RULA, or Rapid Upper Limb Assessment, is a method first proposed by researchers McAtamney and Corlett in a paper they published in the journal Applied Ergonomics (1993). It immediately gained a following because ergonomics practitioners were looking (and continue to do so today) for a method that is fast, observational, meaning you or I could perform the assessment in real time without instrumentation, valid and reliable. With the benefit of hindsight, RULA has lived up to some of these expectations, but not all. It remains a valuable assessment tool, but only when applied in specific ways, and only when applied and interpreted by a trained professional. Like most ergonomics analysis techniques, RULA’s results are not absolute.
Once an assessor has been trained to use RULA, it can be applied fairly quickly, and it can also be applied in real time while observing a person performing the subject task(s). With experience, some ergonomists can estimate a RULA score without even putting finger to keyboard, or pen to paper. Instead, it’s the validity and reliability that sometimes concerns me.
First, let’s review how RULA works, which will then lead me to add a caveat about how fast we can apply it. RULA actually considers the entire body, not just the upper limbs, as the name implies. The figure below is a screenshot of a paper form Ergoweb developed for training and field application purposes. Notice that the left side of the sheet captures upper limb scoring; the right side captures scoring for the rest of the body, and the tables are then referenced to arrive at a final score.
Trained ergonomists know that there are several key risk factors that must be considered when assessing risk for a given task, including:
- repetition (or frequency)
- Duration (of the event(s), and of the work day)
As you review the scoring form you’ll notice that most of the questions deal exclusively with posture. Step 6 captures only a small bit of information pertaining to “Muscle Use” in the arm and wrist, which is actually a question pertaining to repetition and duration (Step 13 asks the same questions, but for the rest of the body). With only two choices, the analyst must either select “static” (which implies long duration) or “repetitive”. Step 7 and Step 14 ask us to rate the Force/Load for the Arm and Wrist, giving us only some very basic categories to choose from.
So, RULA has a strong focus on posture, but a weak focus on force, repetition and duration. The Ergonomics Report™ subscribers may recall a recent study we reviewed that highlighted the importance of Duty Cycle, which is essentially the portion of a task that’s spent in exertion, a measure of duration of exertion. The researcher found DC to be so important in predicting upper extremity risk that he was able to derive an equation using only DC to predict acceptable levels of force exertion for repetitive tasks. Therefore, it’s significant that RULA does not adequately consider duration, let alone its weak recognition of force and repetition.
This isn’t necessarily bad, but it does suggest that RULA is probably best applied to jobs and tasks that do not involve a great deal of force or repetition. Jobs that are characterized by static postures, for example, are good candidates for RULA. Since office work involves long term static postures, but low forces and repetition (except for keying and mousing activities, of course), such seated office work is a good candidate for RULA. However, somewhere along the timeline between 1993 and today, practitioners have “tweaked” RULA to add questions that deal with common office activities. For example, one version adds the following question to Step 1:
+ 1 point = Work with raised shoulders OR speak on the phone on average at least 10 minutes per hour AND sometimes “scrunch” neck when speaking on the phone. (Maximum of 1 point for any of these conditions)
You can find reference to this, for example, at Humanics Ergonomics, where you’ll also see this statement:
Unlike the original, this modified version has not been validated.
Interested readers will find that other versions of RULA have surfaced over the years, though it’s likely none have been validated in the scientific literature.
There are other RULA characteristics that can lead to misapplication and misinterpretation of the tool, including:
- RULA is applied to a single snapshot in time;
- for asymmetric postures, RULA must be applied to each side of the body separately (i.e., 2 analysis must be performed for a single posture)
Imagine a job, like most real jobs do, that involves dynamic postures. Technically, if we’re really interested in the overall posture risk for the job, we would need to apply RULA to each and every posture, then somehow weight the scores by the amount of time — duration — the person spends in each. If we did this, RULA would no longer be the fast and efficient tool I suggested above. Instead, many job evaluators simply watch a job and identify the most extreme posture, or postures, and then apply RULA only to those points in time. The obvious concern with this approach is that an evaluator can simply pick one extreme posture — even if that posture is held for only an instant — and produce an analysis that suggests the job is very high risk and requires immediate change. In other words, based on the analyst’s decision as to which posture or postures to analyze, the same job could be characterized as a high risk or a low risk. In the hands of a trained professional, this is not necessarily bad, because he or she can consider the results and weigh them against experience and combine them with the results of other tools in their analysis toolbox to arrive at an informed opinion. In the wrong hands, however, RULA can be horribly misapplied, and horribly misinterpreted.
In summary, RULA remains a useful tool in the occupational ergonomist’s toolbox, but only with proper training in its application and interpretation. It’s best applied to jobs characterized by static postures with lower concern for force and repetition factors. Jobs that involve multiple postures will require additional analysis time and effort if a complete risk analysis is desired. In such cases, the results of RULA are best considered along with the results of other evaluation tools (e.g., Strain Index, Kodak/Rogers Muscle Fatigue Analysis) and tempered with professional experience and knowledge. It’s easy to overestimate the risk of a job with RULA if the analyst focuses only on extreme posture(s), especially if those extremes have short durations. In other cases, such as jobs involving forces, repetition and durations, RULA may underestimate risk. Careful consideration must be applied in the use and interpretation of RULA.
RULA Help Section, Ergoweb Enterprise Help Document, Ergoweb Inc.
This article originally appeared in The Ergonomics Report™ on 2012-01-25.