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