Fig. 9. Jumping performance of models 3 and 4. (A) Models 3 and 4 were both placed in the normal starting position. The colored arrows represent the ground reaction forces (GRFs) as in Figs 6 and 7 for both models. Note that the GRF generated by internal rotation at the knee is mostly lateral in direction (i.e. out of the page) and hence is not shown. (B) The path of the center of mass (COM) of model 3 during the ground-contact phase for 500 simulation runs in which the magnitudes of hindlimb torques were randomly varied. The red path in B-D represents the simulation run in which the actual torques produced by the real frog were used to drive the degrees of freedom (DOFs) in model 3. The blue path represents the simulation run in which the same torque pattern was used to drive model 4. (C) The vertical V_V and horizontal V_H velocities of the COM for the red simulation run matched those of the real frog (black lines) over the first 70ms. At this time, model 3 was maximally extended and the simulation ended. The vertical and horizontal velocities of the COM of model 4 more closely matched those of the real frog over the entire 90ms take-off phase (i.e. addition of the distal joint allowed model 4 to extend further during the remaining 15ms of the jump). (D) The predicted jump distance for model 3 was less than that of the real frog. However, the predicted jump distance for model 4 closely approximated that of the real frog. (E) As in model 2, vertical and horizontal velocities in model 3 were not correlated. (F) The magnitude of only the hip extensor (HE) torque was significantly (P<0.01, r²=0.71) correlated with variations in the peak horizontal velocity among the simulation runs in model 3. No single torque component was significantly correlated with variations in vertical velocity. In trials in which the ankle extensor (AE) torque was greater than 0.3 N cm (boxed region in the V_V versus AE torque graph), the time (T) taken for the ankle to extend past 90° was significantly (r²=0.61, P<0.05) correlated with variations in vertical velocity (right panel). The later the ankle extended during the ground-contact phase, the larger the vertical velocity.

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