FIGURE 1.
(A) Schematic figure of the custom-developed perturbation-system for the quick release experiment. (B) Spring model of the trunk with stiffness K, damping B, resting angle θ0 (hypothetical resting angle of spring stiffness), trunk length L (measured from the L4/L5 to the T9 joints), gravitational trunk force Fg, and instantaneous angle of the trunk θ(t).