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industrial ergonomics > exam 1 > Flashcards

exam 1 Flashcards

1
Q

What does “ergonomics” mean in Greek?

A

ergon - work

nomos - law

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2
Q

ergonomics

A

the process of designing or evaluating products, tasks, environments, and systems to improve performance and/or reduce the risk of injurt

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3
Q

industrial ergonomics

A

application of ergonomics and human factors methods to the design, evaluation, improvement of work tasks, tools, environments to improve performance, productivity, quality or decrease injury, fatigue, waste

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4
Q

What are side effects of ignoring ergonomics?

A
  • compromises worker and company performance
  • lower quality work and productivity
  • absenteeism
  • turnover
  • training
  • morale
  • accidents
  • acute of chronic musculoskeletal disorders
  • occupational injuries and illnesses in the US is $150b annually
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5
Q

3 areas of ergonomics

A
  • physical: human anthropometry, musculoskeletal, metabolic, cardiovascular, environmental issues; working posture, MH, repetitive movements, workplace layout, health and safety
  • cognitive: mental processes as they affect interactions among humans and other elements of the system; mental workload, decision making, HCI, work stress, training
  • organizational (marcoergo): sociotechnical systems, including organizational structures, policies, and processes; shift work, scheduling, job satisfaction, motivational theory, teamwork, ethics
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6
Q

4 types of physical ergonomics

A
  • anthropometric: concern physical dimensional conflicts between functional space geometry and the human body
  • musculoskeletal: concern forces, moments, postures, and mechanical stress on muscles and skeletal system
  • metabolic/cardiovascular: concern stress on metabolic energy and cardiovascular system (heart rate, breathing rate, etc.)
  • environmental: concern exposure to excessive environmental stress (heat, vibration)
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7
Q

What is the ergonomic process?

A
  1. characterize existing or potential problems
  2. perform job analysis
  3. implement controls
  4. evaluate effectiveness of controls; educate employees on ergonomics
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8
Q

What is the overarching goal of ergonomics?

A

prevent disorders through proactive design and vigilance

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9
Q

What is the guiding principle of ergonomics?

A 
D = task demand
C = human capability or capacity

maintain D < C

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10
Q

6 types of interaction

A
  • **human with machine (H->M): control actions provided by human
  • **machine with human (M->H): information feedback and forces generated by machine
  • human with environment (H->E): effect of human on local environment
  • **environment with human (E->H): influence of environmental factors on human performance
  • machine with environment (M->E): alteration of work environment by machine
  • environment with machine (E->M): machine function altered by environment
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11
Q

What are indicators for the need of ergonomics?

A
  • waste production is too high
  • too many rejects
  • production accidents too frequent
  • higher medical costs
  • absenteeism is high due to injuries
  • frequent complaints about job requirements
  • production output or efficiency is low
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12
Q

5 components of the muscle system

A
  • connective tissue: bones, ligaments, tendons, fascia, cartilage
  • joints: unions with more than 1 degrees of freedom
  • skeletal muscle: muscle fibers, connective tissue, nerve excitation
  • nerves: afferent (sensory) and efferent (motor)
  • brain: central and peripheral nervous systems
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13
Q

4 functions of bone

A
  1. support and motion
  2. protection of organs
  3. mineral storage (calcium and phosphorus)
  4. formation of blood cells
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14
Q

2 types of bone

A
  • cortical (compact): dense compact shell provides strength and impact resistance; very strong
  • cancellous or trabecular (spongy): organization of trabeculae tend to be distributed along lies of principal loads of stresses and strains
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15
Q

2 mechanical properties of bone

A

stress: force/initial cross-sectional area
strain: change in length/original length

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16
Q

What type of material is bone?

A

anisotropic

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17
Q

Wolff’s Law

A

bone adapts to its mechanical environment: it will be deposited where needed and be reabsorbed where not needed; bone growth stops but thickness and diameter can change

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18
Q

ligament

A

a connective tissue that binds bone to bone

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19
Q

tendon

A

a connective tissue that binds muscle to bone

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20
Q

cartilage

A

a connective tissue that is a smooth elastic tissue that covers the ends of long bones at joints to provide a low-friction surface for movement

can be a structural component

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21
Q

fascia

A

a band or sheet of connective tissue - primarily collagen - beneath the skin that attaches, stabilizes, encloses, and separates muscles and other internal organs

surrounds muscles or other structures

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22
Q

viscoelasticity

A

material response to force/displacement depends not only on force/displacement but also time

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23
Q

creep

A

change in strain for a constant stress

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24
Q

load (stress) relaxation

A

change in stress for a constant strain

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25
Q

What is the relevance of viscoelasticity?

