title: Low-intensity exercise reverses chronic muscle pain in the rat in a naloxone-dependent manner.
abstract: OBJECTIVE
  To determine the effects of low-intensity exercise on chronic muscle pain and potential activation of the endogenous opioid system.
  
  
  METHODS
  Randomized placebo-controlled trial.
  
  
  METHODS
  Animal laboratory.
  
  
  METHODS
  Sixty-three male Sprague-Dawley rats.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: Physical Therapy Department, Integrative Neuroscience Research Center, College of Health Sciences, Marquette University, Milwaukee, WI 53201, USA. mariehoeger.bement@marquette.edu
authors.forename: Marie K Hoeger
authors.initials: MK
authors.lastname: Bement
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Sluka
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D019540:Area Under Curve; D004195:Disease Models, Animal; D008297:Male; D009135:Muscular Diseases / Q000503:physiopathology / Q000534:rehabilitation*; D009270:Naloxone / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology / Q000534:rehabilitation*; D010147:Pain Measurement; D010805:Physical Conditioning, Animal / Q000379:methods*; D011336:Probability; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
chemical_list: D009270:Naloxone