Obesity does not increase external mechanical work per kilogram body mass during walking

Abstract 

Walking is the most common type of physical activity prescribed for the treatment of obesity. The net metabolic rate during level walking (W/kg) is ~10% greater in obese vs. normal weight adults. External mechanical work (W_ext) is one of the primary determinants of the metabolic cost of walking, but the effects of obesity on W_ext have not been clearly established. The purpose of this study was to compare W_ext between obese and normal weight adults across a range of walking speeds. We hypothesized that W_ext (J/step) would be greater in obese adults but W_ext normalized to body mass would be similar in obese and normal weight adults. We collected right leg three-dimensional ground reaction forces (GRF) while twenty adults (10 obese, BMI=35.6kg/m² and 10 normal weight, BMI=22.1kg/m²) walked on a level, dual-belt force measuring treadmill at six speeds (0.50–1.75m/s). We used the individual limb method (ILM) to calculate external work done on the center of mass. Absolute W_ext (J/step) was greater in obese vs. normal weight adults at each walking speed, but relative W_ext (J/step/kg) was similar between the groups. Step frequencies were not different. These results suggest that W_ext is not responsible for the greater metabolic cost of walking (W/kg) in moderately obese adults.

Keywords: Biomechanics, Obesity, Metabolic cost, Physical activity