Relation of physical activity time to incident disability in community dwelling adults with or at risk of knee arthritis: prospective cohort study

OBJECTIVE: To investigate whether objectively measured time spent in light intensity physical activity is related to incident disability and to disability progression. DESIGN: Prospective multisite cohort study from September 2008 to December 2012. SETTING: Baltimore, Maryland; Columbus, Ohio; Pittsburgh, Pennsylvania; and Pawtucket, Rhode Island, USA. PARTICIPANTS: Disability onset cohort of 1680 community dwelling adults aged 49 years or older with knee osteoarthritis or risk factors for knee osteoarthritis; the disability progression cohort included 1814 adults. MAIN OUTCOME MEASURES: Physical activity was measured by accelerometer monitoring. Disability was ascertained from limitations in instrumental and basic activities of daily living at baseline and two years. The primary outcome was incident disability. The secondary outcome was progression of disability defined by a more severe level (no limitations, limitations to instrumental activities only, 1-2 basic activities, or ≥3 basic activities) at two years compared with baseline. RESULTS: Greater time spent in light intensity activities had a significant inverse association with incident disability. Less incident disability and less disability progression were each significantly related to increasing quartile categories of daily time spent in light intensity physical activities (hazard ratios for disability onset 1.00, 0.62, 0.47, and 0.58, P for trend=0.007; hazard ratios for progression 1.00, 0.59, 0.50, and 0.53, P for trend=0.003) with control for socioeconomic factors (age, sex, race/ethnicity, education, income) and health factors (comorbidities, depressive symptoms, obesity, smoking, lower extremity pain and function, and knee assessments: osteoarthritis severity, pain, symptoms, prior injury). This finding was independent of time spent in moderate-vigorous activities. CONCLUSION: These prospective data showed an association between greater daily time spent in light intensity physical activities and reduced risk of onset and progression of disability in adults with osteoarthritis of the knee or risk factors for knee osteoarthritis. An increase in daily physical activity time may reduce the risk of disability, even if the intensity of that additional activity is not increased.