Fig. 2.

Example of postural responses to rightward discrete and biphasic perturbations. Kinematics of center of mass (CoM) motion in the frontal (x) plane are shown for discrete, forward biphasic, and backward biphasic perturbations. The directions of CoM kinematic components relative to the feet during rightward platform acceleration (shaded region) were oriented in similar directions during discrete perturbations. However, in biphasic perturbations, the direction and magnitude were more dissociated. Muscular responses lagged behind CoM acceleration onset by ∼100 ms (compare shaded boxes with black dotted lines) and varied across perturbation types. Disp and d, displacement; v, velocity; a, acceleration; EMG, electromyograph; VLAT, vastus laturalis; TA, tibialis anterior; MGAS, medial gastrocnemius.