title: Effect of naloxone on perceived exertion and exercise capacity during maximal cycle ergometry.
abstract: We assessed the effects of naloxone, an opioid antagonist, on exercise capacity in 13 men and 5 women (mean age = 30.1 yr, range = 21-35 yr) during a 25 W/min incremental cycle ergometer test to exhaustion on different days during familiarization trial and then after 30 mg (iv bolus) of naloxone or placebo (Pl) in a double-blind, crossover design. Minute ventilation (Ve), O(2) consumption (Vo(2)), CO(2) production, and heart rate (HR) were monitored. Perceived exertion rating (0-10 scale) and venous samples for lactate were obtained each minute. Lactate and ventilatory thresholds were derived from lactate and gas-exchange data. Blood pressure was obtained before exercise, 5 min postinfusion, at maximum exercise, and 5 min postexercise. There were no control-Pl differences. The naloxone trial demonstrated decreased exercise time (96% Pl; P < 0.01), total cumulative work (96% Pl; P < 0.002), peak Vo(2) (94% Pl; P < 0.02), and HR (96% Pl; P < 0.01). Other variables were unchanged. HR and Ve were the same at the final common workload, but perceived exertion was higher (8.1 +/- 0.5 vs. 7.1 +/- 0.5) after naloxone than Pl (P < 0.01). The threshold for effort perception amplification occurred at approximately 60 +/- 4% of Pl peak Vo(2). Thus we conclude that peak work capacity was limited by perceived exertion, which can be attenuated by endogenous opioids rather than by physiological limits.
authors.affiliation: Department of Physical Education and Exercise Science, Brooklyn College, Brooklyn, NY 11210, USA.
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Sgherza
authors.forename: Kenneth
authors.initials: K
authors.lastname: Axen
authors.forename: Randi
authors.initials: R
authors.lastname: Fain
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hoffman
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Dunbar
authors.forename: François
authors.initials: F
authors.lastname: Haas
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D018592:Cross-Over Studies; D005080:Exercise Test; D005221:Fatigue / Q000378:metabolism; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D009270:Naloxone / Q000008:administration & dosage*; D009292:Narcotic Antagonists / Q000008:administration & dosage*; D018847:Opioid Peptides / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects*; D010465:Perception / Q000187:drug effects*; D005082:Physical Exertion / Q000187:drug effects*; D013177:Sports
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D019344:Lactic Acid; D009270:Naloxone