Fig 4. Speed scaling of temporal variables concerning the GRF in birds and humans.

Times are normalized to the duration of stance. (A, B) Time of positive peak F_x. (C, D) Time of negative peak F_x. (E, F) Time at which F_x is zero. (G, H) The magnitude of F_z when F_x is zero. (A), (C), (E) and (G) are for birds, (B), (D), (F) and (H) are for humans. In (E), the relationship with speed varies with body mass, and so this has been demonstrated with several different masses. In (F), major axis fits for both walking and running have been applied; they have the same elevation at the walk-run transition. Regression equations for birds are reported in Table 3.