Sit-to-Stand Performance, Moderate-to-Vigorous Physical Activity, and Health-Related Quality of Life in Knee...

Knee osteoarthritis (KOA) is the most common form of arthritis, leading to illness, decreased physical function, and reduced health-related quality of life (HR-QoL). Sit-to-stand (STS) testing is a commonly used measure of physical capacity in KOA. This study examined whether STS performance and moderate-to-vigorous physical activity (MVPA) helped account for the association between KOA pain and subsequent HR-QoL.

Data across 2 years (at year 6 and year 8 visits) were used from the Osteoarthritis Initiative (OAI), a multisite, longitudinal study of people with or at risk for KOA. We used serial mediation analysis to examine whether year 6 STS performance and year 8 MVPA accounted for the association between year 6 KOA pain and year 8 HR-QoL, adjusting for age, sex, and race.

Significant correlations among all model variables supported model testing. The serial mediation model revealed that an increase in KOA pain predicted worse STS performance (β = .15; P < .001). MVPA was reduced by an increase in KOA pain (β = -.13; P < .001) but not STS (β = -.02; P = .46). MVPA subsequently predicted HR-QoL (β = .12; P < .001). The overall indirect pathway was significant (β = -0.02; 95% CI, -0.040 to -0.009), but the direct pathway also remained significant (β = -0.47; 95% CI, -0.536 to -0.410), denoting a partial mediation effect.

STS performance and MVPA partially mediated the relationship between KOA pain and HR-QoL, highlighting mechanisms to address in future interventions for improving HR-QoL. These results support STS as a complementary tool to pain for understanding MVPA participation and HR-QoL in KOA patients. The findings also underscore the importance of integrating self-management strategies to address pain in behavior-change interventions.