Physical fitness in older women with low-, middle-, and high-body mass index

Abstract

The age-related decreases in physical fitness observed in previous studies cannot be completely explained by differences in body mass index (BMI). Therefore, the purpose of this study was to examine the relationship between age and selected physical fitness items in low-, middle-, and high-BMI groups. We recruited 439 older adult women, aged 6079 years, living independently in communities. The subjects completed 8 physical fitness tests related to activity of daily living (ADL), and were categorized into three groups using percentile rank of BMI: (a) low BMI (<21.4, n = 90), (b) middle BMI (23.126.7, n = 87), (c) high BMI (≥26.7, n = 87). BMI was calculated as body weight in kg divided by the squared height (kg/m²). The eight physical fitness tests (total physical fitness) were summarized as three domains: whole body locomotion, upper limb strength, and change of posture. To determine cross-sectional changes in physical fitness with increasing age, Pearson's correlation coefficient was calculated, and linear regression analysis was performed with physical fitness domain as the independent variable (y) and age as the dependent variable (x). Then differences in the regression coefficient and intercept between the entire group and three BMI groups were compared. Physical fitness domains were compared among the three groups with one-way ANOVA. The major findings were the following: (1) upper limb strength was lower in the low-BMI group; (2) total physical fitness, whole body locomotion, and the changes of posture were lower in the high-BMI group; (3) three physical domains and total physical fitness declined with age in all groups; and, (4) the declines in total physical fitness and the change of posture were higher in the low-BMI group, and the declines in the same domains were lower in the middle- and high-BMI groups. Due to the nature of cross-sectional analysis, it is observed that decreases in physical fitness are associated with its initial level. These results suggest that low BMI, high BMI and advancing age are associated with decreases in physical fitness among older women, and thereby impacting the ability to perform ADL.