Ergonomic risks in sitting and standing workplaces

Dr. Igor Grabovac

Department of Social and Preventive Medicine

Center for Public Health

Medical University of Vienna

58% of the population over the age of 10 spends 1/3 of their

life at the workplace.

Only 5-10% of workers in developing countries and 20-50% of those in industrialized

countries have access to occupational medicine and

safety services.

Public health aspects

• In Europe: • 33% of all workers are exposed to tiring or painful positions

• 46% exposed to repetitive hand and arm movements

• 31% are working in front of the computer for at least half of their working time

• 34% have access to ergonomic counseling

• 33% european workers claim that their job tasks influence their expeirence of back pain

• MSD: • Multifactorial

• Prevalence on the raise

• Among top 10 reasons that account for the highest number of DALYs

• Costs assocaited range in hundrets of billions of US dollars

Neutral position

• Gravitational influence forces all parts of the body downwards

• Parts of the body that are in contact with supporting structures (seats, floor, etc) will put pressure on these structures to balance this force

• Parts of the body not in contact with supporting structures will use muscles to balance the gravitational pull

Neutral position is: The body position that has the highest strenght to handle the pressure felt by supporting structures while causing the least amount of strain on the muscles

Sitting workplaces - Overview

• One of the oldest ergonomic concerns

• Chair design and seating are not only related to ergonomic aspects but also by sitter safety and productivity

• Biomechanical aspects rarely reported in literature

• One of the most common working positions (wide variety of professions)

Sitting workplaces – Consequences

• Poor sitting is associated with health risks, discomfort and accidents

• Most widely recognized health issue arising from poor sitting are musculosceletal disorders (MSD)

Back pain:

• load to the spine • spinal posture • degree of lumbar

kyphosis

Other factors contributing to MSD:

• highly frequent movements • postures deviating from the

neutral position • positions held for long periods

Sitting requires a fixed position of the neck, trunk, head and shoulders in a fixed position, this:

• Squeezes the blood vessels in the mussles

• Reduces the blood flow and oxygen supply when muscles are in an isokynetic contraction

• As a result: accelerates fatigue and makes muscles prone to injury

Sitting on the edge of a chair creates pressure to the popliteal region, which:

• Reduces the venous blood flow

• Increases the blood pressure in the legs

• Creates swelling of the feet and legs

• Can contribute to thrombosis and varicose venes

Sitting workplaces – Consequences

Long periods of sitting poses strain on the cardiovascular system

Sitting workplaces – Consequences

Additionally:

• Sitting posture decreases the space in the trunk and increases the pressure on internal

organs

• Has an influence on decreased oxygen uptake

• Is associated with stomach issues and colon cancer

• Discomfort makes leads to compensatroy activities and creates distraction fromt he main task

Sitting workplaces – Posture

Being constrained into an awkward position with no

relief or possibility to change causes most MSD

Poor posture can also originate from poor job design and the physical

arrangement of work space elements (tools, surfaces, equiptment, etc)

Posture is influenced by movement ability and climate

Limited mobility and localised tension (usually neck and lower back): • Reduces movement and

may cause muscles to strain, cramp or pull

• Causes tension in the body

• Causes on compression of interverterbral disks contributing to degeneration

What makes a good sitting position?

A good sitting position does not impede a persons‘

breathing or circulation

Sitting work is dynamic (visual, manual and foot

tasks in combinations are often required)

Visual tasks create tension on the neck, trunk and pelvis

workplace needs to be designed to reduce the strain if not possible; workers need to spend less time on each task

The arrangement of the workplace needs to allow the workers to keep their spine vertica No lifting or horzontal punshing of

loads in the sitting position

If workers use pedals these need

to be infront directly to prevent

hip twisting

Sitting workplaces need to allow the worker to

frequently change between a variety of

body positions !!

Sitting workplaces – maintaining a neutral position

Hands, wrists and forearms straight, parallel to the floor

Head is leveled or slightly bent facing forward

Erect and upright spine

Relaxed shoulders with the arms hanging beside the body

Elbows close bent between 90 and

120 degrees

Feet fully supported

Back is supported when upright or bent backwards

Supported tighs and hips and parallel to the floor

Knees at hip height

No twisting of the upper torso

Sitting workplaces – chair

Basic ergonomic rule: no such thing as an „average“ person providing a specially designed chair to every employee is impractical: Solution is to offer fully

adjustable chairs that accomodate 95% of the populous

Chair has to allow adjustability of height and tilt as well as backrest hight and angle

Trial period is recommended

To be avoided: Tilting head

forward Sitting without

lumbar support Working with

raised arms Bending wrists Unsupported

forearms

NO CHAIR FITS ALL!

