Exercise has purported benefits for patients with osteoarthritis but dosing effects are not remarkable and poorly understood. We used serum levels of cartilage oligomeric matrix protein (COMP) to determine the effect of exercise duration on cartilage stress.

Six men and 11 women, mean age 49.3 years (range: 25-69) who met inclusion criteria were enrolled with in-formed consent. The cohort consisted of those with (n=6) and without (n=11) joint pathology. Two separate bicycling ses-sions were conducted lasting 20 or 40 minutes. Session order was randomized. Pedaling resistance was adjusted to enable consistent speed (50 RPM) without exceeding 65% maximum HR. Venous blood, obtained before and after each session, was analyzed using a commercial COMP ELISA. Subjects also completed an AAOS Hip and Knee Outcomes Question-naire. Data were analyzed by repeat measures ANOVA and Pearson correlation.

After 20 minutes, mean COMP levels decreased from 811 ± 326.8 ng/ml to 768 ± 337.3 ng/ml; after 40-minutes,from 723 ± 311.8 to 693 ± 312.2 ng/ml. Neither duration of exercise or pathology significantly affected COMP. AAOS outcome scores were 83.7 (range: 65 to 94) for those with and 99.1 (range: 94 to 100) for those without patholo-gy/OA; scores did not correlate to COMP.

Our data show that moderate, non-weight bearing exercise up to 40 minutes does not elevate serum COMP, suggesting it is to be non-injurious to joint cartilage for periods of this duration. Given the small subset of subjects with OA, additional study is warranted.