Fig. 6. Representative ground forces, center of mass (COM) velocites, and COM mechanical energies during a `mechanical walk' (A) and a `mechanical run' (B). For each trial, a single complete stride is shown. For the walking trial, animal weight=0.083 N; speed=0.10 m s^-1; stride frequency=2.2 Hz; phase shift=147°; recovery=24.3%; duty factor=0.74; same-side limb (SSL) phase=36.2%; diagonal limb (DL) phase=13.0%; congruity=39.9%; external mechanical power=0.11 W kg^-1. For the running trial, animal weight=0.085 N; horizontal velocity=0.19 m s^-1; stride frequency=3.0 Hz; phase shift=3.4°; recovery=14.5%; duty factor=0.73; SSL phase=38.1%; DL phase=14.3%; congruity=61.1%; external mechanical power=0.21 W kg^-1. E_k, horizontal kinetic energy; E_p, gravitational potential energy.