Knee extension strength is a significant determinant of static and dynamic balance as well as quality of life in older community-dwelling women with osteoporosis.

Background: Determinants of balance have not been well studied in women with osteoporosis yet falls are the major cause of fracture in this population.

Objective: To describe the associations among knee extension strength, medication history, medical history, physical activity and both static and dynamic balance in women diagnosed with osteoporosis.

Methods: We assessed health history, current medication and quality of life by questionnaire in 97 community-dwelling women with osteoporosis. Static balance was measured by computerized dynamic posturography (Equitest), dynamic balance by timed figure-eight run, and knee extension strength by dynamometry.

Results: The 97 participants (mean (SD) age 69 (3.2) years) had a mean lumbar spine BMD of T = -3.3 (0.7) and total hip BMD of -2.9 (0.4). In stepwise linear regression, the significant determinants of static balance that explained 18% of total variance were knee extension strength (10%, p < 0.001), age (5%, p < 0.01) and tobacco use (3%, p < 0.05). The significant predictors of dynamic balance were knee extension strength (26%, p < 0.001), medications (6%, p < 0.05), age (4%, p < 0.05), height (4%, p < 0.001), as well as years of estrogen use (2%), tobacco use (2%) and weight (2%) (all p < 0.05). Knee extension strength was also associated with quality of life (r(2) = 0.12, p < 0.001). Based on these models, a 1 kg/cm ( approximately 3%) increase in mean knee extension strength was associated with 1.2, 2.4 and 3.4% greater static balance, dynamic balance and quality of life, respectively.

Conclusions: Knee extension strength is a significant determinant of performance on static and dynamic balance tests in 65- to 75-year-old women with osteoporosis. In this cross-sectional study, knee extension strength explained a greater proportion of the variance in balance tests than did age. Investigation into the effect of intervention to improve knee extension strength in older women with osteoporosis is warranted.