Bianchi L, Angelini D, Orani G P, Lacquaniti F
Human Physiology Section, Scientific Institute S. Lucia, National Research Council, University of Tor Vergata, 00179 Rome, Italy.
J Neurophysiol. 1998 Apr;79(4):2155-70. doi: 10.1152/jn.1998.79.4.2155.
Twenty-four subjects walked at different, freely chosen speeds (V) ranging from 0.4 to 2.6 m s-1, while the motion and the ground reaction forces were recorded in three-dimensional space. We considered the time course of the changes of the angles of elevation of the trunk, pelvis, thigh, shank, and foot in the sagittal plane. These angles specify the orientation of each segment with respect to the vertical and to the direction of forward progression. The changes of the trunk and pelvis angles are of limited amplitude and reflect the dynamics of both right and left lower limbs. The changes of the thigh, shank, and foot elevation are ample, and they are coupled tightly among each other. When these angles are plotted one versus the others, they describe regular loops constrained on a plane. The plane of angular covariation rotates, slightly but systematically, along the long axis of the gait loop with increasing V. The rotation, quantified by the change of the direction cosine of the normal to the plane with the thigh axis (u3t), is related to a progressive phase shift between the foot elevation and the shank elevation with increasing V. As a next step in the analysis, we computed the mass-specific mean absolute power (Pu) to obtain a global estimate of the rate at which mechanical work is performed during the gait cycle. When plotted on logarithmic coordinates, Pu increases linearly with V. The slope of this relationship varies considerably across subjects, spanning a threefold range. We found that, at any given V > 1 m s-1, the value of the plane orientation (u3t) is correlated with the corresponding value of the net mechanical power (Pu). On the average, the progressive rotation of the plane with increasing V is associated with a reduction of the increment of Pu that would occur if u3t remained constant at the value characteristic of low V. The specific orientation of the plane at any given speed is not the same in all subjects, but there is an orderly shift of the plane orientation that correlates with the net power expended by each subject. In general, smaller values of u3t tend to be associated with smaller values of Pu and vice versa. We conclude that the parametric tuning of the plane of angular covariation is a reliable predictor of the mechanical energy expenditure of each subject and could be used by the nervous system for limiting the overall energy expenditure.
24名受试者以0.4至2.6米/秒之间不同的自由选择速度（V）行走，同时在三维空间中记录运动和地面反作用力。我们考虑了矢状面内躯干、骨盆、大腿、小腿和足部仰角变化的时间过程。这些角度指定了每个节段相对于垂直方向和向前行进方向的方向。躯干和骨盆角度的变化幅度有限，反映了左右下肢的动力学。大腿、小腿和足部仰角的变化幅度较大，且它们彼此紧密耦合。当将这些角度相互绘制时，它们描绘出受平面约束的规则环路。随着V的增加，角度协变平面沿着步态环路的长轴轻微但系统地旋转。通过平面法线与大腿轴（u3t）的方向余弦变化来量化的旋转，与随着V增加足部仰角和小腿仰角之间的渐进相移有关。作为分析的下一步，我们计算了质量比平均绝对功率（Pu），以获得步态周期中机械功执行速率的全局估计。当绘制在对数坐标上时 Pu 随 V 线性增加。这种关系的斜率在不同受试者之间变化很大，跨度为三倍。我们发现，在任何给定的V>1米/秒时，平面方向（u3t）的值与净机械功率（Pu）的相应值相关。平均而言，随着V增加平面的渐进旋转与如果u3t保持在低V特征值时Pu的增量减少相关。在任何给定速度下平面的特定方向在所有受试者中并不相同，但平面方向存在有序的偏移，这与每个受试者消耗的净功率相关。一般来说，u3t值越小往往与Pu值越小相关，反之亦然。我们得出结论，角度协变平面的参数调整是每个受试者机械能消耗的可靠预测指标，并且可以被神经系统用于限制总体能量消耗。
