Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON, L2S 3A1, Canada.
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON, L2S 3A1, Canada.
Neurosci Lett. 2021 Jan 19;743:135583. doi: 10.1016/j.neulet.2020.135583. Epub 2020 Dec 19.
There are isolated instances in the literature that suggest the 'onion skin' phenomenon is not always present. That is, newly recruited high threshold motor units (MU) have higher discharge rates than previously recruited low threshold MUs. Therefore, the purpose of this paper was to investigate the presence of the 'onion skin' phenomenon in a large sample of intramuscular myoelectric recordings from low to maximal force outputs. Forty-eight participants performed rapid isometric dorsiflexion contractions at 20, 40, 60, 80 and 100 % MVC while intramuscular electrical activity was recorded. A bivariate frequency-distribution of the motor unit discharge rate and motor unit action potential peak-to-peak (P-P) amplitude was assessed. There was a significant difference in bivariate frequency-distribution across force levels (D's = 0.1083-0.3094, p's < 0.001). Newly recruited high threshold MUs did have lower discharge rates, but there was an increase in the presence of high threshold, large P-P amplitude MUs with higher discharge rates than lower threshold MUs (reverse onion skin) during the stable portion of the force output. The recruitment of high threshold MUs with higher discharge rates decreased the level of common drive from the cross-correlation (R) = 0.79 at 20 % MVC to R = 0.68 at 100 % MVC (p < 0.01), but it remained high. As the interference pattern becomes more complex with the recruitment of more motor units at higher force outputs, intramuscular electrodes may be more discriminating while recording motor unit activity leading to the identification of both the 'reverse onion skin' and 'onion skin' phenomenon being present.
文献中有一些孤立的例子表明，“洋葱皮”现象并不总是存在。也就是说，新募集的高阈值运动单位（MU）的放电率高于先前募集的低阈值 MU。因此，本文的目的是在从低到最大力输出的大量肌内肌电记录中研究“洋葱皮”现象的存在。48 名参与者以 20%、40%、60%、80%和 100%最大握力（MVC）的速度进行等长背屈收缩，同时记录肌内电活动。评估了运动单位放电率和运动单位动作电位峰峰值（P-P）幅度的双变量频率分布。在力水平上，双变量频率分布存在显著差异（D'=0.1083-0.3094，p'<0.001）。新募集的高阈值 MU 的放电率确实较低，但在力输出稳定部分，高阈值、大 P-P 幅度 MU 的放电率高于低阈值 MU（反向洋葱皮）的出现有所增加。具有较高放电率的高阈值 MU 的募集减少了交叉相关（R）从 20% MVC 的 0.79 到 100% MVC 的 0.68（p<0.01）的共同驱动水平，但仍很高。随着在更高的力输出下募集更多的运动单位，干扰模式变得更加复杂，肌内电极在记录运动单位活动时可能更具辨别力，从而识别到“反向洋葱皮”和“洋葱皮”现象的存在。
