Psy 552 Ergonomics & Biomechanics - PowerPoint by J0vi4YEw

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									Psy 552 Ergonomics &
Biomechanics
Lecture 18
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
       …
       …
       …
Floor Friction
   Friction is important, but:
       …

       …

       …

       …
Asymmetric handling
   Very limited literature

   Asymmetric handling increases:
       …

       …
Sitting
   Advantages:
       …
       …
       …
       …


   The study focuses on the shape of the spine.
 Spine shape
         Lordosis

         Kyphosis




Image fromhttp://www.spineuniverse.com/displayarticle.php/article1286.html
Sitting factors
   The chair
   The task
   Sitting habits

   The ideal posture will vary according to these
    factors
Sitting defined
   Anterior…



   Middle…



   Posterior…
Evaluating seated work
   There is no one accepted metric

   Common measures include
       …
       …
       …
       …
       …
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
Balans Chair
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
Legs and sitting (cont)
   Seat too low
       …
       …
       …
       …
   Seat too high
       …
       …
Chair characteristics
   Adjustable
   Dimensions to consider
       Seat height, …



       Back rest height, …
Chair characteristics (cont)
   Arm rest length, …
Work surface
   Consideration should be provided to:
       …
       …
       …
       …

								
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