Absolute Strength and Loss of Strength as Predictors of Mobility Decline in Older Adults: The InCHIANTI Study

Theoretical definitions of sarcopenia traditionally emphasize age-related loss of muscle strength; however, most analyses of the association between strength and mobility examine strength at a single time point. This study sought to identify sex-specific cutpoints for muscle strength and power (at one time point) and 3-year changes in strength and power that would maximize prediction of 3-year mobility decline. Longitudinal analysis of 934 adults aged >= 65 years enrolled in the Invecchiare in Chianti study was conducted. Grip strength, knee extension strength, and lower extremity power were measured at baseline and 3 years postenrollment. Mobility function (gait speed and self-reported mobility disability) was measured at 3 and 6 years postenrollment. Classification and regression tree analysis was used to predict mobility decline from Years 3 to 6. Men with knee extension strength < 19.2 kg and grip strength < 39.0 kg had clinically meaningful declines in gait speed of .24 m/s. Furthermore, men with power < 105 W were nearly nine times more likely to develop incident mobility disability (likelihood ratio = 8.68; 95% confidence interval = 3.91, 19.44). Among women, knee extension strength < 18.0 kg was associated with a minimal gait speed decline of 0.06 m/s, and women with leg power < 64 W were three times more likely to develop incident mobility disability (likelihood ratio = 3.01; 95% confidence interval = 1.79, 5.08). Three-year changes in strength and power did not predict mobility decline in either sex. Findings suggest that strength and power measured at one time point are more predictive of mobility decline than 3-year changes and that low strength and power are particularly powerful risk factors in men.