Fig. 4. Segmental angular displacements and instantaneous angular velocities during single representative cycles of a diagonal sequence walk (left column) and a rotary gallop (right column) at treadmill speeds of 1.68 m s^–1 and 2.56 m s^–1, respectively. Note that in this gallop cycle (B), the head is pitching through less than 20° and is not rotating in any other plane. The (A,B) segmental displacement graphs depict changes in head-to-space (H–S,), trunk-to-space (T–S), and head-to-trunk (H–T) angles. Earth horizontal is indicated by 0° (dashed horizontal line), and negative values indicate a nose-down angle of the head axis and a shoulders-down angle of the trunk axis. The horizontal lines depict the support phases of the left hind limb (LH), left forelimb (LF), right forelimb (RF) and right hind limb (RH). The remaining graphs depict instantaneous angular velocity changes of (C,D) the head relative to space, (E,F) the trunk relative to space and (G,H) the head relative to the trunk. In (C,D) the head-to-space velocity graphs, the solid horizontal lines indicate 350° s^–1 that, at least in humans, is the saturation velocity for the vestibulo–ocular (VOR) reflex (Pulaski et al., 1981).