What is an Ergonomics Risk Factor?

Specific causes of Cumulative Trauma Disorders (CTDs) in the workplace are often difficult to identify because many ergonomics risk factors may interact simultaneously to bring about or aggravate the condition.  It also may be difficult to isolate occupational factors from non-occupational factors or leisure activities and individual susceptibility (possible hereditary traits).  However, let’s start by defining what an ergonomics risk factor is. An ergonomics risk factor is any attribute, experience or exposure that increases the probability of the occurrence of a disease or disorder, although it is not necessarily a causal factor.  Ergonomic risk factors can cause, aggravate or precipitate Cumulative Trauma Disorders.  However, it is important to note that the mere presence of an ergonomic risk factor does not necessarily mean that the employee performing the job is at an excessive risk of injury. 

Dose-Response Relationship

The dose-response relationship refers to the specific outcome following an exposure to a specific agent or ergonomic risk factor.  The outcome resulting from the exposure to ergonomic risk factors refers to any adverse health effect, and may range from acute injury to long-term disease and loss of function.  In general, a higher frequency and longer duration of exposure to single agent or ergonomic risk factor, is found to be positively correlated with the development of a particular outcome.   This relationship is true also with ergonomic risk factors.  Hence, prolonged or repeated exposure to an ergonomic risk factor increases the likelihood of developing a musculoskeletal injury or Cumulative Trauma Disorder. 

An exact dose-response relationship of ergonomic risk factors has not yet been established.  However, the more ergonomic risk factors that are present, the higher the level of risk is for developing consequent injury.  In fact, according to the National Safety Council, it is possible that the interaction between various ergonomic risk factors has a multiplicative effect instead of an additive.  The multiplicative effect, in effect significantly increases the likelihood of disease development with multiple ergonomic risk factor interaction.  Having more than one ergonomic risk factor present significantly increases the probability of incurring micro-trauma.  On the other hand, if the identified risk level is low or there appears a sufficient provision of rest or recovery time, the actual risk may be minimal.  Most importantly, reducing the amount of ergonomic risk factors present will reduce the occurrence of Cumulative Trauma Disorders. 

Computer-Related Ergonomic Risks

The recent literature identifies the following Occupational and Non-occupational Ergonomic Risk Factors as potential risk factors leading to work related injuries or Cumulative Trauma Disorder for computer users.  The most important contributing factor to the development of Cumulative Trauma Disorders is the production of local tissue fatigue and micro trauma, as the working tissues are overloaded.  Sufficient blood supply is the most important factor in controlling tissue overload and fatigue.  By maintaining an adequate supply of oxygen-enriched blood to working tissues, metabolic efficiency can be maintained, thus minimizing the adverse effects of fatigue and preventing excessive micro-trauma.  The key to maintaining adequate blood flow to active tissues is in the balance of the relationship between work and human physiology.  These ergonomic risk factors increase the likelihood of developing fatigue and micro trauma because they may impair blood flow to the working tissues. 

Computer-Related Ergonomics Risk Factors

These computer-related ergonomic risk factors increase the likelihood of developing fatigue and micro trauma because they may impair blood flow to the working tissues due to the use of computers.  Computer-related ergonomic risk factors include: high task repetition, static work, posture and mechanical pressure. The following section describes each computer-related ergonomic risk factor and provides various methods for controlling or reducing the level of risk. As the level of risk for each ergonomic risk factor is reduced, the likelihood of injury development is also reduced. 

High Task Repetition

Most computer-related work tasks involve repetition of some degree.  A task cycle is the length of time that is takes to complete one job cycle.  High task repetition is an ergonomic risk factor for the development of Cumulative Trauma Disorders.  A job task is classified as highly repetitive if the cycle time is equal to, or less than 30 seconds, or if more than 50% of the time involves performing the same type of fundamental cycle.   With high task repetition, as with computer use and typing and mousing, the more rapid and frequent the muscle contractions need to be.  The consequence of rapid and repeated muscle fiber activity and recruitment is less metabolic efficiency, as anaerobic metabolism becomes the primary energy source.  Secondly, at lower metabolic efficiency levels, a higher degree of muscle effort is required, thus requiring greater time for physiologic recovery.  If a work task is highly repetitious and recovery time is insufficient, soft tissue injuries may occur. 

High repetition of any tasks can actually magnify the effects of all the other risk factors; therefore control methods are very important.

Methods to control for fatigue with highly repetitive tasks include:

·         Task Rotation.  Task rotation can be a way of reducing the overall exposure to an ergonomic risk factor. Task rotation simply means alternating tasks in order to reduce the duration spent performing a single task, this will reduce the repetition of the task.

·         Adjusting computer set up in accordance with desktop office ergonomic guidelines and laptop ergonomics & recommended guidelines.  This way, even though tasks may be repetitive, the body is in the correct posture and will absorb less strain due to the optimal positioning of joints and muscles. 

·         Implementing rest or stretch breaks. Rests or stretch breaks will provide an opportunity for tissue recovery, and improve circulation to prevent tissue fatigue and micro-trauma. 

Static Work or Static Muscle Contractions

Static muscle contractions are ergonomic risk factors that can lead to local muscle fatigue within minutes and hours, even with short-duration and low-intensity tasks.  Static muscle contractions mean the muscle is contracting constantly, the same muscles are being used without rest. We see this often in computer work with typing and computer mouse activities.  The blood flow to working muscles can be reduced, therefore the rate of muscle fatigue increases, this is the first step in the development of pain, swelling, injury and cumulative trauma. Static muscle contraction endurance time is affected based on the intensity of the muscle contraction, or the higher the percentage of muscle Maximum Voluntary Contraction (MVC).  When the endurance time required for the static work is long, or the %MVC required is high, the risk for developing micro-trauma increases.  The muscle-skeletal tissues over exert to accomplish the work. 

