Objective: Cross-sectional studies show that active individuals are leaner than their
sedentary counterparts. The purpose of this paper is to determine the extent that this is due
to self-selection bias, specifically to initially leaner men and women choosing to exercise
longer and more intensely. Methods: Walking quantity (weekly distance) and intensity
(speed) were compared to current body mass index (BMI)(BMI current) and BMI at the start
of walking (BMI starting) in 20 353 women and 5174 men who on average had walked …

Although cross-sectional studies show active individuals are leaner than their sedentary
counterparts, it remains to be determined to what extent this is due to initially leaner men
and women choosing to exercise longer and more intensely (self-selection bias). In this
report walking volume (weekly distance) and intensity (speed) were compared to current
BMI (BMIcurrent) and BMI at the start of walking (BMIstarting) in 20,353 women and 5,174
men who had walked regularly for exercise for 7.2 and 10.6 years, respectively. The …