The influence of physical activity on pain sensitivity and functional abilities in knee osteoarthritis

Exercise is regarded as a primary treatment modality for knee osteoarthritis (OA) but the mechanisms behind its efficacy are unknown. This thesis investigates the possibility that the phenomenon of exercise-induced analgesia (EIA) plays a role in the benefits of exercise for people with knee OA. An initial study was performed to assess the reliability of a novel measure of pressure pain tolerance at the knee, which was found to be reliable over three non-consecutive days. Following this, a randomised crossover trial was conducted to assess whether EIA occurs in individuals with knee OA. Three groups (OA, old healthy and young healthy) underwent baseline pressure pain threshold and tolerance testing then performed a bout of upper or lower limb resistance exercise on separate days followed by repetition of the pain testing. The results indicated that all groups experienced increased pain thresholds but no change to pain tolerance following upper limb resistance exercise. However the response of the OA group to lower limb exercise was varied with some individuals experiencing symptom exacerbation. A further study was undertaken to assess whether there is a relationship between daily physical activity and pain sensitivity in individuals with knee OA. Individuals with knee OA underwent baseline pain and sensory testing then their physical activity and symptoms were monitored for a week using an accelerometer and a log. The results of this study indicated that pressure pain thresholds were positively correlated with physical activity, whereby people who were more physically active had less pain sensitivity. The temporal associations between pain ratings and physical activity measured repeatedly over a week showed a pattern of symptom exacerbation following increased physical activity in some of the cohort and little evidence of EIA. In conclusion, individuals with knee OA were able to experience EIA when exercising a non-affected limb but responses to exercise of an affected limb varied from analgesia to symptom exacerbation. Also, increased physical activity was related to lower pain sensitivity and disease severity, but symptom exacerbation appeared to play a stronger role in the pain experience than exercise-induced analgesia during general physical activity