Evaluation of Strength and Work Capacity

1. Evaluation of Strength and Work Capacity • Readings - Occupational Ergonomics Handbook Ch 21 Gallagher and Moore p 371-383 • Matheson et al, Standard evaluation of work capacity p 249-264 • Jackson - supplemental • Outline

2. Worker strength evaluation • Psychophysical method - strength of population of workers used to design job so that majority of workers find the exertion acceptable • using this in design - reduce WMSD by 33% (WMSD - work-related musculoskeletal disorders) • focus of chapter - • basics of strength • characterize methods of testing • describe use of techniques • strength - capacity to produce a force or torque with a voluntary muscle contraction

3. Strength • Measurement of human strength • at interface between subject and device - many possibilities - types of devices • 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 • Types of muscular strength • dynamic - motion around joint • variability - speed - difficult to compare • static - isometric- no motion • easy to quantify and compare - not representative of dynamic activity

4. 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 • 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Evaluation of Work Capacity • Matheson - 1996 • standardized method of evaluating work capacity • 2 hour protocol • paper demonstrates unbiased for gender and age • results can be applied to disability rating system • work capacity - objective quantification of occupational disability - used to • provide compensation • measure progress of treatment • compare effect of different treatments • must be defined within application

12. Standardized Evaluation • Occupational Disability - individuals uncompensated short falls in responding to work demands • Fig 1 • requires comparison to work capacity of prior to pathology • allows us to rate impairment • pre injury capacity usually not known • must estimate - age, normative data?? • California Division of Industrial Accidents • consider diagnosis, work capacity, occupation and age together • Steps 1 - 8 p 251 • Rating based on occupational impact of standard disability rating

13. CAL - FCP • California Functional Capacity Protocol • standardized method to measure work consequences musculoskeletal injury • measurement by physician • info used with Cal disability determination model • assess injury 30 days post • if not returned to work or still being treated • Description of System • Fig 2 - steps in decision process • allows ID of disability category • combine with info from exam • physician provides report pertinent to occ disability rating model

14. CAL - FCP • Development of test criteria • context of workers comp system • standards of APA and APTA • 5 issues - hierarchy • safety • reliability • validity • practicality • utility • eg. P 254 - more detail useful in application • Evaluation Tasks • 1. structured interview • patient profile, functional abilities • table 2 - MAW - maximal acceptable weight

15. Evaluation Tasks • 2. Health Questionnaire • 3. Perceived physical capacity • spinal functional sort ref 41 • work on self paced basis • Pain and Sensation Drawing • symptoms important indicators of injury - objectivity - standardization • factors • location • type • intensity - worst / usual • frequency - worst / usual • Table 3 - pain - 10 cm visual scale • Table 4 - pain - frequency ratings

16. Evaluation Tasks • 5. Job demands questionnaire • patients perception of job demands • used for comparison against performance measures • 6. Lateral Pinch test • 7. Power grip test • JAMAR hand dynamometer • 8. Standing ROM - table 5 • 15 sec each posture - 1 min rest • 9. Lift Capacity • ELC - Epic lift capacity test • large normative data base, safe, reliable • first three segments

17. Evaluation Tasks • 10. Carrying Test - loads from ELC • evaluate with table 2 • 11. Climbing Test • simulate 10 ft flight of stairs • 15 cycles - 1 step/ sec • evaluate up to ELC #3 weight • scale from table 2 • Effort Rating • some tests - built in • others - subjective evaluation • 3 point scale • reliable, questionable, unreliable • Test order • invariant - Table 6