Knee pain may preclude participation in higher intensity physical activity in people with knee osteoarthritis and benefits of light activity are unclear. The effect of replacing sedentary time with light intensity activity on incident functional limitation 2 years later was investigated. Included were people with or at high risk of knee osteoarthritis without baseline functional limitation using data from the Osteoarthritis Initiative collected between August 2008 and July 2010. Data were analyzed between May 2016 and August 2016 for time in sedentary, light, and moderate to vigorous physical activity from accelerometer monitoring. Incident functional limitation was defined as (1) slow gait speed <1.0 meters/second during a 20-meter walk, (2) Western Ontario and McMasters University Osteoarthritis Index physical function ≥28, or (3) Short Form 12 Physical Component scale <40.
Inclusion criteria were met by 1,873 people (mean age=65.0 [SD=9.0] years, mean BMI=28.4 [SD=4.7] kg/m2). Replacing 60 minutes/day of sedentary time with 60 minutes/day of light activity was associated with a 17% reduced risk for incident slow gait speed 2 years later (Hazard Ratio=0.83, 95% CI=0.70, 0.99) after adjustment. Approximately 5 minutes/day of moderate to vigorous physical activity would be necessary to receive the equivalent benefit of 60 minutes/day of light activity. Effects in secondary patient-reported outcomes did not reach statistical significance. Replacing sedentary time with light activity may reduce the risk of performance-based functional limitation. As expected, moderate to vigorous physical activity rather than light provided stronger risk reduction. When moderate to vigorous physical activity is not an option, pursuing light activity may be a beneficial alternative to being sedentary.