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First published online January 12, 2004
Journal of Experimental Biology 207, 587-596 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00793

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Mechanical work and muscular efficiency in walking children

B. Schepens, G. J. Bastien, N. C. Heglund and P. A. Willems^*

Unité de Physiologie et Biomécanique de la Locomotion, Université Catholique de Louvain, 1 Place Pierre de Coubertin, B-1348 Louvain-la-Neuve, Belgium

^* Author for correspondence (e-mail: patrick.willems{at}loco.ucl.ac.be)

Accepted 17 November 2003

The effect of age and body size on the total mechanical work done during walking is studied in children of 3–12 years of age and in adults. The total mechanical work per stride (W_tot) is measured as the sum of the external work, W_ext (i.e. the work required to move the centre of mass of the body relative to the surroundings), and the internal work, W_int (i.e. the work required to move the limbs relative to the centre of mass of the body, W_int,k, and the work done by one leg against the other during the double contact period, W_int,dc). Above 0.5 m s^–1, both W_ext and W_int,k, normalised to body mass and per unit distance (J kg^–1 m^–1), are greater in children than in adults; these differences are greater the higher the speed and the younger the subject. Both in children and in adults, the normalised W_int,dc shows an inverted U-shape curve as a function of speed, attaining a maximum value independent of age but occurring at higher speeds in older subjects. A higher metabolic energy input (J kg^–1 m^–1) is also observed in children, although in children younger than 6 years of age, the normalised mechanical work increases relatively less than the normalised energy cost of locomotion. This suggests that young children have a lower efficiency of positive muscular work production than adults during walking. Differences in normalised mechanical work, energy cost and efficiency between children and adults disappear after the age of 10.

Key words: walking children, mechanical work, energy cost, muscular efficiency

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