This document discusses various risk factors for cumulative trauma disorders (CTDs) including repetitiveness, forceful exertions, stressful postures, mechanical stress, temperature extremes, and vibration. It provides examples of how exceeding the body's limits through prolonged exposure to these risk factors can lead to fatigue, pain, and injury over time rather than immediately. The six general occupational risk factors are defined and examples are given of stressful postures for various body parts like the hands, wrists, shoulders, neck, and how tools can cause mechanical stress.

2. Risk factors of CTD
• Work does not have to be harmful if the limits of the human
body are understood and not exceeded
Example:
You will not take your family car and roar down
a country road banging through pot holes and
screeching around corners. The mechanical stress
would cause fatigue in parts of your car that would
eventually cause serious damage
• Just like cars, people have certain limits
• If we work outside those limits we will cause fatigue in body
parts, shortening their functional life
• If we exceed the capacity of the body, the components will
fatigue, become unreliable and eventually fail

3. Risk factors:
• Risk factors usually have their harmful effects on the operator
in some combination
Example:
when we talk about a stressful posture, we imply that this posture is potentially
harmful when it is used repeatedly (Risk factor = REPETTITIVENESS),
normally in association with muscular exertion (risk factor = FORCEFULNESS)

4. • Risk factors of concerned usually have their
harmful effects through prolonged exposure.
The injuries are mainly cumulative.
• That means that they develop over a period of
time, usually months or even years
‘chronic vs acute’

5. Six general occupational risk factors:
• Repetitiveness - Repeated or sustained
exertions
• Forceful Exertions - Also called forcefulness
• Stressful Postures - Also called awkward
postures
• Mechanical Stress - Also called mechanical
stress concentration
• Temperature Extremes - The effect of heat and
cold
• Vibration - Both high and low frequencies

6. REPETITIVENESS
If you think of what is
involved in many jobs
you will realize that they often
require the worker to constantly
repeat certain sequences of
movements or to maintain
certain stressful postures for
prolonged period of time.
• Such movements or postures, which are normally
harmless when used once in a while or briefly, may
cause injury when they are used repeatedly on daily
basis
• Example: if we lightly squeeze a soft drink can with
our hands. Initially the sides of the can crinkle, but it
regain shape.
– The force we applied was not strong enough to
immediately destroy the can. However, if we
repeatedly apply this same pressure say 15 to 20
times, the can will develop fatigue and tear apart

7. The result of repetitive force
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• It is the same with the human body, but instead of 15 or 20
times, the frequency is measured in hundred and thousands of
repetitions.
• The repeated application of force that is not strong enough to
cause immediate damage, but over time it will fatigue in the
tissues.
• This usually means that this job soon become a hassle.
• After a period of time, there will be pain as the tissues involved
(the skin, muscles, tendons, joint, ligaments, nerves, and blood
vessels) are repeatedly rubbed, compressed and stretched
from movement and exertion.
• If these tissues are not allowed to recover, the cumulative
damage will result in serious injury.

8. • Unfortunately there are no precise guidelines for the rate
of repeated or sustained exertions that would cause
injury
• The degree of stress and the resulting risk of injury
depends on the kind of muscular movements involved
and on the presence of other risk factors such as
forcefulness and postures used.

9. FORCEFUL EXERTIONS
(FORCEFULNESS)
• When you contract your muscles, you exert force in order to
move your limbs, lift of hold an object, operate a tool, or
maintain a posture.
• As your muscles contract and relax, the tendons are
stretched. They may rub or press on adjacent tissues. The
degree of musculoskeletal strain depends on how much force
you exert.
FORCE = amount of work which the muscles, tendons, joints and
adjacent tissues must do in order to perform the
particular action.
• The force exerted depends on a variety of factors, including
posture, weight, friction and recovery time.

10. Importance of force and posture
You can perform work more efficiently
with some postures than others.
• In certain posture you have to exert more force to perform the
same job.
• Example; pinch grip requires more force than a hook grip.
• To demonstrate yourself, compare what it feels like to pick up
and hold a heavy book by the binding in two ways
Between your
thumb and the pads
of your fingers,
with your hand
above the book
Hooking your fingers
under the book
and holding it
against your forearm
Which is easier?

