title: Effects of naloxone on exercise performance.
abstract: This study was designed to investigate the effects of naloxone on athletic performance in humans. Two groups of elite middle-distance runners performed a maximal or a submaximal exercise protocol following the double-blind intravenous injection of either naloxone (0.15 mg X kg body wt-1) or saline. The maximal test (group M) was comprised of a short-duration treadmill run to maximal intensity; the submaximal test (group S), a prolonged submaximal treadmill run to exhaustion. O2 uptake, heart rate, ventilation, and perceived exertion were determined during each test. Perception of pain was assessed after exercise by use of a modified McGill pain questionnaire. No significant differences between placebo and naloxone treatments were found in any of the measured variables at the usually accepted 5% (P = 0.05) confidence level; however, evidence suggesting differences (i.e., P = 0.1 to 0.05) in these important respects was observed. In group M, maximal exercise performance measured by maximal O2 consumption was not different between placebo and naloxone; results suggest that VE was increased (P = 0.08) following naloxone, but only at the final work stage. In group S, exercise performance time was reduced following naloxone (P = 0.09), whereas the affective component of pain was increased (P = 0.06); no differences in the measured physiological variables were observed. These results suggest the following: 1) the opiate receptor-endorphin system may alter the perception of pain associated with prolonged high-intensity submaximal exercise with a resultant significant effect on performance; and 2) it may play a role in the control of ventilation during maximal exercise.
mesh_terms: D000293:Adolescent; D000328:Adult; D004311:Double-Blind Method; D004723:Endorphins / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D010101:Oxygen Consumption; D010146:Pain; D010465:Perception / Q000187:drug effects; D010807:Physical Endurance / Q000187:drug effects; D005082:Physical Exertion / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D012119:Respiration; D012420:Running; D013997:Time Factors
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid; D009270:Naloxone