Data from: Stability of phase relationships while coordinating arm reaches with whole body motion

The human movement repertoire is characterized by the smooth coordination of several body parts, including arm movements and whole body motion. The neural control of this coordination is quite complex because the various body parts have their own kinematic and dynamic properties. Behavioral inferences about the neural solution to the coordination problem could be obtained by examining the emerging phase relationship and its stability. Here, we studied the phase relationships that characterize the coordination of arm-reaching movements with passively-induced whole-body motion. Participants were laterally translated using a vestibular chair that oscillated at a fixed frequency of 0.83 Hz. They were instructed to reach between two targets that were aligned either parallel or orthogonal to the whole body motion. During the first cycles of body motion, a metronome entrained either an in-phase or an anti-phase relationship between hand and body motion, which was released at later cycles to test phase stability. Results suggest that inertial forces play an important role when coordinating reaches with cyclic whole-body motion. For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship. When the latter was imposed, it readily transitioned or drifted back toward an in-phase relationship at cycles without metronomic entrainment. For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships. Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns. We discuss how predictive control and impedance control processes could be considered important mechanisms underlying the rhythmic coordination of arm reaches and body motion.

人类运动的核心特征为多身体部位的流畅协同，涵盖上肢动作与全身整体运动。该协同运动的神经调控机制极为复杂，原因在于不同身体部位拥有各自独特的运动学与动力学特性。通过探究该协同模式所涌现出的相位关系（phase relationship）及其稳定性，可推导得到针对该协同问题的神经调控方案的行为学推论。本研究聚焦于被动诱发全身运动时，上肢伸臂动作与全身运动的协同模式所对应的相位关系。受试者乘坐以0.83Hz固定频率振动的前庭功能椅（vestibular chair），沿横向进行位移运动。受试者需在两个与全身运动方向平行或正交的目标物之间完成伸臂动作。在全身运动的初始周期中，通过节拍器（metronome）使手部运动与全身运动形成同相（in-phase）或反相（anti-phase）的相位关系，后续周期解除节拍器约束以测试相位关系的稳定性。研究结果表明，在伸臂动作与周期性全身运动的协同过程中，惯性力（inertial forces）发挥着关键作用。针对与运动方向平行的伸臂动作，我们观察到同相相位关系稳定，而反相相位关系则不稳定。当施加反相约束时，在无节拍器牵引的周期中，反相关系会快速转变或漂移回同相关系。针对与运动方向正交的伸臂动作，我们未观察到同相与反相相位关系在稳定性上存在显著差异。计算机模拟进一步显示，以最小化能量消耗（energy expenditure，即净力矩net torques）或伸臂末端位置方差（endpoint variance）为目标的代价模型（cost models），无法完全解释观测到的协同运动模式。本研究还探讨了预测控制（predictive control）与阻抗控制（impedance control）过程如何作为核心机制，支撑伸臂动作与全身运动的节律性协同。