Figure 13.

Four basic mechanisms for balance control during locomotion. A, The limb transfer mechanism controls the limb landing position. B, The limb displacement compensation mechanism regulates the limb abduction-adduction during stance. C, The limb load compensation mechanism controls the extensor activity during stance. D, The trunk configuration mechanism controls the trunk shape. Crosses and circles indicate the points of body fixation and suspension, respectively, which allow isolation of the different mechanisms. See text for explanations. E, Integration of limb and trunk postural mechanisms in the reaction to lateral push. E1, Unperturbed configuration of the hindquarters during locomotion. E2, Push to the right causes a rightward displacement of the pelvis accompanied by abduction (Δγ) of the supporting (left) limb in relation to the trunk. This abduction triggers LDCM, which counteracts the lateral pelvis displacement and reduces its value. E3, At the same time the right limb, due to the activity of its LTM, is transferred forward and landed at a standard angle γ in relation to the pelvis. However, because of the trunk bending, it lands at a much more lateral position than the stance position in normal steps (indicated by small squares). After landing of the right limb, its LLCM comes into operation. Also, the push-caused lateral trunk bending activates TCM, which results in the trunk straightening (E3, E4) during the St phase of the right limb. Because of the restored straight trunk configuration, LTM causes landing of the left and right limbs in the subsequent steps (E5 and E6) at the normal mediolateral position. Thus, due to the operation of the limb and trunk mechanisms, the normal locomotor body configuration is restored.