Sitting in a too high high chair:

Destabilization of the body leading to tiredness

Puts pressure on the tighs increasing pressure in the legs and feet

Pressure on the sciatic nerve causing pain and discomfort

Inappropriate lumbar support

Sitting in a too low chair:

Disrupts lower leg circulation leading to swelling

Exessive pressure to the internal organs

Breathing problems

Exessive pressure on the buttocks causes discomfort

Disc pressure normalized to standing (percent)

• All seated tasks need to be designed to maintain the vertical spine allignment and avoid stress of the shoulders

• Provide materials slightly below elbow height

• Provide arm rests when appropriate (eg. Moving the chair)

• Avoid heavy hand tools

• Avoid the need for excessive reach

Sitting workplaces – manual tasks

Standing position is preffered over seating when:

• Job taks cannot be preformed with the employees keeping their hand at the side

• The work area ist too large to be comfortably reached

• The worker works in more than one area

• The work surface does not allow to rest the legs comfortably under the surface without obstruction

• Working at the counter or with a drawer located underneath the working surface

Standing posture is usually found in:

• Assembly work, packaging and painting lines

• Welding and sheet metal production

• Kitchens and gastronomy

• Health care

• Maitenence, inspectors

• Firefighters

Standing work - overview

Standing work - posture

Standing work is not really static

• Erect people are unstable, constantly swaying

• People adopt asymmetrical standing positions 4 times more often as symetrical

• Shifting the weight between feet is a relief mechanism

• People often stand with one foot forward for more stability

• Standing people constantly sway anterior-posterior and lateral – compensatory muscle activity is often necessary.

Standing work – health concerns

Venous pooling as a result of prolonged standing:

• Creates more exerction for the heart (increasing the HR)

• Mean venous pressure was found at 87 mm during standing (opposed to 56 mm for sitting)

• Causes edema, swelling and varicose venes

• Walking drops the pressure at the ankle level to around 20 mm after only 10 steps

• 2-4 min of walking for every 15 min of standing work is more comfortable

• Body sway influences the blood flow in the feet

• Standing work is associated with increased hospitalizations and carotid atherosclerosis and ischemic heart disease

• Additional health problems by standing work:

• Sore feet

• General muscular fatigue

• Low back pain

• Stiffness of the neck and shoulders

• Excessive standing may cause the large joints in the body to be temporarily immobilized and locked – this may lead to degenerative damage as well as rheumatic diseases

Standing work – footrests

• Footrests can reduce interverterbral disc stress by preventig exessive lordosis

• Studies showed that workers used foot rest options significantly more when given the option

• In a study that investigated the difference in use of a bar, flat platform or a platform with an 15 degree angle: the paltforms were used more often than a bar (59% vs 80%)

Standing work – floormats

• Floormats are designed to allow for the antural sway of the body and to encourge the subtle movements

• Research supports the notion that floormats are preffered over concrete floors for stnading work

• In a study that compared the comfort of work on a hard wood floor with standing on a floor mat, wearing shoes with insoles and a combination found that insoles and mats were more comfortable than standing on a hard wood block floor.

• However, no difference found between insoles and floormats

• Too much cushioning needs to be avoided

• Floors need to be clean and non slippery

Standing work – shoes

Recommendations:

• Do not wear shoes that change the shape of the feet

• Shoes need to mold to the feet and cause minimum pressure

• Due to feet swelling half-size larger shoes should be used

• Shoes that allow movement or the toes should be used

• Shoes need to have arch support

• Firm grip on the heel is necessary to prevent the foot to slip

• Flat shoes or shoes with a high heel should be avoided

• Heels should be wide base between 2 and 2.5 cm high

Standing work – workplace considerations

• The worker should have the opportunity to change between positions – this involves more muscles and provides a better distribution of loads

• Working tables and benches need to be adjustable

• If the worksurface cannot be adjusted than platforms for shorter workers or pedestals on top of the surface for tall workers need to be implemented

• Organization of the workplace needs to minimise the need for bending or twisting and there should be enough room to move

