Download WHAT IS WORK?

ERGONOMICS
“WORK”
WHAT IS WORK?
 Work can be thought of simply
as activity - either mental or
physical. Your body is working
constantly even when you are
asleep!
 You carry out mental work whenever you use
your brain to do something - reading, watching
television, solving a problem, etc.
 You carry out physical work whenever you use
your body to do something - walking, sitting,
lifting, etc. Your body still works when you are
asleep to digest food, repair tissues, keep you
breathing, etc.
Types of physical work
 Physical work is carried out by your muscles
and is therefore often called “muscular work”.
There are 2 types:
 STATIC
 DYNAMIC
STATIC
(or isometric meaning 'same length'):
 this is where a
muscle remains
contracted for a
period of time
but there is no
movement, as in
holding a picture
against the wall or
carrying a bag of
shopping.
DYNAMIC
(or isotonic meaning 'same tension'):
 This is where there is
rhythmical contraction
and relaxation of a
muscle which does result
in movement, as in
pulling open a drawer or
walking up stairs.
Dynamic work is less
tiring and more
efficient than static
work.
This is because during
dynamic work a muscle
contracts and relaxes
rhythmically which
makes it act like a pump
for the flow of blood in
the blood vessels,
allowing the blood to
supply more oxygen and
take away more lactic
acid than during static
work.
 Hold a small book in each hand. Put
one arm straight out in front of you and
keep it in that position. This arm is
doing static work. With your other arm,
keep your elbow at your side and move
your forearm up and down repeatedly.
This arm is doing dynamic work. Which
arm gets tired first? It's probably the
one holding the book still in front of you
and apparently doing nothing!
DYNAMIC AND STATIC WORK
Types of muscle
 There are three types of muscle tissue in your body:
 Smooth muscle tissue - located within the walls of
various body organs;
 Cardiac muscle tissue - which forms the heart; and
 Skeletal muscle tissue - which forms the muscles that
make you move.
 Skeletal muscle is made up of bundles of muscle fibres which
can contract together in one direction. During movement, when a
muscle contracts, the muscle fibres reduce in length so the
amount of movement that the muscle can produce depends on
the original length of these fibres. The strength of the muscle will
depend on the number of fibres that it contains and the crosssectional area of the muscle.
Muscular endurance and strength
 “Muscular endurance” is the ability of
a muscle or a muscle group to remain
contracted over a period of time.
 Endurance can be static or dynamic.
Static endurance can be determined
by the length of time a limb can
maintain a certain position, whereas
 Dynamic endurance can be measured
by the number of times a limb can
perform a movement against a certain
resistance.
 “Muscular strength” is the maximum
amount of force that a muscle can exert
under maximum contraction.
 The amount of force that can be exerted
by your limbs depends on body posture and
the direction of force.
 For example,when standing, you can exert
more force when pushing backwards than
when pushing forwards.
There are several factors that influence
your muscle strength and endurance:
Age: your strength
increases in your
teens and early 20s,
reaches its maximum
by the middle to late
20s, remains at this
level for 5 to 10 years,
and afterwards begins
to decrease gradually.
Sex:
 In general, women
are about two thirds
as strong as men.
This is because men
have greater muscle
mass as a percentage
of body mass
compared to women.
Body build:
 Usually the 95th
percentile person of a
population will be
stronger than the 5th
percentile person; the
athletic or muscular
looking person will tend to
be stronger than others;
among people of equal
body size, differences in
strength may be due to
the amount of muscle
tissue, body shape and
proportions.
Fatigue:
 The build up of lactic acid in the
muscles due to static muscle
work causes a gradual decline in
muscle strength; fatigue can be
delayed by adopting comfortable
working postures, changing your
posture now and again, decreasing
the intensity or duration of muscular
effort, training or practice, having
adequate rest periods, and good
nutrition.
Exercise:
 You can increase
your muscle strength
and endurance
through exercise up
to the limits of your
maximum physical
potential, which is
mainly determined by
the genes you inherit
from your parents.
Heat:
 Heat, especially when
combined with high
humidity, decreases
muscular
performance,
especially endurance.
Cold:
 Cold will not affect
muscle strength if you
wear adequate
protective clothing,
but it may affect your
manual dexterity.
Clothing & equipment:
 Bulky clothing may make
movement more difficult
and you may not be able
to achieve the best
positions for exerting
maximum force. Clothing
and any equipment you
carry will add to your
overall weight and
therefore you will need
extra muscular energy to
move.
