Work%20Load%20and%20Pre%20Employment

1
Work Load and Pre Employment

• Astrand ch. 13 p 453-472
• Gallagher and Moore - Occupational Ergonomics
  Handbook Ch 21 p 371-383
• Jackson p53, 58-70
• Assessment of work load in relation to work
  capacity
• variability in capacity
• variability in response
• expression of workload by absolute Vo2 alone is
  almost meaningless
• of individual max requires determination of
• individual VO2 max
• VO2 of imposed load
• assessment of muscle groups and the of max
  strength - fatigue onset

2
Assessment

• Maximal aerobic power
• direct - VO2 max test
• estimation - predictive tests
• Assessment of Workload
• measure O2 uptake during work
• validity and assumption around indirect
  calorimetry addressed last week
• Fig 13-2 O2 uptake vs bike/work
• portable devices, rapid analysis of VCO2 and VO2
  - large data base
• field studies - collect expired air
• or - flow meter and sampling of air
• Fig 13-3 commercial fisherman
• subject often affected - test atypical

3
Indirect assessment

• Recall linear relationships between HR and VO2,
  VO2 and work rate
• HR may be used to estimate workload - on
  individual basis
• same muscle groups environmental
  temperature,emotional stress
• Fig 13-4 - criterion of HR response
• Continuously recorded HR
• provides general picture of overall activity
  level during entire day
• along with time activity studies collected by
  observers
• possible to separate different activities with
  respect to HR
• Fig 13-5 - fisherman

4
Comparison studies

• Fig 13-6 - strong day - day consistency - mean HR
• Fig 13-7 comparison of direct vs indirect
  measurement /- 15
• Fig 13-8 arm vs leg work
• strong discrepancy - difficult and inaccurate
  comparison
• O2 uptake for work load must be expressed as
  max of individual
• indicates relative degree of exertion

5
Nervous Response

• Inc sympathetic tone - inc HR
• influence linear relationship
• HR vs workload
• Hormonal response
• total stress reflected by sympathetic response
• measured with urinary excretion or ep and nor ep
  (blood samples)
• Fig 13-9, 13-10
• Catecholamines - inc with standing, phsyical
  exertion, cold,emotional factors
• inc with duration and severity of muscular
  exertion

6
Energy Expenditure

• Practical limits
• 30 - 40 VO2 max for 8 hour day
• 40 of max strength in repetitive muscular work
  restwork 21
• physiological and psychological responses
  influenced by
• individual max aerobic power
• size of muscle being engaged
• working position
• type of activity (intermittent or continuous)
• environmental conditions
• Classification - O2 uptake and HR
• Table p 462

7
Daily Energy Expenditure

• Important for
• calculation of energy needs
• determine physical activity of groups
• role of physical activity in health
• Methodology
• 24 hr recorded HR
• time activity data
• assessment of daily energy intake to maintain
  body weight
• all fairly accurate /- 15
• show large individual variability
• 1300-5000 kcal /day
• Table 13-1 (1964)
• Fig 13-11 - work expenditure

8
Energy expenditure

• Manual labour
• technique can influence significantly
• inc energy with speed, 10X with stairs
• only rough estimate of efficiency
• driving nails eg.
• Bench, wall, ceiling
• same O2 consumption, difference in efficiency
• same HR as cycling - different O2, different BP
  response
• variability in work output and physiological
  response with tools and position
• even at same energy expenditure

9
Strength

• Gallegher - OEH ch 21
• Strength - capacity to produce a force or torque
  with a voluntary muscle contraction
• Measurement of human strength
• at interface between subject and device
• influences measurement
• Fig 21.1 Biomechanical eg.
• Q (F a)/b or c or d
• results specific to set of circumstances, force
  from muscle is always the same
• dynamic - motion around joint
• variability - speed - difficult to compare
• static - isometric- no motion
• easy to quantify and compare - not representative
  of dynamic activity

