What is “repetitive”?

We are often asked to define the term “repetitive”.

When it comes to an injured worker, the definition should come from the employee’s health care provider.   Each worker’s injury is unique, and one health care provider might have a unique idea of what “repetitive” means for his/her patient. (No matter what you’ve heard, there is no gold standard.) If the health care provider is reading our physical demands descriptions (PDD), then s/he can see how we’ve defined “repetitive”. We have published default thresholds, which are aimed at ensuring that injuries are not aggravated. (Of course, a health care provider can and should specify a higher or lower threshold, if that’s appropriate for the patient!)

For instance, in a PDD we might say that a job that requires reaching the arms so that the shoulders are flexed as shown in the graphic above, more than 2 times per minute, requires “repetitive” shoulder movement. Someone with a restriction against “repetitive shoulder movement” probably shouldn’t do this job without accommodations.

Would this frequency of shoulder movement cause an injury? That really depends on how long the worker has to hold that posture each time, and whether there is weight in the hands. For example, if the worker has to hold 5 kg in this posture, for 10 seconds , twice every minute, then we would be concerned about safety for most workers. However, this same posture, with no weight in the hands, could be done by most healthy workers, 3 times per minute, for 1 second at a time, safely, according to a detailed ergo analysis (U of Michigan’s 3D Static Strength Prediction Program, and Potvin’s 2012 duty cycle equation).

Over the years, we have come to learn that, in general, “repetition” on its own is not as hazardous as we once thought. The focus in MSD prevention needs to be on forceful exertions in awkward postures, and on the overall exposure (combining the length of time that a postures is held, AND repetition).

If you are using information contained in a PDD (or physical demands analyses) to interpret the risk of injury, please consider this! Just because a job is “repetitive” does not automatically make it “high risk”.

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