Ergonomics in sitting posture

By Dr. Rajal Sukhiyaji(M.Pt. in sports science)

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

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.

“ 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 )

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 )

Overview of Ergonomics :-

Physical Ergonomics

Cognitive Ergonomics

Organizational Ergonomics

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)

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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

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.

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.

There are mainly three types of chair design:- Fixed posture chair

Dynamic chair design

Combination chair

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.

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.

Workstation consideration :-Reduce work-related musculoskeletal disorders developed by workers when their jobs involve…

Awkward postures Static positions Forceful exertion Repetition Contact stress

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

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

Increased stress, decreased circulation…

Equipment set-up examplerisk identification…

Elbow and shoulder away from body, reaching increased, strain on shoulder and wrist

Elbow and shoulder more relaxed and closer to body

decreased strain on shoulder and wrist

Forward placement of document holders and monitor

prevents excessive turning and bending stress in neck, upper back and torso

Posture:keeping it straight!

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

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.

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.

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.

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.

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.

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.

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.

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.

New folder\Poor sitting posture and a heavy schoolbag as contributors to musculoskeletal pain in children an ergonomic school education intervention program.htm

New folder\The effectiveness of a chair intervention in the workplace to reduce musculoskeletal symptoms_ A systematic review.htm

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

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