Fig. 5. Model collisional energy losses for a step with full ranges of forelimb–hindlimb phases. A ±25% limb phase suggests exactly even timing between hind- and forefoot contacts (H-F-H-F-, represented by vertical grey broken lines). Dotted lines represent energy lost at hind-foot contact; broken lines the energy lost at forefoot contact; solid lines the total energy lost for a step (one hind- and one forefoot contact). Three hypothetical powering strategies are shown: immediate recovery of energy loss (black); energy recovery only directly after forefoot contact (red) (most realistic); energy recovery only after hindfoot contact (blue). (A) Results for a fore-aft symmetrical walking dog with even fore- and hindleg lengths and a centre of mass (COM) mid-way along the body. (B) As for A, but with a realistic bias in leg lengths (foreleg = 0.47 m, hindleg = 0.46 m). (C) As for A, but with a realistic bias in mass position, with the COM towards the shoulders (p=0.6). (D) Results using realistic values of both limb length and mass bias. The underlying grey box represents the observed range of mean phases for walking dogs.