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A Comparison of Leg Power and Leg Strength Within the InCHIANTI Study: Which Influences Mobility More?

¹ Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Boston, Massachusetts.
² Hebrew Rehabilitation Center for Aged, Boston, Massachusetts.
³ Laboratory of Clinical Epidemiology, INRCA Geriatric Department, Florence, Italy.
⁴ Epidemiology, Demography and Biometry Program
⁵ Longitudinal Studies Section, Clinical Research Branch, Gerontology Research Center, National Institute on Aging, Bethesda, Maryland.

Background. In a clinical study evaluating the functioning of mobility-limited elders, muscle power accounted for more of the variation in function than strength did. There was also evidence that the power–function relationship may be described as curvilinear. However, these findings have never been confirmed in a representative population.

Methods. An analysis was conducted using data from the InCHIANTI study, a population-based cohort of 1032 adults living in Italy. To assess the relationships between impairments in power and strength and mobility performance, we created separate multivariate linear and log-transformed regression models as well as separate logistic regression models.

Results. Subjects were age 65 years, predominately female (54%), with a mean age of 74.2 years, and most had mild–moderate mobility limitations (Short Physical Performance Battery score 10.5 ± 2.1). Though leg extension power and isometric hip extension strength were closely associated, in several separate multivariate linear regression models, leg power consistently explained more of the variance than strength did in several measures of physical performance. Differences were even larger when observed in curvilinear models of power and strength. Using separate multivariate logistic regression models to examine the odds ratios for mobility limitations in persons with low muscle power versus high muscle power, and in persons with low muscle strength versus high muscle strength, we found that both factors influenced risk for mobility limitations, but low power was associated with a 2–3-fold greater likelihood than low strength.

Conclusion. These findings identified muscle power to be a more influential proximal determinant of physical performance than impairments in strength and emphasized muscle power as an important determinant of mobility skills in older adults.

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