Mirka G A
Department of Industrial and Systems Engineering, Ohio State University, Columbus 43210.
Ergonomics. 1991 Mar;34(3):343-52. doi: 10.1080/00140139108967318.
Electromyography (EMG) and normalized EMG have been accepted as methods of quantifying the activity level of a muscle. Normalized EMG, in conjunction with the EMG/force relationship and muscle cross-sectional area data, allows researchers to estimate the amount of muscle force exerted across a joint. An accurate description of this muscle force is a critical input to models designed to describe the risk of injury of a task. In order to be able to make statements about the relative intensity of an EMG signal, researchers who use normalization procedures take a given EMG activity level, at a known joint angle, and relate it to some reference activity level obtained at that particular joint angle. However, there have been studies where the EMG activity of an unrestricted dynamic task, such as walking, cycling, performing an occupational task, etc., has been normalized with respect to an EMG value taken during a single maximum voluntary contraction performed at one reference joint angle. This practice will render inaccurate results because at different joint angles there are changes in the portion of the muscle within the viewing area of the electrode, as well as changes in the length/tension relationship of the muscle which would cause changes in the maximum EMG value. The present study was an attempt to quantify the errors associated with normalization relative to a reference EMG value collected at an arbitrary joint position. Four subjects performed a series of controlled trunk extension exertions. As they performed these exertions the EMG activities were collected for eight trunk muscles. The task EMG values that resulted were then: (1) all normalized with respect to the maximum EMG at a single arbitrary trunk angle and (2) each normalized with respect to that specific trunk angle's maximum EMG. The results show that for the primary trunk extensors (erector spinae) large errors (greater than 75%) resulted from normalization using a single reference point and the magnitude of these errors followed consistent patterns within subjects as a function of trunk angle.
肌电图（EMG）和标准化肌电图已被公认为量化肌肉活动水平的方法。标准化肌电图结合肌电图/力关系和肌肉横截面积数据，使研究人员能够估计跨关节施加的肌肉力量大小。准确描述这种肌肉力量是设计用于描述任务受伤风险模型的关键输入。为了能够对肌电图信号的相对强度做出说明，使用标准化程序的研究人员会在已知关节角度下获取给定的肌电图活动水平，并将其与在该特定关节角度获得的某个参考活动水平相关联。然而，有研究表明，对于无限制的动态任务，如行走、骑自行车、执行职业任务等，其肌电图活动已根据在一个参考关节角度进行的单次最大自主收缩期间获取的肌电图值进行标准化。这种做法会得出不准确的结果，因为在不同的关节角度，电极视野内肌肉的部分会发生变化，以及肌肉的长度/张力关系也会发生变化，这会导致最大肌电图值发生变化。本研究旨在量化与相对于在任意关节位置收集的参考肌电图值进行标准化相关的误差。四名受试者进行了一系列受控的躯干伸展运动。在他们进行这些运动时，收集了八块躯干肌肉的肌电图活动。然后，得到的任务肌电图值：（1）全部相对于单个任意躯干角度的最大肌电图进行标准化，（2）每个都相对于该特定躯干角度的最大肌电图进行标准化。结果表明，对于主要的躯干伸肌（竖脊肌），使用单个参考点进行标准化会导致较大误差（大于75%），并且这些误差的大小在受试者内部随躯干角度呈现一致的模式。
