Oude Nijhuis Lars B, Bloem Bastiaan R, Carpenter Mark G, Allum John H J
Department of Otorhinolaryngology, University Hospital, Basel, Switzerland.
J Neurophysiol. 2007 Nov;98(5):3047-59. doi: 10.1152/jn.01303.2006. Epub 2007 Sep 26.
Knee movements play a critical role in most balance corrections. Loss of knee flexibility may cause postural instability. Conversely, trained voluntary knee flexions executed during balance corrections might help to overcome balance deficits. We examined whether bilateral knee flexion could be added to automatic balance corrections generated by sudden balance perturbations. We investigated how this could be achieved and whether it improved or worsened balance control. Twenty-four healthy subjects participated in three different test conditions, in which they had to flex their knees following an auditory cue (VOLUNTARY condition), had to restore their balance in response to multidirectional rotations of a support surface (REACTIVE condition), or the combination of these two (COMBINED condition). A new variable set (PREDICTED), calculated as the mathematical sum of VOLUNTARY and REACTIVE, was compared with the COMBINED variable set. COMBINED responses following forward rotations were close to PREDICTED, or greater, suggesting adequate integration of knee flexion into the automatic balance reactions. For backward rotations, the COMBINED condition resulted in several near-falls, and this was generally associated with smaller knee flexion and smaller EMG responses. Subjects compensated by using greater trunk flexion and arm movements. Activity in several muscles displayed earlier onsets for the COMBINED condition following backward rotations. We conclude that healthy adults can incorporate voluntary knee flexion into their automatic balance corrections and that this depends on the direction of the postural perturbation. These findings highlight the flexibility of the human balance repertoire and underscore both the advantages and limitations of using trained voluntary movements to aid balance corrections in man.
膝关节运动在大多数平衡矫正中起着关键作用。膝关节灵活性的丧失可能导致姿势不稳定。相反，在平衡矫正过程中进行训练有素的主动膝关节屈曲可能有助于克服平衡缺陷。我们研究了在突然的平衡扰动产生的自动平衡矫正中是否可以增加双侧膝关节屈曲。我们研究了如何实现这一点，以及它是改善还是恶化了平衡控制。24名健康受试者参与了三种不同的测试条件，在这些条件下，他们必须根据听觉提示屈曲膝盖（主动条件），必须响应支撑面的多方向旋转来恢复平衡（反应条件），或者这两者的组合（联合条件）。将一个新的变量集（预测值）与联合变量集进行比较，该预测值是通过主动和反应条件的数学总和计算得出的。向前旋转后的联合反应接近预测值，或更大，这表明膝关节屈曲已充分整合到自动平衡反应中。对于向后旋转，联合条件导致了几次险些摔倒，这通常与较小的膝关节屈曲和较小的肌电图反应有关。受试者通过更大程度的躯干屈曲和手臂运动进行补偿。向后旋转后，联合条件下几块肌肉的活动出现得更早。我们得出结论，健康成年人可以将主动膝关节屈曲纳入他们的自动平衡矫正中，这取决于姿势扰动的方向。这些发现突出了人类平衡能力的灵活性，并强调了使用训练有素的主动运动来辅助人类平衡矫正的优点和局限性。
