Associations Between Physical Activity, Self-reported Joint Function, and Molecular Biomarkers in Working Age Individuals With Hip and/or Knee Osteoarthritis

Objective: Previous research has suggested an association between physical activity (PA), joint function, and molecular biomarkers, but more studies are needed. The aim of this study was to explore the associations between PA or self-reported joint function and molecular biomarkers of cartilage and inflammation in individuals with hip and/or knee osteoarthritis (OA). Specific objectives were to explore the correlations between (1) the change over 3 months in self-reported PA/joint function and the change in molecular biomarkers (2) objectively measured PA and molecular biomarkers measured at 3-month follow-up. Design: Working age participants (n = 91) were recruited from a cluster randomized controlled trial. Self-reported PA, joint function, and serum samples were collected at baseline and after 3 months. Serum concentrations of the inflammatory marker C-reactive protein (CRP)and the cartilage markers Alanine-Arginine-Glycine-Serine (ARGS)-aggrecan, cartilage oligomeric matrix protein (COMP), and type II collagen C2C were analyzed by immunoassays. Objectively measured PA (steps/day) was collected during 12 weeks from activity trackers used by 53 participants. Associations were analyzed with Spearman's rank correlation. Results : There was a weak negative correlation between the change in self-reported PA and the change in COMP (r(s) = -0.256, P = .040)but not for the other molecular biomarkers. There were no correlations between the change in self-reported joint function and the change inmolecular biomarkers or between the average steps/day and the molecular biomarkers at follow- up (r(s) <= - 0.206, P >= .06). Conclusion: In general, no or only weak associations were found between PA/joint function and molecular biomarkers. Future research recommends including participants with lower PA, extend the follow-up, and use a design that allows comparisons.