Matheson Philosophy on Workplace Safety and Work Injury Evaluation

What Does "Repetitive" Mean?

The term repetitive is often used in work restrictions. When most of us look at the term repetitive, we need to question what is the intended use of the word.

Repetitiveness means different things according to the context in which we must use it. In ergonomics, repetitiveness is defined as a frequency multiplier for physical demands. It is not something in itself although "common sense" (boy, do I hate that phrase) may tell us when something is repeated or repetitive. The NIOSH definition of "repetition" warns us as to using the term without careful understanding of the task.  

I have made quite a career in Quebec, Canada, defining repetitive in courts...(sigh...). Certain guidelines in ergonomics would have you think that the repetitiveness factor can be taken out of its context and considered by itself, but be careful and read the whole guideline.

Frequency is one of the multipliers of many physical demands, and so are two others: Duration and Intensity. Unless we understand these three concepts, we have no idea what we are talking about. This is why it is difficult to define repetitiveness by itself: it never occurs in a vacuum.

So, what is repetitive? Is it a cycle time of less than one minute with the use of the hand at least 50% of the time, like many of us have heard? Read that definition and get to the core of it: it was defined by a researcher to establish the criteria under which certain jobs were to be included in the study of repetitive motion disorder. It was never intended to "define" repetitiveness for itself. What if the hands are not the body parts to which the limitation applies? What if it's the back? Are we going to use that same definition? Of course, not.

The above video is posted to Matheson's Ergonomic Evaluation YouTube channel.

You probably see the term repetitive in a medical or therapists note recommending limitations for a particular client. If you remember that the intent of a functional restriction is to protect the patient from further injury, then the term repetitive means: "occurs too often to be deemed safe and acceptable to the patient" (from the Sonia Paquette's dictionary, not yet even in press).

In ergonomics, there are 2 different concepts for which there are words in French, but I have not seen their translation in English yet. The 1st term is what I can better translate into "objective strain". The French term is: "contrainte". This represents the actual physical movements in terms of frequency, intensity, and duration. Its joined-at-the-hip sister term is probably better translated into "subjective strain" but does not quite give it justice. The French term is "astreinte". What it means is that the same physical movements requirements will pose a different strain of a person who executes them depending on a variety of factors such as height, fitness level, experience etc. . It usually intuitively makes sense to people that two different persons will experience a different strain even when performing the same exact activity (e.g. playing hockey as it is played in the NHL is definitely easier for Sydney Crosby than it is for me). That is what is captured by the term "astreinte". When we are looking at a "normal" population, the two terms are (mistakenly, in my opinion) often used interchangeably. However, as soon as we enter the realm of disability and "abnormal" people, we should take the subjective strain very seriously.

To make matters worse, it is not possible, at this point in the science, to predict the capacity of a person to perform repetitively very specific tasks unless we experiment it with him/her. There is a possibility to draw hypothetical inferences from the data gathered in careful analysis of a person's use of their body in different tasks, which are further analyzed according to their physical demands and the three multipliers.

I agree that it would be nice to have a standard definition of repetitive. If it was simple...! But it's not and that's why we need to understand it to better explain it - as a thinking evaluator.

 

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How To Measure Ergonomic Risk Factors

Now that you know how to determine ergonomic risk factors, read this post to learn the methods recommended for measuring and quantifying these risk factors.

Risk Factor Properties

Magnitude

Magnitude quantifies the extent to which each physical stress is involved.

Measurements of force, posture, recovery, vibration and cold magnitude is reported in terms of the average, peak, or root means square levels for the duration of the specific exertion, motion, or posture.

Repetition

Repetition measure depends on the level.  At the most detailed level, each time a specific exertion is repeated, such as striking a nail with a hammer, one repetition about the elbow occurs. Likewise, striking a key on a keyboard would be considered one repetition. A higher order of quantification for repetition may be the frequency that a cycle for a task repeats.  In the case of the hammer, one repetition may be counted every time another nail is hammered. A less detailed study may quantify for many times a hammer is used in the course of a shift. Consequently, different studies quantifying repetition may not be measuring the same thing. This has made it difficult to compare different studies.  It is therefore important that repetition measurements specify the specific action and level of detail being measured (micro, element, cycle, task, etc.).

Duration

Duration is quantified as the time elapsed when a specific exertion is performed or a posture is assumed. At the most detailed level, duration is the movement time or exertion time for a specific muscle-tendon group or body region (e.g., right hand and wrist). Less detailed analyses use element times, cycle times, or task time as measures of duration.

