Energy cost of walking in boys who differ in adiposity but are matched for body mass

Purpose: To compare the energy cost of treadmill walking, in pairs of obese and lean adolescents who were matched for total body mass. Methods: Metabolic energy expenditure was determined at 67, 83, and 100 m-min(-1), in nine obese and nine nonobese 11- to 18-yr-old boys. Total adiposity and fat distribution in the trunk and limbs were assessed using DXA. Results: There were no intergroup differences in the net (exercise minus rest) energy cost at the two lower speeds, but the obese boys expended more energy at 100 m.min(-1) (12%, P<0.05). Heart rate was consistently higher in the obese boys: 18% at 67 m.min(-1), 22% at 83 m.min(-1), and 28% at 100 m.min(-1). Pooling all subjects together, body mass, rather than adiposity, was the main predictor of energy cost: 89.1%, 76.3%, and 62.1% (P<0.05 for all) of the total variance at 67, 83, and 100 m.min(-1), respectively. The variance explained by total body fat was only 2.1%, 8.4%, and 16%, respectively. There was no relationship between (V)over dot O-2net, and the proportion of fat in body segments. Conclusion: It is total body mass, more than adiposity (total and regional) per se, that affects the energy cost of locomotion in obese boys.