Mechanical Work-Capacity Evaluation Flashcards
Worker selection
purpose of worker selection and placement programs is to assign the right worker to a particular job
Why do we do worker selection?
Reducing injury risk
Performance
Human rights legislation
Reducing injury risk
Avoid mismatch btw workers capabilities and the job demands
Workers injury compensation claims and costs to employer and insurance
Costs and losses for injured employee
Performance
Physical levels required for execution of task
Minimum level of skill or excellence to be successful
As good as seasoned workers?
Training and retraining required
Several potential job postings
Human rights legislation
Social justice and equal opportunity
ADA - limit amount of pre employment screening
Employment quotas and gov. contractors - more than 25 employees needs to be representative of the population
Equal employment opportunity commission - fighting to reduce discrimination
Worker screening criteria
Safety
Accuracy
Sensitivity
Specificity
Worker screening criteria - sensitivity
Detect workers who will develop disease or injury
Must detect true positives
Worker screening criteria - specificity
Correctly identify workers who will not develop future problems
Must detect true negatives
Worker screening tests
Medical history General medical exam X rays Anthropometry ROM Muscle strength - general fitness
Screening tasks -
How to evaluate (screen) an individuals ability to perform work related tasks
Interaction with the environment - depends on
Joint motion Muscle strength (GMT)
Planes of motion
Sagittal
Frontal
Transverse
Axes of motion
Mediolateral (frontal)
Anterior-posterior (sagittal)
Vertical (transverse)
Factors affecting ROM
Type of joint - injury, degenerative disease Tissue arrangements Clothing Past injury Age Gender Soft tissue ratio (mm:fat) Multi-joint affect
ROM workplace considerations - Individual
Joint motion reflects lifestyle
Joint motion reflects injury history
ROM workplace considerations - environment
can be accommodated for reduced ROM
ROM workplace considerations - task
can be assigned according to ROM
Why it is important to understand and evaluate strength in the workplace
Many jobs require high levels of exertion
This has a direct impact on safety and performance
Strength =
Capacity to produce force or torque with voluntary muscle contraction
Max strength =
capacity to produce force or torque with a max voluntary muscle contraction
Human strength
Voluntary mm contractions should only be measured by the effort the person is willing to put forth
What is important when testing human strength
The test equipment
The tests persons familiarity
The interface btw the tested person and the test equipment
Purpose of strength measurement in ergonomics
Worker selection/placement
Job design
Worker selection/placement can serve to do what
reduce harmful physical effects caused by job/worker mismatch given adherence to three principles
Three principles to adhere to
Strength measured closely simulates
Predictive value for who is at risk
The training/skills of the ergonomist administering the test
Musculoskeletal disorders account for what percent of all lost workdays and illnesses
34%
Muscle strength - neural factors
Synchronization - trainable
Recruitment - trainable
Summation - trainable
Neural quality (age factors)
Muscle strength - psychological factors
Motivation - desire to return to work if evaluating post injury
Muscle strength - physiological factors
Fatigue
Available energy
Both of these are trainable
Muscle strength - mechanical factors
Length-tension relationship
Force-velocity relationship
Angle (posture) –> torque
Torque (moment of force) –>
tendency of a force to cause rotation
Torque =
force * distance
force * moment arm
Moment arm
Perpendicular distance from line of action of the force to axis of rotation
Moment arm and torque vary throughout
the ROM
Individual muscles interact in what way
as a group to produce torque at a joint
What we know about strength
Max force (torque) producing capability varies considerably btw people and btw tasks
Strongest 6-8 times stronger than the weakest
Static strength is not necessarily correlated with dynamic strength
Additional gender issues with strength
Diff in upper body greater than lower body
Diff almost entirely explained by differences in muscle size
Psychophysical limits -
Voluntary dec in max with inc dimensions of boxes
Dec with inc height (shoulder to above)
Male about 2x Female
LOAD workplace summary - individual
Screen people for sufficient strength to a task
Load should not exceed capacity of least capable employee
LOAD workplace summary - environment
Reduce package weight, alter layout, new equipment
LOAD workplace summary - task
redesign, additional workers
