Limitation of Work Performance in Normal Adult Males in the Presence of Beta-Adrenergic Blockade

Abstract

The effect on work performance of a single oral dose of the cardioselective .beta.-adrenoreceptor blocking agent metoprolol was compared with an equipotent dose of the nonselective agent propranolol in the same subjects. A number of biochemical and physiological variables including heart rate, O2 consumption, ventilation, lactate, free fatty acid and glucose levels were measured. After exercise in the presence of both active drugs, subjects complained of excessive leg fatigue. For the group there was a significant reduction in the total work performed and the maximum heart rate achieved on both drugs. There was a significant correlation between plasma levels of metoprolol, reduction in total work performed and reduction in maximum heart rate. After propranolol, there was a wide variation in work performed at a time when the reduction in maximum heart rate was similar for all subjects. Apparently for propranol a reduction in heart rate alone is an inappropriate guide to the impairment of work performance. There was a fall in the circulating level of free fatty acids at the end of exercise in the presence of both drugs and it is possible that this biochemical variable contributed to the decrease in work performance.