Morrison S, Hong S L, Newell K M
School of Physiotherapy and Exercise Science, Gold Coast Campus Griffith University, PMB 50 Gold Coast Mail Centre, Gold Coast, QLD, 9726, Australia.
Exp Brain Res. 2007 Aug;181(2):347-58. doi: 10.1007/s00221-007-0928-x. Epub 2007 Mar 21.
The aim of this study was to investigate the postural center of pressure (COP) and surface muscle (EMG) dynamics of young adult participants under conditions where they were required to voluntarily produce random and regular sway motions in contrast to that of standing still. Frequency, amplitude and regularity measures of the COP excursion and EMG activity were assessed, as were measures of the coupling relations between the COP and EMG outputs. The results demonstrated that, even when standing still, there was a high degree of regularity in the COP output, with little difference in the modal frequency dynamics between standing still and preferred motion. Only during random conditions was a significantly greater degree of irregularity observed in the COP measures. The random-like movements were also characterized by a decrease in the level of synchrony between COP motion on the anterior-posterior (AP) and medio-lateral (ML) axes. In contrast, at muscle level, the random task resulted in the highest level of regularity (decreased ApEn) for the EMG output for soleus and tibialis anterior. The ability of individuals to produce a random motion was achieved through the decoupling of the COP motion in each dimension. This decoupling strategy was reflected by increased regularity of the EMG output as opposed to any significant change in the synchrony in the firing patterns of the muscles examined. Increased regularity across the individual muscles was accompanied by increased irregularity in COP dynamics, which can be characterized as a complexity tradeoff. Collectively, these findings support the view that the dynamics of muscle firing patterns does not necessarily map directly to the dynamics at the movement task level and vice versa.
本研究的目的是调查年轻成年参与者在被要求自愿产生随机和规则摆动运动的条件下，与静止站立相比的姿势压力中心（COP）和表面肌肉（肌电图，EMG）动态变化。评估了COP偏移和EMG活动的频率、幅度和规律性指标，以及COP和EMG输出之间的耦合关系指标。结果表明，即使在静止站立时，COP输出也具有高度的规律性，静止站立和偏好运动之间的模态频率动态变化差异不大。仅在随机条件下，COP测量中观察到明显更大程度的不规则性。类似随机的运动还表现为前后（AP）和内外侧（ML）轴上COP运动之间的同步性水平降低。相比之下，在肌肉水平上，随机任务导致比目鱼肌和胫骨前肌的EMG输出具有最高水平的规律性（近似熵降低）。个体产生随机运动的能力是通过每个维度上COP运动的解耦实现的。这种解耦策略表现为EMG输出规律性增加，而不是所检查肌肉放电模式同步性的任何显著变化。单个肌肉规律性的增加伴随着COP动态变化不规则性的增加，这可被描述为一种复杂性权衡。总体而言，这些发现支持以下观点，即肌肉放电模式的动态变化不一定直接映射到运动任务水平的动态变化，反之亦然。
