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 (Vo2) during the fixed work load (1.7 mph/10% grade), Vo2 at the ventilatory threshold, or Vo2max. After training, Vo2max was significantly increased (p less than 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 (Vo2/heart rate) at the fixed work load or at the ventilatory threshold, whereas the controls increased Vo2/heart rate at the fixed work load by 9% (p less than 0.05) and at the ventilatory threshold by 22% (p less than 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.