A
  • joint stiffness and load distribution change over time

- repeated loads or movements can accumulate over time to have larger effects than just one repetition

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26
Q

3 types of joints

A
  • synovial: common, large motion, synovial fluid forms interface; elbow, knee, shoulder
  • fibrous: relatively immobile, fibrous connective tissue bridges the joint; ribs, pelvis, skull
  • cartilage: bridges the joint; lumbar motion segment
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27
Q

What is the function of joints

A

motion between bones

pulleys for tendons

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28
Q

synovial joint: the knee

A
  • capsule includes a synovial membrane that produces synovial fluid
  • some joints contain menisci to protect articular cartilage and distribute loads
  • VERY LOW coefficient of friction
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29
Q

cartilage joint: intervertebral discs

A

composition:

  • nucleus pulposus: gel-like material
  • annulus fibrosus: layers of fibrous connective tissues with varying orientation
  • disc height decrease throughout the day in response to loading
  • discs have no direct blood supply which makes them extremely slow to heal
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30
Q

What are potential causes of back pain?

A
  • prolonged static loading -> decreased disc height -> misalignment of facet joints -> pain
  • weakened annulus (disc degeneration)
  • disc bulging, compression of spinal nerve roots; can lead to disc rupture
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31
Q

skeletal muscle

A
  • constitutes 50% of body weight
  • ~400 skeletal muscles in the body
  • basic function: generate moments about joints and help maintain joint stability
  • can only actively contract
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32
Q

muscle names

A
  • origin: bony end at proximal end of muscle
  • belly: thicker middle region of muscle between origin and insertion
  • insertion: bony attachment at distal end of muscle
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33
Q

5 structural units of skeletal muscle

A 
(in decreasing order)
muscle
fascicle
muscle fiber/cell
myofibril
myofilaments
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34
Q

sarcomere

A

the basic contractile unit of muscle

delineated by its z-lines, thick filaments, and thin filaments

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35
Q

How does a muscle contract?

A
  • contract by sliding
  • the amount of overlap determines the amount of force that can be generated
  • a sarcomere with vertical z discs has horizontal thin filament perpendicularly attached; thick filament lies between the thin
  • when thick filaments are pulled between thing –> contraction
  • more cross bridges formed = more force
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36
Q

WMSD

A

Work-related MusculoSkeletal Disorders

  • involve injury to soft tissues of the body and joints
  • tend to develop gradually/cumulatively over time
  • work performance and environment contribute significantly to the condition; likely make it worse or persist longer
  • injury event or exposure to the event involves: bodily action
  • NOT sudden injuries from slips, trips, falls, or MV accidents
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37
Q

What are examples of WMSDs?

A
  • tendonitis
  • low back pain
  • sprains, strains, tears
  • carpal tunnel syndrome
  • hernia
  • bursitis
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38
Q

How prevalent and significant are WMSDs?

A
  • account for 1/3rd of all worker injury and illness cases
  • difficult to diagnose because seen as normal aches and pains
  • 1/2 of US workers are employed in occupations with high risk for WMSDs
  • ~$20b annually in direct costs; worker compensation, legal and medical expensive
  • 5xs direct costs = indirect costs; training, accident investigation, lost productivity, repairs, lower morale, absenteeism
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39
Q

risk factor

A

an individual characteristic or exposure associated with an increased risk of a disease or injury

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40
Q

workplace risk factors

A
  • high force exertions
  • highly repetitive or static work
  • awkward/extreme postures
  • vibration
  • mismatched anthropometry
  • psychosocial job factors
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41
Q

2 types of mental risk factors (psychosocial job factors)

A

influence the mental state of the individual (mental stress, supervisory control, autonomy, job security, interactions with coworkers, anxiety)

  • psychological factors: individual level
  • social factors: organizational level
42
Q

individual risk factors

A 
age
sex
obesity (anthropometry)
systemic diseases (diabetes)
acute trauma
congenital defects
pregnancy
43
Q

What are industries and jobs with high WMSDs prevalence?