11. Other factors to consider
• The weight of load that has to be moved or manipulated
is very important.
• All things being equal, a heavier load requires a greater
exertion, that is, more force to manipulate it
• The friction of an object moved if it is also slippery, will
require more force to keep it in your hand
• Similarly, you will have to work harder to push a cart if
your feet tend to slip on the floor than if your footing is
secure

12. Forceful
Exertion
• Although force, can be estimated by measuring the number of
muscular exertions, there are no fixed guidelines for what
degree of force is harmful.
• As with repetitiveness, the hazard from force, depends on:
– What part of the body is exerting the force
– What kind of movement is involved
– The presence of other risk factors, such as repeated
exertions

13. STRESSFUL POSTURES
• Certain postures, when used repeatedly or when
sustained, can be stressful to the structures of the body,
especially when force is exerted.
• posture is so critical to ergonomics and affects various
parts of the body

14. Hand postures
in which the hand is wrapped
around and object with
continuous contact between
the tip of the thumb and the
fingers
In which only the pads of
thumb and fingers touch the
object, is best for precision
task
Power grip
Pinch grip
USE POWER GRIP
AVOID PINCH GRIP
• Using a pinch grip when you have to exert a lot of force can result in
pain and injury
• Unless the work being performed is very precise, the pinch should
be replace with power grip.
• Also important to provide for a good grip of objects being handled.
• Avoid slippery handles
• Increase friction by providing tool handles with textures or coated
handle coverings or by providing gloves with non-slip palms.

15. Wrist posture
• The least stressful posture for the wrist is called the
neutral posture.
• The wrist normally assumes this posture when your hand
is hanging comfortably at your side.

16. Wrist posture
•Non-neutral wrist postures are potentially stressful
Hyper-Extension
(hand bent backward away
from the palm)
Flexion
(hand bent toward the palm)
Ulnar Deviation
(hand bent toward the little finger)
Radial Deviation
(hand bent toward the thumb

17. Important of hand and wrist posture:
• Cumulative Trauma
Disorders (CTD) of
the upper
extremities are
“wear-and-tear”
injuries that affect
many people who
do hand-sensitive
work.
Posture of hand and
wrist that must be
avoided

18. SHOULDER POSTURES
• Stressful postures of the shoulder can cause a
significant reduction in endurance
Awkward postures of the shoulder

19. • All stressful postures result in strength reduction
• Notice in the table below, that when the arms are fully
extended, we are at our weakest
EXTREME POSTURE % STRENGTH REDUCTION
from NEUTRAL POSTURE
Ulnar Wrist Deviation 25%
Radial Wrist Deviation 20%
Wrist Extension 25%
Wrist Flexion 55%
Arm Fully Extended 81%
Floor Level Lift 40%
High Vertical Lift 60%
45° Twist During Lift 15%
90° Twist During Lift 30%

20. NECK POSTURES
• Any improper neck postures may lead to muscles fatigue and/or
headaches.
•The neck is stresses by holding the tilted forward of backward more than
20° for extended period of time
Neck ≤20° Backwards
• Care must also be taken to prevent moving the head repeatedly from
side to side and excessive twisting.
• Stressful neck postures should not be repeated more than 2 times/min
Sideways Twisted

21. MECHANICAL STRESS
• Mechanical stress is produced by the contact between some
parts of the body and the sharp edges of tools, parts, work
surfaces or work pieces
(a)
(b) (c)
• Hand tools are common cause of mechanical stress. The figure
above gives a good example of how a hand tool can compress finger
tendons. (a) A sharp-edged tool (b) is more likely to produce injury
than a rounded tool (c).

22. Other parts of the body are also quite sensitive to
mechanical stress. They include:
• Backs and sides of
fingers
• Inside of wrist
• Soft tissues of the
thighs during
prolonged sitting
 Elbow (“funny bone”)
 Armpit and chest
 Tops of feet
 Front of lower legs

23. TEMPERATURE EXTREMES
• Extremes of both cold and heat can be stressful
• Skin temperature should not be allowed to fall below
68°F (20°C) due to contact with air, tool exhaust or cold
materials
• This conditions may impair the sense of touch and
reduce dexterity in the hands.
• When the hands are cold and numb, you tend to
misjudge the amount of force necessary to perform a
task.
• Additional stress is created by a tendency to over-exert
under these conditions.

