Effects of β-Adrenergic Blockade on Endurance and Short-Time Performance in Respect to Individual Muscle Fiber Composition*

Abstract

Nine physically active males were studied three times with four different exercise tests after administration of placebo, 0.1 g atenolol, or 0.08 g propranolol in random order. The test modals were: bicycle ergometer exercise at 50% of V̇O₂max, peak torque during knee extension, the Wingate muscle power test, and 2000 m track running. Muscle fiber composition had previously been determined. In subjects with a high percentage of slow-twitch fibers the β-blockers caused a more marked impairment in the exercising muscles. This effect was more pronounced with the unselective β-blocker propranolol than with atenolol. One interpretation of our findings is that peripheral sympathetic β₂-receptors in skeletal muscles may contribute to regulating muscle metabolism.

Key words

selective and unselective β-adrenergic blockade - muscle fiber types in man - short-term exercise - endurance exercise