption (unblocked) under placebo-control and beta-blockade (100 mg atenolol) conditions performed on separate d ays. These tests were repeated at the same power output after training (10 consecutive days, 1 h of cycling per day). Before training, beta- blockade significantly (P < 0.05) decreased heart rate (HR) and cardia c output and increased stroke volume in both men and women. After trai ning, the increase in stroke volume and decrease in HR with beta-block ade was significantly less while cardiac output was reduced more. Ther e were no gender differences in the effects of beta-blockade on HR, st roke volume, or cardiac output. These data indicate that, during exerc ise with beta-blockade, exercise training for 10 days does not enhance the compensatory increase in stroke volume and that men and women hav e a similar cardiac reserve capacity for increasing stroke volume.