Nonlinear relationships between weekly walking distance and adiposity in 27,596 women.

INTRODUCTION/
PURPOSE: Data from vigorously active women (runners) suggested that declines in adiposity with weekly running distance were nonlinear and dependent on whether the women are relatively lean or fat. The purpose of the current study is to assess the cross-sectional relationship between the amount of moderate-intensity physical activity (walking distance) and indicators of adiposity.
METHODS: Cross-sectional analyses (i.e., quadratic polynomial regression, regression for percentiles of adiposity) of body mass index (BMI), body circumferences, and bra cup sizes in 27,596 women.
RESULTS: The estimated percent reductions between walking 40-50 km.wk(-1) and <10 km.wk(-1) were greatest for BMI, intermediate for waist circumference and cup size, and least for hip and chest circumferences. The relationships of walking distance to BMI and body circumferences were all nonlinear (convex). In addition, the inverse relationship between weekly walking distance and adiposity was greatest at the highest percentile of BMI, body circumferences, and cup size, and least at the lowest percentiles. Thus, the decline in adiposity per kilometer per week increment in walking distance was greatest in overweight mostly sedentary women and least in lean active women. The decline in BMI per kilometer per week of exercise was greater in the walkers than previously reported for runners. However, based on the relationships between walking distance and percentiles of the BMI distribution reported here, we show that the majority of this difference is attributable to the leanness of the runners and greater fatness of the walker.
CONCLUSION: These data suggest that in women the greatest benefit of walking may be among the most obese and that at higher weekly distances the declines in weight associated with walking diminish. Whether these relationships are causal remains to be determined.