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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)

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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

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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

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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

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Code of position

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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).

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Head / neck posture

40

Back

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Arm posture

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Wrist posture

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Hand / finger grip

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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).

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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

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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

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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

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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

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2. Secondary Task Techniques

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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

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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

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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).

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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

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