Mortality Risk among Older People Who Did Versus Did Not Sustain a Fracture : Baseline Prefracture Strength and Gait Speed as Predictors in a 15-Year Follow-Up

BACKGROUND: Physiological reserve, as indicated by muscle strength and gait speed, may be especially determinant of survival in people who are exposed to a health stressor. We studied whether the association between strength/speed and mortality risk would be stronger in the time period after a fracture compared to other time periods. METHODS: Participants were population-based sample of 157 men and 325 women aged 75 and 80 years at baseline. Maximal 10-meter gait speed and maximal isometric grip and knee extension strength were tested at the baseline before the fracture. Subsequent fracture incidence and mortality were followed up for 15 years. Cox regression analysis was used to estimate fracture time-stratified effects of gait speed and muscle strength on mortality risk in three states: 1) non-fracture state, 2) the first post-fracture year and 3) after the first post-fracture year until death/end of follow-up. RESULTS: During the follow-up, 20% of the men and 44% of the women sustained a fracture. In both sexes, lower gait speed and in women lower knee extension strength was associated with increased mortality risk in the non-fracture state. During the first post-fracture year, the mortality risk associated with slower gait and lower strength was increased and higher than in the non-fracture state. After the first post-fracture year, mortality risk associated with lower gait speed and muscle strength attenuated. CONCLUSIONS: Lower gait speed and muscle strength were more strongly associated with mortality risk after fracture than during non-fracture time, which may indicate decreased likelihood of recovery.