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Evaluation of Strength and Work Capacity

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1 Evaluation of Strength and Work Capacity
Readings - Occupational Ergonomics Handbook Ch 21 Gallagher and Moore p Matheson et al, Standard evaluation of work capacity p 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 Fig 21.1 Biomechanical eg.
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 Dynamic strength
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 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 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 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 5 issues - hierarchy
context of workers comp system standards of APA and APTA 5 issues - hierarchy safety reliability validity practicality utility eg. P 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 6. Lateral Pinch test
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 11. Climbing Test
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

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