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2016-05-24
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1
Workload
Workload
The amount of work that is expected to be
done
The impact of each factor influencing on
human organismus and changing its
physiological parameters
Caused by exertion
The reason of fatigue
Fatigue Deviance of neurophisiological functions
from equillibrium state
Feeling of lack of energy and motivation that can be physical, mental or both.
The temporary loss of power to respond that is induced in a sensory receptor by continued stimulation
Always occur in normal individuals that experience physical or mental activity (or both)
Reversible state
Reduces productivity
Fatigue Symptoms
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Decrease of attention
Slowed and impaired perception
Decrease in motivation
Decrease in the speed of physical and mental performance
Decrease in accuracy and increase in errors
Greater energy expenditure to keep up the same output
Feelings of dullness, tiredness, irritability
Cumulative effect of daily causes of
fatigue (Grandjean, 1968)
5
Intensity and length of manual and
mental tasks -
Mental and physical demands of work
Concentrating for extended periods of time,
performing repetitious or monotonous work
performing work that requires continued
physical effort
Work scheduling and planning
night work
extended shifts
Overloading or underloading of workers
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Surroundings (environment)
Heat / cold
Vibration
Noise
Improper lighting
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Individual factors and factors outside
the work
Lifestyle
Child care responsibilities,
Voluntary work,
Having more than one job,
Level of phisical activity
Social life
Diet
Home environment
Noisy neighbourhood
Improper resting / sleeping conditions
Health conditions
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Workload
Biomechanical
Dynamic
Static
Mental
Body posture
the position or bearing of
the body whether
characteristic or assumed
for a special purpose
Awkward or neutral
Factors influencing on body posture
Body dimensions of worker
Working pace dimensions
Layout od work elements
Working task
Accuracy
Force
Working object dimentions
Worker’s preferences and habits
Neutral position
Ideal working posture
Straight back
Elbows at the side of the
torso
Wrists neutral
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Awkward position
Any fixed or constrained body position that
overloads muscles and tendons or loads joints
in an uneven or asymmetrical manner
Deviation from the ideal working posture
any position of the body while performing work
activities that is associated with an increased
risk for injury
reaching behind,
twisting
Forward or backward bending
Squatting
work objects’ layout
work objects’ dimensions
Reasons of awkward positions
Awkward postures effects
Most common arduousness in Polish companies
/ Instytut Medycyny Pracy, 2003/
The second reason of medical appointment in USA
Main reason of Musculoskeletal Disorders (MSD)
MSD of building worker
42% - neck and shoulders
43% - wrists and hands
70% - low back
46% - knees
/The University of Iowa Construction Survey, 1996/
MSD of office workers
69% - neck and shoulders
61% - back
55% - forearms and hands
/J.Bugajska, Centralny Instytut Ochrony Pracy, 1994/
Dynamic work:
• isotonic meaning 'same tension')
• rhythmical contraction and relaxation of a muscle
which does result in movement
• less tiring and more efficient than static work.
• Muscles act like a pump allowing the blood to supply
more oxygen and take away more lactic acid
Static work:
• isometric meaning 'same length‘
• a muscle remains contracted for a period of time but there
is no movement
• very tiring as muscles don't get time to relax.
• A muscle which is heavily contracted squeezes against the
blood vessels next to it, restricting blood flow.
