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_xy) = 0.79 at 20 % MVC to R_xy = 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.

文献中有孤立的实例表明“洋葱皮”现象并不总是存在。也就是说，新招募的高阈值电机单元（MU）的放电率比以前招募的低阈值MUs高。因此，本文的目的是研究从低到最大力输出的大量肌内肌电记录样本中“洋葱皮”现象的存在。48名参与者在20％，40％，60％，80％和100％MVC下进行了等距背屈快速收缩，同时记录了肌内电活动。评估了电机单元放电率和电机单元动作电位峰峰（PP）振幅的双变量频率分布。跨力水平的双变量频率分布存在显着差异（D = 0.1083−0.3094，p <0.001）。新招募的高阈值MU确实具有较低的放电率，但是在力输出的稳定部分中，高阈值，大PP振幅MU的放电率高于较低阈值MU（反洋葱皮）的情况有所增加。较高放电率的高阈值MU的募集从20％MVC时的互相关（R _xy） = 0.79降至100％MVC时的R _xy = 0.68（p <0.01），但仍然很高。随着干扰模式变得越来越复杂，同时在更高的力输出下招募更多的电机单元，在记录电机单元活动的同时，肌内电极可能会更加有区别，从而导致同时存在“反洋葱皮”和“洋葱皮”现象的识别。