Work Load and Pre Employment

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 ; 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

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

11. 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

19. 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