Association between Quadriceps Strength and Self-Reported Physical Activity in Individuals with Knee Osteoarthritis

Abstract

Limited quadriceps strength is common with knee osteoarthritis (OA) and may lead to activity avoidance and low physical activity (PA) levels. PURPOSE: To investigate the association between quadriceps strength and self-reported PA in individuals with knee OA. Secondary analyses evaluated the association between a change (Δ) in quadriceps strength and self-reported PA following a 4-week physical therapy intervention designed to improve lower extremity strength. METHODS: Ninety individuals with radiographic knee OA were enrolled in the current study (43% male; Kellgren-Lawrence grade: 2-4). Assessments occurred at baseline, post intervention, and 4 weeks after intervention completion. At each testing visit, participants completed the Physical Activity Scale for the Elderly (PASE), the Western Ontario and McMaster Universities Arthritis Index pain subscale, and a quadriceps maximal voluntary isometric contraction (MVIC) performed at 70° of knee flexion measured with an isokinetic dynamometer. Multiple regression analyses were conducted to assess the association between MVIC normalized to body mass (nMVIC - predictor variable) and PASE after accounting for age, body mass index, radiographic OA severity, and pain. RESULTS: For all participants at baseline, there was a significant association between greater nMVIC and greater PASE (ΔR2=0.049, p=0.033) after accounting for covariates. When stratified by sex, nMVIC was not associated with PASE (Males: ΔR2=0.045, p=0.197; Females: ΔR2=0.011, p=0.432). There was no association between the ΔnMVIC and ΔPASE following the intervention (Total: ΔR2=0.043, p=0.072; Males: ΔR2=0.071, p=0.106; Females ΔR2=0.008, p=0.585), or 4 weeks post intervention (Total: ΔR2=0.001, p=0.845; Males: ΔR2=0.009, p=0.629; Females: ΔR2=0.002, p=0.773). CONCLUSIONS: Although greater quadriceps strength was associated with greater self-reported PA, nMVIC only explained 4.9% of the variance in PASE. Post intervention, a change in strength was not associated with a change in PA. Therapeutic interventions aimed at increasing strength may not lead to a subsequent increase in PA. Future studies should investigate the influence of interventions incorporating PA and strength on health and physical function in individuals with knee OA. Supported by NIH NIAMS 1R21AR067560-01.