Static muscle contractions are very common and prevalent with computer-work, computer users are typically in the same posture, using the same muscles for hours at a time.  Static muscle contractions are a very important ergonomic risk factor for computer users and must be addressed.

Methods to control fatigue and tissue micro-trauma from static muscle contractions include:

• Limit static muscle contractions based on effort level.  Limit high effort static contractions to less than 10 seconds, limit moderate effort level contractions to less than 60 seconds, and limit light effort static contractions to less than 4 minutes. 
• Provide Postural Variability and Support.  Position variability and support provides an opportunity to frequently alternate postures and reduces the amount of work the muscles do, especially when they are called upon to hol dstatic contractions.  Utilize foot rests for foot, leg and lower back support, ergonomic- adjustable keyboard trays for adjustability and flexibility to promote optimal positions and document holders that encourage proper spine posture and document positioning. Computer mouse should fit the hand, use left hand computer mouse for left handed user, right handed computer mouse for right handed user, fit computer mouse to hand, use small computer mouse for small hand and large computer mouse for large hand.(See hand/ computer mouse sizing chart) The Roller Mouse station is a tremendous product and offers the #1 best solution for computer mouse alternatives.
• Utilize computer accessories that maintain neutral joint postures.  Neutral joint positions are optimal. They allow maximum blood flow and produce minimal strain, computer accessories should provide optimal joint positioning, such as the Evoluent Vertical Computer Mouse.

Poor Posture / Awkward Positions

Posture refers to the position of a specific body part or joint relative to an adjacent body segment, determined by the joint connecting the two segments. Awkward postures, or poor posture, often caused by poor ergonomic set-up of a desktop or laptop computer can overload muscles and tendons.  In addition, awkward positions load joints in an asymmetric manner, thus increasing joint compressive forces and impose a static load on the active working muscles.  Postural ergonomic risk factors are positions that cause excessive strain on the joints and should be avoided, or minimized for prolonged and repeated exertions, these are positions of the body that are out of neutral joint position. The simplest way to describe neutral joint positions is the position when there is least amount of stress on a joint and its surrounding muscles and ligaments. It is usually the straightest position of a joint. 

Methods for Reducing Poor Postures

Poor postures should be avoided, especially when they are repeated or maintained for long duration without recovery time as with computer-related work.  Ways to reduce fatigue and tissue micro-trauma from awkward or poor computer-related postures include:

• Provide postural variability.  Position variability provides an opportunity to frequently alternate postures.  Utilize foot rests for foot, leg and lower back support, ergonomic- adjustable keyboard trays for adjustability and flexibility to promote optimal positions and document holders that encourage proper spine posture and document positioning. Computer mouse should fit the hand, use left hand computer mouse for left handed user, right handed computer mouse for right handed user, fit computer mouse to hand, use small computer mouse for small hand and large computer mouse for large hand.(See hand/ computer mouse sizing chart) The Roller Mouse station is a tremendous product and offers the #1 best solution for computer mouse alternatives.
• Utilize computer accessories that maintain neutral joint postures.  Neutral joint positions are optimal. They allow maximum blood flow and produce minimal strain, computer accessories should provide optimal joint positioning, such as the Evoluent Vertical Computer Mouse.

Contact Stress

Frequent or continuous leaning on work surfaces with hard or sharp edges such as desk tops can cause direct compression against peripheral nerves and blood vessels, thus impeding blood flow and nerve conduction, this is called contract stress. (see article on Carpal Tunnel Syndrome and anatomy of wrist).  

 Methods for Reducing Contact Stress

Methods to reduce pressure on the wrist and avoid contact stress include: 

• Utilize gel padded wrist rests for typing , mouse and keyboard activities.  This gel material absorbs the pressure, this will eliminate mechanical pressure to the hands and wrist. 
• Utilize computer accessories that promote optimal positioning and design principles.  These desktop ergonomic set-up and posture tips and latptop ergonomics computer set up guidelines help to ensure that you are positioned properly thus eliminating the poor postures that often lead to pressure on the hand and wrist.
• Utilize computer accessories and laptop accessories that provide support and adjustability.

 Summary

This article defined what an ergonomics risk factor is and how various ergonomic risk factors found in computer or office settings can increase the likelihood of developing a Cumulative Trauma Disorder.  An ergonomic risk factor is a work-related attribute, experience or exposure that increases the probability of the occurrence of a disease or disorder, although it is not necessarily a causal factor.  In general, the greater the exposure is to a single ergonomic risk factor or a combination of ergonomic risk factors, the greater the risk of developing a Cumulative Trauma Disorder.  In addition, the more ergonomic risk factors that are present, the higher level of risk of developing consequent injury.  Therefore it is imperative to identify and evaluate the risk factors that are present, then determine or assess the actual level of risk.  To prevent Cumulative Trauma Disorders we must modify both ends of the spectrum: reduce the rate and intensity of damage and increase the rate of tissue repair.  This can be accomplished with ergonomic risk factor control methods which, with computer use, focus on the proper ergonomic set up, proper fit, the addition of computer accessories and most importantly, posture adjustability.