Ergonomics in Sitting Posture

1. Ergonomics in sitting posture
By Dr. Rajal Sukhiyaji
(M.Pt. in sports science)

2. Contents :-
 Introduction
 Overview of ergonomics
 Ergonomic sitting
 Anthropometry
 Biomechanics of sitting
 Sitting posture
 Ergonomic chair design
 Workstation consideration
 References

3. What is Ergonomics ????
 Ergonomics derived from two Greek
words
 Ergon means “ WORK “
 Nomos means “ LAW “
 Thus, Ergonomics focuses on the study
of work performance with an emphasis
on worker safety and productivity.

4.  “ Ergonomics (or Human factor ) is the scientific discipline
concerned with the understanding of interactions among
humans and other elements of system, and the profession
that applies theory, principles, data and other methods to
design in order to optimize human well-being and overall
system performance.” (According to the International
Ergonomics Association )

5.  Ergonomics emerged as a scientific discipline in the 1940s
as a consequence of the growing realisation that, as
technical equipment became increasingly complex, not all
of the expected benefits would be delivered if people
were unable to understand and use the equipment to its
full potential. (According to the Institute of Ergonomics
and Human factor )

6. Overview of Ergonomics :-
Physical Ergonomics
Cognitive Ergonomics
Organizational Ergonomics

7. Ergonomics Applies to…
 Workstation Design—(desks, chairs, space, layout)
 Work Postures (sitting, standing, reaching, lifting)
 Work Organization (Pace, Breaks, Variety)
 Tools, Equipment, and Furniture Design---(body size, height, gender,
promoting neutral postures, reduced vibration, exposure to acceptable lighting,
noise, temperature)
 Manual Materials Handling—(lifting, lowering, pulling, pushing, carrying and
holding materials)
 Work Environment—(ventilation, noise, temperature & humidity, lighting and
vision)

8. Ergonomic sitting
 Sitting :-
 The weight transferred to a supporting area by the ischial tuberosities
 Remove weight from the feet and maintain a stable posture
 Muscles not directly involved with the work can relax.
 Ideally, There is no single ideal sitting posture. Illustrated 90-degree
person sitting posture is for anthropometric reference only. Can't design a
chair for the best single way to sit. We need a variety of chairs that allow
different users to each sit in a variety of postures.
 Adjustable chair

9. Ergonomic sitting
 Comfortable working posture with neutral alignment of
all your joints from head to toes.
 Helps to reduce the stress and strain on the muscles,
tendons, and skeletal system thus reducing the risks of
developing a Ergonomic problems.

10. Anthropometry
 Anthropos means “human” and metron means “measure”.
 Thus, It is the “measurement of human individuals.”
 It is the science of measurement of human body, provides
therapists to understand the complexities of the human
form and how is interfaces with its environment.

11. Anthropometric measurement in sitting
posture :-
 The person sit erect and look straight ahead.
 The sitting surface is adjusted so that the person’s thighs are parallel to the floor
and the knees are bent to a 90 degree angle with the feet fiat on the floor.
 The upper arm is relaxed and perpendicular to the horizontal plane, and the
forearm is at a right angle to the upper arm and thus also parallel to the floor.
 Measurements in sitting are made using a horizontal reference point, either the
ground or the seat, and vertical reference point am imaginary line that touches
the back of the uncompressed buttocks and shoulder blades of the subject.

13. Biomechanics of sitting :-
 Depending on chair and posture, some proportion of total body weight is transferred
to the floor via the seat pan and feet, armrests, and backrest.
 When sitting, the pressure fall on to the two small “sit bone” or ischial tuberosities.
 Compressive stresses exerted on areas of buttocks beneath the tuberosities .
 When sit upright, approximately two thirds of body weight is distributed to the chair
seat, with the backrest ,armrest , and floor supporting the remainder.

14.  Pelvis - The sacrum is fixed to the pelvis, so rotational movement of the
pelvis affects lumbar vertebrae.
 Forward rotation - of the pelvis leads to increased lordosis of the
lumbar spine, helping to maintain an upright trunk position. When sitting
unsupported, tilt the pelvis forward to re-establish a “ neutral “ lumbar spinal
posture.
 Maintaining this posture requires muscle activity and will be easier to sustain
if the individual is involved in regular fitness activities.

