Assessment of an EMG-based method for continuous estimates of low back compression during asymmetrical occupational tasks

Variables, such as peak and accumulated moments and spine compression force s, have been shown to be risk factors for occupational low back pain. Estim ates of these forces during prolonged, dynamic, asymmetric tasks using biom echanical models is complex and time-consuming. A simple technique for cont inuous measurement of these variables over a prolonged period is needed to measure the distribution of spinal loading during both sagittal plane lifts and complex asymmetrical jobs. The aim of this study was to determine whet her a linear normalization of erector spinae EMG to spine compression force , called compression normalized EMG (CNEMG), could be used to estimate spin al loading for simulations of asymmetrical occupational tasks. The estimate s of spine compression force obtained using the normalized EMG are presente d in the form of an amplitude probability distribution function and are com pared with estimates of a three-dimensional biomechanical model. The per ce nt time a worker spends above particular levels of spinal loading of intere st, such as the NIOSH action limit for compression, are displayed. Five mal es performed simulated occupational tasks. The exposure time at a specific level of spine compression force for a combination of three tasks, estimate d by CNEMG, was, on average, within 6.5% of the time calculated by the biom echanical model. However, if the task combination was dominated by an axial twisting moment, then the difference was, on average, 13.4%. The differenc e in magnitude of spine compression at a specific probability was, on avera ge, 14.9% and when axial trunk twist dominated, 30.7%. It is concluded that CNEMG can estimate probability at a specific level of spine compression fo rce when the task combination is characterized by a predominant extensor mo ment in the sagittal plane. Estimates of spine compression at a specific pr obability, and estimates obtained during task combinations dominated by an axial twisting moment, are poor.