Strength, balance, and the modifying effects of obesity and knee pain: Results from the Observational Arthritis Study in Seniors (OASIS)

OBJECTIVE: To examine the relationship between muscular strength and dynamic balance in a sample of older adults with knee pain and to determine the role that obesity and severity of knee pain play in the ability to maintain balance. DESIGN: Cross-sectional study designed to examine the association between strength and balance in a cohort of older adults with chronic knee pain. SETTING: A university health and exercise science center. PARTICIPANTS: A cohort of 480 adults age 65 and older with knee pain. MEASUREMENTS: Force platform dynamic balance measure of the center of pressure excursion during a forward and subsequent backward lean. Isokinetic strength measures of concentric and eccentric knee flexion and extension and concentric ankle plantar flexion and dorsiflexion. Body mass index (BMI) and a knee pain scale were used to measure obesity and knee pain, respectively. RESULTS: A regression model was developed to investigate the relationship between dynamic balance and muscular strength while controlling for gender, BMI, radiographic severity, knee pain, and foot length. Knee strength alone explained 18.4% of the variability in dynamic balance. The addition of knee pain, BMI, radiographic severity, gender, and foot length explained an additional 6.7%. When the knee-ankle interaction, ankle strength, and knee strength-pain interaction variables were added to the regression model, 28.9% of the variability in dynamic balance was explained. CONCLUSIONS: Strength appears to play a significant role in maintaining balance in an older, osteoarthritic population. We found that mean knee strength accounted for approximately 19% of the variability in dynamic balance. Hence, greater knee strength was associated with better dynamic balance. The best dynamic balance performances occurred in participants that had a combination of strong knees and strong ankles. However, knee osteoarthritic patients with weak knee strength could still maintain high levels of dynamic balance by having strong ankle strength. Moreover, we have shown that obesity is associated with attenuated dynamic balance performance and that poorer balance is associated with higher pain scores in the presence of weaker knees. For stronger knees, however, pain does not appear to be related to balance.