Sawers Andrew, Pai Yi-Chung Clive, Bhatt Tanvi, Ting Lena H
Department of Kinesiology, University of Illinois at Chicago, Chicago, Illinois;
Department of Physical Therapy, University of Illinois at Chicago, Chicago, Illinois.
J Neurophysiol. 2017 Feb 1;117(2):509-522. doi: 10.1152/jn.00699.2016. Epub 2016 Nov 2.
How does the robust control of walking and balance break down during a fall? Here, as a first step in identifying the neuromuscular determinants of falls, we tested the hypothesis that falls and recoveries are characterized by differences in neuromuscular responses. Using muscle synergy analysis, conventional onset latencies, and peak activity, we identified differences in muscle coordination between older adults who fell and those who recovered from a laboratory-induced slip. We found that subjects who fell recruited fewer muscle synergies than those who recovered, suggesting a smaller motor repertoire. During slip trials, compared with subjects who recovered, subjects who fell had delayed knee flexor and extensor onset times in the leading/slip leg, as well as different muscle synergy structure involving those muscles. Therefore, the ability to coordinate muscle activity around the knee in a timely manner may be critical to avoiding falls from slips. Unique to subjects who fell during slip trials were greater bilateral (interlimb) muscle activation and the recruitment of a muscle synergy with excessive coactivation. These differences in muscle coordination between subjects who fell and those who recovered could not be explained by differences in gait-related variables at slip onset (i.e., initial motion state) or variations in slip difficulty, suggesting that differences in muscle coordination may reflect differences in neural control of movement rather than biomechanical constraints imposed by perturbation or initial walking mechanics. These results are the first step in determining the causation of falls from the perspective of muscle coordination. They suggest that there may be a neuromuscular basis for falls that could provide new insights into treatment and prevention. Further research comparing the muscle coordination and mechanics of falls and recoveries within subjects is necessary to establish the neuromuscular causation of falls.
NEW & NOTEWORTHY: A central question relevant to the prevention of falls is: How does the robust control of walking and balance break down during a fall? Previous work has focused on muscle coordination during successful balance recoveries or the kinematics and kinetics of falls. Here, for the first time, we identified differences in the spatial and temporal coordination of muscles among older adults who fell and those who recovered from an unexpected slip.
在跌倒过程中，稳健的行走和平衡控制是如何瓦解的？在此，作为确定跌倒的神经肌肉决定因素的第一步，我们检验了这样一个假设，即跌倒和恢复的特征在于神经肌肉反应的差异。通过肌肉协同分析、传统的起始潜伏期和峰值活动，我们确定了跌倒的老年人与从实验室诱导滑倒中恢复的老年人之间肌肉协调的差异。我们发现，跌倒的受试者比恢复的受试者募集的肌肉协同更少，这表明运动指令库更小。在滑倒试验中，与恢复的受试者相比，跌倒的受试者在主导/滑倒腿上的膝屈肌和伸肌起始时间延迟，并且涉及这些肌肉的肌肉协同结构也不同。因此，及时协调膝盖周围肌肉活动的能力对于避免因滑倒而跌倒可能至关重要。在滑倒试验中跌倒的受试者独有的特征是双侧（肢体间）肌肉激活更大，以及募集了具有过度共同激活的肌肉协同。跌倒的受试者与恢复的受试者之间在肌肉协调上的这些差异，无法用滑倒开始时（即初始运动状态）与步态相关变量的差异或滑倒难度的变化来解释，这表明肌肉协调的差异可能反映了运动神经控制的差异，而不是由扰动或初始行走力学施加的生物力学限制。这些结果是从肌肉协调角度确定跌倒原因的第一步。它们表明，跌倒可能存在神经肌肉基础，这可为治疗和预防提供新的见解。有必要进一步开展研究，比较受试者内部跌倒和恢复的肌肉协调与力学情况，以确定跌倒的神经肌肉原因。
与预防跌倒相关的一个核心问题是：在跌倒过程中，稳健的行走和平衡控制是如何瓦解的？以往的研究主要集中在成功的平衡恢复过程中的肌肉协调或跌倒的运动学和动力学方面。在此，我们首次确定了跌倒的老年人与从意外滑倒中恢复的老年人之间在肌肉空间和时间协调方面的差异。
