Psy 552 Ergonomics & BiomechanicsLecture 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:

… … … …