Principles of Ergonomics

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Ergonomics is a wide ranging field that seeks to design tools, equipments and tasks to optimize human capabilities. The term ergonomics was coined from Greek word 'ergon' (meaning "work") and 'nomous' (meaning "rule"), so the literal meaning is "the rule of work" which is a handy concept to think about and then apply. 

Rehabilitation practitioners (Occupational Therapist and Physiotherapist) have a distinct value in the area of ergonomics based on understanding the complex and dynamic interactions of the person, the task (i.e., job), and the context and environment (e.g., culture and personality, and where the task occurs). The skills and knowledge of rehabilitation practitioners in anatomy, physiology, and activity analysis make them highly qualified to work in the area of ergonomics, often within an interdisciplinary team. Rehabilitation practitioners are well equipped to facilitate the successful return of patient to optimal function through education and intervention of person, and adaptation or modification of physical environment like home, workplace or public areas.

In last blog we learned about Introduction to Ergonomics and it's benefits to common man and specially abled (disabled) people. Click on the link to know more : https://otpthealthcarerehab.blogspot.com/2020/10/introduction-to-ergonomics.html

Principles of Ergonomics :

Principles of ergonomics : Simple things and techniques to keep in mind while performing any activity in order to keep your body joints in correct and well aligned posture. This will prevent you from muscular strain and soft tissue injuries.

To find right ways or methods to work is an ergonomic practice. Before performing any task you should have an "Ergo Eyes" or wear your "Ergonomic Glasses". While designing any activity or workplace, following Ergonomics principles should be kept in mind :

1) Work in neutral posture : this provides minimal stress on the body and keeps the joints aligned i.e. awkward posture of body or joint is prevented while working. 

• Minimize the stress on muscles, tendon, ligaments and nerve. It allows for maximal control and force production during activity performance.
• Opposite to neutral is 'awkward' posture : in this posture the body or joint moves away or deviates from normal alignment i.e towards extremes of range of motion. This puts more stress on musculoskeletal aspects of body and therefore should be avoided.
• For example : 
• Pistol grip vs. inclined grip drivers to maintain neutral wrist position.
• Whether sitting or standing, it is important to maintain the natural S-curve of the back.
• Keep the neck aligned: Adjusting the heights of  chair or tilting the equipment or the worksurface often helps.
• While working on computer, the mouse should be handled by maintaining the wrist is neutral position (forearm pronated) with no ulnar or radially deviated wrist.

Fig : Body and joint postures to maintain them in neutral alignment

2) Reduce excessive force : It is one of the most primary risk factor. Muscle efforts increases in response to high force demands which increases energy expenditure, fatigue and also increase risk of musculoskeletal injury. Applying excessive force to perform a task can slow down the effort and interfere with the ability to perform the task well.

• Idea is to recognize 'which' job or task and 'when' a particular job or task requires excessive force and then find ways to reduce the force.
• Applied force can be reduced by using mechanical assists, counter balance systems, adjustable height lift tables or workstations, powered equipment and ergonomic tools, which will reduce work efforts and muscle exertion.
• For example : 
• Place heavy objects on a trolley or wheeled table to push or pulls for transporting them from one place to other. Use good carts — Heavily loaded carts often require high force to be moved. Improvements include increasing wheel size, adding handles and providing better flooring. 
• Use power tools, machines and cylinders — Perhaps the most obvious way to reduce force is to completely mechanize the activity. Air and hydraulic cylinders are particularly useful when moderate force is needed.
• Use appropriate grip size — The optimal size for a power grip is roughly that which permits the thumb and the forefinger to overlap or touch slightly. If the grip is significantly larger or smaller, then more force is needed to accomplish the same work.
• If heavy weighted objects are to lifted manually then avoid lifting in singly or individually, instead take assistance or help from co-workers. This will divide the workload and decrease the energy expenditure and injury risk of a single person. You can also use 'Shoulder or forearm forklift lifting and moving strap' for heavy and large size items.

Fig : Methods to decrease excessive force production by using helping hands, use trolley, forklift lifting and moving straps.

3) Reduce excessive motion : Repetitive motion is another risk factor. Many work tasks and cycles are repetitive in nature, and are frequently controlled by hourly or daily production targets and work processes.

• High task demands + High force requirement + Awkward posture + High repetitive task/motion leads to musculoskeletal disorders. A job or task is highly repetitive if cycle time is 30 seconds or less.
• Minimizing the number of motions required to do a task can lessen the wear and tear on your body and also improve efficiency. 
• Avoid excessive or unnecessary motion by using control methods like job enlargement, breaking large task into subtasks, job rotations, counter active stretch breaks, use powered machines.
• Following methods can be adopted :
• Let the tool do the work — One of the best ways to reduce repetition is to allow machines and tools to do the work. Machines are good at performing repetitive tasks endlessly, so they should be exploited.
• Improve working techniques by educating the employee about the equipment, machinary, ergonomics, lifting techniques and work patterns and work design.
• Improve work design layouts: Workstation changes to improve the heights, reaches, locations and orientations of materials can eliminate many unnecessary hand and arm motions. 
• Even if a motion cannot be eliminated altogether, it might be reduced. It’s usually better to slide items, rather than pick them up one at a time and place them in their locations. Although motions are still required, the total number is usually reduced. 

