Data from: Evaluation of the phase-dependent rhythm control of human walking using phase response curves

Humans and animals control their walking rhythms to maintain motion in a variable environment. The neural mechanism for controlling rhythm has been investigated in many studies using mechanical and electrical stimulation. However, quantitative evaluation of rhythm variation in response to perturbation at various timings has rarely been investigated. Such a characteristic of rhythm is described by the phase response curve (PRC). Dynamical simulations of human skeletal models with changing walking rhythms (phase reset) described a relation between the effective phase reset on stability and PRC, and phase reset around touch-down was shown to improve stability. A PRC of human walking was estimated by pulling the swing leg, but such perturbations hardly influenced the stance leg, so the relation between the PRC and walking events was difficult to discuss. This research thus examines human response to variations in floor velocity. Such perturbation yields another problem, in that the swing leg is indirectly (and weakly) perturbed, so the precision of PRC decreases. To solve this problem, this research adopts the weighted spike-triggered average (WSTA) method. In the WSTA method, a sequential pulsed perturbation is used for stimulation. This is in contrast with the conventional impulse method, which applies an intermittent impulsive perturbation. The WSTA method can be used to analyze responses to a large number of perturbations for each sequence. In the experiment, perturbations are applied to walking subjects by rapidly accelerating and decelerating a treadmill belt, and measured data are analyzed by the WSTA and impulse methods. The PRC obtained by the WSTA method had clear and stable waveforms with a higher temporal resolution than those obtained by the impulse method. By investigation of the rhythm transition for each phase of walking using the obtained PRC, a rhythm change that extends the touch-down and mid-single support phases is found to occur.人类与动物能够在多变环境中调控自身行走节律，以维持稳定的运动状态。诸多研究已通过机械与电刺激手段，对调控行走节律的神经机制展开了探索。然而，针对不同时刻施加扰动时的节律变化进行定量评估的相关研究仍较为匮乏。行走节律的这类特性可通过相位响应曲线（Phase Response Curve，PRC）进行描述。针对具有行走节律变化（即相位重置）特性的人体骨骼模型开展动力学仿真，研究人员揭示了有效相位重置对运动稳定性的影响与PRC之间的关联，并证实触地时刻附近的相位重置可提升行走稳定性。此前已有研究通过牵拉摆动腿的方式估算人类行走的PRC，但这类扰动几乎不会对支撑腿产生影响，因此难以探讨PRC与各类行走事件之间的内在关联。为此，本研究聚焦于人类对跑步机速度变化的响应。不过这类扰动会带来一项新的问题：摆动腿仅会受到间接且微弱的扰动，导致PRC的估算精度降低。为解决这一问题，本研究采用了加权尖峰触发平均（Weighted Spike-Triggered Average，WSTA）方法。该方法采用连续脉冲扰动作为刺激手段，与传统的间歇式脉冲扰动刺激法存在显著差异。WSTA方法可针对每个扰动序列分析大量刺激所引发的响应。在本次实验中，研究人员通过快速加减速跑步机皮带对行走受试者施加扰动，并分别采用WSTA方法与传统脉冲法对测得的实验数据进行分析。相较于脉冲法得到的结果，WSTA方法得到的PRC拥有清晰且稳定的波形，且时间分辨率更高。借助所获得的PRC对行走各阶段的节律转变展开研究后，本研究发现存在一类会延长触地阶段与单支撑中期阶段的节律变化。