Force

Forces may be either external or internal forces. An external force can be defined as a force applied, voluntarily or involuntarily, to the surface of the body.  In general, internal forces increase joint's torque, angular velocity or acceleration. Since internal forces are not conveniently measured, the term "force" shall refer to external forces unless specifically indicated.

 

The following methods are available for quantifying force:

• Rough approximations
• Simple mechanical scales
• Electronic load cells

 

 Simple mechanical devices such as a spring scale or dynamometer can be used to estimate lift/pull/push forces in many instances. (Note: Care must be taken to ensure the alignment of the scale or dynamometer with the actual axis of the exertion.)  Electronic versions of these devices can be connected to a recording device or computer to provide more accurate force-time data for dynamic tasks.

Direct force measurements are often difficult to obtain.  Forces can often be roughly calculated using the weight of the objects, estimates of the frictional forces, the power settings on tools, and simple physics equations.

Internal muscle forces are difficult to measure, but can be estimated with Electromyography (EMG) by trained personnel using specialized equipment. Under controlled conditions, internal muscle forces can be estimated by simulating the motions and exertions in a laboratory setting.  If internal forces are measured, sufficient replicate measurements should be made to account for variability within and between individuals performing the task.

Pressure and force can be measured using ink force sensors and strain gauges, but this is rarely done due to difficulties in using the equipment. The conditions that cause high contact stresses are well recognized and are usually eliminated without measuring the level of stress.

Element exertion and recovery periods should be measured for each relevant muscle- tendon group, body region or joint.

Posture and Motion

Posture angles are measured in terms of the number of degrees a specific joint deviates from neutral.

Body landmarks for measuring angles are described in the American Academy of Orthopedic Surgeons' "Joint Motion Methods of Measuring and Recording" (1963).

Angular velocity refers to the speed at which a limb's position relative to the adjacent limb changes about an axis of rotation. Angular acceleration refers to the rate at which velocity (speed) changes about an axis of rotation.

In work situations, posture can be measured in several ways. In many cases, postures can be adequately estimated by direct observation. Observations may be estimated with videotapes, which may be played in slow motion or stopped for better viewing.  Videotapes also can be used for identification of other stresses and to maintain a permanent record of the job for comparison with the job after interventions are implemented.

Manual goniometers can be used for quantitative measurement of static postures.  Electrogoniometer can be calibrated in some cases to track posture for static or dynamic exertions. The accuracy and precision of electrogoniometer must be determined for each application.  Their calibration should be checked each time they are used. When used with a computerized data acquisitions system, these systems can be used to track posture over a period of time.

Electromechanical goniometers, placed over a joint's axes of rotation, can be used to obtain the relative orientation (position) of the respective body segments. An electrogoniometer also can be used in conjunction with videotape to document work activities and corresponding postural angles; however, the accuracy and precision of the goniometer system must be certified. These measurements may be differentiated to obtain the angular velocity, or differentiated again to obtain the angular acceleration.

Videotaping or still photography can be used alone if the camera's line of sight is perpendicular to the planes of the measured body segment. In this case, measurements can be made directly form the videotape image. Postural angles may also be measured from a combination of video and live observations, using one to verify the other. The evaluation of awkward postures ordinarily does not require the fine detail that the foregoing techniques/instruments provide.

Vibration

Measurements of the maximum amount of vibration available to the hand (e.g.,  "hazard level") are performed using the "basicentric" system.  Hand-arm vibration measurements and analyses should be performed according to ANSI S3.34, ACGIH-TLV, and NIOSH 89-106 recommendations.  As far as we are concerned, any and all vibration is hazardous.

Cold

Ambient temperature should be measured by using a thermometer.  A calibrated thermistor or thermocouple can also be used to measure surface temperature readings (e.g., measuring cold exhaust of an air tool venting across the wrist).

Cold temperature magnitude is quantified in degrees Celsius. Exposure pattern is measured as the number of contacts with cold exposure pre minute, and exposure duration is quantified in minutes of exposure.

 

Work Organization/Psychosocial/Psychophysical

There is a large body of literature on methods of assessing work organizations and organizational stresses. There are several instruments available.

Qualities of a Good Checklist

A Checklist helps to identify ergonomic risks and to predict severity.

