What Does "Repetitive" Mean?
Posted on Mon, Jul 19, 2010 @ 09:00 AM
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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