Motivation and emotional state:
 Fear, anger or
excitement can
temporarily increase
your muscular
strength but skill and
accuracy may suffer.
Nature of your job:
 Manual workers are significantly stronger than
other types of worker.
Postural aids:
 Backrests increase
pushing strength by
directing all your
strength forwards.
Postural aids:
 Footrests increase
pulling strength by
allowing you to brace
your legs.
The amount of force that can be exerted by
your limbs depends on your body posture
and the direction of force that you apply.
Maximum pulling forces
(as percentage of body weight)
Maximum pushing forces
(as percentage of body weight)
Physical changes during muscular
work
When you use your muscles and become
active, several physical changes occur in
your body:
You need and use more oxygen
Your breathing rate and depth increases
Your heart rate and blood flow increases
You sweat more
The chemical make up of your blood and urine
changes
Oxygen supply and consumption
 Muscular work involves the contraction of muscles, a process which
requires energy. This energy is obtained through the breakdown of
energy-rich glucose or fat.
 When you are not being very active, oxygen is readily available and
enough is supplied to the muscles to allow them to completely break
down glucose and fat into energy, water and carbon dioxide. This
process is called aerobic respiration.
 When you are being very active, your muscles need more oxygen
but it can't be supplied fast enough by the blood and glucose can't
be broken down completely. Lactic acid is a by-product of this
anaerobic respiration process and builds up in your muscles which
you feel as an ache or pain in your muscles.
 When you rest again and you supply enough oxygen to your
muscles, this lactic acid is converted into glycogen and the muscle
ache disappears.
 People who are physically fit can sustain the aerobic process for a
longer time than those who are unfit, that is, they are able to supply
oxygen to the working muscles at a higher rate and therefore lactic
acid doesn't accumulate as fast as in unfit people.
 For light work, you need from 0.5 to 1.0 litre of oxygen
per minute
 For moderate work, you need from 1.0 to 2.0 litres of
oxygen per minute
 For heavy work, you need more than 2.0 litres of
oxygen per minute
 During light or moderate activity your oxygen supply
keeps pace with the requirements of your muscles. At
this stage work is being done aerobically. A steady
state of oxygen consumption is reached and maintained
throughout the period of muscular work. However, during
industrial or recreational activities, a steady rate of work
is seldom maintained for a prolonged period so the
steady state is rarely attained.
 During heavy work, the oxygen supply increases
but soon becomes inadequate and the aerobic
processes are replaced by anaerobic.
 At this point your muscles become short of
oxygen which results in an 'oxygen debt'. This
'oxygen debt' refers to the extent to which
anaerobic processes contribute to the
performance of work. This must then be paid off
at the end of the work period. The harder you
work and therefore the greater the anaerobic
contribution, the longer it takes you to recover.
Heart rate
 During increased activity the volume of blood flowing into
the heart increases as the working muscles help to pump
the blood back to the heart. This stretches the heart
muscle which then contracts more forcefully, so more
blood is expelled with each beat (called the stroke
volume). The nervous system also increases the
number of heart beats per minute (the heart rate). Both
of these together result in much more blood being
pumped by the heart.
 During hard work your heart rate increases up to about
three times its resting value (for example from 60 beats
to 180 beats per minute). When the activity stops, your
heart rate returns to resting levels. The speed with which
the rate falls back to resting levels depends on your
fitness; the fitter you are, the faster your recovery.
Your level of fitness affects your physical
state during work and your recovery in
several ways:
Measurement
Fit person
Unfit person
Oxygen consumption
Same
Same
Heart rate
Lower
Higher
Stroke volume
Larger
Smaller
Lactic acid concentration in blood
Lower
Higher
Return of heart rate to normal after work
Faster
Slower
Fatigue can describe a variety of
conditions such as:
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
Fatigue can result from hard physical effort
or prolonged but less physical activity.
Your efficiency in a job depends on a number of
things, for example, your ability to do the tasks
involved, your capacity for physical work, the
design of the instruments, tools and machines
that you use, your workplace layout, and your
training.
However, any prolonged work, physical or
mental, is tiring and you can't work all your
waking hours without fatigue.
