Fig. 7. Phase shift (A), %Recovery (B) and %Congruity (C) as a function of forward speed. Walking (open circles) was considered to occur when the phase shift between horizontal kinetic energy (E_k) and gravitational potential energy (E_p) of the center of mass (COM) was out-of-phase or near 180°; running (filled circles) was considered to occur when the phase shift between the E_k and E_p of the COM was in-phase or near 0°. Those trials during which the phase shift was neither in- nor out-of-phase were categorized into an intermediate gait (crosses). (B) %Recovery generally decreased with speed. (C) %Congruity increased with forward speed and generally showed a similar separation as %Recovery with respect to walking and running mechanical trials.