Gabriel David A, Kamen Gary
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, Canada L2S 3A1.
J Electromyogr Kinesiol. 2009 Jun;19(3):437-48. doi: 10.1016/j.jelekin.2007.10.009. Epub 2008 Jan 18.
This study investigated possible motor unit (MU) firing patterns underlying changes in biceps brachii (BB) surface electromyographic (SEMG) activity in 96 participants who performed isometric actions of the elbow flexors at 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVC). We also conducted a modeling investigation to determine the extent to which a model would fit the experimental results. Experimentally, there was a linear increase (277%; p<0.01) in root-mean-square (RMS) amplitude with increasing force. The mean power frequency (MNF) remained stable from 40% to 80% of MVC, but there was a decrease (8.2%; p<0.01) between 80% and 100% of MVC. A modeling approach was taken wherein well-known recruitment and rate-coding schemes activated MUs whose basic building block was the muscle fibre action potential. Two conditions were investigated: (1) an increase in firing rate (rate-coding) and (2) synchronization. The levels of rate-coding and synchronization were selected to produce a linear RMS-force relationship as observed in the experimental data. Then, the impact of these two strategies on changes in MNF was assessed. The MNF remained stable from 40% to 80% of maximum excitation for both the rate-coding and synchronization conditions. There was a decrease in MNF between 80% and 100% of maximum excitation for both modeling conditions, similar to that observed for the experimental data. Thus, at these high forces at which experimental data are technically difficult to obtain, the model supports the idea that both rate-coding and synchronization are responsible for the changes observed in surface EMG amplitude and frequency characteristics.
本研究调查了96名参与者在以最大自主收缩（MVC）的40%、60%、80%和100%进行肱二头肌（BB）等长收缩动作时，肱二头肌表面肌电图（SEMG）活动变化背后可能的运动单位（MU）放电模式。我们还进行了一项建模研究，以确定一个模型与实验结果的拟合程度。在实验中，均方根（RMS）振幅随力量增加呈线性增加（277%；p<0.01）。平均功率频率（MNF）在MVC的40%至80%之间保持稳定，但在MVC的80%至100%之间有所下降（8.2%；p<0.01）。采用了一种建模方法，其中著名的募集和速率编码方案激活了以肌纤维动作电位为基本组成部分的运动单位。研究了两种情况：（1）放电频率增加（速率编码）和（2）同步。选择速率编码和同步水平以产生如实验数据中观察到的线性RMS-力关系。然后，评估这两种策略对MNF变化的影响。在速率编码和同步条件下，MNF在最大兴奋的40%至80%之间均保持稳定。在两种建模条件下，MNF在最大兴奋的80%至100%之间均有所下降，这与实验数据中观察到的情况相似。因此，在这些技术上难以获得实验数据的高力量水平下，该模型支持速率编码和同步均导致表面肌电图振幅和频率特征变化的观点。
