Low-intensity exercise reverses chronic muscle pain in the rat in a naloxone-dependent manner

Arch Phys Med Rehabil. 2005 Sep;86(9):1736-40. doi: 10.1016/j.apmr.2005.03.029.


Objective: To determine the effects of low-intensity exercise on chronic muscle pain and potential activation of the endogenous opioid system.

Design: Randomized placebo-controlled trial.

Setting: Animal laboratory.

Animals: Sixty-three male Sprague-Dawley rats.

Interventions: Rats performed a low-intensity exercise protocol for 5 consecutive days after the induction of chronic muscle pain. In a separate experiment, naloxone or saline was administered systemically before 5 low-intensity exercise sessions.

Main outcome measure: Mechanical hyperalgesia was measured using von Frey filaments to determine the mechanical withdrawal threshold.

Results: Low-intensity exercise increased mechanical withdrawal threshold in the chronic muscle pain model. Naloxone attenuated the antihyperalgesic effects of low-intensity exercise.

Conclusions: Low-intensity exercise reversed mechanical hyperalgesia in the chronic muscle pain model through activation of the endogenous opioid system.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analysis of Variance
  • Animals
  • Area Under Curve
  • Disease Models, Animal
  • Male
  • Muscular Diseases / physiopathology
  • Muscular Diseases / rehabilitation*
  • Naloxone / pharmacology*
  • Pain / physiopathology
  • Pain / rehabilitation*
  • Pain Measurement
  • Physical Conditioning, Animal / methods*
  • Probability
  • Random Allocation
  • Rats
  • Rats, Sprague-Dawley
  • Sensitivity and Specificity


  • Naloxone