15.  Backward rotation - of the pelvis leads to increased flattening of
the lumbar spine and eventually increases kyphosis. When we sit , our
hamstring muscles pull on and rotate our pelvis, which flattens the
lumbar spine.
 Sitting with the straight spine puts additional pressure on the front of
the spinal disks and creates additional strain on ligaments.

16.  Disc pressures also change dramatically when a person moves among
standing, upright and slouched seated postures.
 Disc pressure is greater during sitting than standing and disc pressures
drop with an inclination of chair backrest, especially when it is tilted
from vertical to 110 degrees.

19. How to Sit Properly ???
Neutral Position (Good sitting posture)
Sitting like this is known as
sitting in a “neutral
position.” This position
reduces the amount of
stress on muscles.

20. Benefits of good ergonomic sitting
posture :-
 Maintaining a good sitting posture can not only help to improve your
appearance but it can also alleviate pain in the neck and back.
Benefits include:
 Easier breathing
 Healthier joints
 Better concentration
 Good digestion
 Prevent Back pain
 Reduced tension
 Improve muscle tone

21. Different sitting posture :-
 Forward posture - center of mass in front of the ischial
tuberosities. Floor supports more than 25% of body
weight. Common posture for desk work.

22. Upright posture :-
 It involves the trunk being upright and straight, with the seat and
backrest at an approximate 90 degree angle and center of mass
directly above ischial tuberosities. Floor supports 25% of body weight.
 The classic upright seated position with perfect 90 degree torso angles
is perfectly acceptable, but rarely used.

23. Reclined posture-
 Center of mass behind ischial tuberosities. Floor supports less
than 25% of body weight. Common for chairs with large,
inclined, backrests. Preferred for resting.
 Although this posture reduces the pressure on the discs, it is
not necessarily functional for working because it also
increases viewing distance and arm reach to the work area.
 It can also increases the strain on the neck if user flexes his or
her head forward for viewing , without the benefits of a high
backrest or even a head rest.

24. Poor sitting posture :-
For people who spend a large part of their day in one position for a long
time can lead to a number of problems. These problems can happen so
slowly that hardly notice but it is often difficult to undo some of the
damage that poor posture can cause once it is done.
 Poor posture in sitting can lead to:
 Muscle shortening -
 Pressure ulcers (sores)
 Pain
 Increased spasms
 Breathing difficulties
 Loss of balance
 Problems keeping your head upright

25. The body’s need for movement :-
 We often sit because of fatigue that result from standing.
 Sitting is more efficient way to perform many occupational and non-
occupational task.
 Sitting in many jobs makes good sense, as it relieves the body’s
supporting muscles, offers them a chance to rest , and is less
demanding on the blood circulation to the legs.
 Sitting allows the chair ,to support the seated person’s body mass.
 For all this said ,it must be realized that the body was designed not to
sit ,but rather to move.

26. Ergonomic Chair design :-
 It provides easily adjustable and accessible features for seat height,
backrest and level of lumbar support , and seat inclination.
 It gives stability by providing good support to the buttocks via the seat
pan and to the back via the backrest.
 It allows the seated person to freely move within the seated position.

27. There are mainly three types of chair
design:-
 Fixed posture chair
 Dynamic chair design
 Combination chair

28. Basic features of well design ergonomic
chair:-
 A seat height is easily adjustable and had pneumatic pedestal base.
 Ability of user to easily make all adjustment while seated.
 Good lumbar support.
 A backrest that adjusts vertically to support the lumbar spine as well
as in an anterior – posterior direction and that is narrow enough to
allow freedom of arm movement without chair interference.
 Dynamic movement options of the backrest and seat pan.
 A seat pan with a curved front or waterfall edge to reduce pressure
behind the knees.

29.  A tension adjustment that affects the ease of forward and backward
inclination of the backrest.
 A four or five prong base of support to prevent the chair from tipping.
 Casters that are sturdy and allow for both mobility and stability.
 Seat padding that is soft but not too soft, to allow even distribution of
pressure.

