Fig. 5. Normalisation by the Froude number. Percentage of recovery of mechanical energy (A) and correlation coefficients between E_p and E_k (B) for toddlers at the first unsupported steps (blue), 1–5 months later (cyan), children older than 2 years of age (violet) and adults (red). Data points for individual steps are plotted as a function of Froude number (Fr=V²g^–1L^–1, where V is the average speed of locomotion, g the acceleration of gravity, and L the lower limb length). Continuous lines represent second-order-polynomial fittings.