Felici Francesco, Quaresima Valentina, Fattorini Luigi, Sbriccoli Paola, Filligoi Gian Carlo, Ferrari Marco
Department of Human Movement and Sport Sciences, Istituto Universitario di Scienze Motorie, Piazza Lauro De Bosis 6, 00194 Roma, Italy.
J Electromyogr Kinesiol. 2009 Apr;19(2):e1-11. doi: 10.1016/j.jelekin.2007.07.010. Epub 2007 Sep 24.
Surface myoelectric signal changes occurring during sustained isometric contractions have been extensively studied with quantitative surface electromyography (sEMG) and are described by means of some sEMG global variables in time and frequency domain (such as the median power spectral frequency). Recently, the possibility of studying local muscle O(2) saturation during exercise using non-invasive methods has been enhanced thanks to the use of near-infrared spectroscopy (NIRS). The purpose of this work was to combine NIRS and sEMG techniques to analyze the relationship between modifications of sEMG parameters and the underlying metabolic status of the exercising biceps brachii muscle. This relationship was tested under different isometric contraction modalities, namely static (ST) at 20, 40, 60 and 80%MVC and sinusoidal (SIN) at 40+/-20 and 60+/-20%MVC. Results clearly indicated the presence of an initial fast phase of muscle O(2) desaturation followed by a slow phase, regardless of the contraction modality. Moreover, the initial rate of muscle O(2) desaturation was related to the level of force output (R=0.92), but it was independent on the contraction modality (p<0.05). Similarly, changes in sEMG parameters were related to force level (Conduction Velocity-CV vs. Force: R=0.87; sEMG Median Frequency-MDF vs. Force: R=0.86). The high correlation found between CV-MDF and Tissue Oxygenation Index (TOI) slope (R=0.73 and 0.72, respectively) suggests a strong relationship between NIRS and sEMG data. This study indicates that muscle O(2) demand during isometric contractions from low to high force levels is influenced by the type of active motor units and not from the type of isometric exercise modality.
利用定量表面肌电图（sEMG）对持续等长收缩过程中发生的表面肌电信号变化进行了广泛研究，并通过一些时域和频域的sEMG全局变量（如中位功率谱频率）进行描述。最近，由于近红外光谱（NIRS）的应用，使用非侵入性方法研究运动期间局部肌肉氧饱和度的可能性得到了提高。本研究的目的是结合NIRS和sEMG技术，分析sEMG参数变化与肱二头肌运动时潜在代谢状态之间的关系。在不同的等长收缩模式下对这种关系进行了测试，即20%、40%、60%和80%最大随意收缩（MVC）的静态（ST）收缩以及40±20%和60±20%MVC的正弦（SIN）收缩。结果清楚地表明，无论收缩模式如何，肌肉氧饱和度都存在一个初始快速下降阶段，随后是一个缓慢阶段。此外，肌肉氧饱和度的初始下降速率与力输出水平相关（R = 0.92），但与收缩模式无关（p < 0.05）。同样，sEMG参数的变化与力水平相关（传导速度-CV与力：R = 0.87；sEMG中位频率-MDF与力：R = 0.86）。CV-MDF与组织氧合指数（TOI）斜率之间的高度相关性（分别为R = 0.73和0.72）表明NIRS和sEMG数据之间存在密切关系。本研究表明，等长收缩过程中从低到高力水平的肌肉氧需求受活动运动单位类型的影响，而不受等长运动模式类型的影响。
