Researchers Mohsen Makhsous, Fang Lin, David Hanawalt, Shannon Lynn Kruger, and Angie LaMantia conducted a study that compared five different office chair designs. Specifically, they looked at pressure distributions between the body and chair, and tissue perfusion in the buttock-thigh area.
In the following review, text between quotation marks, (example: "text") is quoted directly from the Makhsous et al article, referenced below, and text that appears in italics preceded by my initials (example: PB: text) are questions or thoughts that came to my mind as I read the article.
The researchers begin their article by summarizing low back pain (LBP) statistics, referencing numerous other researcher articles:
They postulate that chair design and its influence on sitting posture may play "an active role in causing and relieving LBP associated with sitting." This theory is intuitively appealing, and reflects the anecdotal experience of many ergonomists, but how strong is the scientific evidence to support it (PB: Recall Marras' recent review of our understanding of LBP and low back disorders; The Complex Spine: Understanding and Preventing Low Back Pain and Disorders)? Makhsous et al point to previous studies that touched on the question:
Makhsous et al recognize that the weight of the head, arms and trunk are carried primarily by the ischia (PB: the so called 'sitting bones') and surrounding tissues during sitting (PB: especially in the absence of arm rests and back rests/supports). They go on to suggest that:
PB: This is an ongoing challenge in chair research; what quantitative biomechanical or physiological measures do we have that correlate well with comfort, let alone pain, discomfort or injury, specifically in the lower back region?
As a physiological measure, Makhsous et al use tissue perfusion (PB: capillary level blood flow), which they state "has a significant effect on the occupant’s sitting comfort." Specifically, they measured transcutaneous partial pressures of oxygen (tcPO2) and carbon dioxide (tcPCO2) from the posterior buttock-thigh area with sensors attached directly to the skin, citing research by another researcher that "reported that transcutaneous oximetry is a useful tool in assessing tissue comfort in a study on mobile and immobile participants."
Posture Instructions; participants were:
Pressure distributions and tissue perfusion variables were measured using equipment detailed in the article, as are detailed testing protocols and data analysis methods, and interested readers are encouraged to read more in the original source. A few key portions of the protocol are worth mentioning here:
The remainder of this articles are comments from the reviewer, Peter Budnick:
I found it challenging to sift through the results section and piece together a coherent description of their findings. Makhsous et al present their data in summary bar graphs and paragraph form, but do not provide a summary in table form, which would have made it much easier to understand, compare chairs, and appreciate their findings. The bar graphs do provide a visual understanding and comparison for the pressure distributions, but the tissue perfusion data was not summarized in a useful comparison format. So, I turned to their discussion to see if they might pull things together there, and rather than bringing clarity, it left me with even more questions.
Regular readers of The Ergonomics Report know we do a lot of research reviews, which means we often pour through pages and pages of sometimes boring and sometimes confusingly written text to pull applicable meaning from the articles. If you read a lot of research articles, you begin to understand that what is not said, or the peculiar way in which something is said, is where the "meat" of the findings and conclusions sometimes lives. This article kept making me ask more questions than it was answering, and one of those questions had to do with "bicompliant," the descriptor for one of the chairs tested. So, I turned to Google, which quickly turned up some interesting additional information that left me asking even more questions.
Here's what I found:
A search for "bicomplaint", which is not recognized by spell checkers, turned up links to the very article I was reviewing, followed by a series of links to a specific chair from a specific manufacturer that used the term "bi-compliant" to describe a portion of their chair design. One of those links included a summary of research, dated 2008, by the same first two authors for the article being summarized herein. That research, being described by a representative of the manufacturer, contained a great deal of interpretation, something that seemed to be missing in the paper I was reviewing. I could not be certain whether the data and study she referred to in the 2008 source was the same as that being described in the 2012 article I was reviewing, or whether this was a new study, presenting new data and findings. Further, what conclusions can really be drawn from this research?
Rather than speculate, I am going to reach out to the researchers and the manufacturer to see if they would be willing to comment and help us understand. I'll write a follow-up that I hope will shed additional light on this research and its applications.
Mohsen Makhsous, Fang Lin, David Hanawalt, Shannon Lynn Kruger and Angie LaMantia, (2012), The Effect of Chair Designs on Sitting Pressure Distribution and Tissue Perfusion, Human Factors, published "online first," 27 August, 2012, DOI: 10.1177/0018720812457681. At the time of this writing, it was available to Human Factors subscribers at: http://hfs.sagepub.com/content/early/2012/08/24/0018720812457681
This article originally appeared in The Ergonomics Report™ on 2012-09-18.