Workplace biomechanics

What does analyzing the task in the worker capacity model involve?

Evaluating task demand compared to worker capacity in relation to performance quality fatigue discomfort and injury

What does the worker capacity model emphasize?

Factors related to both the task and the worker

What are material characteristics in task demands?

Symmetry coupling and dimensions

What are task/workplace characteristics in task demands?

Frequency distance moved work height and obstructions

What are organizational characteristics in task demands?

Paced work autonomy and medical services

What are environmental characteristics in task demands?

Heat cold and vibrations

What are personal characteristics in worker capacities?

Age weight smoking and injury history

What is physiological capacity?

Physical work capacity and conditioning

What is psychological capacity?

Coordination and psychosocial perceptions including understanding the work

What is biomechanical capacity?

Spinal strength and joint strength

What level of evidence links heavy physical work to low back disorders?

Moderate to strong evidence

What level of evidence links lifting and forceful movements to low back disorders?

Strong evidence

What level of evidence links bending and twisting to low back disorders?

Moderate to strong evidence

What level of evidence links whole body vibration to low back disorders?

Moderate to strong evidence

What level of evidence links static work posture to low back disorders?

Insufficient or no conclusion

What level of evidence links length of exposure to physical stressors to low back disorders?

Weak or no evidence

What level of evidence links sedentary work to low back disorders?

Weak or no conclusion

What does an odds ratio (OR) of 1 indicate?

No increased risk association

What does an odds ratio (OR) of 2 indicate?

Doubled risk

What is the OR for peak lumbar shear force?

1.7

What is the OR for cumulative lumbar disc compression?

2

What is the OR for peak hand force?

1.9

What is the OR for combined biomechanical risk factors?

10.6

What is the OR for perception of poor social workplace environment?

2.6

What is the OR for higher job dissatisfaction?

1.6

What is the OR for poor co-worker support?

1.6

What is the OR for perception of being less highly educated?

2.2

What is compression force?

Two opposing forces acting on a body to squeeze it

What is tension force?

Two opposing forces acting on a body to pull it apart

What is shear force?

Sliding force where two structures slide opposingly on each other

What is rotation/torque?

Twisting force

What is bending force?

Combination of tension and compression in structures under force

How do forces commonly occur in the body?

In combination with one another

What is the equation for torque?

Torque = Force x distance from point of rotation

What is the unit for torque?

Newton meters

Is torque a scalar or vector quantity?

Vector quantity

What is a moment arm?

Perpendicular distance between line of force and center of rotation

What direction is considered negative rotation?

Clockwise

What direction is considered positive rotation?

Anti-clockwise

What is required for force static equilibrium?

Weight torque must equal muscle torque

What else must be considered in static equilibrium besides external load?

Weight of body segments

Why must muscles often exert greater force than the external load?

Muscles usually have shorter moment arms while loads are further from the joint increasing torque

What are common potential injury points in the spine?

Spinous processes pedicle facet joint intervertebral disc abdominal muscles and obliques

What roles do spinal structures play?

Absorbing forces allowing flexibility and restricting movement

Which spinal structures are susceptible to cumulative trauma and fatigue failure?

Muscles tendons vertebrae discs ligaments and facet joints

What is the margin of safety in acute trauma?

Difference between spinal loading force and tolerance limit

How does acute trauma occur?

A single trauma exceeds the tolerance limit causing failure

What happens during cumulative trauma?

Frequent loading decreases tolerance limit until no margin of safety remains

What causes decreased tolerance limits in cumulative trauma?

Fatigue

What is the biomechanical approach to manual handling assessment?

Designing tasks that do not exceed musculoskeletal system capacity

What are two commonly used biomechanical criteria for MH assessment?

Compression/shear force limits and maximum joint torques/moments

What spinal levels are commonly assessed in MH tasks?

L4/L5 and L5/S1

What models are used to demonstrate moments acting on joints?

2D and 3D models

At what age is spinal compressive strength highest?

Around age 20

How does spinal compressive strength change with age?

Steadily declines

Who generally has greater compressive spinal strength?

Males

What is the action limit for lumbar compressive force?

3.4 kilonewtons

What should happen if a task exceeds 3.4KN?

Manual handling technique should be redesigned

What is the maximum permissible limit for lumbar compressive force?

6.4 kilonewtons

What should happen if a task exceeds 6.4KN?

Immediate redesign is required

How does compressive tolerance limit (CTL) change with age?

Decreases by 10-22% per decade

How do female CTLs compare to males?

Approximately 67% of male CTLs

How does body weight affect CTL?

CTLs increase with body weight

What is the average compressive strength per kg of body weight?

90.5N/kg

How does posture affect spinal tolerance limits?

Hyperflexion reduces tolerance limit to about 66%

Which spinal region has the highest CTL?

Lumbar spine

How does CTL change across vertebrae?

Average 14% increase with each successive lumbar vertebrae

Is spinal shear well understood?

No

What shear limit is acceptable for occasional exposure?

1000N

What shear limit is appropriate for repetitive loading?

700N

What does the 3D SSPP software predict?

Static strength requirements for tasks

What tasks can 3D SSPP analyze?

Lifts presses pushes and pulls

What outputs does 3D SSPP provide?

Strength capability spinal compression forces and comparison to NIOSH guidelines

What is psychophysics?

Study of subjective perceptions and physical stimuli or strain

What is the psychophysical power function?

S = KI^n

What do S K and I represent in the power function?

Sensation constant and physical stimulus intensity

What has been shown to reduce back injuries in psychophysical job design?

Designing tasks acceptable to most workers

What types of tasks can psychophysics assess?

Lifting carrying pushing and pulling

What does MAWL stand for?

Maximum acceptable weight of lift

What instruction is given to workers during psychophysical testing?

Work as hard as possible without straining or becoming unusually tired overheated weakened or out of breath

What is the overall goal of psychophysical task design?

Reduce workplace back injury risk

What is anthropometry?

Measurement of humans for design purposes

What body factors are included in anthropometry?

Body size shape proportions strength mobility flexibility and work capacity

What fields commonly use anthropometry?

Industrial clothing architectural and health design

What percentile range is commonly used for ergonomic design?

5th to 95th percentile

Why are extreme percentile limits less commonly used?

They benefit few people and increase costs

When are extreme percentile limits often used?

Emergency situations such as escape doors

Why is postural variability important in sedentary work?

To reduce prolonged static posture throughout the day

What are Hedge's 3S's ideal work pattern recommendations?

20 minutes sitting 8 minutes standing and 2 minutes stretching every 30 minutes

How many hours of sitting does Hedge's 3S's equal daily?

5 hours

How many hours of standing does Hedge's 3S's equal daily?

2 hours

How much moving/stretching does Hedge's 3S's equal daily?

0.5 hours

How many sit to stand transitions are recommended daily?

16