A unified approach towards understanding the electromyographic signal

整个肌肉可能包含数十万个单独的肌纤维。这些纤维被分组为由单个运动神经元激活的功能单元（10 - 1000个纤维）。一个运动神经元和它激活的所有肌肉纤维被称为运动单位。运动单位是力量产生的基本组成部分。可以通过招募额外的运动单位来增加力量，或者通过增加每个运动单位每秒被激活的次数（速率编码）来增加力量。更频繁地激活运动单元允许由运动单元产生的力在时间上更大程度地重叠并且更有效地相加。类似地，神经系统也可以更同步地招募运动单元组，从而形成近乎完美的力的总和。当运动单位被神经系统招募时，它会产生电活动，可以通过将电极植入肌肉来监测。不幸的是，留置电极记录的是有限体积的组织，这不能代表整个肌肉。留置电极也可能是痛苦的，它们的使用受到限制。幸运的是，来自许多运动单位的电活动可以充分地相加，以使用表面肌电图从皮肤表面检测到。这类似于使用心电图从皮肤表面记录心肌的电活动。表面肌电图具有记录大量运动单位的电活动的优点，但单个运动单位的电活动是“模糊的”。令人困惑的是，表面肌电电极是测量肌肉电活动的最简单方法。然而，表面肌电信号的能力，以提供深入了解肌肉力量的分级背后的神经机制是有限的。拟议的一系列研究将留置和表面方法与肌电信号的建模和模拟相结合，以统一的方法开发和验证非侵入性技术，以研究神经系统如何在非疲劳和疲劳条件下调节肌肉力量。

A whole muscle may contain several hundreds of thousands of individual muscle fibers. These fibers are grouped into functional units (10 – 1000 fibers) activated by a single motor neuron. A single motor neuron and all the muscle fibers that it activates is a call a motor unit. The motor unit is the basic building block of force production. Force can be increased by recruiting additional motor units, or by increasing the number of times per second (rate-coding) that each motor unit is activated. Activating motor units more frequently allows the forces generated by the motor units to overlap in time to a greater degree and sum up more efficiently. Similarly, the nervous system can also recruit groups of motor units more synchronously so that there is a near perfect summation of forces. When a motor unit is recruited by the nervous system, it generates electrical activity that can be monitored by implanting an electrode into the muscle. Unfortunately, indwelling electrodes record from a limited volume of tissue, which is not representative of the whole muscle. Indwelling electrodes can also be painful and their use is being limited. Fortunately, the electrical activity from many motor units can sum up sufficiently to be detected from the skin surface, using surface electromyography. This similar to the use of electrocardiography to record the electrical activity of heart muscle from the skin surface. Surface electromyography has the advantage of recording the electrical activity of a large population of motor units, but the electrical activity of individual motor units is “obscured”. The perplexing dilemma is that surface electromyographic electrodes are the easiest way to measure muscle electrical activity. Yet, the ability of the surface electromyographic signal to provide insight into the neural mechanisms underlying the gradation of muscle force is limited. The proposed series of studies combines indwelling and surface methodologies with modeling and simulation of the electromyographic signal in a unified approach towards developing and validating non-invasive techniques to investigate how the nervous system regulates muscle force during non-fatiguing and fatiguing conditions.