Exercise is the most common treatment recommended by health care providers for treatment of musculoskeletal pain. We examined whether voluntary running wheel exercise improves pain and bone remodeling in rats with monosodium iodoacetate (MIA)-induced unilateral knee joint pain. During acquisition of wheel running prior to OA treatment, rats separated into two groups characterized by either high or low levels of voluntary wheel running as indicated by distance and peak speed. Following induction of knee joint OA, all rats showed diminished voluntary wheel running throughout the study. Voluntary wheel running failed to alter evoked nociceptive responses evaluated as weight asymmetry or hindpaw tactile thresholds at any time-point of the study. In contrast, relief of ongoing pain was demonstrated by conditioned place preference produced by lidocaine injection into the MIA-treated knee in high but not low running rats. Both high and low voluntary runners showed diminished trabecular bone loss compared to sedentary controls. These observations indicate that both high and low intensity exercise is beneficial in protecting against bone remodeling in advanced OA. The data suggest that similar to clinical observation, bone remodeling does not correlate with pain. Additionally, these results suggest that higher intensity exercise may relieve persistent ongoing OA pain while maintaining movement-evoked nociception. The relief of ongoing pain can potentially offer significant improvement in quality of life while preservation of responses to movement-evoked pain may be especially important in protecting the joint from damage due to overuse.
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