Plain language summary
Exercise improves pain and function in adults with knee pain due to osteoarthritis. To date, no studies have investigated if changes in physical activity level can explain this improvement in pain and function. This longitudinal study aimed to investigate if change in physical activity during exercise interventions is associated with future pain and physical function in older adults with knee pain. Participants were adults over the age of 45, who were already taking part in a trial of exercise interventions on knee pain. Change in physical activity was measured using a self-reported scale from baseline to 3 months. Pain and physical function were measured at baseline, 3 months and 6 months. Change in physical activity level was not associated with pain or physical function at 3 or 6 months. The authors suggest that other factors may be responsible for clinical improvements following exercise interventions, and recommend further investigation into the responsiveness of commonly used physical activity measures.
Abstract
BACKGROUND Exercise interventions improve clinical outcomes of pain and function in adults with knee pain due to osteoarthritis and higher levels of physical activity are associated with lower severity of pain and higher levels of physical functioning in older adults with knee osteoarthritis in cross-sectional studies. However, to date no studies have investigated if change in physical activity level during exercise interventions can explain clinical outcomes of pain and function. This study aimed to investigate if change in physical activity during exercise interventions is associated with future pain and physical function in older adults with knee pain. METHODS Secondary longitudinal data analyses of a three armed exercise intervention randomised controlled trial. Participants were adults with knee pain attributed to osteoarthritis, over the age of 45 years old (n = 514) from Primary Care Services in the Midlands and Northwest regions of England. Crude and adjusted associations between absolute change in physical activity from baseline to 3 months (measured by the self-report Physical Activity Scale for the Elderly (PASE)) and i) pain ii) physical function (Western Ontario and McMaster Universities Osteoarthritis Index) and iii) treatment response (OMERACT-OARSI responder criteria) at 3 and 6 months follow-up were investigated using linear and logistic regression. RESULTS Change in physical activity level was not associated with future pain, function or treatment response outcomes in crude or adjusted models at 3 or 6 months (P > 0.05). A 10 point increase in PASE was not associated with pain β = - 0.01 (- 0.05, 0.02), physical function β = - 0.09 (- 0.19, 0.02) or likelihood (odds ratio) of treatment response 1.02 (0.99, 1.04) at 3 months adjusting for sociodemographics, clinical covariates and the trial intervention arm. Findings were similar for 6 month outcome models. CONCLUSIONS Change in physical activity did not explain future clinical outcomes of pain and function in this study. Other factors may be responsible for clinical improvements following exercise interventions. However, the PASE may not be sufficiently responsive to measure change in physical activity level. We also recommend further investigation into the responsiveness of commonly used physical activity measures. TRIAL REGISTRATION ( ISRCTN93634563 ). Registered 29th September 2011.
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