10
Strength

• Isometric strength
• standardized procedures
• 4-6 sec, 30 sec to 2 min rest
• standardized instruction
• postures, body supports, restraint systems, and
  environmental factors
• worldwide acceptance and adoption
• Dynamic strength (isotonic)
• isoinertial - mass properties of an object are
  held constant
• Psychophysical - subject estimate of (submax)
  load - under set conditions
• isokinetic strength
• through ROM at constant velocity

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Factors Affecting Strength

• Gender
• Age
• Anthropometry
• Psychological factors - motivation
• table 21.1
• Task influence
• Posture
• fig 21.2 angle and force production
• Duration
• Fig 21.3
• Velocity of Contraction
• Fig 21.4
• Muscle Fatigue
• Temperature and Humidity
• inc from 20-27 C - dec 10-20 in capacity

12
Strength Measurement

• Strength assessment for job design
• psychophysical methods
• workers adjust demand to acceptable levels for
  specified conditions
• provides submax endurance estimate
• Procedure -
• subject manipulate one variable-weight
• two tests start heavy and start light
• add or remove weight to fair workload
• without straining, becoming over tired, weakened,
  over heated or out of breath
• large s of subjects
• evaluate / design jobs within capacity
• 75 or workers rate as acceptable
• over this 3 times the injury rate

13
Measurement for Job Design

• Summary
• Table 21.2 (Snook and Cirello)
• advantages
• realistic simulation of industrial tasks
• very reproducible - related to incidence of low
  back injury
• Disadvantages
• results can exceed safe as determined through
  other methodology
• biomechanical, physiological

14
Worker selection and Placement

• General recommendations
• Key principles
• job relatedness
• must be tied to biomechanical analysis
• use of strength tests only to identify workers at
  high risk of injury
• similar rates of overexertion injuries for strong
  and less strong
• Isometric analysis fig 21.5
• for each task - posture of torso and extremities
  is documented (video)
• recreate posture - software
• values compared to population norms - industrial
  workers
• estimate capable of level of exertion
• predict forces acting on lumbar spine

15
Job placement

• Isoinertial testing
• SAT - strength aptitude testing
• air force standard testing
• preselected mass - increase to criterion level -
  success or failure
• found incremental weight lifted to 1.83m - safe
  and reliable
• PILE - progressive inertial lifting evaluation
• lumbar and cervical lifts -progressive weight -
  variable termination
• voluntary, 85 max HR, 55-60 body weight
• standards normalized for age, gender and body
  weight

16
Job placement testing

• Isokinetic testing
• humans do not move at constant velocity
• isokinetic tests usually isolated joint movements
  -
• may not be reflective of performance ability
• attempts to redesign - multi joint simulation
  tasks for industry
• fig 21.8
• core stability required
• still in progress, limited validity

17
Pre Employment Physical Evaluation

• Physical ability test - negative impact on
  females (.80)
• strength, VO2 max, body fat
• integration of psychometric measurement theory,
  biomechanics, ergonomics and work physiology
• Injury rates
• some jobs - high low back injuries
• not serious but prevalent - 80
• lifting, twisting, bending, pulling
• approaches
• redesign job
• pre employment testing
• education and training

18
Job Analysis

• essential component in developing pre employment
  test
• Workers rate tasks (psychophysical)
• RPE - rate of perceived exertion
• Borg, Likert scales
• compare to text book ratings
• .8 correlation - not biased by gender or
  experience
• components - strength, CV endurance and movement
  quality
• Biomechanical methods
• heights and weights of objects lifted
• forces - opening, pulling, pushing
• evaluate potential stress on lower spine
• Physiological - CV components - O2
• HR - actual/simulated - estimate work

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Validation Strategies

• Determine accuracy with which test measures
  important work behaviors
• Reliability - ability to differentiate among true
  levels of performance
• Relevance - defining qualities being tested
• Criterion related validity
• significant correlation between pre employment
  test and job performance
• Concurrent / predictive
• Content validity
• work sample or simulation
• Construct validity
• link important constructs and multiple indicators
  of job performance