If you have a light industrial job, you might
perform one or more of the following tasks:
 Repetitive work: you repeat the same
sequence of operations continuously, for
example on assembly lines
 Monitoring: you watch for signals which may
occur at infrequent intervals, for example in
control rooms, or production inspection
 Driving: you drive railway locomotives, road
vehicles, cranes or rolling mills
 Machine minding: you watch automatic or
semi-automatic machines for changes
 Quality control: you check goods for faults
 After any of these tasks has been continued for
some time, you would probably need a break, or
your performance would deteriorate.
 There is a limit to the length of time you can
keep up maximum concentration which depends
on you and the type of task you are doing. In a
continuous task, you might start to work
unevenly, or you might miss signals or make
some other mistake, or even have an accident.
Fatigue may not necessarily arise due
to having too much work to complete.
 Boredom or monotony are special factors that
can lead to fatigue. These occur when there is
no stimulation in either the work itself or the
working environment and may happen when:
 You're not interested or motivated by the work
 The work makes no demands on your skills
 The work rate is too slow for you
 Your work environment is dull
 In order to reduce fatigue, you need to take
a break from the activity that has made you
fatigued. This can be either a complete rest
or just a change of activity.
If a break or a rest pause is taken at
appropriate times, a fresh period of
optimum activity will result.
There are four types of work pauses:
Spontaneous: taken by the worker,
especially during strenuous work.
Disguised: these may form secondary
work that is not necessary at a given
moment for the task in hand, e.g. cleaning
a machine part, tidying the work bench,
etc.
Work-conditioned: these are waiting
periods dependent on the organisation of
the work or the movements of a machine.
On conveyor belts, the length of the workconditioned pause depends on the skill
and work rate of the operator. The waiting
time for the next piece of work increases
with the skill at which work is performed.
Prescribed: these are usually taken at a
set time in the form of tea breaks or lunch
breaks.
The following work-rest programmes are
usually recommended for industrial workers:
 Medium intensity work with waiting times
created by the working process: one break in the
morning and one in the afternoon, of 10-15
minutes each. Refreshments should be
available.
 High intensity work without waiting time and
with a high work rate: a refreshment pause in the
morning and in the afternoon, and one or two
short pauses of 5 minutes each during each half
of the working day.
Increasing your ability for work
Physical activity
 Mechanical devices and electronic instruments
are taking over the more physical parts of many
jobs, with the result that workers do not need to
be so fit to do the same job.
 This decrease in activity at work is thought to be
one of the factors contributing to the increase in
coronary heart disease in developed countries.
Coronary heart disease is twice as frequent in sedentary
(sabit, oturarak çalışan) people as it is in active people.
Medical evidence also suggests that an
increase in physical activity acts both as a
preventive measure against coronary
heart disease and results in improved
physical fitness, that is, a greater capacity
to cope with work, leisure activities and
neuromuscular (sinir-kas) stress.
Nutrition
 A diet that contains a variety of foods in sufficient
quantity to maintain normal body weight and support
growth is usually adequate for all individuals whether
they are sedentary or athletic.
 A normal, balanced diet means eating appropriate
amounts of carbohydrates, proteins, fats and oils,
vitamins and minerals. Carbohydrates include sugar and
starchy foods and form the body's main source of
energy. They are an essential, but not exclusive, fuel for
muscles. Proteins are used for growth and for repairing
body tissues. Protein may also be used as fuel if
carbohydrates and fats are not available, for example,
during starvation. If you are training for an athletic event,
it is recommended that your diet should include
approximately 60% carbohydrate and 15% protein.
 Fats are an important source of energy at rest and for
low intensity exercise, and are readily stored in the body.
All foods contain stored energy. The amount of energy
that your body can obtain from food is measured in
kilojoules (kJ). Your body can obtain 17kJ from 1 gram of
carbohydrate or protein and 38kJ from 1 gram of fat but
as it requires more oxygen to do this, it is not used when
the oxygen supply can't meet the extra requirement, for
example when you are doing heavy work.
 Different activities require different energy levels. The
table below gives examples of energy requirements for
some activities, in kilojoules per hour (for a 25 year old
man weighing 65kg).
Activity
level
Every day
activities
Examples of activity
Energy
requirement
kJ/h
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, bricklaying
10-20
Moderate
work
&
recreation
Gardening, tennis, dancing, cycling up to
20 km/hr, digging, shovelling, nonmechanised agricultural work,
21-30
Strenuous
work &
recreation
Coal mining, steel furnace work, squash,
cross-country running, football,
swimming
Over 30