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.

Effect of naloxone on perceived exertion and exercise capacity during maximal cycle ergometry

“…1, A-D) but that effort above the putative point of endogenous opioid release is perceived as greater after naloxone administration (Fig. 1E), are consistent with the suggestion of Surbey et al (22) that the endogenous opioid system may alter the perception of discomfort associated with high-intensity exercise, thus significantly affecting maximum exercise capacity without changing the physiological response to exercise.…”

“…Several investigations that used naloxone to study the role of endogenous opioids on maximum exercise capacity (5,12,20,22) concluded that endogenous opioids do not have a significant role in the circulatory or ventilatory response to exercise in healthy humans. Although these studies do not agree with our demonstration that naloxone results in premature cessation of exercise (Fig.…”

“…Although a small number of investigations have assessed the role of opioid blockade on maximum exercise capacity (5,12,20,22), the effect in healthy subjects has not been thoroughly defined. To assess the possible impact of endogenous opioids on effort perception in determining maximum exercise capacity, we assessed the effects of a large dose of naloxone, a competitive opioid antagonist, on maximum exercise capacity and cardiopulmonary and metabolic parameters of exercise in a group of self-trained endurance athletes.…”

“…Surbey et al (22) have speculated that effort sensation, in turn, may be modulated by endogenous opioid release.…”

Brain Circuits Encoding Reward from Pain Relief

“…Earlier studies with opioid antagonists established a critical role of endogenous opioid system for innate analgesia during traumatic and stressful situations or during “runners high” (52, 53). ACC neurons express high levels of endogenous opioid neuropeptides and their receptors (54) suggesting that at least part of the endogenous analgesic effects could be mediated by opioid activity in this region (55).…”