Background/Purpose: Preservation of function in older adults is critical to maintaining independence. Physical activity interventions often focus on increasing activity while giving limited attention to reducing sedentary behaviors.  This study examined whether time spent in objectively measured sedentary behaviors is related to subsequent physical function loss among independent community-dwelling adults with or at high risk for knee osteoarthritis (OA).

Methods:  Longitudinal data (2008-2012) from 1659 Osteoarthritis Initiative participants ages 49-83 years were used to evaluate the relationship of baseline time spent in sedentary behaviors (percentage of awake hours and average daily hours) to functional loss (gait speed and chair stand testing) after 2 years of follow-up. Average daily hours of sedentary- and moderate-vigorous intensity physical activity were objectively assessed at baseline by ActiGraph accelerometer monitoring. The relationship of sedentary hours to functional loss was examined by multiple linear regression.

Results: This cohort spent almost 2/3 of their waking hours (average 9.8 hours) in sedentary behaviors.  Sedentary time was significantly associated with subsequent functional loss in both gait speed (-1.66 feet/minute decrease per 10% increment increase in percentage sedentary waking hours,  95% confidence interval (CI): -3.15, -0.18) and chair stand rate (-0.75 repetitions/minute decrease, 95% CI: -1.30, -0.20) after controlling for baseline function, socioeconomic (age, sex, race/ethnicity, income, education), health factors (obesity, depression, comorbidities, knee symptoms, knee osteoarthritis severity), and time spent in moderate-vigorous activity.  These findings were consistent across subgroups defined by gender and weight, and age among older adults (>65). (Figure)

Conclusion:   Being more sedentary was related to more future decline in physical function. Importantly, this finding is independent of time spent in moderate-vigorous activity.  This independent relationship supports a dual strategy for designing physical activity interventions.  Both limiting sedentary activities and promoting physical activity in adults with knee osteoarthritis may be important in maintaining function.