• This cuts down the delivery of oxygen to the muscle and the
removal of a waste product
Dynamic and static work of muscles
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Biomechanical workload assessment
Objective
Analysis of body segments torques
Analysis of body reaches and vision field of a
worker
Subjective
Pain questionnaire
SOWA (Subjective Overall Work Analysis)
Normal distribution
20
Restraining values – 5 and 95 percentile
Mode
Median
Mean
Men
Women
0
20
40
60
80
100
120
140
160
180
200
szyj
a
krzy
ż
bark
praw
y
bark
lewy
łoki
eć p
raw
y
łoki
eć le
wy
nadga
rste
k pra
wy
nadga
rste
k le
wy
biodr
o pra
we
biodr
o le
we
kola
no pra
we
kola
no lewe
kost
ka p
raw
a
kost
ka le
wa
Mo
men
t siły [
Nm
]
m5c
m95c
Analysis of body segments torques
System Apolinex
Analysis of body reaches and vision
field of a worker - Antropos
Pain questionnaire
Pain scale
Phisical activity
Personal data
0 — No pain
1 — Low noticable pain
2 — Noticable pain
3 — Painful feeling
4
— Pain hard to endure
Dynamic workload
Physical activity: any bodily movement
produced by the skeletal muscles that results
in an increase in energy expenditure.
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Activity level Examples of activity Energy
kJ/h
Every day
activities
Sitting 6
Standing 7
Washing, dressing 15
Walking slowly 13
Walking moderately quickly 21
Walking up and down stairs 38
Light work
& recreation
Most domestic work, golf, light
industrial and assembly work,
carpentry, brick-laying
10-20
Moderate work
& recreation
Gardening, tennis, dancing, cycling up
to 20 km/hr, digging, shovelling, non-
mechanised agricultural work,
21-30
Strenuous work
& recreation
Coal mining, steel furnace work,
squash, cross-country running,
football, swimming
Over 30
Energy expenditure assessment
Calorymetry
Direct
Indirect
Günter Lehmann’s chart (1966)
Posture
Muscles load
Work time
Indirect calorymetry
Workload Heart rate
[per min]
Lung
ventilation
[l/min]
Oxygen flow
[l/min]
Very light
Light
Medium
Hard
Very hard
Extremely hard
<75
75-100
100-125
125-150
150-175
>175
8-10
10-20
20-35
35-50
50-65
>65
<0,5
0,5-1,0
1,0-1,5
1,5-2,0
2,0-2,5
>2,5
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Lehmann chart
Body Position (A) Energic expenditure
kcal/min kJ/min
Sitting 0.3 1.26
On knees, squading 0.5 2.1
Standing 0.6 2.51
Standing bended 0.8 3.35
Walking 2.6 10.89
Workload of Muscles (B)
Work of fingers, palms, forearm 0.5-1.0 2.1-4.2
Work of one forearm 1.0-2.0 4.2-8.4
Work of both forearms 2.0-3.0 8.4-12.6
Work of whole body (muscles of torso and
limbs) 3.0-10.0 12.6-41.9
Energic expenditure = (A+B) x time of work [min]
Lehmann chart
Workload level
Net energic expenditure/workshift [kJ]
men women
Light to Medium Hard Up to 6300 Up to 3700
Hard 6300-8400 3700-5000
Extremely Hard over 8400 over 5000
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Static work
Thermal and electric
activity of muscles
Static work effects
Ovako Working Posture Analysis
(OWAS)
1. Find a code of position
2. Find a static workload category
3. Correct a workstation (if necessary)
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Code of position
34
1. Back (1-4)
2. Upper limbs (1-3)
3. Lower limbs (1-7)
4. Load
1. below10 kg
2. 10-20 kg
3. Above 20 kg
Code of position
35
Code of position
36
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Static workload category
Category Interpretation
1 Natural, neutral work positions
Acceptable workload
No need of changes
2 Potentially negative workpositions
Almost acceptable workload
No need of immediate changes
3 Workpositions impact on musculoskeletal system
High workload
Need of fast changes
4 Workpositions impact very negatively on
musculoskeletal system
Extremely high workload
Need of immediate changes
Awkward postures assessment
If the posture is not awkward, the colour is
Green.
The colour is Yellow if the posture is
awkward for a part of the time (i.e. 15-30%
of the cycle time).
The colour is Red if the posture is awkward
for more than half the time (i.e. more than
50% of the cycle time).
