Fig. 7. (A) The phase angle (rad) between the peak in the forward push of the back leg (peak F_f,back) and the beginning of the double contact phase is presented as a function of the walking speed expressed as a Froude number. Each age group is presented with a different symbol (filled circles, 3-4 years; squares, 5-6 years; diamonds, 7-8 years; triangles, 9-10 years; inverted triangles, 11-12 years). (B) The mass-specific work per distance done by one leg against the other (W_int,dc; J kg^-1 m^-1) is presented as a function of the Froude number for all age groups. The broken lines show the adult trends.