Journal of Applied Physiology, Vol 76, Issue 6 2461-2466, Copyright © 1994 by American Physiological Society
Effect of selective and nonselective beta-blockade on skeletal muscle excitability and fatiguability
C. M. Cupido, A. L. Hicks, R. S. McKelvie, D. G. Sale and A. J. McComas
Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
The effects of beta-blockade on skeletal muscle excitability and
fatiguability during exercise were examined. Ten healthy males (mean age
21.9 +/- 1.1 yr) performed a 4-min fatigue protocol consisting of
intermittent isometric voluntary contractions of the knee extensors in one
leg. Subjects performed the exercise after treatment with placebo, 100 mg
metoprolol, or an equipotent dose of propranolol (60 mg, n = 1; 80 mg, n =
8; 100 mg, n = 1) twice a day for 76 h before testing according to a
randomized double-blind design. The evoked twitch torque, maximal voluntary
torque, and maximal M-wave amplitude were unaffected by the beta-blockade
treatments before fatigue. During the placebo trial, there were significant
reductions in the evoked and voluntary torques (77 +/- 15 and 55 +/- 11%,
respectively) after the fatigue protocol; however, both the voluntary
electromyogram and evoked M waves were well maintained throughout fatigue.
The beta-blockade treatments had no significant effect on torque or
electromyogram activity over the course of the exercise. Thus, despite
evidence for an impairment of dynamic exercise performance with beta 1- and
beta 1,2-blockade, there appears to be no effect of these agents on muscle
excitability and fatiguability during isometric muscle activity.
