Assessment%20of%20Work%20Load%20and%20Pre-Employment%20Evaluation

1
Assessment of Work Load and Pre-Employment
Evaluation

• Astrand pp 453-472
• Jackson pp 53, 58-70
• Gallagher and Moore pp 371-383

2
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.
• Should be a of individual VO2 max

3
Assessment

• Maximal aerobic power
• direct - VO2 max test
• estimation - predictive tests (HR)
• Measure O2 uptake during work
• portable devices, collect expired air
• Measure HR during work
• indirect
• Fig 13-2, O2 uptake vs bike/work
• depends on weight and fitness of a subject

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• Fig 13-3, Commercial fisherman
• O2 uptake only represents work at the time the
  sample was collected
• Subject often affected - test atypical
• Test equipment may ? HR, Ventilation
• Continuous HR monitoring gives a good indication
  of the activity level for the day

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Indirect Assessment

• Linear relationships between HR and VO2
• HR may be used to estimate workload
• Estimation of O2 consumption from HR may be
  inaccurate.
• Continuously recorded HR
• provides a comprehensive evaluation of
  circulatory strain imposed by workloads of
  varying intensity.
• Fig 13-5 - fisherman
• HR is a good estimation of work load when the
  work involves large muscle groups.
• HR is higher in arm work than in leg work for the
  same work load (Fig 13-8).

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• Computer analysis of continuous HR data can
  generate mean values, peak values, distribution
  and heart rate variability.
• Heart rate reserve (HRmax-HRrest)
• Circulatory strain is best expressed as a
  percentage of an individuals HR reserve.

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Assessment of the Organisms Response to the
Total Stress of Work

• The total stress imposed on the organism by a
  given work situation (physical or psychological)
  is generally reflected by a certain nervous and
  hormonal stimulation, more or less proportional
  to the degree of the stress.

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Nervous Response

• ? sympathetic stimulation - ? HR
• ? by emotional and physical stress
• may influence linear relationship
• Hormonal response
• total stress reflected by sympathetic response
• measured with urinary excretion or ep and nor ep
  (blood samples)
• Fig 13-9, Catecholamines ? with standing,
  phsyical exertion, cold, emotional factors. ?
  with duration and severity of muscular exertion.
• Fig 13-9, there is considerable individual
  variation in catecholamine elimination under
  comparable stress situations.

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Energy Expenditure

• Proper work/rest cycles for an 8 hour day.
• Establish limits for permissible physical work
  loads.
• The manner in which the work is performed is
  important.
• Large individual differences in physical work
  capacity.
• 30 - 40 VO2 max for 8 hour day is reasonable.
• 40 of max strength in repetitive muscular work.

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• Physiological and psychological effects of a
  given energy output is influenced by
• individual VO2max
• size of muscle being engaged
• working position
• type of activity (intermittent or continuous)
• environmental conditions
• Prolonged Work Classification
• O2 uptake and HR (Table p 462)
• Average person aged 20 to 30

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Daily Energy Expenditure

• Important for
• calculation of energy needs
• determine physical activity of groups
• role of physical activity in health
• Methodology
• 1) 24 hr recorded HR
• 2) time activity data
• 3) assessment of daily energy intake to maintain
  body weight
• all fairly accurate /- 15

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• Wide individual variability in energy output
• occupation
• leisure activity
• physical activity
• environmental temp has a small effect (lt4)
• daily rates 1300 to 5000kcal
• regularly active male 2900kcal/day (Table 13-1)
• regularly active female 2100kcal/day
• Fig 13-11, Energy expenditure for different
  activities

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Energy Expenditure

• Work expenditures
• Most light work lt 5 kcal/min (300 kcal/hr)
• Some physical jobs 7.5 - 10 5 kcal/min (600
  kcal/hr)
• Permissible limits for daily work 2000 - 2500
  kcal (300kcal/hr)
• Limits are difficult due to individual
  differences in work capacity or fitness.
• The individual will usually self regulate the
  rest pauses.
• Peak load is more important than mean energy
  expenditure.
• You can attain a higher8-hour energy expenditure
  if the work is consistent and does not have peak
  loads.
• Basal Metabolic Rate the rate of energy
  metabolism in a resting individual 14 to 18 hours
  after eating.

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Energy Expenditure

• Recreational Activities
• Different activities have different energy
  expenditures.
• Cycling race 13 kcal/min (170lb or 77kg)
• Golf 6 kcal/min
• Skiing uphill fast 21 kcal/min
• Swim (fast crawl) 13 kcal/min
• Running (530 pace) 22 kcal/min
• Individuals do activities at different
  intensities

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Worker Strength EvaluationJob Design and Worker
Selection

• Gallegher - Chapt. 21
• Muscular strength is a very complex function that
  can vary greatly upon the methods of assessment.
• Strength capacity to produce a force or torque
  with a voluntary muscle contraction.
• Measurement of human strength
• We cannot directly measure force within a muscle.
  
• Indirectly measure force at an interface between
  subject and a measurement device.
• The cuff placement will influence the force
  measured.
• Move cuff away from joint ? force.

