Effect of aerobic conditioning on cardiovascular response to isometric exercise

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.