Association between walking distance and percentiles of body mass index in older and younger men

Objective: To assess the association of weekly walking distance to body weight and waist circumference in elderly ( age >= 75 years), senior ( 55 <= age < 75 years), middle- aged ( 35 <= age < 55 years), and younger men ( 18 <= age < 35 years old). Design: Cross-sectional analyses of baseline questionnaires from 7082 male participants of the National Walkers' Health Study. Results: Standard regression analyses showed that body mass index (BMI) was inversely and significantly associated with walking distance (kg/m(2) per km/week) 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 (-0.090 (0.025), -0.122 (0.012) and -0.091 (0.015) cm per km/week, 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/week walked were greater at the higher than the lower percentiles of the BMI distribution. In men >= 74 years old the decline per km walked was 4.9-fold greater among the heaviest men ( that is, 90th BMI percentile; -0.076 kg/m(2) per km/week) than among the leanest men ( that is, 10th BMI percentile; -0.015 kg/m(2) per km/week). The differences in slope at the 90th compared to the 10th BMI percentile were 5.4-fold among men 55-74 years old and sixfold among men 35 54 years old. Per km/week 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/week walked reported here are consistent with those reported previously per km/week run in male runners 35-54 years old (-0.036 (0.001) kg/m(2) per km/week) and >= 50 years old (-0.038 ( 0.001) kg/m(2) per km/week), 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.