Background: Poor balance is a risk factor for falls and fracture in older adults, but little is known about modifiable factors affecting balance in younger women. This study aimed to examine whether lower limb muscle strength (LMS) in young women and changes in LMS with ageing are independent predictors of balance in middle-age.
Methods: Additional 10-yr follow-up of 467 women aged 25-44 years at baseline who previously participated in a 2-yr randomized controlled trial of osteoporosis educational interventions. LMS was measured by dynamometer. Static and dynamic balance was assessed by timed up and go test (TUG), step test (ST), functional reach test (FRT) and lateral reach test (LRT). Multivariable linear regression was used to examine associations of baseline and 12-year change in LMS with balance measures.
Results: LMS declined by a mean of 17.3 kg over 12 years. After adjustment for confounders and change in LMS, LMS at baseline was associated with better performance on the TUG [-0.007 sec/kg (95% confidence interval (CI): -0.010, -0.005)], ST (0.047 steps/kg: 0.024, 0.070), FRT (0.054 cm/kg: 0.026, 0.081) and LRT (0.028 cm/kg: 0.009, 0.048) 12 years later. After adjustment for baseline LMS, slower decline in LMS was significantly associated with better performance on TUG (-0.005 sec/kg: -0.008, -0.002) and FRT (0.073 cm/kg: 0.043, 0.102). An association with LRT approached statistical significance (0.019 cm/kg: -0.001, 0.040) (p=0.06) but there was no association with ST.
Conclusions: Among young women, greater LMS at baseline and slower decline over time are both associated with better balance in midlife. Analogous to the contributions of peak bone mass and bone loss to fracture risk, this suggests that both improvement of muscle strength in younger age and prevention of age-related loss of muscle could be potentially useful strategies to improve balance and reduce falls risk in later life.