Abstract
BACKGROUND: Knee pain reduces activity, while inactivity can increase pain. The central nervous system modulates both pain and activity. The 8-item Central Aspects of Pain (CAP) questionnaire measures self-reported symptoms associated with current and future knee pain severity and psychophysical evidence of central pain sensitivity. The objective was to explore associations between CAP and physical inactivity in people with knee pain. METHODS: Participants from the Investigating Musculoskeletal Health and Wellbeing cohort who reported their knee as their most troublesome joint with numerical rating scale pain severity ≥1/10 completed questionnaires at baseline and 12 months addressing demographic and clinical characteristics, CAP questionnaire, and physical inactivity (Frail Non-Disabled questionnaire item). Chi-squared, correlations and multivariable logistic regression were performed. RESULTS: Seven hundred twenty-two participants provided baseline data and 404 longitudinal data. Higher baseline CAP scores were associated with higher baseline pain severity {OR: 1.25 (95% confidence interval [CI]: 1.02-1.53); P = 0.032} and physical inactivity (OR: 1.18 [95% CI: 1.11-1.25]; P < 0.001). Increasing CAP scores over 12 months were associated with becoming physically inactive (OR: 1.16 [95% CI: 1.01-1.32]; P = 0.032). The effects of CAP on physical inactivity were not fully explained by pain severity nor by any single characteristic of widespread pain distribution, emotional or cognitive factors, sleep disturbance, or fatigue. CONCLUSION: Central aspects of pain questionnaire displays cross-sectional and longitudinal associations with physical inactivity. Central nervous system manifestations of pain appear to link pain with physical activity and may be more important than pain severity.