Body Mass Index and Physical Functioning in Older Adults

Abstract

Several researchers have reported that elevated body mass index (BMI) increases the risk of poor physical functioning. In most studies, physical functioning has been measured using self-reported questionnaires. For this study, we explored the relationship between BMI and two objective measures of physical functioning, gait speed and peak knee extensor power. We analyzed data from the population-based NCHS’ National Health and Nutrition Examination Survey (NHANES 1999-2002). Gait speed was determined with a 20-foot timed walk test and peak knee extensor power was calculated as the product of isokinetic peak leg torque (peak force multiplied by arm length of dynamometer) and peak force velocity for subjects aged 60 years and older. BMI was specified as a continuous variable. The relationship between BMI and gait speed differed by race/ethnicity (P = 0.044) and the relationship between BMI and peak knee extensor power differed by gender (P = 0.002). Among non-Hispanic whites, the association

between BMI and gait speed was the strongest (P < 0.001). With every unit increase in BMI (kg/m2), gait speed decreased by 0.011 meters/second. Among non-Hispanic blacks, with every unit increase in BMI (kg/m2), gait speed decreased by 0.006 meters/second (P = 0.001). Among Hispanics, no linear relationship was found (P = 0.435). Regarding leg power, with every unit increase in BMI (kg/m2), leg power increased by 1.09 watts (P < 0.001) for women and by 1.86 watts (P < 0.001) for men. With the growth of the older population, our results may facilitate the planning of public health interventions directed toward the most vulnerable groups.