A
  • industry: agriculture, construction, manufacturing, mining, transportation
  • jobs: meat packers, keyboard entry work, sewing operations, packing operations
44
Q

2 categories of WMSDs

A
  • by tissue or bodily system; muscular, tendon, neurovascular, joint, spinal disorders
  • by body location; neck, back, elbow, wrists, fingers, shoulders
45
Q

tendon disorders

A

WMSD characterized by tissue or bodily system

result from repetitive or prolonged activities, forceful exertion, awkward and static posture, vibration, localized mechanical stress

two types: tendinitis, tenosynovitis

46
Q

carpal tunnel syndrome

A

WMSD characterized by tissue or bodily system

tendinitis of the flexor tendons of the fingers which leads to compression of the median nerve

contributing factors: repetitive forceful wrist extension/flexion, high speed finger movements, pressure on base of hand

47
Q

neurovascular disorders

A

WMSD characterized by tissue or bodily system

result in compression or damage to both nervous and vascular tissues; increase inadequate blood supply and localized muscle fatigue

48
Q

neck WMSD

A

WMSD characterized by body location

contributing factors: prolonged static and restricted posture, prolonged unnatural posture of the head/neck/shoulder

49
Q

back WMSD

A

WMSD characterized by body location

contributing factors: prolonged static load on the upper torso musculature, non-neutral posture, constant lifting of objects from the floor

50
Q

shoulder WMSDs

A

WMSD characterized by body location

contributing factors: prolonged shoulder flexion/abduction, frequent high reaching, prolonged load, repetitive throwing

51
Q

What are commonalities seen among contributing factors to WMSDs?

A 
repetitive movements
extreme movements
prolonged postures
vibration
forceful extertions
52
Q

What are commonalities seen among prevention and control of WMSDs?

A 
vary jobs/movements
minimize extreme movements
vary postures
protective materials to absorb vibration
reduce forceful exertions
53
Q

ergonomic process relating to WMSDs

A
  1. characterize existing or potential problems
    - identify jobs with high risk factors
    - tracking and quantifying injuries
  2. perform job analysis
    - **goal is to identify and quantify risk factors
  3. implement controls
    - **goal is to reduce exposure to risk factors
    - hierarchy of controls: elimination, substitution, engineering controls, administrative controls, PPE
    - **engineering controls: change the task/environment
    - **administrative controls: change the work procedures or methods (exposure to the task)
  4. evaluate effectiveness of controls and educate employees on ergonomics
    - job analyze to ensure elimination or reduction of risk factors
    - ensure no new risk factors were created
54
Q

3 types of occupational risk factors

A
  • workplace: associated with the work task and work area
  • individual: associated with an individual and may predispose them to risk
  • psychosocial: psychological factors (individual) and social factors (organizational) that influence the mental state of the individual
55
Q

3 job analysis quantifiers

A

frequency, duration, magnitude

56
Q

posture

A

includes all of your joint and body segment angles

57
Q

5 classifications of repetition rates

A
  1. very high
    - body parts in constant motion
    - difficulty maintaining pace
  2. high
    - hands in constant rapid motion
    - wasted motions or difficulty with equipment would result in worker immediately falling behind
  3. medium
    - hands in steady motion
    - no difficulty keeping up
    - worker may pause or rest if necessary
  4. low
    - obvious pauses in each work cycle
    - worker may wait for equipment to cycle
    - hand used only to remove occasional defects
  5. very low
    - hands are idle most of the time
58
Q

constant mechanical stress

A

stress or pressure directly on nerves and tendons can aggravate existing injuries and possibly lead to WMSDs

increase applied force area; less stress when using a power grip (whole hand) vs. a pinch grip (small area)

59
Q

What factors should be considered when selecting tools?

A

posture
forceful exertions
repeated/sustained exertions
contact mechanical stress

60
Q

What should hand tools be designed to fit?

