Relationships between walking distance and percentiles of BMI in older and younger men

Paul T Williams ^1*

¹ Lawrence BerkeleyLaboratory, United States

^* To whom correspondence should be addressed. E-mail: ptwilliams{at}lbl.gov.

Accepted 7 February 2008

Abstract

Objective: To assess the relationships of weekly walking distance to body weight and waist circumference in elderly (age75 years), senior (55age<75 years), middle-aged (35age<55 years), and younger men (18age<35 years old). Design: Cross-sectional analyses of baseline questionnaires from 7,082 male participants of the National Walkers' Health Study. Results: Standard regression analyses showed that BMIs were inversely and significantly associated with walking distance (kg/m2 per km/wk) in elderly (slope ± SE: -0.032±0.008), senior (-0.045±0.005), and middle-aged men (-0.037±0.007), as were their waist circumferences (-0.091±0.025, -0.045±0.005, and -0.091±0.015 cm per km/wk, respectively), and that these slopes remained significant when adjusted statistically for reported weekly servings of meat, fish, fruit, and alcohol. However, percentile regression analyses showed that the declines in BMI per km/wk walked were greater at the higher than lower percentiles of the BMI distribution. In men ?75 years old the decline per km walked was 5.1-fold greater among the heaviest men (i.e., 90th BMI percentile, -0.100 kg/m2 per km/wk) than among the leanest men (i.e., 10th BMI percentile; -0.018 kg/m2 per km/wk). The differences in slope at the 90th compared to the 10th BMI percentile were 5.9-fold among men 55-74 years old and 6.7-fold among men 35-54 years old. Per km/wk walked, the declines at the 90th percentile of waist circumference were also greater than at its 10th percentile, and intermediate for percentiles in between. Whereas standard regression analyses suggest that the average declines in BMI per km/wk walked reported here are consistent with those reported previously per km/wk run in male runners 35-54 (-0.036±0.001 kg/m2 per km/wk) and ?50 years old (-0.038±0.001 kg/m2 per km/wk), percentile regression analyses showed that when adjusted to the leaner body weights of the runners the declines per km walked were between 49% and 59% less for walkers than runners. Conclusions: Declines in BMI and waist circumferences with walking distance depend upon the percentile of the BMI distribution, with the decline per km walked being significantly greater among heavier men.