24. Extreme heat are harmful in two ways.
First
• Handling hot tools, surfaces or work pieces without protective
gloves can result in burns
Second
• Environmental heat, especially if accompanied by high humidity,
can increase the physiological strain during whole-body exertions.
• This is because muscular activity produces heat.
• The body can release most of this heat through perspiration under
normal circumstances.
• As the temperature in the air and humidity rise, the body must work
harder to give off this heat. Various heat related disorders can result,
among them are heat stress and heat stroke
• NOTE: Work which can be performed easily in a comfortable
temperature can cause excessive stress on the body in hot, humid
working conditions.

25. VIBRATION
EXPOSURE MEDIUM EFFECT DESCRIPTION
TO :
Normally
associated with
people who
drive vehicles,
eg: fork trucks,
platform trucks
Increase an
individual risk for
back injuries
• Back
• Buttock
Low-frequency
vibration
Can occur with
the use of
powered hand
tools and
impact tools
Damage to the
nerves, blood
vessels and
bones of the
hands and arms
Vibration • Hands

26. PERSONAL RISK FACTORS
• Also recognized as other factors.
• Factors may affect an individuals overall risk for overexertion
injuries:
– Age
– Fitness level
– History of injury
– Medical conditions
– Smoking
– Obesity
– Gender
– Physical structure

27. The “HIT LIST”
• A method of helping us become more aware and
experienced in ergonomics is to summarize the most
common risk factors seen in the plant.
The Ergonomic “ Hit List”

28. the Washrag.
• It is a summary of the stressful hand and wrist
postures making it very easy to spot
Continuous movement of the wrist and hands, increase like likelihood of
repetitive motion disorders

29. There are three postures that commonly observes in the
plant have a direct effect on the low-back
• “Butts Up” position
• It is the most common in the plant
• A good indicator of risk for possible low-back problems
Can be seen off-loading
conveyors,
pushing and positioning
component carts lifting
and loading material,
etc

30. • “ Horizontal Distance”
• Usually seen when loads are being handled away from
the body
• This can put great forces on the spine
Anytime there is a lack of
clearance which prevents
the worker from getting
close to the load there will
be trouble.
Look for this around
conveyors and tables

31. • “Twist and Shout”
• Usually seen when loads are being moved from one
location to another.
• The twisting motion puts extremely high forces on the
lower back
Look for transferring
components or finished product
from one surface to another
such as off-loading conveyors,
repetitive splicing type
operations or transferring
product from a conveyor to a
pallet.

32. There are two postures that are the result of failure to locate
the work to be done in the proper place
• “Shoulder Too High/Shoulder Too Low” position
This usually the result of
controls or tools located at
the wrong height.
Look for this at work
stations, especially product
assembly

33. • “Comfort Zone” position
• Usually seen when loads are being lifted from floor level
or t work stations
Observe work
stations to make sure
that the work is
located well within
reach.
This can also greatly
effect product quality
and productivity

34. There are two positions s commonaly observed when tools
are being used
• “Tool/Target” position
This can also result from working
too high or to low.
Look for this posture whenever
tools are used

35. • “Elbow Out”
This is most common
where screwdrivers and
pliers are used.
It can also be observed
when the product is being
worked on or manipulated

36. There are two postures that are not seen as often but also
can cause ergonomic injury/illness problems
• “Hungry Head” position
This usually the result of
inspection and/or handling
material.
Look for this at work stations in
final finish, maintenance and
inspection areas

37. • “Sit-Stand” position
• Usually seen when around conveyors and tables
Observe work stations
to make sure that there
is adequate space for
the feet and that there
are no knee
obstructions

38. • “Bad Vibes”
• This is a problem that can occur with powered hand tools
This can result from
using pneumatic tools
that are worn out.
It can also occur when
the work is performed
on or around vibrating
bins or feeders.

39. • “Don’t Give Me Static” position
• This position occur when stationary positions are
maintained.
Look for instances of
prolonged standing or
holding.
Static problems can also
occur when carrying boxes
or other objects.