Assessment of back load in assemblyline work using electromyography

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Abstract
When the back is loaded, the amplitude of the myoelectric signals in the lumbar region of the back has been found to correlate well to the compression force in the spine measured by means of disc pressure. The purpose of this paper is to use surface electromyography to quantify the load on the back in several working situations. Thirteen male workers participated in a study of three strenuous workstations along the assembly line of a car factory; mounting of a side panel and a sound insulator in the front compartment, mounting of floor mats, and mounting of the left front seat. Electrodes were placed at the level T8, LI and L3 on both sides of the spine. The average load during a work cycle is given as mean values of signal amplitude. Standard deviations are calculated to indicate the average load variations. Amplitude histograms are also presented to illustrate the loading pattern in more detail. The results show that it is possible to record myoelectric signals at the workplace without serious disturbance. The amplitude levels were high at all three workstations. The actual way in which each task was carried out resulted in differences in activity level between the thoracic and lumbar regions of the back which could be used to identify incorrect body postures or work activities. The use of a lifting aid at one workstation was found to give a significant decrease in high amplitude levels. Analysis of myoelectric activity patterns give useful guidance about how to reduce body loading in heavy work situations and also permits quantitative evaluation of such improvements.