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

Abstract

Creating mechanical exposure profiles for multi-component jobs for use in epidemiological studies of work-related musculoskeletal disorders is challenging but becoming more common. Once time-varying mechanical exposure profiles are created, some form of exposure index must be derived. Available techniques typically provide information about the relative amount of time exposed to different levels and durations of stressors. Little or no information concerning the sequence or history of exposure delivery is maintained. The current paper examines an approach to the processing of time varying exposures for epidemiological studies. Shift-long exposure data of 68 production operators (34 cases; 34 controls) from a large epidemiological study of low back pain reporting were used to create individual shift-long internal mechanical exposure profiles. These were processed through a first-order system with varying time constants to generate a range of modelled responses from which two exposure indices were then created. The utility of these mechanical exposure indices was evaluated using low back pain reporting as the health outcome from the same epidemiological study. The modelled response using the first-order system appeared to provide additional exposure information, perhaps time-history sensitive exposure information that was not captured by the unprocessed exposure profiles. Risk estimates from the peak value exposure index derived from an internal exposure processed with a time constant of 2 s were almost doubled compared with the risk estimates of the unprocessed peak value, and the final value, taken from the internal exposure processed with a time constant of 5 000 s, generated higher risk estimates over the cumulative/average exposures. This study suggests a potential analysis approach for epidemiological studies of musculoskeletal disorders where long-duration mechanical exposure data is available.

Neuromuscular manifestations of viscoelastic tissue degradation following high and low risk repetitive lumbar flexion

“…Furthermore, recent experimental work with humans in the author's laboratory (Olson et al, 2004(Olson et al, , 2006(Olson et al, , 2009Li et al, 2007) and in other laboratories around the world (Sanchez-Zuriaga et al, 2010;Little and Khalsa, 2005;Granata et al, 1999Granata et al, , 2005Shin and Mirka, 2007;van Dieen et al, 2003;Kumar and Prasad, 2010;Dickey et al, 2003;Karajcarski and Wells, 2006;McGill and Brown, 1992;Hendershoot et al, 2011) confirm the development of creep, spasms, changes in EMG reflex amplitude and latency, motor control and stability following prolonged cyclic work as was described in the in-vivo feline model of this report. The increase in the neutrophil density and cytokines expression level is yet to be confirmed experimentally in humans exposed to repetitive lumbar work, as only initial confirmation is available to date (Yang et al, 2011).…”

Neuromuscular control of lumbar instability following static work of various loads

“…Excluding scaling and “industrial history,” the similarity of the cat's neuromuscular system and lumbar mechanical behavior allows a certain liberty in expressing some conclusions from feline experiments to be applicable to humans. Finally, and importantly, experiments with human subjects consistently verify the various neuromuscular and mechanical responses observed in the in vivo feline under cyclic and static work, including the development of laxity and neuromuscular disorders 3, 6, 7, 14, 17, 32, 37…”

“…Handling loads of high magnitudes was shown to be especially conducive for low back disorders. Recent biomechanical and neurophysiological confirmation of the epidemiology identify substantial laxity/creep development in lumbar viscoelastic tissues concurrent with an acute neuromuscular disorder in in vivo models2, 15, 25, 30, 31 and in humans 3, 6, 7, 14, 17, 32, 37…”

Neuromuscular neutral zones response to cyclic lumbar flexion

“…The epidemiology was recently confirmed biomechanically and physiologically in in vivo models (Navar et al, 2006;Le et al, 2007;Hoops et al, 2007) and in humans (Granata et al, 2005(Granata et al, , 1999Olson et al, 2004Olson et al, , 2006Shin and Mirka, 2007;Li et al, 2007;Dickey et al, 2003;Karajcarski and Wells, 2006). Prolonged periods of exposure to cyclic lumbar loading were shown to develop substantial laxity/ creep in the viscoelastic tissues and in turn, significant changes in the activation pattern of the spinal musculature.…”