Pushing & Pulling 17-20% of overexertion injuries result from
pushing or pulling activities. The exertion does not adequately convey the
hazards of falling. Optimal handle height depends on criterion:
Posture – Abdominal pressure: Biomechanical strength:
Pushing & Pulling (cont) Hand force changes as a function of:
Feet position One or two-handed pulls/pushes The vertical component of the push
In all cases, create a push/pull task that … … …
Spine shape Lordosis
Kyphosis
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Sitting factors The chair The task Sitting habits
The ideal posture will vary according to these factors
Sitting & low back pain Equivocal data
Some research shows a relationship between low-back pain and prolonged sitting. Others do not.
Drivers who sit longer than 3.5 hours/day have a 3x increase in risk of disc herniation.
Increased postural changes reduce fatigue and decrease absenteeism due to sickness.
CDC recommends 15 min break per hour for VDT operators.
Sitting geometry X-rays can be used to measure the lumbar
angle. In unsupported chair (no back) the angle
decreased an average of 38 degrees causing a flattening of the spine.
With a lumbar support, the total back angle increased as a function of placement.
Disc pressure Disc pressure is 35% less for standing than it
is for sitting without support.
When sitting, the lowest disc pressure occurs when the back is straight.
Disc pressure changes with increases in the trunk moment
Disc pressure and back supports Disc pressure decreased
as seat back angle increased from 90 to 110 degrees
When a lumbar support was used When arm rests were used – expect for increased
back angles.
Muscular Activity Using EMG, activity decreases when
… ... … …
Activity with increase when the chair is too low or too high
Shoulders and sitting Work surface height affect abduction and
flexion of the arms.
Abduction should be … Flexion should be …
Legs and sitting Leg support can reduce load on the ischial
tuberosities and thighs
Feet should be firmly place on floor or foot rest.
Pressure at the popliteal fold can cause swelling
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