Adjusting Grip Strength to Body Size: Analyses From 6 Countries

Abstract

Objectives: Absolute handgrip strength and adjusted by body mass index are useful to identify age-related conditions. However, these values are not accurate for older adults with extreme body size because of the nonlinear relationship between strength, height, and body mass. The purpose of this study was to determine cut-off points for age-related conditions of older adults using allometric coefficients to normalize grip strength by body size.

Design: Cross-sectional study.

Setting and participants: Data from 13,235 older adults of Study on Global Aging and Adult Health conducted in 6 low- and middle-income countries were analyzed.

Methods: Country- and sex-specific allometric exponents for body-size variables (mass and height) were computed with log-linear models. Partial correlation verified whether allometric normalization removed the effect of body size on grip strength. Cut-off points were established (<20th percentile) for low allometrically adjusted grip strength.

Results: Allometric exponents for normalization of grip strength were provided for body-size variables, ranging from 0.19 to 2.45. Allometric normalization removed the effect of body size on grip strength (r < 0.30). Overall, frequencies of low muscle strength were overestimated with international criteria (absolute grip strength) compared with the cut-off points proposed in this study.

Conclusions and implications: The proposed allometric exponents normalized grip strength according to body-size variables. These exponents improved the accuracy in identifying age-related conditions in older adults with extreme body size. The variability between strength reveals the need for developing specific cut-off points for low- and middle-income countries. New cut-off points of low normalized grip strength with automatized applicability were proposed for health care providers use in clinical practice.

Keywords: Allometric models; body composition; geriatric assessment; grip strength; physical function.