viernes, 19 de septiembre de 2014

CDC - NIOSH Science Blog – Accurate and Efficient Assessments of Working Posture

CDC - NIOSH Science Blog – Accurate and Efficient Assessments of Working Posture

Accurate and Efficient Assessments of Working Posture

Categories: Ergonomics
Musculoskeletal disorders (MSDs) account for roughly one-third of workplace illness and injuries in the United States. According to Liberty Mutual Insurance Company, overexertion injuries, which include those from work-related lifting, pushing, pulling, holding, carrying, or throwing, cost U.S. businesses $14.2 billion in direct costs in 2013. To address the burden of preventable musculoskeletal and overexertion injuries, practitioners in the fields of Occupational Safety, Industrial Hygiene and Ergonomics need workplace assessment methods that are both accurate (valid) and time efficient. This need was highlighted in a 2008 NIOSH exposure assessment workshop in which a health/safety/ergonomics practitioner said:
“I’m a consultant, and ….we have to do 450 (facilities) in four years. So speed is essential, and we are using the risk assessment checklist, semi-quantitative measures to estimate risk.”
This practitioner was indicating two important points. First, because he was responsible for conducting a large number of worksite ergonomic assessments, an efficient risk-assessment method was important. Second, like other OS&H practitioners conducting risk assessments, he relies on semi-quantitative observation-based methods to evaluate risk factors, such as postural stress. Even though technology for assessing body kinematics (motion) continues to advance, use of observation-based approaches is commonplace among practitioners conducting workplace assessments of risk factors for musculoskeletal and overexertion injury. While often relied upon, these methods are not standardized, nor were they systematically developed.
These points were part of the motivation for the recent publication Observation-Based Posture Assessment: Review of Current Practice and Recommendations for Improvement; developed by NIOSH and colleagues at the University of Windsor affiliated with the Canadian Centre of Research Expertise for the Prevention of Musculoskeletal Disorders, CRE-MSD. This new document, intended to assist practitioners, is based on a number of recent studies that systematically determined an optimal observational framework for classifying postural stresses in the workplace, among multiple levels of severity. This optimal framework considers the accuracy (validity) of the posture assessment: that is, how many errors are made, and the size of the errors, in visually estimating posture. The optimal framework also considers efficiency: that is, how fast the observer can visually estimate and classify posture among multiple levels. The document distills several scientific publications into a more accessible format for the practitioner.
This blog is an opportunity to re-emphasize the most important information in the document– the recommended framework for optimally classifying working posture of the trunk, shoulder, and elbow depicted in the figure below. The recommended optimal framework is to classify trunk flexion (forward bend) in four categories, trunk lateral (side) bend in three categories, shoulder flexion in five categories, shoulder abduction in five categories, and elbow flexion in four categories, as shown below:
posture 1
One safety resource blogger commented on the new Observation-Based Posture Assessment stating that “This guide from NIOSH looks to be a bit higher level, yet looks suspiciously like the Rapid Upper Body Assessment (RULA) tool.”   The NIOSH/CRE-MSD guide actually looked at RULA and seven other common job analysis methods and the accompanying number of posture levels. For most postures the number of posture levels is equal to, or within one unit of, the optimal number of categories recommended:
number of posture levels (average of 8 previous studies)optimal number of posture levels – DHHS (NIOSH) Pub 2014-131
trunk flexion44
trunk lateral bend23
shoulder flexion/extension45
shoulder abduction/adduction35
elbow flexion34
It turns out that common traditional approaches, on average, have been close to what recent evidence shows to be optimal. In fact, the optimal method presented in Observation-Based Posture Assessment agrees perfectly with RULA1 for shoulder flexion posture (both use five levels), but less so for shoulder abduction/adduction posture (two versus five levels).
We hope that this document helps practitioners decide on the most accurate and efficient posture assessment method for their needs.

Brian D. Lowe, Ph.D.
Research Industrial Engineer, NIOSH, Division of Applied Research and Technology

(Note: The blog author wishes to express gratitude and acknowledgement to Drs. Patricia Weir and David Andrews, University of Windsor, Windsor, Ontario, collaborators in the development of the above-mentioned document.)

1McAtamney L, Corlett EN [1993]. RULA: a survey method for the investigation of work-related upper limb disorders. Appl Ergon 24(2):91–99.

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