Qiao Mu, Jindrich Devin L
*Kinesiology Program, School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ, USA; Department of Kinesiology, California State University, San Marcos, CA 92096, USA.
*Kinesiology Program, School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ, USA; Department of Kinesiology, California State University, San Marcos, CA 92096, USA
Integr Comp Biol. 2014 Dec;54(6):1109-21. doi: 10.1093/icb/icu058. Epub 2014 Jun 19.
Locomotion in a complex environment is often not steady, but the mechanisms used by animals to power and control unsteady locomotion (stability and maneuverability) are not well understood. We use behavioral, morphological, and impulsive perturbations to determine the compensations used during unsteady locomotion. At the level both of the whole-body and of joints, quasi-stiffness models are useful for describing adjustments to the functioning of legs and joints during maneuvers. However, alterations to the mechanics of legs and joints often are distinct for different phases of the step cycle or for specific joints. For example, negotiating steps involves independent changes of leg stiffness during compression and thrust phases of stance. Unsteady locomotion also involves parameters that are not part of the simplest reduced-parameter models of locomotion (e.g., the spring-loaded inverted pendulum) such as moments of the hip joint. Extensive coupling among translational and rotational parameters must be taken into account to stabilize locomotion or maneuver. For example, maneuvers with morphological perturbations (increased rotational inertial turns) involve changes to several aspects of movement, including the initial conditions of rotation and ground-reaction forces. Coupled changes to several parameters may be employed to control maneuvers on a trial-by-trial basis. Compensating for increased rotational inertia of the body during turns is facilitated by the opposing effects of several mechanical and behavioral parameters. However, the specific rules used by animals to control translation and rotation of the body to maintain stability or maneuver have not been fully characterized. We initiated direct-perturbation experiments to investigate the strategies used by humans to maintain stability following center-of-mass (COM) perturbations. When walking, humans showed more resistance to medio-lateral perturbations (lower COM displacement). However, when running, humans could recover from the point of maximum COM displacement faster than when walking. Consequently, the total time necessary for recovery was not significantly different between walking and running. Future experiments will determine the mechanisms used for compensations during unsteady locomotion at the behavioral, joint, and muscle levels. Using reduced-parameter models will allow common experimental and analytical frameworks for the study of both stability and maneuverability and the determination of general control strategies for unsteady locomotion.
在复杂环境中的运动通常并不稳定，但动物用于驱动和控制不稳定运动（稳定性和机动性）的机制尚未得到充分理解。我们使用行为、形态和脉冲扰动来确定不稳定运动期间所采用的补偿方式。在全身和关节层面，准刚度模型有助于描述在机动过程中腿部和关节功能的调整。然而，腿部和关节力学的改变在步周期的不同阶段或特定关节处往往有所不同。例如，跨越台阶涉及在站立的压缩和推力阶段腿部刚度的独立变化。不稳定运动还涉及一些不属于最简单的运动简化参数模型（如弹簧加载倒立摆）的参数，如髋关节力矩。为了稳定运动或进行机动，必须考虑平移和旋转参数之间的广泛耦合。例如，形态扰动（增加旋转惯性转弯）的机动涉及运动的几个方面的变化，包括旋转的初始条件和地面反作用力。可以通过逐次试验采用几个参数的耦合变化来控制机动。身体在转弯过程中增加的旋转惯性可通过几个机械和行为参数的相反作用得到补偿。然而，动物用于控制身体平移和旋转以保持稳定性或机动性的具体规则尚未完全明确。我们开展了直接扰动实验，以研究人类在质心（COM）扰动后维持稳定性所采用的策略。行走时，人类对中侧扰动的抵抗力更强（COM位移更低）。然而，跑步时，人类从最大COM位移点恢复的速度比行走时更快。因此，行走和跑步之间恢复所需的总时间没有显著差异。未来的实验将确定在行为、关节和肌肉层面不稳定运动期间用于补偿的机制。使用简化参数模型将为研究稳定性和机动性以及确定不稳定运动的一般控制策略提供通用的实验和分析框架。
