Background/Purpose: Public health physical activity interventions often focus on increasing exercise but give limited attention to reducing sedentary behavior.  This study examined whether objectively measured time spent in sedentary behavior is related to subsequent physical function independent of time spent in moderate-to vigorous-intensity physical activity (MVPA) among adults with knee osteoarthritis (OA).

Methods: The Osteoarthritis Initiative cohort included 962 patients with radiographic knee OA, ages 49-83 years at baseline (48-month clinic visit) when physical activity was monitored. Physical function was assessed at baseline and 2 years using the 20-meter walk test (feet/second)) and chair stand rate (per minute).  Average daily sedentary behavior and MVPA assessed by accelerometer monitoring was based on 4 or more valid monitoring days (i.e.,10 or more wear hours in a day) for each participant.  The percentage of daily wear hours spent in sedentary behavior (minutes when activity counts< 100) was calculated.  The relationship of baseline sedentary behavior percentage quartiles to subsequent (2-year) physical function was examined by multiple linear regression models adjusted for demographic factors (age, sex, race/ethnicity, and education), health factors (comorbidity, BMI, knee pain, knee OA severity, presence of knee symptoms) and average daily MVPA minutes.

Results: Adults with knee OA spent on average 66% of their daily time in sedentary behavior (range 28~89%).

For both chair stand rate and gait speed, the most sedentary people had the poorest physical function after 2 years.  Compared to the most sedentary group (quartile 1), age-adjusted physical function average  was significantly higher in less sedentary behavior groups (chair stand rate: 28.6, 32.1, 31.4, 32.7 stands/minute, P<0.0001; gait speed: 4.19, 4.48, 4.48 and  4.42 feet/second, P=0.0002). These trends persisted in multivariable analyses that controlled for demographic factors, health factors, and MVPA.

Conclusion:

Being less sedentary is associated with better future physical function independent of time spent in physical activity. Maintaining physical function may be improved by pairing messages to limit sedentary activities with those promoting increasing levels of physical activity in adults with knee OA.

FIGURE—Average Chair Stand Rate (stands/minute) and Gait Speed (feet/second) at 2 Years, by Sedentary Behavior Quartiles at Baseline, adjusted for age (n=962)