The nonlinear relationship between gait speed and falls: the Maintenance of Balance, Independent Living, Intellect, and Zest in the Elderly of Boston Study.

OBJECTIVES: To examine the relationship between gait speed and falls risk.

DESIGN: Longitudinal analysis of the association between gait speed and subsequent falls and analysis of gait speed decline as a predictor of future falls.

SETTING: Population-based cohort study.

PARTICIPANTS: Seven hundred sixty-three community-dwelling older adults underwent baseline assessments and were followed for falls; 600 completed an 18-month follow-up assessment to determine change in gait speed and were followed for subsequent falls.

MEASUREMENTS: Gait speed was measured during a 4-m walk, falls data were collected from monthly post-card calendars, and covariates were collected from in-home and clinic visits.

RESULTS: There was a U-shaped relationship between gait speed and falls, with participants with faster (≥1.3 m/s, incident rate ratio (IRR)=2.12, 95% confidence interval (CI)=1.48-3.04) and slower (<0.6 m/s, IRR=1.60, 95% CI=1.06-2.42) gait speeds at higher risk than those with normal gait speeds (1.0-<1.3 m/s). In adjusted analyses, slower gait speeds were associated with greater risk of indoor falls (<0.6 m/s, IRR=2.17, 95% CI=1.33-3.55; 0.6-<1.0 m/s, IRR=1.45, 95% CI=1.08-1.94), and faster gait speed was associated with greater risk of outdoor falls (IRR=2.11, 95% CI=1.40-3.16). A gait speed decline of more than 0.15 m/s per year predicted greater risk of all falls (IRR=1.86, 95% CI=1.15-3.01).

CONCLUSION: There is a nonlinear relationship between gait speed and falls, with a greater risk of outdoor falls in fast walkers and a greater risk of indoor falls in slow walkers.