4) Minimize Pressure points or contact stress : contact stress results from continuous contact or rubbing between hard or sharp object surface and sensitive soft body tissue life fingers, palm, thigh, feet.

• This contact creates a localised pressure over a small area of the body, which can inhibit blood supply or nerve function of muscle or tendons. 
• For example : 
• Resting wrist on the sharp edge of the desk or workstation while performing task.
• Pressing or digging of tool or bag handle into the palm, when holding it for longer duration and especially when the handle is narrow.
• When office workspace is not adequate for proper sitting posture. Contact stress from sitting on hard surfaces, which is the epitome of discomfort from pressure points, can be lessened with cushioning and contouring. Proper seat height greatly affects pressure points on the legs. If the seat is too high and the legs dangle, the pressure behind the knees can be excessive. If the seat is too low, the weight of the body concentrates on the buttocks, again creating discomfort.
• Wearing heels or shoes with tapering one end (in front), for longer duration, while working or walking can cause corns or bunion of toe.

Fig: Impinging or pressure point stress on the body tissue because of prolonged contact with hard surface edges.

5) Keep things in easy reach : Make your work more user friendly by keeping frequently and regularly used items or tools within easy reach.

• Long reaches often cause you to twist, bend and strain, making work  moredifficult. This principle goes along with that of keeping good posture. Try to keep the daily used objects within the mid ranges of your extremities and spine reach i.e. avoid keeping them at extremes end of joint or spine range of motion.
• Looking at whether a person is able to reach a object is not just enough.  
• Points to consider when reaching for an object :
• the size and weight of equipment or object to reach for, 
• the workstation surface and it's height,
• the body height and posture adopted for reaching.
• Thus evaluate for any awkward body posture plus dimensions of object before performing 'reaching' action.
• This can be done by adopting following ways : 
• keep frequently used materials within the reach envelope of the entire arms.
• Workstation design for the short person should be modified accordingly.

• Rearrange the items on workstation or table so that you could easily move items closer. 
• Reduce work surface size: All too often, the work surface is much bigger than needed. By cutting down its size (making cutouts), you can eliminate long reaches plus increase floor space.  Cutouts reduce reaches yet still allow large workspaces.
• Remove barriers : Many reaches are performed habitually (unknowingly) by crossing barriers that can be eliminated or relocated.
• Tilt — When working out of boxes, it’s possible to use tilt tables or stands or even to prop up the box on one end. Tilted box stands can easily be fitted with hinges, cylinders and rollers to enable easy transfer to carts and conveyors.

6) Work in the power/comfort zone : This can also be called as "hand-shake" zone because power zone for lifting is close to the body between mid thigh and mid chest height.

• This zone is where the arms and back can lift the most with least amount of efforts.
• It ensures that you are working from proper height and arm reaches, which decreases the risk factor of musculoskeletal disorders and allows for more efficient and pain free work. 

7) Work at proper height : A common workplace problem is a mismatch in heights between people and the work surface or workspace that they’re doing. 

• This mismatch leads to poor postures and related fatigue, discomfort and potential damage to soft tissue plus unnecessarily harder work and reduced ability to perform the task correctly.  Special consideration should be taken for above average or below average height workers.
• The work surface height should depend on the type of task i.e. assess whether the task is precision or fine work, light work or heavy work.  Accordingly with respect to the task, the worker should bring variation in height by adding steps/small height platform under the feet or by doing the work in sitting.

• Generally, work is best done at about elbow height, whether sitting or standing. This is true for keyboarding as well as for other kinds of work in manufacturing and assembly. Note that it is the work itself that should be at elbow height, not necessarily the work surface.
• Consider the exceptions — The nature of the work also affects the proper height. Heavier work type, requiring upper-body strength, should be lower than elbow height. Lighter work type, such as precision work and inspection tasks, should be at a higher level.
• Avoid extremes — When it isn’t possible to make every height ideal, it may be feasible to avoid the extremes ranges of body joints i.e avoid working below knee level or above shoulder level (overhead activities). Solution to this is : 
• For work situated at a higher level (above shoulder or head level) a raised platform or stable ladder can be arranged. 
• For work situated at a lower level (below knee level) the person can use a platform lift for increasing the height of that work such that adequate vision is available and awkward postures are avoided.

Fig : Avoid extreme end range postures; instead use steps or platforms to keep objects at a higher level

8) Provide clearance : The workstations should have adequate workspace and easy access to everything you need, with no barriers in the way. 

• Lack of clearance can create bumping hazards or force you to work in contorted postures. It also can increase long reaches, especially if there is inadequate space for the knees or feet. Insufficient knee space is a common problem in the industrial workplace, although every part of the body can be affected — the head, torso, feet and hands.
• Special consideration should be done for tall or above average height employees. To improve access reorganize equipments, shelf height, increase size of opening, adjustable chair height, extra workspace for lower-limb clearance and free movements in sittings position is required.
• Provide hand clearance — Equally important is having sufficient space for the hands in order to avoid “knuckle-buster” injuries and simply to get the job done effectively.

