title: 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.
abstract: 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.
authors.affiliation: Fall-Free BC Research Group: BC Women's Hospital and Health Centre Osteoporosis Program and Faculty of Medicine (Department. of Family Practice), University of British Columbia, Vancouver, BC, Canada.
authors.forename: Nick D
authors.initials: ND
authors.lastname: Carter
authors.forename: Karim M
authors.initials: KM
authors.lastname: Khan
authors.forename: Arthur
authors.initials: A
authors.lastname: Mallinson
authors.forename: Patti A
authors.initials: PA
authors.lastname: Janssen
authors.forename: Ari
authors.initials: A
authors.lastname: Heinonen
authors.forename: Moira A
authors.initials: MA
authors.lastname: Petit
authors.forename: Heather A
authors.initials: HA
authors.lastname: McKay
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control; D000368:Aged; D005260:Female; D006304:Health Status; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D016014:Linear Models; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D015663:Osteoporosis, Postmenopausal / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011237:Predictive Value of Tests; D011788:Quality of Life; D011795:Surveys and Questionnaires