Trajectories of strenuous physical activity and extensive sitting and 10-year incident radiographic knee OA

Abstract

Purpose: Participation in exercise, sport or recreational activities offers multiple health benefits, promotes wellbeing and weight management, and preserves function and quality of life. Staying physically active is particularly important for persons at higher risk for knee OA, before disease development, to help prevent a downward spiral of function decline and disability associated with OA development and progression. While individuals with knee symptoms or past knee injury/surgery recognize the health benefits of regular physical activity, uncertainty about whether strenuous physical activity (PA) will accelerate the development of joint tissue damage has been identified as a common concern. Alternatively, extensive sitting could also be detrimental to joint health. Understanding how activity levels evolve over time and their association with risk of incident radiographic knee OA will help illuminate the impact of engagement in strenuous PA or extensive sitting on joint health and motivate healthy PA behavior. Our objective was to identify distinct trajectories of (1) weekly hours spent in strenuous PA and (2) extensive sitting over 8 years among persons at higher risk for knee OA, and evaluate the association of membership in each trajectory group with incident radiographic knee OA identified during the baseline-to-10-year follow-up period. Methods: The OAI (Osteoarthritis Initiative) is a prospective, observational cohort study of persons with or at higher risk for knee OA. Weekly hours engaged in strenuous PA, such as jogging, swimming, cycling, singles tennis, aerobic dance, skiing (downhill or cross-country) or other similar activities were estimated using items in the PASE (Physical Activity Scale for the Elderly) questionnaire over the baseline-to-8-year follow-up interval. Sitting behaviors, such as reading, watching TV, or doing handicrafts, were assessed using PASE items; extensive sitting was defined by frequent prolonged sitting (5-7 days/week and > 4 hours/day). OAI participants who had baseline K/L grade 0 in both knees and PASE data at baseline and at least 2 follow-up visits were included in the analysis. We used latent mixture modeling to identify subgroups of participants with similar underlying trajectories of weekly hours spent in strenuous PA, and separately used similar methods to identify extensive sitting subgroups. Model fit was assessed using the Bayesian Information Criterion (BIC). Final subgroup assignment was based on the maximum posterior probability. Incident radiographic knee OA was defined as K/L grade ≥ 2 in either knee by the 10-year visit. Person-based logistic regression was used to model associations of membership in strenuous PA trajectories (predictor) with incident radiographic knee OA (outcome), unadjusted and adjusted for age, sex, and BMI. Results are reported as odds ratios (ORs) and 95% confidence intervals (CIs). We used similar analytic approaches for extensive sitting trajectories. Results: Among 1194 OAI participants [age: mean 58.4 (SD 8.9) years, BMI: 26.8 (4.5) kg/m2, 697 (58.4%) women], we identified 4 distinct trajectories of weekly hours spent in strenuous PA (Figure 1) and 3 distinct extensive sitting trajectories (Figure 2). For strenuous PA, nearly 50% of the participants were classified into the “persistently no” subgroup (0 hour/week) and 30% into the “low, slightly improving” subgroup (1-2 hours/week). Over 40% were classified into the “moderate to high frequency of extensive sitting” subgroup. One hundred fifty-five participants (13%) developed radiographic knee OA by the 10-year visit. As shown in Figure 3, compared to persistently no strenuous PA, participating in any (adjusted OR 0.75, 95% CI 0.53-1.07) and low-to-moderate (adjusted OR 0.69, 95% CI 0.48-1.01) strenuous PA over 8 years were each marginally non-significantly associated with a reduced likelihood of incident knee OA over the baseline-to-10-year follow-up period. There was no statistical evidence of an association of extensive sitting trajectories with incident knee OA (data not shown). Conclusions: In persons at higher risk of developing knee OA, 4 distinct trajectories of weekly hours spent in strenuous PA were identified over 8 years. Engagement in strenuous PA assessed over an 8-year period was associated with a reduced risk of incident knee OA, however, after adjustment for age, sex and BMI, the association was marginally non-significant. This suggests the possibility that some level of strenuous PA may be protective. Three distinct trajectories of extensive sitting behavior were identified; trajectory membership was not associated with risk of incident knee OA.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)