  

Fig : Limited workspace and body clearance causes awkward posture and longterm musculoskeletal pain.

9) Move, exercises, stretch and avoid static position : working for longer period of time in a static position will cause your body to fatigue. Overloading people’s physical and mental capabilities can contribute to accidents, poor quality, lost productivity and wear-and-tear-type injuries. 

• Holding the same static position for longer duration can cause fatigue. Continuous stationary position while working can increase static load or stress on the joints and muscles. Static load is especially stressful in combination with high force and awkward posture, but the primary concern is the amount of time that the muscles are contracted. Even if a muscle is only lightly tensed, over an extended time, pain and fatigue can result.
• Examples of static load includes: 

• Keeping your hands raised over your head for continue 30 minutes.
• Remain standing in the same position of next 5 to 7 hours.
• Writing with a pencil or pen for 60 minutes straight.
• Sitting at one place for continuous 3 to 5 hours and doing laptop work. 
• The first few seconds or minutes doesn't seem too bad, but the cumulative effect of holding these seemingly stress-free positions over time will cause fatigue and discomfort.
• You need to stretch : stretching improves muscular balance, posture, prevent joint stiffness and improves blood circulation through muscles and joints. It is beneficial to take periodic stretch breaks over the course of your work day to get your blood moving and restore your energy.
• To be healthy, you need to stretch each joint to the full range of motion periodically throughout the day. Your heartrate needs to rise for a period of time every day. Your muscles need to be loaded on occasion.
• Do follow this : Keep fit, do warm-ups, take energy breaks, change chair positions, do aerobic exercises, allow for alternate position, design for sit-stand arrangements in workplace.

Fig : Simple and easy 'break or rest time' stretches to be performed after sitting in same posture or manually working for prolong duration.

10) Maintain a comfortable environment : For efficient work performance and workers' comfort level, the environmental conditions of the workplace should also be favourable. Excessive heat and humidity slow us down; excessive cold hinders our ability to do effective work. Toxic chemicals can damage our health; vibration can injure sensitive tissue. 

• Environmental Conditions includes amount of light, temperature, vibration, noise level of the workplace.
• Light level : it is the common problem in the workplace. Too little or too much light makes work difficult. Dimly lit work areas can cause eye fatigue, headache and puts the person at a greater risk of injuries.
• Providing worker with an adjustable light source is a simple solution to lightening problem.
• At computer workstation, take steps to control screen glares: make sure that monitors are not placed in front of window or bright background, diffusers or shields to minimize glare, better placement of lights.
• Avoid temperature extremes : Use ventilation defusers or deflectors to keep cold air from blowing directly on people. Add heat shields around furnaces and other heat sources.
• Dampen vibration and shock — Working with tools andequipment that create shock or vibration can cause injury. Excessive vibrations can cause conditions like "Hand Arm Vibration syndrome (HAVS)", specific disease called "white finger" or "Raynaud's syndrome", carpel tunnel syndrome, tendinitis. Excessive and repetitive vibrations involving hand use can cause adverse circulatory and neural effects on fingers. Patient shows symptoms of numbness, pain, blanching (turning pale) in fingers. To decrease vibration grade:
• Use vibration-dampening materials in or on tools.
• Perform routine maintenance.
• Mount equipment on vibration-dampening pads.
• Use cushioned floormats for standing operations.
• Change equipment speeds and feeds.

Various musculoskeletal disorders which can occur because of wrong and awkward working postures, repetitive and excessive motion, poor work design. Each body parts has it potential musculoskeletal disorders (MSD) namely :

• Head and neck MSD : Thoracic Outlet syndrome, cervical spondylosis, tension neck syndrome, cervical disc disorder.
• Shoulder MSD: Rotator cuff tendinitis (impingement syndrome), bicipital tenosynovitis, Frozen shoulder or adhesive capsulitis.
• Elbow MSD: lateral and medial epicondylitis, radial tunnel syndrome, cubital tunnel syndrome.
• Wrist and hand MSD: tendinitis, carpel tunnel syndrome, ganglion cyst, trigger finger, De Quervain's tenosynovitis.
• Lower back MSD: degenerative disc disease (lumbar spondylosis), strain of spinal muscles, sprain of spinal ligaments and capsule, risk of prolapsed intervertebral disc.
• Leg MSD: Plantar fasciitis, tailor's bunion, tarsal tunnel syndrome, heel spurs, stiffness of knee joint.

For more information you can read our previous blogs : 

• Lockdown and low back pain (click on the below link) https://otpthealthcarerehab.blogspot.com/2020/06/lockdown-and-low-back-pain.html

• Office syndrome and it's interventions (click on the link below) https://otpthealthcarerehab.blogspot.com/2020/09/office-syndrome-and-its-intervention.html

• Introduction to Ergonomics (click on the link below) https://otpthealthcarerehab.blogspot.com/2020/10/introduction-to-ergonomics.html

Thankyou for reading !!!!

 Dr.Sheetal Tatar-Dhande, Dr.Ashwini Sangar,  Dr.Pallavi Khadse-Kolhe.