Fig. 6. Comparison of mechanical variables across C (black bars), U (pale grey bars) and V (dark grey bars) treatments, with U trials subdivided into energy exchange modes. Values are means ± s.e.m for all instances of each response. Initial horizontal velocity (V_i,h) was measured at the COM apex during the flight phase prior to the measured step (`begin' point in Fig. 3B). The net change in COM height (s_v) was determined over the time interval illustrated in Fig. 3B. The other mechanical variables were measured over the period of ground contact.