Effects of oral propranolol and exercise protocol on indices of aerobic function in normal man

The exercise responses to two different progressive, upright cycle ergometer tests were studied in nine healthy, young subjects either with no drug (ND) or following 48 h of oral propranolol (P) (40 mg q.i.d.). The ergometer tests increased work rate by 30 W either every 30 s or every 4 min. Propranolol caused a significant (p < 0.05) reduction in peak oxygen uptake (Formula: see text during both the 30-s and 4-min tests (30-s ND, 3949 ± 718 mL∙min −1 Formula: see text; 30-s P, 3408 ± 778 mL∙min −1 ; 4-min ND, 4058 ± 409 mL∙min −1 ; 4-min P, 3725 ± 573 mL∙min −1 ). There was no difference between 30-s ND and 4-min ND for peak Formula: see text. The ventilatory anaerobic threshold was not significantly different between any test (30-s ND, 2337 ± 434 mL O 2 ∙min −1 ; 30-s P, 2174 ± 406 mL O 2 ∙min −1 ; 4-min ND, 2433 ± 685 mL O 2 ∙min −1 ; 4-min P, 2296 ± 604 mL O 2 ∙min −1 ). The Formula: see text at which blood lactate had increased by 0.5 mM above resting levels was significantly lower than the ventilatory anaerobic threshold for the 4-min ND (1917 ± 489) and the 4-min P (1978 ± 412) tests, but was not different for the 30-s ND and 30-s P tests. At exhaustion in the progressive tests, the blood Formula: see text was higher (p < 0.05) in both 30-s tests than 4-min tests. Steady-state submaximal cardiac output was reduced (p < 0.05) by propranolol. This was primarily due to a decrease in heart rate as stroke volume was significantly greater with propranolol than with no drug (p < 0.05). The duration of time at each stage of work rate in progressive exercise did not significantly affect the peak Formula: see text or the Formula: see text at the ventilatory anaerobic threshold. Short duration stages were associated with lower blood lactates for a given submaximal Formula: see text and with higher blood Formula: see text at exhaustion. Propranolol had no significant effect on ventilatory anaerobic threshold or Formula: see text at a 0.5 mM blood lactate increase; however, propanolol did significantly reduce the peak Formula: see text. It is concluded that in submaximal exercise, the cardiorespiratory system can compensate for propranolol induced changes. Above the anaerobic threshold, these compensations are inadequate.