Download Work Load and Pre Employment

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
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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
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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
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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
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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
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Energy Expenditure
• Practical limits
• 30 - 40% VO2 max for 8 hour day
• 40 % of max strength in repetitive
muscular work ; rest:work ; 2:1
• 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
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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
– 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
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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
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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
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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
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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 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
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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
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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
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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
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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
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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
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Job Analysis
• essential component in developing
pre employment test
• Workers rate tasks (psychophysical)
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–
–
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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
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