[论文解读] Patterns of Selection of Human Movements II: Movement Limits, Mechanical Energy, and Very Slow Walking Gaits

Stuart Hagler|arXiv (Cornell University)|Jan 1, 2016

Balance, Gait, and Falls Prevention参考文献 17被引用 3

一句话总结

本文通过机械能守恒和力约束，建立生物力学模型，定义人类步行步态的上下限。研究识别出平均步行速度的下限（约0.45 m/s）和步长上限（约1.5 m），表明极慢速步行（0.45–0.6 m/s）构成一种独特的步态类别，且神经退行性疾病患者的临床步行速度均落于此范围内。

ABSTRACT

The biomechanics of the human body allow humans a range of possible ways of executing movements to attain specific goals. This range of movement is limited by a number of mechanical, biomechanical, or cognitive constraints. Shifts in these limits result in changes available possible movements from which a subject can select and can affect which movements a subject selects. Therefore by understanding the limits on the range of movement we can come to a better understanding of declines in movement performance due to disease or aging. In this project, we look at how models for the limits on the range of movement can be derived in a principled manner from a model of the movement. Using the example of normal walking gaits, we develop a lower limit on the avg. walking speed by examining the process by which the body restores mechanical energy lost during walking, and we develop an upper limit on the avg. step length by examining the forces the body can exert doing external mechanical work, in this case, pulling a cart. Making slight changes to the model for normal walking gaits, we develop a model of very slow walking gaits with avg. walking speeds below the lower limit on normal walking gaits but that also has a lower limit on the avg. walking speed. We note that the lowest avg. walking speeds observed clinically fall into the range of very slow walking gaits so defined, and argue that forms of bipedal locomotion with still lower speeds should be considered distinct from walking gaits.

研究动机与目标

• 建立机械与生物力学约束模型，以界定人类步行步态的范围限制。
• 基于能量与力约束，推导平均步行速度与步长的下限与上限。
• 根据生物力学限制，区分极慢速步行与正常步行。
• 将这些限制与衰老及神经退行性疾病（如帕金森病与阿尔茨海默病）中的临床观察结果关联。

提出的方法

• 构建包含N个肢体段与关节的分段人体模型，用于模拟运动动力学。
• 采用结合肌肉力与速度项的代谢能量模型，估算能量消耗。
• 应用机械能守恒原理，建模步行过程中的能量损失与外功。
• 通过分析步态周期中机械能的恢复过程，推导步行速度的下限。
• 通过约束支撑腿对躯干施加的最大力，建立步长的上限。
• 利用Atzler & Herbst（2005）关于外加负荷下步行的实证数据验证模型。

实验结果

研究问题

• RQ1 哪些生物力学约束定义了正常步态中平均步行速度的下限？
• RQ2 支撑腿最大力生成能力所导致的步长上限是什么？
• RQ3 机械能损失与外功模型如何定义一种独特的极慢速步行步态类别？
• RQ4 为何帕金森病患者及老年人的临床步行速度集中于正常步态以下的特定范围？
• RQ5 力生成能力的改变（如因衰老或疾病所致）如何影响步行速度与步长的极限？

主要发现

• 正常步态的平均步行速度下限约为0.45 m/s，由机械能损失与恢复的约束推导得出。
• 平均步长的上限为1.5 m，由支撑腿最大力容量370 N推导得出。
• Atzler & Herbst的受试者在步长>0.90 m时无法以F_ext = 160 N行走，与模型的力限制一致。
• 模型预测，外加负荷的增加会将有效步长上限下移，从而解释负重行走的困难。
• 极慢速步行（0.45–0.6 m/s）在生物力学上与正常步态截然不同，且包含衰老与神经退行性疾病中观察到的临床步行速度。
• 衰老或疾病导致的步行速度与步长下降，与最大力生成能力（F_max）的降低一致，从而导致步幅缩短与步态变慢。