Wednesday, February 23, 2011

Can occupational sitting cause LBA?


Sociocultural, economic, and manufacturing factors are 3 different major factors that influence sitting. "Correct" seated posture is associated with spine health was known to people possibly from Hippocratic era. But the debate has not dampened yet whether the sitting is directly a cause of LBA or it predisposes or precipitates LBA. From 1980s much of research has been put into ergonomically correct sitting & providing a work environment for correct sitting posture. However there is a question; is there any medically correct sitting posture? The correct sitting posture refers to maintenance of a correct lumbar spine lordosis actively (muscle contraction) or passively (chair or sitting back support) (described below elaborately in neutral spine position). Passive maintenance is sought because it is noticed that within minutes of sitting lordosis is reversed or lost. According to Ernst even the correct sitting is not out of danger because of the repetitive nature of compressive loads on vital spine tissues having multiple avenues of pain production. But certainly correct sitting posture & correct work ergonomics may lead to minimize injury.

Importance of Lordosis in seating ergonomics:

Sagittal balanced spinal posture is a goal for spinal surgery and conservative ergonomics. The configuration of the spine, postural position, and weight transfer is different in the 3 types of sitting: anterior, middle, and posterior. Among these 3 different; flat, long lordosis, short lordosis seating postures, flat posture show the least muscle activity similar to the slump posture.

Ergonomic advices for jobs with sitting: Lumbar lordosis is affected by trunk-thigh angle (THA) and the knee angle (KA). THA 110 to 130 degrees with arm rest, back rest & concomitant lumbar support (or a pneumatic support) has the lowest disc pressures and lowest muscle activity from spinal muscles. A seat-bottom posterior inclination of 5 degrees and armrests can further reduce lumbar disc pressures and muscle activity while seated. To reduce forward translated head postures, a seat-back inclination of 110 degrees is preferable over higher inclinations.

Ergonomic advices for jobs with sitting & whole body vibration: Adjustable seat back incline of 110 degrees from horizontal, a changeable depth of seat back to front edge of seat bottom, adjustable height, an adjustable seat bottom incline, firm (dense) foam in the seat bottom cushion, horizontally and vertically adjustable lumbar support, adjustable bilateral arm rests, adjustable head restraint with lordosis pad, seat shock absorbers to dampen frequencies in the 1 to 20 Hz range, and linear front-back travel of the seat enabling drivers of all sizes to reach the pedals. The lumbar support should be pulsating in depth to reduce static load. The seat back should be damped to reduce rebounding of the torso in rear-end impacts.

This is a part of one of my international seminar on “Occupational health & hygiene” held at bhubaneswar, Orissa, India 23-25 feb 2011. I was invited as a speaker on the first day of the congress. My topic was “Can sitting cause occupational LBA?”

* With due apology we want to mention that the references here are not published.

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