Cm. Cupido et al., EFFECT OF SELECTIVE AND NONSELECTIVE BETA-BLOCKADE ON SKELETAL-MUSCLEEXCITABILITY AND FATIGUABILITY, Journal of applied physiology, 76(6), 1994, pp. 2461-2466
The effects of beta-blockade on skeletal muscle excitability and fatig
uability during exercise were examined. Ten healthy males (mean age 21
.9 +/- 1.1 yr) performed a 4-min fatigue protocol consisting of interm
ittent isometric voluntary contractions of the knee extensors in one l
eg. 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 accordin
g to a randomized double-blind design. The evoked twitch torque, maxim
al voluntary torque, and maximal M-wave amplitude were unaffected by t
he 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; h
owever, both the voluntary electromyogram and evoked M waves were well
maintained throughout fatigue. The beta-blockade treatments had no si
gnificant effect on torque or electromyogram activity over the course
of the exercise. Thus, despite evidence for an impairment of dynamic e
xercise performance with beta(1)- and beta(1,2)-blockade, there appear
s to be no effect of these agents on muscle excitability and fatiguabi
lity during isometric muscle activity.