A
  • minimize wrist angular deviations
  • minimize hand force requirements
  • minimize force concentrations or pressure points
  • maximize grip strength capability
  • accommodate anthropometric variability
61
Q

2 types of occupational risk factors

A

temperature

  • cold: work has higher incidences of WMSDs, decreased circulation
  • hot: fatigue quickly

vibration
-causes reflex reduction, decrease circulation, loss of sensations, unconscious increases in force level

62
Q

challenges of WMSD prevention

A
  • multi-factorial nature
  • complex unknown interrelationships between risk factors
  • long development cycles
  • inconsistency amongst workers with and without WMSD
  • reducing injury risk and maintaining/improving productivity may be in conflict
63
Q

anthropometry

A

the study of the physical dimensions of the human body

64
Q

What is anthropometry data for?

A

design of dimensions of seating, furniture, tools, workspaces, and many places that humans occupy

in biomechanical models to:

  • predict human reach, force, and space requirements
  • analyze work demands
65
Q

2 types of anthropometric data

A 
static anthropometry: physical dimensions of the body
-body segment length
-body segment mass
-body segment COM
body segment moments of inertia

functional/dynamic anthropometry: physical dimensions for completing particular activities or tasks

  • reach distance
  • motion envelop
66
Q

center of mass

A

the point at which all mass of a body can be concentrated so that its results in forces and moments equivalent to the actual distributed mass

67
Q

3 design strategies for anthropometric variance

A

average

  • emphasize the center of a population distribution
  • both extremes of users won’t be accommodated
  • minimizes manufacturing costs

extremes (max or min)

  • emphasizes one tail of distribution
  • clearance: 95th male
  • reach: 5th female
    safe: accomodate > 99% of population
  • must select to account for min or max

adjustability

  • emphasize that all potential users are “equal”
  • preferred method
  • expensive and involved
  • range and degrees of adjustment can be difficult to specify
  • must select “acceptable” range
  • a wider the range means the process/tool/task is more important
68
Q

standard normal distribution equation

A

X = mean +/- Z * std

X = value of interest
mean = mean of distribution
Z = standard deviations above (+) or below (-) the mean
std = standard deviation of the distribution
69
Q

procedure for anthropometric design

A
  1. identify key anthropometric measurements
  2. determine the population and/or percentiles to target
  3. develop a scaled drawing (often side view) where body parts could be locate with adjustments
  4. from 2D mannequins, develop initial estimates of population effects
  5. use functional anthropometric data or computer based human models to verify predictions
  6. build mock-up with 3D mannequins and test with extremes to verify and validate
70
Q

What are limitations of anthropometric design?

A
  • population based data can have selection bias
  • averages and proportions do not represent individuals; people are not proportional
  • muscle strength not considered; capable of reaching but not moving or moving safely
  • functional data may vary with clothing, protective equipment, etc
  • even if guidelines, standards are followed, the workstation may not be completely functional, usable, or comfortable
71
Q

Why evaluate ROM and strength?

A
  1. both are components of worker capacity; goal is to design or improve tools, tasks, and environments so that demands are less than or equal to capacity
  2. identify high risk workers
  3. asses “return to work” status
  4. understand how individual factors affect worker capacity
72
Q

range of motions (ROM)

A

the maximum angular deviation of segments forming a joint

73
Q

2 types of ROM

A

passive

  • external force used to reach ROM limits
  • more dependent on passive elasticity of MLTs

active

  • muscle force used to reach ROM limits
  • dependent on muscle contraction

active ROM < passive ROM

74
Q

anatomical position

A

universally accepted reference position

standing, feet together, arms at sides, palms facing forward

75
Q

anatomical planes of motion

A

sagittal: divides left and right sides of the body
frontal: divides front and back portions of the body
transverse: divides upper and lower portions of the body

76
Q

What movements occur in the sagittal plane?

A

flexion and extension

77
Q

What movements occur in the frontal plane

A

abduction: away from mid sagittal plane
adduction: toward mid sagittal plane

78
Q

What movements occur in the transverse plane?

A

rotation

79
Q

What methods are used to measure join ROM?

A

manual goniometer
electrogoniometer
inclinometer

80
Q

How should ROM data be presented?

