When mechanical work meets energetics: Obese versus non-obese children walking.

Abstract

What is the central question of this study? The aim was to compare the cost of transport and mechanical work between obese and non-obese children at different walking speeds. What is the main finding and its importance? Our data show that the cost of transport, mechanical efficiency and work are similar and directly mass dependent in obese and non-obese children. The optimal walking speed (most economical walking speed) is reduced in obese children. Although studies have shown the influence of gait biomechanics on the metabolic economy in obese adults and adolescents, little is known regarding obese children. We compared the metabolic cost of transport, apparent mechanical efficiency and gait biomechanics (assessed by mechanical energy fluctuations) in obese children (n=12; mean±SD: 8.6±0.51 years of age, 1.38±0.04m, 44.6±6.65kg, 24.1±3.50kgm-2 ) and age- and sex-matched non-obese children (n=12, 7.8±0.90 years of age, 1.31±0.08m, 26.8±2.24kg, 16.4±1.40kgm-2 ) while walking at different speeds (from 1 to 5kmh-1 ) on a treadmill. We found that the mechanical efficiency was higher at 3kmh-1 compared with the remaining speeds for both groups (P<0.05). Although the internal mechanical work has been greater in obese compared with non-obese children at 4 and 5kmh-1 , the external, total mechanical work and the mechanical efficiency remained similar between obese and non-obese children at all speeds. Likewise, the cost of transport was similar in the two groups, although the optimal walking speed was an average of 0.4kmh-1 slower in obese children. Clearly, these results show that the walking economy is associated with the total mechanical work in obese and non-obese children. Finally, the reduced functional mobility in obese children observed in previous studies seems to be associated with a reduction in optimal walking speed in comparison to non-obese children.