Psy 552 Ergonomics Biomechanics Lecture 18 Pushing Pulling

Psy 552 Ergonomics & Biomechanics Lecture 18

Pushing & Pulling o o o 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: n n Posture – Abdominal pressure: Biomechanical strength:

Pushing & Pulling (cont) o Hand force changes as a function of: n n n o Feet position One or two-handed pulls/pushes The vertical component of the push In all cases, create a push/pull task that n n n … … …

Floor Friction o Friction is important, but: n … n …

Asymmetric handling o Very limited literature o Asymmetric handling increases: n …

Sitting o Advantages: n n o … … The study focuses on the shape of the spine.

Spine shape o Lordosis o Kyphosis Image fromhttp: //www. spineuniverse. com/displayarticle. php/article 1286. html

Sitting factors o o The chair The task Sitting habits The ideal posture will vary according to these factors

Sitting defined o Anterior… o Middle… o Posterior…

Evaluating seated work o There is no one accepted metric o Common measures include n n n … … …

Sitting & low back pain o Equivocal data n n Some research shows a relationship between lowback pain and prolonged sitting. Others do not. Drivers who sit longer than 3. 5 hours/day have a 3 x 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 o o o 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 o Disc pressure is 35% less for standing than it is for sitting without support. o When sitting, the lowest disc pressure occurs when the back is straight. o Disc pressure changes with increases in the trunk moment

Disc pressure and back supports o Disc pressure decreased n n n 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 o Using EMG, activity decreases when n n o …. . . … … Activity with increase when the chair is too low or too high

Balans Chair

Shoulders and sitting o Work surface height affect abduction and flexion of the arms. o Abduction should be … Flexion should be … o

Legs and sitting o Leg support can reduce load on the ischial tuberosities and thighs o Feet should be firmly place on floor or foot rest. o Pressure at the popliteal fold can cause swelling

Legs and sitting (cont) o Seat too low n n o … … Seat too high n n … …

Chair characteristics o o Adjustable Dimensions to consider n Seat height, … n Back rest height, …

Chair characteristics (cont) o Arm rest length, …

Work surface o Consideration should be provided to: n n … …