Background/Purpose:

Engaging in adequate levels of moderate to vigorous physical activity (MVPA) reduces the risk of functional limitation in people with knee osteoarthritis (OA). Sedentary behavior (SED) is common in those with either high or low level of MVPA, and is also linked to poor health outcomes in people with knee OA. However, it remains unclear whether being sedentary regardless of MVPA level increases one’s risk of developing functional limitation in people with knee OA. The purpose of this study was to examine the association of MVPA and SED with incident functional limitation 4 years later in people with knee OA.

Methods:

We used publically available data from the Osteoarthritis Initiative (OAI). Our primary exposures were time spent in MVPA and SED that were collected at the 48-month OAI visit (baseline) using an accelerometer (Actigraph GT1M) worn for >10 hours/day for ≥4 days. We classified people as having at least one 10 min bout/week in MVPA defined as ≥2020 counts/min. SED was defined as time spent at <100 counts/mins standardized to wear time. We classified people as being Active-Low SED (≥1 MVPA bouts and lowest SED tertile i.e. less sedentary), Active-High SED (≥1 MVPA bouts and top two SED tertiles, i.e. more sedentary), Inactive-Low SED (No MVPA bout and lowest SED tertile), and Inactive-High SED (No MVPA bout and top two SED tertiles). We defined our outcome, incident functional limitation, as >12 sec for the 5 repetition sit-to-stand test (STS) and <1.22 m/sec gait speed during a 20-meter walk at the 96-month OAI visit (4 years later). To examine the association of MVPA and SED with incident function limitation, we calculated risk ratios and 95% confidence intervals [RR (95%CI)] adjusted for potential confounders.

Results:

We included 1927 people with valid exposure data (55% female, age [mean±(SD)] 65.1±8.8 years, BMI 28.4±4.9 kg/m²) at baseline. Of those free of the outcome at baseline and had follow-up data, 15% (n=162/1091) and 21% (n=236/1133) developed functional limitation 4 years later measured by STS and gait speed, respectively. The Active-High SED group had a similar risk of functional limitation compared with the Active-Low SED group. The Inactive-High SED group had 1.5 times the risk of incident functional limitation compared with the Active-Low SED group. The Inactive-Low SED group had 1.5 to 1.6 times the risk of incident functional limitation compared with the Active-Low SED group (Table).

Conclusion:

For active people, high SED was not associated with incident functional limitation compared to those who were low SED. However, those who were inactive had an increased risk of incident functional limitation regardless of SED compared with people who were Active-Low SED. Thus, being active may potentially offset the functional consequences of SED. Effective clinical interventions to improve MVPA are needed for people with knee OA.