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Types of Muscular Strength

• Dynamic exertions
• motion around the joint
• different testing techniques
• variable speed - difficult to compare
• Isokinetic strength strength throughout a range
  of motion at a constant velocity.
• Isometric or Static exertions
• no motion around the joint
• force against a stationary load measuring device
• use proper protocol (4 to 6 sec contraction, 30
  sec to 2 min rest)
• easy to quantify and compare - not representative
  of dynamic activity

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Factors Affecting Strength

• Gender
• Age
• Anthropometry
• Psychological factors (Table 21.1)
• Task influence
• Posture (Fig 21.2 joint angle and force
  production)
• Duration of exertion (Fig 21.3 Strength vs
  Endurance)
• Velocity of contraction (Fig 21.4 Force -
  velocity curve)
• Muscle Fatigue
• Temperature and Humidity
• ? temp from 20 to 27oC ? lifting capacity by 20

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Strength Measurement

• Strength Assessment for Job Design
• Psychophysical methods
• workers adjust demand to acceptable levels for
  specified conditions
• provides submax endurance estimate
• Procedure
• subject manipulates 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

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Worker Selection and Placement

• Used to ensure that worker can tolerate physical
  job.
• Key principles
• The strength test employed must be directly
  related to the work requirements.
• Use of strength tests only to identify workers at
  risk of injury.
• similar rates of overexertion injuries for strong
  and weaker

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• Isometric analysis (Fig 21.5)
• for each joint there is a limit to the strength
  that can be produced
• observe worker doing the task (video)
• postures recreated using software
• values compared to population norms - industrial
  workers
• estimate of population capable of this level of
  exertion
• predict forces acting on lumbar spine

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• Isoinertial testing
• SAT - strength aptitude testing
• air force standard testing
• match strength of individual with job
  requirements
• preselected mass - increase to max level
• 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

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• Isokinetic testing
• evaluates muscular strength throughout a range of
  motion and at constant velocity
• 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
• whole body lifting strengths (Fig 21.8)
• core stability required
• still in progress, limited validity

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Pre Employment Physical Evaluation

• A. Jackson
• Early pre-employment tests focused on cognitive
  abilities.
• Physical ability tests have adverse impact on
  females.
• potential legal review
• federal civil rights legislation
• documented differences in strength, VO2 max,
  body fat
• Employers must show that the pre-employment
  screening test measures only those abilities
  required to perform essential job functions.

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INJURY RATES

• Pre-employment tests are implemented to reduce
  work-related injuries.
• Many occupations have a high incident of back
  injuries
• 80 of adults will experience a low back injury
• back injuries caused by lifting, twisting,
  bending, pulling
• 3 Ergonomic approaches used to reduce industrial
• back injuries.
• Job redesign
• Engineering approach to reduce exposure to risk
  factors
• lower stacking heights, hydraulic lifts
• biomechanical lifting model
• define maximum permissible lifting limits

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3 Ergonomic Approaches cont

• Pre-employment testing
• preferred ergonomic approach for physically
  demanding jobs that cannot be redesigned
• select individuals with the capacity to safely
  perform job
• strength testing
• relationship between probability of injury and
  the percentage of capacity to perform the task
• Training and education
• train worker to lift properly
• has not been successful
• lifting pattern of individuals vary
• lifting pattern affected by speed, size, shape

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Fitness

• Fitness level appears to be related to injury.
• High levels of aerobic fitness, strength and
  flexibility were inversely related to workers
  compensation costs of fire fighters.
• Fitness programs should reduce musculoskeletal
  injuries.
• only 20-40 of employees will use worksite
  exercise facilities
• only 33 of these will train at the appropriate
  frequency, duration and intensity

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Job Analysis

• The goal of job analysis is to identify the
  important work behaviours demanded by the job.
• Reduce job actions to words.
• Essential component in developing pre-employment
  test.
• Court cases regarding physical tests show the
  importance of job analysis.

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Job Analysis Methods

• Can use a combination of the following
• Psychophysical (workers rate tasks)
• RPE - rate of perceived exertion
• .8 correlation - not biased by gender or
  experience
• components strength, CV endurance and movement
  quality
• Physiological
• CV components - O2, HR
• Biomechanical methods
• heights and weights of objects lifted
• forces - opening, pulling, pushing
• evaluate potential stress on lower spine

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Validation Strategies

• Determine accuracy with which test measures
  important work behaviors.
• Validity depends on reliability and relevance.
• Reliability ability to differentiate among true
  levels of performance
• Relevance defining qualities being tested
• Criterion related validity
• data showing a significant correlation between
  pre-employment test and job performance

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• Content validity
• logical relationship between the pre-employment
  test and job requirements
• the test represents the content of the job
• Construct validity
• establish that a construct is required for job
  success
• the test measures that same construct
• the degree to which a test measures an attribute
  that cannot be directly measured (coordination)
• link important constructs and multiple indicators
  of job performance
• tests theoretical and empirical relationships
• relationship between physical ability and job
  constructs
• FDNY physical ability test was found to
  discriminate against women as constructs were not
  related to the job

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Physical Ability Test Selection

• Content validation studies
• Tests that simulate work tasks
• Advantages
• Simulate actual working conditions
• fire fighter drags a dummy
• lineman climbs a telephone pole
• Disadvantages
• safety (applicants are highly motivated)
• do not measure maximal capacity

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• Motor ability and fitness test items
• static strength (exert maximal force)
• dynamic strength
• balance
• flexibility
• Cut Score
• the test score that an applicant must obtain to
  be considered for a job.
• difficult to establish a cut score.
• should you hire someone that just meets the
  minimal requirement?

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Summary

• Employers are using pre-employment tests to
  enhance worker productivity and to minimize the
  threat of litigation for discriminatory hiring
  practices and to reduce the risk of
  musculoskeletal injuries.
• The most common reason reason for ruling an
  employment practice invalid is the failure to
  show that the test measured important job
  behaviours.