Purpose

• Standardize way of looking at/for risk factors
• Doesn't wait for employees to come forward
• Qualitatively characterizes levels of risk factors (severity)

Tailored to Risk factors and Worksite

• Assess magnitude, repetition, and duration of every identified risk factor
• Allows for the identification of jobs with multiple risk factors

Simple to Administer/Understand

• Standardized
• Reproducible
• Language -Culturally Appropriate

Doesn't Require Special Tools

Generally Low Administration Time

 

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What Kind of Tools Should You Use for an Ergonomic Evaluation?

One of the common questions we receive here at Matheson is, "What kind of tools and equipment will I need to do an ergonomic evaluation?"

We ended up creating a list to send to the those inquiring and we want to share it with you here.

So, without further ado, here is a rather comprehensive list of tools and/or equipment that one may use during an ergonomic assessment.

(Please note that not every tool gets used every time; it needs to make sense with the assessment you are performing.)

• Video camera with date and time
       2 blank tapes
       2 charged batteries
       Battery charger
• 35 mm still camera with at least ASA 400 color film
• Tripod for video and still cameras
• Graph paper
• Clipboard
• Calculator
• Tape measure (distances)
• Cloth tape measure (circumferences)
• Straight ruler
• Calipers (diameters)
• Job Evaluation Forms
• Force gauge dynamometer (Jamar)
• Pressure transducers (FSR)
• Weight scale
• Writing devices (pens, pencils, markers)
• Inclinometers (goniometers)
• Light meter
  
• Push-Pull gauge
  
• Vibration meter
• Torque wrenches
• Digital camera
• Tape recorder
• Personal protective equipment (PPE) (no jewelry)

If you have any other tools or pieces of equipment that you feel should be added to the list, by all means let us know! 

What tools do you usually use and what types of assessments do you typically perform??

 

 

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What Are Ergonomic Risk Factors?

 
Currently available data have identified that risk factors for Work-Related WrMSDs include exposure to physical stress in manual work. Physical stress arises from physical attributes of the work, workstation, tools, materials and equipment. Properties of physical stress are affected by job design and work organizational factors. The presence or absence of physical stresses and the level of their properties are assessed through job analyses.

Typically job analyses addresses the following physical stresses:

• Force
• Posture and motions
• Vibration
• Temperature

Job analysis quantifies the following properties of each physical stress factor:

• Magnitude
• Repetition or frequency
• Duration
• Recovery

Job analysis also considers job and work organization factors that can alter the characteristic properties of physical stress exposure.

A combination of risk factors rather than any single risk factor may be responsible for the occurrence of WrMSDs. Therefore, identifying all the risk factors that may be present in the job is important.

For an identification of the different types of ergonomic risk factors and workplace hazards download our Free 14-Page Whitepaper: Determining Ergonomic Risk Factors.

 

And don't forget to bookmark this blog and come back next week for the follow-up post: How to Measure Risk Factors 

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What is an Ergonomic Evaluation?

Ergonomic Evaluation is a work station or task evaluation designed to measure a job's potential for injury or fatigue. The evaluation is based on the applied science of ergonomics, which maximizes productivity by designing equipment and work flow to reduce operator fatigue and discomfort. Standardized risk assessment tools are used to quantify risk. The evaluation takes place in both industry and office settings.

Ergonomic EvaluationWherever strenuous or repetitive work is done, ergonomic evaluation provides strategies for risk remediation. Ergonomic evaluation of a job usually focuses on a handful of issues, including awkward postures, long duration repetitive movements and tasks requiring high levels of physical effort. This multidisciplinary field touches on occupational medicine and psychology, engineering design, industrial manufacturing and engineering management.

The Ergonomic Evaluation Certification Program

Effective injury prevention programs are based on employer/employee education and a sound ergonomic evaluation program. Successful programs work within the product goals of the facility while guarding the safety and well-being of the worker. Performing ergonomic evaluations requires

• thorough knowledge of a person's physical abilities and capacity to do work,
• the risk factors for disease development associated with poor ergonomic design,
• accepted evaluation protocols,
• and a sense of what is practical.

In 1993, The Matheson System recognized the need for an in-depth ergonomic evaluation training program that would appeal to those from the allied health and safety professions. This program for non-engineers would focus on evaluation techniques, rather than engineering-control issues, germane to office and industrial ergonomics. The Ergonomics Evaluation Certification Program is a result of this recognition. Under the direction of Dr. John LaCourse, CPE #82, the course has grown in influence and popularity since its inception.

Ergonomic Evaluation training >>

Ergonomic Evaluation certification >>

Ergonomic Evaluation software >>

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