Attenuation of exercise training effects in patients taking beta blockers during early cardiac rehabilitation

Cardiorespiratory responses to graded treadmill tests administered 1 month after myocardial infarction or coronary bypass surgery and again after 4 weeks of aerobic training were compared in 24 patients taking beta blockers and 15 control patients. There were no significant differences before training between the groups in age, weight, ventricular ejection fraction, oxygen uptake (V̇O 2) during the fixed work load (1.7 mph/10% grade), V̇O 2 al the ventilatory threshold, or V̇O 2max. After training, V̇O 2max was significantly increased ( p < 0.05) by 16% in the beta-blocker group and by 21% in controls. However, the group taking beta blockers showed no significant change in oxygen pulse (V̇O 2/heart rate) at the fixed work load or at the ventilatory threshold, whereas the controls increased V̇O 2/heart rate at the fixed work load by 9% ( p < 0.05) and at the ventilatory threshold by 22% ( p < 0.05). Metabolic and ventilatory responses to submaximal exercise should therefore also be considered when evaluating the efficacy of exercise training in patients taking beta blockers.