33. Workstation consideration :-
Reduce work-related musculoskeletal disorders developed by workers
when their jobs involve…
 Awkward postures
 Static positions
 Forceful exertion
 Repetition
 Contact stress

34. Static and awkward postures lead to:
 Decreased movement
 Decreased circulation
 Increased stress and fatigue

35. Computer workstation ergonomics
 Chair
 Monitor
 Keyboard
 Mouse
 Document holders
 Lumbar pad
 Eye strain
 Footrests
 Wrists pads
 Keyboard trays
 Laptops
 Arm rests

37. Increased stress, decreased
circulation…

38. Equipment set-up example
risk identification…
Elbow and shoulder away from body,
reaching increased, strain on
shoulder and wrist

39. Elbow and shoulder more relaxed and
closer to body
decreased strain on shoulder and
wrist

40. Forward placement of document holders
and monitor
prevents excessive turning and bending
stress in neck,
upper back and torso
Posture:
keeping it
straight!

41. Ergonomic Controls-Administrative
Administrative controls = procedures and methods that
significantly reduce daily exposure to MSD hazards by
altering the way in which work is performed.
Examples:
 Employee Rotation
 Job task enlargement
 Adjustment of work place
 Redesign of work methods
 Alternative tasks
 Rest breaks

42. Office Exercises/Stretches
1. Perform all exercises in comfort zone, if discomfort persists STOP
immediately.
2. Stretch regularly throughout your day.
3. Stretches should be done slowly and smoothly.
4. Change activity. Where possible, every hour, take a few minutes to
alternate your work activities. This will help to relieve muscle aches,
eyestrain and stress.
5. If you are under treatment, or have any concerns regarding the
exercises, please contact physician before doing any of the following
suggested exercises.

43. Wrist and forearm stretches:-
a) Shake your arms
• Drop your arms and hands to your side
• Shake them gently for a few seconds
b) Wrist stretches
• Keep your elbows straight, grasp hand and slowly bend
wrist until feel a stretch
• Hold stretch for 6-10 seconds.

44. Shoulder/Arm Stretches:
• Reach with your arm across the chest
• Grasp opposite shoulder with opposite hand
• Gently pull the elbow across your chest towards the body
• When the stretch is felt in the shoulder
• hold this position for 6-10 seconds.

45. Shoulder Shrug:-
• Sit in the chair with your back straight against the backrest.
• Let your head relax.
• Squeeze your shoulders up to your ears.
• Follow by stretching shoulders down with fingers pointing to the
floor, draw chin in gently.
• Slowly change from one position to another.

46. Executive Stretch:-
• Lock your hands behind your head.
• Stretch slowly backwards in your chair.
• Arch your back slightly and gently.
• Hold stretch for 6-10 seconds.
• Repeat 5 times with 5-10 second rest period between stretches.

47. Upper Back Stretch:-
• Extend your arms out in front of chest, keeping them at shoulder height.
• Interlock fingers with palms facing away from your body.
• Keep elbows straight, do not over-extend.
• Reach forward while maintaining an upright posture.
• Hold stomach muscles tight to avoid arching your lower back.
• Hold this stretch position for 6-10 seconds.
• Raise your arms over your head and hold this position for 10 seconds.
• Repeat 5 times.

48. Neck Stretches:-
• Sit in chair with back straight
• Draw chin in gently and bend head to the right so that your right ear
moves towards your right shoulder.
• Hold the stretch for 5 seconds.
• Repeat to the other side.

49. Review :-
 Repetitive motion tasks can lead to Musculo-Skeletal Disorders (MSDs).
 Maintain correct posture while sitting/standing/walking.
 Stretch muscles before and after work.
 Take regular breaks.
 Exercise regularly.
 Ensure workstation set up to be ergonomically correct.
 Ensure lighting in your work area is adequate.
 Report ergonomic hazards or symptoms to supervisor.

50.  New folderPoor sitting posture and a heavy schoolbag as contributors to
musculoskeletal pain in children an ergonomic school education intervention
program.htm
 New folderThe effectiveness of a chair intervention in the workplace to
reduce musculoskeletal symptoms_ A systematic review.htm

51. References :-
 Ergonomics for Therapist – Third edition , Karen Jacobs
 Office ergonomics , practical application– Céline McKeown ,
CRC Press, Taylor & Francis Group
 Easy ergonomics for desktop computer user, Department of
Industrial Relations ,Cal/OSHA Consultation Service, Research
and Education Unit
 Cornell University Ergonomics Web, DEA 3250/6510 CLASS
NOTES
 Iowa State University , environmental health and safety

52. THANK YOU