title: Effect of selective and nonselective beta-blockade on skeletal muscle excitability and fatiguability.
abstract: 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.
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Cupido
authors.forename: A L
authors.initials: AL
authors.lastname: Hicks
authors.forename: R S
authors.initials: RS
authors.lastname: McKelvie
authors.forename: D G
authors.initials: DG
authors.lastname: Sale
authors.forename: A J
authors.initials: AJ
authors.lastname: McComas
mesh_terms: D058671:Adrenergic beta-1 Receptor Antagonists; D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D004311:Double-Blind Method; D004576:Electromyography / Q000187:drug effects; D005080:Exercise Test; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D011433:Propranolol / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology
chemical_list: D058671:Adrenergic beta-1 Receptor Antagonists; D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D011433:Propranolol; D000254:Sodium-Potassium-Exchanging ATPase; D008790:Metoprolol