A
  • use accepted terminology to describe posture or motion
  • describe subject population
  • describe the measurement method
81
Q

What factors affect ROM?

A 
age
sex
training (stretching and changes in flexibility)
genetics
2 joint muscle effect
82
Q

muscle strength

A

the maximum force/moment a group of muscles can develop under prescribed conditions

83
Q

4 types of strength

A

isometric: no motion
isokinetic: constant velocity

free dynamic: nonconstant force/motion

psychophysical: the maximum load that can be handled for an extended period of time without overexertion; subjectively determined

84
Q

What are the pros and cons of static strength measurements?

A

reliant on posture due to:

  • force-length relationship
  • changes in tendon moment arm with respect to the joint
  • changes in weight moment arm
  • two-joint muscles

pros:

  • simplicity
  • person stands in fixed positions
  • instrumentation is relatively cheap and easily used

cons:
-poor association with dynamic performance capability

85
Q

What are the pros and cons of dynamic strength measurements?

A

isokinetic is the most common dynamic strength measurement

pros:
-more realistic to real tasks

cons:
-testing is difficult given the range of potential postures and velocities

86
Q

What are the pros and cons of psychophysical strength measurements?

A

lab simulation of task

pros:

  • dynamic trial using the actual task
  • measures worker preference
  • expectation that design based on preferred limits will minimize injury

cons:

  • 30 min session does not always correlate to 8h workday
  • workers may not effectively judge risl
  • expensive
  • very sensitive to variables; instructions, procedures, motivation
87
Q

What factors affect muscle strength?

A

sex
age
obesity (1/3 obsese, 1/3 overweight)

88
Q

5 types of muscle contractions

A

isometric: constant length
concentric: muscle shortening
eccentric: muscle lengthening
isokinetic: constant velocity
isotonic: constant force

89
Q

3 muscle groupings

A

co-contraction: two or more muscles at a joint contracting at the same time

agonist: contributes to desired effort at a joint
antagonist: opposes desired effort at a joint

90
Q

3 mechanical properties of muscle

A

force-length (length-tension)
force-velocity (velocity-tension)
force-activation

91
Q

force-length relationship

A

the amount of force a muscle can produce depends upon its length and passive tension

muscle length changes with posture -> the amount of force a muscle can produce depends on posture

92
Q

force-velocity relationship

A

the amount of force a muscle can produce depends upon its velocity (rate of change of length)

concentric contractions: increasing velocity decreases the amount of force a muscle can produce

eccentric contractions: increasing velocity increases the amount of force a muscle can produce

93
Q

force-activation relationship

A

the amount of force a muscle can produce depends upon its activation level (0-100%)

94
Q

motor unit

A

a single motor neuron and all of the muscle fibers it innervates

ratio (nerve:muscle fibers)

  • 1:5 precise control (eye)
  • 1:1000 gross control and high forces (thigh and back muscles)
95
Q

What stimulates a motor unit?

A

a motor unit potential elicits a twitch of tension in the motor unit’s muscle fibers

96
Q

3 types of muscle fibers

A

slow: Type I
fast: Type IIa and IIb

Type I:

  • more fatigue resistance
  • oxidative (aerobic)
  • “postural” muscles

Type 2:

  • larger cross-sectional area
  • higher maximum tension and rate of force development
  • glycolytic (anaerobic)
  • “working” muscles
97
Q

What is the effect of aging on muscles?

A
  • decrease of strength with increase of age
  • loss of muscle mass and number of muscle fibers
  • conversion of type II to type I
98
Q

What is the effect of sex on muscles?

A

females show higher or equal endurance than males

99
Q

Why is awkward/extreme posture bad?

A

physical risk factor

  • more effort is required to generate same force
  • can cause pressure between adjacent anatomic structures

minimize frequency, duration, and magnitude

100
Q

Why are high force exertions bad?

A

physical risk factor

  • cause large deformation of tissue
  • reduce/completely stop circulation
  • increase localized fatigue

minimize frequency, duration, and magnitude

101
Q

Why are high repetition and sustained exertions bad?

A

physical risk factor

  • affected by other factors: force, contact stresses, posture, vibration, temperature
  • 5 classifications of rates

minimize frequency, duration, and magnitude

industrial ergonomics (1 decks)

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