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Electromyography in ergonomics
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
Jonsson (1970) reported the functions of individual muscles in the lumbar region of the erectores spinae, more specifically the multifidi, longissimus, and iliocostalis at different lumbar vertebral levels. He inserted wire electrodes guided by TV fluoroscopy to place them in the pick-up area accurately. He also used a common gain for all channels for studying static contractions in prone, standing and sitting postures. He graded all EMG recordings on a three-point scale: 0 = no activity, 1 = slight activity (individual action potentials were perceptible and the baseline was not obscured), and 2 = marked activity (the base line was obscured by the action potentials). He only measured the mean activity. Using this simple scoring system, Jonsson (1970) was able to demonstrate that there was no significant difference between muscle loads to left and right sides of the body in symmetrical postures. Furthermore, he reported no difference between the medial or lateral placement of electrodes in the longissimus. He also concluded that there were differences in function between the multifidi, longissimus, and iliocostalis muscles even at the same level; sometimes differences in function occur between different vertebral levels even in the lumbar region.
Modeling and simulation of tissue load in the human spine
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
N. Arjmand, B. Bazrgari, A. Shirazi-Adl
As the trunk flexes forward from upright posture, initially both active and passive components of forces in global extensor muscles increase with the formers reaching their peak values at about 45° (Figure 3.3). Thereafter, up to the trunk flexion of about 95°, active forces in thoracic extensor muscles diminish despite the continuous increase in net external moment reaching its maximum of 118 Nm. On the contrary, passive muscle forces as well as passive ligamentous moment increase throughout the movement to peak lumbar flexion (Figures 3.3 and 3.5). The progressive relief in activity of global back muscles is due, therefore, to higher passive contribution of muscles and ligamentous spine as the lumbar rotation increases. As the trunk flexion exceeds about 95° (at about 3.3 sec), lumbar rotation (Figure 3.3) and consequently both passive muscle force and moment resistance of the ligamentous spine, remain nearly unchanged, while the activity of back muscles continues to drop. In this case, the reduction in net external moment due to the decrease in the effective lever arm of the trunk centre of mass (COM) is the primary cause in progressive decrease in back muscle activities. Global longissimus [LGPT] and iliocostalis [ICPT] become completely silent at trunk flexion angles of about 114° and 95°, respectively.
Sensitivity of muscle and intervertebral disc force computations to variations in muscle attachment sites
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Riza Bayoglu, Ogulcan Guldeniz, Nico Verdonschot, Bart Koopman, Jasper Homminga
Grand OSI corresponding to each muscle is shown as stacked columns in Figure 2. Similar to the changes in disc forces, relatively higher values were found for certain muscles (quadratus lumborum, intercostales interni, intercostales externi, longissimus thoracis, and iliocostalis lumborum) located in the rib cage and lumbar regions. For all other muscle groups, cumulative OSI was below 10%.