• Where possible a seat should be provided for the workers to sit occasionally

Standing work – workplace considerations

• Different tasks require different work surface heights

• Precision work – cca 5 cm above elbow height

• Light work – cca 5-10 cm below elbow height

• Heavy work – 20-40 cm below elbow height

Workers should avoid:

• Reaching behind shoulder line

• Overreaching

• Reaching above the shoulder line

Standing work – rest

• Breaks are important to reduce the incidence of MSD

• Rate of recovery is not constant, in standing it is exponential

• Short breaks with shorter work periods have been found more beneficial as more recovery was accomplished

• Leg swelling recovery is a longer process where breaks of 15 minutes were found necessary – sitting does not help

• In order to reduce MSD:

• Cumulative load needs to be reduced

• Variation in body positioning is necessary

• Provide sufficient recovery time

Standing vs Sitting work

• Static work positions, sitting or standing are not recommended

• Workers need to be provided with a station and a job task that allows the employee to change posture and switch between standing, sitting and walking

Sitting and Standing workplaces – evaluation

1) Loadings: • Interverterbral disk pressure • EMG • Gravital load • Intraabdominal pressure • Blood pressure and flow

2) Posture: • Spinal curvature • Range of motion

3) Comfort: • Ratings of discomfort, exerction • Pain and disorders • Pleasure • Preferences

Performance: • Work speed • Errors

Implementation of Ergonomic Solutions • Example: weighing ingridients in the food industry

• 67% of the total working time is done in an unfavorable position

• Solution: rasing of the electronic scale

• Total costs: 145 Euros

Implementation of Ergonomic Solutions

• Example: Transfering load in a packing facility

• 3451 N of force at the L5/S1, exceeding the maximum

• Solution: raising the palets or a mechanical vacuum transfer system

• Price: 450 Euros or 6000 Euros

Implementation of Ergonomic Solutions

• Example: Strawberry farm problem

• 3,5 acers greenhouse

• Strawberries are grown on raised platforms

• Current solution: stilts

Implementation of Ergonomic Solutions

• Example: Strawberry farm problem

• Stilts are problematic:

• Move the center of gravity for more than 30 cm

• Contribute to lower back stifness and pain

• Present a serious hazard

Solution?

• Nursing staff has one of the highest rates of reported back pain

• In the USA 52% of nurses complain of chronic back pain

• 12% are changing their profession due to pain

• 38% had time off for therapy due to back pain

• One of the major issues: transferring patients

Special workplaces: Nursing

Occupational Risks in Nursing

Loading forces up to 4800 N

98% of all transfers still done manually

Leads to high absenteeism, low productivity and low patient satisfaction due to inconsistency of health care workers involved

MANUAL TRANSFER TECHNIQUES

INEFFECTIVE, HIGHLY STRESSFUL,

UNSAFE AND UNCOMFORTABLE

Ergonomic Aids

Effective and accessible

High cost

Education & Job Design

Refusal to use mechanic aids:

Common problems identified by the researchers were lack of proper training in mechanical aid use, mechanical aids and slings being unavailable or inaccessible, arbitrary use of mechanical aids and spatial constraints to mechanical aid use.

Student nurses were frequently unable to use recommended techniques in practice. The most frequent explanation given was the influence of other nurses. Results that male students and younger students were more susceptible to socialization into poor ward practice than others.

© Štefanac S, Grabovac I, Karabatid S: “Unified Patient Transfer Algorithm”

Contact:

Dr. Igor Grabovac

Department of Social and Preventive Medicine

Center for Public Health

Medical University of Vienna

igor.grabovac@meduniwien.ac.at

References

Canadian Centre for Occupational Health and Safety. Working in a Standing Position – Basic Information: https://www.ccohs.ca/oshanswers/ergonomics/standing/standing_basic.html

Canadian Centre for Occupational Health and Safety. Working in a Sitting Position – Overview: http://www.ccohs.ca/oshanswers/ergonomics/sitting/sitting_overview.html

Salvendy, G. Handbook of Human Factors and Ergonomics. Wiely:UK,2012

Kumar, S. Biomechanics in Ergonomics. Taylor and Francis: UK, 1999.

Grabovac I, Stefanac S, Mustajbegovic J. Unified Algorythm for Safe Patient Transfers: An Ergonomic Solution. Nursing Journal. 2017;22:37-43.

Ebben J. M. Improved Ergonomics for Standing Work. Occup Health Saf. 2003;72(4):72-6.