1 Work Load and Pre Employment Astrand ch. 17 p Gallagher and Moore - Occupational Ergonomics Handbook Ch 21 p Jackson p53, Outline Assessment of workload –Relative VO 2, HR, Hormonal response Energy expenditure over workday –Energy systems, work rest ratio Strength testing –Onset of fatigue –Isoinertial, isometric, isokinetic, psychophysical Job analysis –validation

2 Work Load and Pre Employment Astrand ch. 17 p Gallagher and Moore - Occupational Ergonomics Handbook Ch 21 p Jackson p53, Assessment of work load in relation to work capacity –variability in capacity –variability in response expression of workload by absolute VO 2 alone is almost meaningless Need work load as % of individual max Assessment requires the determination of –individual VO 2 max –VO 2 requirement of imposed load –assessment of muscle groups being utilized, and the % of their maximum strength -to determine fatigue onset

3 Assessment Maximal aerobic power –direct - VO 2 max test –estimation - predictive tests Assessment of Workload –measure O 2 uptake during work Fig 17-2 O 2 uptake vs bike/work –portable devices, rapid analysis of VCO 2 and VO 2 - large data base –field studies - collect expired air Douglas bag –or - use flow meter to determine volume of air, and take samples of air for content analysis Fig 17-3 commercial fisherman –subjects often affected - test atypical –Eg. Breathing through mouth not nose

4 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, and emotional stress 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 fisherman

5 Comparison studies Fig strong day - day consistency Computer analysis of HR data provides ; –mean values, peak values, distribution and HR variability Fig 17-8 comparison of direct vs indirect measurement +/- 15 % HR is good estimate of workload when work uses large muscle groups Fig 17-9 arm vs leg work –HR is higher in arm work than leg work for the same work load. O2 uptake for work load must be expressed as % max of individual –indicates relative degree of exertion HR reserve (HR max - HR rest) –Circulatory strain is best expressed as a percentage of an individuals HR reserve

6 Stress of Work The total stress imposed on the organism by a given work situation (physical or psychological) is generally reflected by nervous and hormonal stimulation –Proportional to the degree of stress Nervous Response Inc sympathetic tone - inc HR –influence linear relationship –Eg HR vs workload Hormonal response –total stress reflected by sympathetic response –Measure ep and/or nor ep with urinary excretion or blood samples Fig 1716, Catecholamines - inc with standing, cold and emotion –Also inc with duration and severity of muscular exertion

7 Energy Expenditure Need to establish practical limits for physical work loads Type of work and work/rest cycles are important Large individual differences in physical work capacity – % VO 2 max for 8 hour day –40 % of max strength in repetitive muscular work; rest:work ratio of ; 2:1 physiological and psychological responses influenced by –individual max aerobic power –size of muscle being engaged –working position –intermittent vs continuous activity) –environmental conditions

8 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 – kcal /day Table 17-1, 17-2

9 Energy expenditure O2 uptake and HR - Table 17-1 Important for ; –Calculation of energy needs –Determine physical activity of groups –Role of physical activity in health Methodology All fairly accurate +/- 15% –24 hr recorded HR ; Time activity data –Assessment of daily energy intake to maintain body weight Wide individual variability in energy output - Table 17-1,2 –Occupation –Leisure activity / Physical activity –Environmental temp –Daily rate kcal Reg active male 2900 kcal/day Reg active female 2100 kcal/day

10 Energy Expenditures Work expenditures Most light work < 5 kcal /min Some physical jobs kcal/min Permissible limits for daily work kcal Limits are difficult due to individual differences in work capacity or fitness Individuals will usually self regulate the rest pauses Peak load is more important than mean energy expenditure You can attain a higher 8 hour energy expenditure if the work is consistent and does not have peak loads Basal Metabolic rate (BMR) - rate of energy metabolism in a resting individual hours after eating

11 Energy Expenditure Recreational activities McArdle, Katch and Katch –Appendix C (on reserves) Different activities have different energy expenditures –Cycling race13 kcal/min –Golf6 kcal/min –Skiing uphill fast21 kcal/min –Swimming -fast13 kcal/min –Running 5:30 mile22 kcal/min Individuals do activities at different intensities Must take body weight into account

12 Strength Gallagher - OEH ch 21 Muscle strength is a complex function that can vary with the methods of assessment Strength - capacity to produce a force or torque with a voluntary muscle contraction Measurement of human strength –Cannot be measured directly –interface between subject and device influences measurement –Fig 21.1 Biomechanical eg. Q = (F * a)/b or c or d force from muscle is always the same results are specific to circumstances dynamic strength - motion around joint –variable speed - difficult to compare static or isometric strength- no motion –easy to quantify and compare –not representative of dynamic activity

13 Strength Testing Isometric strength testing 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 –isoinertial (isotonic)- mass properties of an object are held constant –Psychophysical - subject estimate of (submax) load - under set conditions –isokinetic strength through ROM at constant velocity

14 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 C - dec 10-20% in capacity

15 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

16 Psychophysical (cont) 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

17 Worker selection and Placement Used to ensure that worker can tolerate physical aspects of job Key principles –Strength test employed must be directly related to work requirements 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 stronger and weaker workers Isometric analysis fig 21.5 –for each task - posture of torso and extremities is documented (video) recreate postures using software –values compared to population norms industrial workers –estimate % capable of level of exertion –predict forces acting on lumbar spine

18 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 to be 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

19 Isokinetic Testing Isokinetic testing –Evaluates muscular strength throughout a range of motion at a constant velocity –However; humans do not move at constant velocity isokinetic tests usually isolated joint movements may not be reflective of performance ability attempts to redesign isokinetic testing –multi joint simulation tasks for industry fig 21.8 core stability required still in progress, therefore limited validity

20 Pre Employment Physical Evaluation Early tests focused on cognitive abilities Physical ability tests have adverse impact on female applicants –Due to differences in size, strength, VO 2 max, % body fat Improvements attempt to integrate –psychometric measurement theory, biomechanics, ergonomics and work physiology Employers must show that the pre- employment screening test measures only those abilities required to perform essential job functions –(*Assignment two *)

21 Injury Rates Pre-employment tests are used to reduce work related injuries –some jobs - high low back injuries –not serious but prevalent - 80% –lifting, twisting, bending, pulling 3 Ergonomic approaches to reduce industrial back injuries – job Redesign Engineering approach to reduce exposure to risk factors –pre employment testing Preferred approach for physically demanding jobs that cannot be redesigned Select individuals with capacity to safely perform job Relationship between probability of injury and the % of capacity to perform task –education and training Train to lift properly - not successful

22 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 % of employees will use work site exercise facilities –Only 33% of these will train at the appropriate frequency, duration and intensity

23 Job Analysis Goal is to identify the important work behaviours demanded by job Reduce job actions to words essential component in developing pre employment test Job analysis methods can use a combination of; Psychophysical, biomechanical and physiological approaches 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

24 Job analysis methods Biomechanical methods –heights and weights of objects lifted –forces - opening, pulling, pushing –evaluate potential stress on lower spine Physiological - CV components –O2, HR - actual or simulated to estimate work load

25 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 –significant correlation between pre employment test and job performance –Concurrent / predictive Content validity –work sample or simulation of work –Test represents the content of the job

26 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 measure (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

27 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

28 Physical ability (cont) 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?

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