Roy S H, Bonato P, Knaflitz M
NeuroMuscular Research Center, Boston University, MA 02215, USA.
J Electromyogr Kinesiol. 1998 Aug;8(4):233-45. doi: 10.1016/s1050-6411(98)00010-8.
A new approach to estimating the frequency compression of the surface EMG signal during cyclical dynamic exercise is described. The basic properties of the method are first developed using simulated EMG signals. Spectral compression is measured by defining the instantaneous median frequency from time-frequency representations of the signal derived from a transformation of the Cohen class. The technique is then used to process real EMG signals from paraspinal muscles during repetitive lifting. Our purpose was to use this new procedure to identify (a) whether changes in the instantaneous median frequency among concurrently active paraspinal muscles during repetitive trunk extension produces a 'fatigue pattern' that is indicative of normal functioning, and (b) whether this pattern is different when the subject produces a sustained isometric trunk extension. Four healthy subjects (26 +/- 4 years; 3 males, 1 female) were tested in both a Back Analysis System, for the production of a sustained static isometric contraction, and a LIDO-Lift Controller (Loredan), for repetitive lifting and lowering of a weighted box. EMG signals were recorded concurrently from six bilateral lumbar paraspinal regions during these tasks. The results demonstrate that static and dynamic tasks result in very different patterns of EMG spectral changes, suggestive of differences in load-sharing and underlying metabolic fatigue processes. Unlike the linear decrease in median frequency observed for static contractions, during dynamic contractions instantaneous median frequency behavior is non-linear and more complex. Examples are provided in which distinct periods of instantaneous median frequency decay are followed by periods of recovery during a single trial of repetitive lifting. It is hypothesized that this difference reflects a complex strategy of utilizing muscle load-sharing during strenuous dynamic exercise to provide periods of metabolic recovery that limit localized fatigue. New analysis procedures to characterize this complex behavior are needed to enhance the technique for assessment of impairment in patients with lower back pain.
本文描述了一种估计周期性动态运动期间表面肌电信号频率压缩的新方法。该方法的基本特性首先通过模拟肌电信号进行开发。通过从科恩类变换导出的信号的时频表示中定义瞬时中位数频率来测量频谱压缩。然后将该技术用于处理重复提举过程中来自椎旁肌的真实肌电信号。我们的目的是使用这种新程序来确定：（a）在重复躯干伸展过程中同时活跃的椎旁肌之间的瞬时中位数频率变化是否产生指示正常功能的“疲劳模式”；（b）当受试者进行持续的等长躯干伸展时，这种模式是否不同。对四名健康受试者（26±4岁；3名男性，1名女性）进行了测试，分别在背部分析系统中进行持续静态等长收缩，以及在LIDO-Lift控制器（Loredan）中进行加权箱的重复提举和放下。在这些任务期间，同时从六个双侧腰椎旁区域记录肌电信号。结果表明，静态和动态任务导致肌电频谱变化的模式非常不同，这表明在负荷分担和潜在的代谢疲劳过程方面存在差异。与静态收缩中观察到的中位数频率线性下降不同，在动态收缩期间，瞬时中位数频率行为是非线性的且更复杂。文中提供了一些示例，其中在单次重复提举试验中，瞬时中位数频率衰减的不同阶段之后是恢复阶段。据推测，这种差异反映了在剧烈动态运动期间利用肌肉负荷分担的复杂策略，以提供限制局部疲劳的代谢恢复阶段。需要新的分析程序来表征这种复杂行为，以增强评估下背痛患者损伤的技术。
