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

Abstract

Variables, such as peak and accumulated moments and spine compression forces, have been shown to be risk factors for occupational low back pain. Estimates of these forces during prolonged, dynamic, asymmetric tasks using biomechanical models is complex and time-consuming. A simple technique for continuous 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 whether a linear normalization of erector spinae EMG to spine compression force, called compression normalized EMG (CNEMG), could be used to estimate spinal loading for simulations of asymmetrical occupational tasks. The estimates of spine compression force obtained using the normalized EMG are presented in the form of an amplitude probability distribution function and are compared with estimates of a three-dimensional biomechanical model. The per cent time a worker spends above particular levels of spinal loading of interest, such as the NIOSH action limit for compression, are displayed. Five males performed simulated occupational tasks. The exposure time at a specific level of spine compression force for a combination of three tasks, estimated by CNEMG, was, on average, within 6.5% of the time calculated by the biomechanical model. However, if the task combination was dominated by an axial twisting moment, then the difference was, on average, 13.4%. The difference in magnitude of spine compression at a specific probability was, on average, 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 force when the task combination is characterized by a predominant extensor moment in the sagittal plane. Estimates of spine compression at a specific probability, and estimates obtained during task combinations dominated by an axial twisting moment, are poor.

Influences of posterior-located center of gravity on lumbar extension strength, balance, and lumbar lordosis in chronic low back pain

“…Furthermore, compared to a normal person, his/her postural sway increases in the standing posture [24,25]. His/her medial and lateral postural sway also increase [13]. However, in this study, with eyes closed and open in static balance, the P-COG group's results for static and dynamic COG speed and distance were more decrease than those of the C-COG group (p < 0.05).…”

“…Na et al [12] indicated that trunk muscle weakness was associated with pelvic variables, thereby affecting changes in the lumbar lordosis angle and the lumbosacral angle. On the other hand, according to Mientjes et al [13] the COG was not located posterior to the center in every chronic low back patient. However, Byl and Sinnott [14] indicated that the COG in many chronic low back pain patients was located posterior to the center.…”

The time variation pattern of mechanical exposure and the reporting of low back pain

“…Long-term, mechanical exposure time histories are now being collected via data loggers (e.g. shift long moment or compression normalized EMG, Mientjes et al 1999). The process outlined in this study suggests a potential analysis approach for future epidemiological studies of musculoskeletal disorders where long-duration mechanical exposure data are available (Wells et al 2004).…”

Factors affecting the risk of developing lower back musculoskeletal disorders (MSDs) in experienced and inexperienced rodworkers

“…The Biometrics EMG system allows the researcher to collect raw EMG signals within the range of 15e450 Hz, with a common mode rejection ratio (CMRR) at 60 Hz (dB) of more than 96 dB (typically 110 dB), and an input impedance of more than 10 15 Ohms. EMG of the T9 ES has been shown to be a practical method for estimating continuous compression of the spine (Mientjes et al, 1999;Jackson et al, 2008;Potvin et al, 1990). While EMG of the ES was collected at two levels, the T9 and L4/L5, L4/L5 EMG will not be further discussed because it was not as strongly correlated with L4/ L5 moments as the T9 EMG.…”