39
Head / neck posture
40
Back
41
Arm posture
42
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Wrist posture
43
Hand / finger grip
44
Tips to help assess posture
select intermediate scores
strategies of awkward postures assessment:
Make sure you view the task from several
different viewpoints
Ask workers to demonstrate the task in slow
motion or pause at particular moments during
the task
Ask workers if they mind rolling up or removing
any loose clothing that might obscure postures
during the demonstration (provided it is safe,
hygienic and appropriate to do so).
45
Basic rules
Think about
users’ dimensions
Fit the workstation to the user
Adjust the workstation
Remember about
number of degrees of
freedom
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Avoid:
Awkward positions
Static work
Remember about
Changing of body
position
Lifting and carrying
loads as close as
possible
51
Mental workload
Definitions
Mental workload is a portion of operator’s
limited mental capacities actually required to
perform a particular task
Mental reserves are the difference between
capacity required and capacity available.
Mental effort is the voluntary matching of
mental capacities with that needed for task
success.
Increase in Mental Workload often precedes
Performance Failure.
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Psychological Stressors
Fear, embarrassment, loss of esteem, etc.
Effects
Perceptual / attention narrowing or tunneling
cognitive tunnel vision
working memory loss
strategic shifts, e.g., tendency to react too quickly
Effect depends on individual factors –
personality traits
level of experience
life stress
and on level of physiological arousal induced
by the stressor
54
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Mental workload assessment
1. Primary Task Performance - measure the
influence of mental workload
2. Secondary Task Techniques - measure the reserve
capacity
3. Subjective Response
4. Physiological Assessment (Central and Peripheral)
allow non-intrusive measures
55
How well are you Flying? How well are you Driving?
1. Primary Task Performance
Example of Primary Task
Performance
Time required / Time available (TR/TA) ratio
Based on task analysis
Percentage computed per time unit on task timeline
Useful predictor, but difficult to construct
57
2. Secondary Task Techniques
58
Secondary Task Measures
Primary Task Demand (PTD)
Perf
orm
ance
Level
Difficult (D) Easy (E)
Maximum Capacity (Without Impaired Performance).
Moderate (M)
P P
P
S3 S2
S1
PTD
E M D
S1
S2
S3
Subjective Responses
Different questionairres i.e. SOWA and
NASA-TLX
The advantage: easy to do and high face
validity
The disadvantage: often performance and
perception deviate
60
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NASA-TLX (Task Load Index)
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NASA-TLX (Task Load Index).
Developed by NASA
6 Sources of Workload: Temporal Demand, Effort,
Stress, Own Performance, Frustration, Physical
Demand
Each is Compared Pairwise against the Others to
give a Rank Order (0-5)
Subjects rate each EVENT by giving a 0-100 score
for each Source.
These values are multiplied by the RANK and the
total is divided by 15 to get the Workload Score on
a 0-100 Scale
62
Eyeblink & Reflex
Modification
Electroencephalography
(EEG)
Pupillometry/
Eyetracking
Electrocardiography
(ECG)
Physiological Reflections of Mental Workload
Mental workload assessment
1. Primary Task
Performance
2. Secondary Task
Techniques
3. Subjective Response
4. Physiological
Assessment (Central
and Peripheral)
Data easily available,
future failure
unpredictable
Intrusive diagnostic
and administration
High face validity,
often dissociate
Unobtrusive,
Expensive data (but
getting cheaper).
64
Aviation • Pilot workload
Maritime • Ship navigation
Ground • Car and bus driver’s workload
Air traffic control • “Automation cueing modulates cerebral
blood flow and vigilance in a simulated air traffic control task”
Shift-work • Performance dependent upon shift and
workload
Peacekeeping • Differential workload of peacekeepers
Business costs • “… employee benefits managers are
hoping that technology … will help them cope with increasing workloads”
• Employee burnout
• Training effectiveness
• Human computer interaction
• Home-care
• Nursing
• Hospital readmissions
• Parenting
• Consumerism
• Professor productivity – to improve academic quality
• Student success
Current Applications and Future Directions
66