A dimensional paradigm for identifying the size-independent cost of walking.

PURPOSE: The purpose of this investigation was to present an alternative paradigm to that of dividing the rate of oxygen consumption by body mass (VO2.M-1, mL.min-1kg-1) for comparing walking economy in humans.
METHODS: The paradigm used dimensional analysis and similarity theory to derive a measure of size-independent cost (SIC), defined as the net oxygen cost to move a mass of one kilogram a distance equal to stature. Mass-specific gross oxygen cost per kilometer, mass-specific net oxygen cost per kilometer, and SIC were used to analyze results from 184 subjects who performed level treadmill walking. Subjects were 63 children, 40 adolescents, 42 adults, and 39 seniors (approximately equal numbers of male and female subjects) walking at treadmill speeds from 0.9 to 1.8 m.s-1.
RESULTS: Comparisons of metabolic cost between children and the older groups were dependent on the measure of metabolic cost and speed. At each speed, VO2gross.M-1 was higher in children than in older groups, whereas VO2net.M-1 of children was higher at 1.1 and 1.3, but similar at 0.9 m.s-1. SIC of children was similar at 1.1 and 1.3 m.s-1 but lower than the older groups at 0.9 m.s-1.
CONCLUSIONS: Higher mass-specific metabolic costs of children were explained by differences in standing metabolism and stature. When these variables were considered, children had similar or lower metabolic costs than older subjects. Alternatives to using mass alone to normalize locomotor economy are warranted.