BODY MASS INDEX AND SEX INFLUENCE THE ENERGY COST OF WALKING AT SELF-SELECTED SPEEDS

Abstract

PURPOSE To examine the effect of body mass index and sex on the energy cost of walking at self-selected speeds. METHODS 258 healthy adults (M=107, F=151) of varying age (19–85 yrs.) and body mass index (BMI, 17.9–43.7 kg/m2) were studied. Energy expenditure (EE) was measured using indirect calorimetry while sitting at rest for 10 minutes, and walking on a motorized treadmill for 10 minutes at each of the two self-selected walking speeds (normal and brisk). Multivariate models to predict the net energy cost (walking EE – sitting EE, in kcal/1000 step) of walking at each speed were developed using BMI and sex as predictors. RESULTS At the normal walking speed, the net EE of walking for men was predicted by the equation EE = 2.7423 + (1.5024 * BMI), whereas for the women EE = 14.1825 + (0.9177 * BMI). The interaction of sex and BMI on net EE at the normal self-selected speed was significant (P=0.016). Likewise, at the brisk walking speed, the equations were EE = 9.9169 + (1.9897 * BMI) for men and EE = 30.3222 + (0.9917 * BMI) for women, and the interaction term was significant (P=0.015). CONCLUSION There is a fairly strong interaction between sex and BMI for the net EE of walking at both normal and brisk self-selected walking speeds. For brisk walking the slope in men is approximately twice that of women, i.e. for an increase in 1 BMI unit, a male's net EE increases by twice that of female. These data suggest that either a) overweight and obese men are less successful at selecting the most economical walking speed than overweight and obese women, or b) the increased energy cost per step in men versus women is related to the different distribution of body fatness in overweight and obese men (abdominal) and women (gluteal). Supported by NIH DK48520 and R01 DK42549