Heterogeneity in rate of decline in grip, hip, and knee strength and the risk of all-cause mortality: the Women's Health and Aging Study II

Objectives: To assess the relationship between rate of change in muscle strength and all-cause mortality.

Design: Prospective observational study of the causes and course of physical disability.

Setting: Twelve contiguous ZIP code areas in Baltimore, Maryland.

Participants: Three hundred seven community-dwelling women aged 70 to 79 at study baseline.

Measurements: The outcome was all-cause mortality (1994-2009); predictors included up to seven repeated measurements of handgrip, knee extension, and hip flexion strength, with a median follow-up time of 10 years. Demographic factors, body mass index, smoking status, number of chronic diseases, depressive symptoms, physical activity, interleukin-6, and albumin were assessed at baseline and included as confounders. The associations between declining muscle strength and mortality were assessed using a joint longitudinal and survival model.

Results: Grip and hip strength declined an average of 1.10 and 1.31 kg/year between age 70 and 75 and 0.50 and 0.39 kg/year thereafter, respectively; knee strength declined at a constant rate of 0.57 kg/year. Faster rates of decline in grip and hip strength, but not knee strength, independently predicted mortality after accounting for baseline levels and potential confounders (hazard ratio (HR) = 1.33, 95% confidence interval (95% CI) = 1.06-1.67, HR = 1.14, 95% CI = 0.91-1.41, and 2.62, 95% CI = 1.43-4.78 for every 0.5 standard deviation increase in rate of decline in grip, knee, and hip strength, respectively).

Conclusion: Monitoring the rate of decline in grip and hip flexion strength in addition to absolute levels may greatly improve the identification of women most at risk of dying.