An electromyographic analysis of seated and standing lifting tasks.
Ergonomics 1992 Jul; 35(7/8):889-898
An electromyographic analysis of seated and standing lifting tasks was conducted. The study group consisted of six physically active male volunteers, mean age 26.8 years. The subjects were instrumented with electromyographic electrodes attached to the erector spinae muscles of the low back, the trapezius and rhomboid muscles of the upper back, the deltoid muscles, and the external and internal oblique muscles of the abdominal region. The subjects lifted a wooden tray with slotted handles that contained 15.9 kilograms of lead weights under maximum or submaximum static, or dynamic conditions while standing or sitting. The dynamic standing lifts were performed with a vertical or bent forward posture. The dynamic sitting lifts were performed with a bent forward or twisted posture. Electromyographic data were recorded at 3 second intervals during each lift. When categorized according to posture, electromyographic activity in the upper and low back and shoulder muscles during the sitting lifts was significantly greater than during the standing lifts. Dynamic lifting induced greater activity in these muscle groups than lifting under static conditions. In the abdominal muscles, lifting from the sitting forward posture induced the greatest electromyographic activity for this muscle group. Dynamic lifting from the sitting forward position induced greater activity than static sitting lifting. Abdominal muscle activity did not vary significantly across the other lifts. The authors suggest that lifting tasks performed from a sitting position induce more muscle electrical activity, indicative of more stress, than those performed using a standing posture. This is especially true for muscles in the low and upper back and shoulder.
NIOSH-Publication; NIOSH-Grant; Musculoskeletal-system-disorders; Ergonomics; Humans; Manual-lifting; Laboratory-testing; Musculoskeletal-system; Physical-stress; Muscle-contraction; Electrophysiological-measurements; Manual-materials-handling
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