Acute resistance exercise and pressure pain sensitivity in knee osteoarthritis: a randomised crossover trial

Objective: To determine whether a single bout of resistance exercise produces an analgesic effect in individuals with knee osteoarthritis (OA). Design: Eleven participants with knee OA (65.9 +/- 10.4 yrs), and 11 old (613 +/- 8.2 yrs) and 11 young (25.0 +/- 4.9 yrs) healthy adults performed separate bouts of upper and lower body resistance exercise. Baseline and post-exercise pressure pain thresholds were measured at eight sites across the body and pressure pain tolerance was measured at the knee. Results: Pressure pain thresholds increased following exercise for all three groups, indicating reduced pain sensitivity. For the young and old healthy groups this exercise-induced analgesia (EIA) occurred following upper or lower body resistance exercise. In contrast, only upper body exercise significantly raised pain thresholds in the knee OA group, with variable non-significant effects following lower body exercise. Pressure pain tolerance was unchanged in all groups following either upper or lower body exercise. Conclusion: An acute bout of upper or lower body exercise evoked a systemic decrease in pain sensitivity in healthy individuals irrespective of age. The decreased pain sensitivity following resistance exercise can be attributed to changes in pain thresholds, not pain tolerance. While individuals with knee OA experienced EIA, a systemic decrease in pain sensitivity was only evident following upper body exercise.