Energy Expenditure During Walking in Adults: Impact of Body Mass Index and Sex

Purpose: The aim of this study was to determine if the linear and nonlinear coefficients of the energy expenditure-walking speed relationship are influenced by body mass index (BMI; kg/m 2 ) and sex. Methods: Participants (n=182; 96 females) ages 18-60 yr walked at 0.89 m/s (2.0 mph), 1.34 m/s (3.0 mph), and 1.79 m/s (4.0 mph) for six min each while oxygen uptake (V̇O 2 ; mL/kg/min) was calculated via indirect calorimetry and converted to energy expenditure (EE; W/kg). Net W/kg was calculated by subtracting standing W/kg from gross W/kg. Polynomial random coefficient regression (PRCR) was employed to produce individual-level linear and quadratic coefficients to assess whether BMI influenced W/kg during walking. Net energy cost of walking (Cw; J/kg/m) was also determined for each walking speed. Results: Net W/kg and Cw were not significantly correlated with BMI at 0.89 m/s and 1.79 m/s, but were weakly inversely correlated (r 2 < 0.03) with BMI at 1.34 m/s. BMI was not significantly correlated with the linear coefficient for net or gross W/kg (both r = 0.07), but was weakly correlated with the quadratic coefficient for net (r = 0.17, P = 0.02) and gross (r = 0.16, P = 0.04) W/kg (r 2 < 0.03 for both). However, PRCR coefficients did not differ between normal weight BMI (n=32; 18.5-<25.0 kg/m 2 ), overweight (n=74; 25-<30.0 kg/m 2 ) and obese (n=76; > 30.0 kg/m 2 ) groups. Females had higher W/kg, but sex differences were eliminated after controlling for height. Conclusions: We conclude that BMI has little impact on the EE of walking at speeds between 0.89 m/s and 1.79 m/s, and that sex differences in walking EE are eliminated after controlling for height.