Laboratory of Neuromotor Physiology, Scientific Institute Foundation Santa Lucia, 00179 Rome, Italy.
J Neurophysiol. 2010 Feb;103(2):746-60. doi: 10.1152/jn.00499.2009. Epub 2009 Dec 2.
Friction and gravity represent two basic physical constraints of terrestrial locomotion that affect both motor patterns and the biomechanics of bipedal gait. To provide insights into the spatiotemporal organization of the motor output in connection with ground contact forces, we studied adaptation of human gait to steady low-friction conditions. Subjects walked along a slippery walkway (7 m long; friction coefficient approximately 0.06) or a normal, nonslippery floor at a natural speed. We recorded gait kinematics, ground reaction forces, and bilateral electromyographic (EMG) activity of 16 leg and trunk muscles and we mapped the recorded EMG patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron (MN) pools to characterize the spatiotemporal organization of the motor output. The results revealed several idiosyncratic features of walking on the slippery surface. The step length, cycle duration, and horizontal shear forces were significantly smaller, the head orientation tended to be stabilized in space, whereas arm movements, trunk rotations, and lateral trunk inclinations considerably increased and foot motion and gait kinematics resembled those of a nonplantigrade gait. Furthermore, walking on the slippery surface required stabilization of the hip and of the center-of-body mass in the frontal plane, which significantly improved with practice. Motor patterns were characterized by an enhanced (roughly twofold) level of MN activity, substantial decoupling of anatomical synergists, and the absence of systematic displacements of the center of MN activity in the lumbosacral enlargement. Overall, the results show that when subjects are confronted with unsteady surface conditions, like the slippery floor, they adopt a gait mode that tends to keep the COM centered over the supporting limbs and to increase limb stiffness. We suggest that this behavior may represent a distinct gait mode that is particularly suited to uncertain surface conditions in general.
摩擦和重力是陆地运动的两个基本物理约束，影响着运动模式和双足步态的生物力学。为了深入了解与地面接触力相关的运动输出的时空组织，我们研究了人类步态对稳定低摩擦条件的适应。受试者以自然速度在滑溜溜的走道（7 米长；摩擦系数约为 0.06）或正常、不滑的地板上行走。我们记录了步态运动学、地面反作用力以及 16 条腿部和躯干肌肉的双侧肌电图（EMG）活动，并将记录的 EMG 模式映射到脊髓中，以近似的头足侧位置描绘运动神经元（MN）池的运动输出的时空组织。结果揭示了在滑表面行走的几个特殊特征。步长、周期持续时间和水平剪切力明显较小，头部方向趋于在空间中稳定，而手臂运动、躯干旋转和横向躯干倾斜则大大增加，脚的运动和步态运动学类似于非跖行步态。此外，在滑表面上行走需要稳定臀部和身体质心在额状面，这在实践中显著改善。运动模式的特点是 MN 活动水平显著提高（大约两倍），解剖协同作用的大幅解耦，以及在腰骶部增大中 MN 活动中心没有系统位移。总的来说，结果表明，当受试者面临不稳定的表面条件时，如滑溜溜的地板，他们会采用一种步态模式，这种模式倾向于保持质心位于支撑肢体上方，并增加肢体刚度。我们认为，这种行为可能代表一种独特的步态模式，特别适合一般不确定的表面条件。
