The effect on exercise performance and on the subjective perception of fatigue of
the opioid receptor blocker naloxone, the nonselective beta-blocker timolol, and the
combination of these two was studied in a double-blind randomized cycle ergometry
test in healthy young men. Cumulative work at exhaustion was reduced by 25% after
timolol (P < 0.002) and by 34% after naloxone/timolol (P < 0.02) but not after naloxone, compared with placebo. Naloxone alone had no influence
on the subjective perception of fatigue (Borg scale rating), but significantly higher
ratings were obtained by timolol and by naloxone/timolol. The present study does not
support the hypothesis that opioid peptides are of importance for maximal exercise
capacity and subjective perception of fatigue during short-term dynamic exercise in
healthy young men.
Adrenergic beta-receptor blockers - opioid receptor blockade - exercise test
