Research: It’s Time to Update Chair Design Standards to Accomodate Overweight and Obese Populations

Texas A&M researchers Benden, Fink and Congleton conducted an in situ study of user habits that affect office chair design (in situ — meaning they tested participants in actual chair use in real office conditions). The motivation for their study was in part to understand whether chair design and testing protocols might need to be updated, given that many of the testing parameters were developed decades ago. In their introduction, they provide revealing statistics related to the weight distributions among the USA adult population, noting that the combined percentage of overweight and obese individuals, as measured by Body Mass Index (BMI), now exceeds 67%. BMI is calculated by dividing a person’s weight (in kilograms) by their height (in meters) squared (yielding kg/m²). The National Institutes of Health (NIH) provides the following definitions:

• Overweight: a BMI of 25 to 29.9 kg/m²
• Obese: a BMI of 30 or more kg/m²
• Severely Obese: a BMI of more than 35 kg/m²

The authors present a table showing that between 1960 and 2004, the weight of the average US adult male has increased by 14%, and increased by 17% for females. Further, during the same period, BMIs >40 have increased by 5.3%; BMIs >30 increased by 21.7%; and BMIs >25 increased by 0.7%.

The authors note that seating is really a modern convenience, and that some have suggested that the assumption that office work should be performed while seated may, at least in part, be at the root of the injury, illness and obesity trends.

The results of this study are intended to provide data that can be used to support two new industry design standards being contemplated by USA based Business and Institutional Furniture Manufacturers Association (BIFMA):

1. General Purpose – Heavy Duty Office Seating: GPHD x5.11-201X
2. Bariatric Seating Units: BAS8.1-201X

Current testing protocols are defined in ANSI/BIFMA X5.1-2002: Guidelines for Testing of Chairs. The tests, which specify the force magnitude, location, cycle duration and cycle times for dynamic chair testing, are based on expected forces for 8 hr shift, 40 hrs per week office work, for a usage period of 10 yrs.

In the study authors words:

It is our contention that many key points in the test parameters in Sections 5, 8 through 10, 13, 14, 17, and 20 were determined from best practices that predate the modern use of computers in office work and obese worker trends.

Methods

There is an extensive section describing the research methods and testing protocols, and interested readers are encouraged to read the original article, referenced below. The following brief overview is provided.

51 participants were randomly selected from a group of 200 office workers. Based on their BMIs, the participants were broken into two groups:

1. Group 1, 21 participants, represent the population within the parameters of the current testing standards; and
2. Group 2, consisting of 27 participants, represent the population outside the parameters of the current testing standards

The testing protocols included the use of pressure mapping equipment applied to the seat pan and backrest, roll-distance monitoring equipment applied the the casters.

The independent variables were the two different groups. The dependent variables included:

1. quantity of time per shift spent seated;
2. quantity of cycles with the backrest;
3. frequency of seat cycles per shift; and
4. average distance rolled per shift

Overview of Results and Discussion

The researchers found statistically significant differences between the groups for all four dependent variables. Specifically, they found:

• 54% more seat cycles per hour for Group 1 workers than for Group 2 workers;
• 62% more back cycles per hour for Group 2 workers than for Group 1 workers;
• 20% more seated time per shift for the Group 2 workers, who averaged 77% of the shift seated, compared with 64% of the shift seated for Group 1 workers;
• Extrapolated from the data set:
  • Group 2 seat cycles per decade would be 89,946; 
  • Group 1 seat cycles per decade would be 138,348 per decade;
  • (Compare these figures to the current standard 120,000 cycles)
• Neither gender nor age were not found to be a significant bias;
• The amount of time seated, by Job Type, was statistically significant, with managers spending less time seated than clerical and technical;
• Roll distance was significantly different between the two groups (mean for Group 1 = 800 cm/hr, Group 2 = 1,122 cm/hr); and
• The extrapolated average distance rolled per decade for the two groups combined was more than 25,400,000 cm, with one participant trending toward 38,000,000 cm per per decade (compare this to the current testing standard calling for only 15,240,00 cm per per decade).

The authors make these key recommendations for updating existing chair test standards and for any new standards being developed for the overweight and obese populations:

• Increase the number of testing cycles to 140,000 to cover typical habits of all current
  workers;
• Combine the roll and drop tests such that the drop tests are performed after each cycle;
• Revise caster roll test criteria by increasing the weight load and the roll distance:
  • Increase test load weight to at least the latest 95th-percentile male numbers from the more recent, large-scale studies, such
    as CEASAR (Robinette et al., 2002;
  • Roll distance should be at least three standard deviations
    from the group mean determined in this
    study;
  • If a seating test for obese users is developed, specify less roll distance than the Group 1 standard, but apply a heavier weight.

The authors make another interesting observation:

… management positions had less seated time than clerical and technical positions. This difference may not be significant to design, but it is significant in noting that the people most often called on to select and purchase seating for workers are also those who use their primary chair the least during a shift.

Study Limitations

The primary limitation in this study was the use of a single model of chair. While this was far more cost effective from a research standpoint, other chair styles and models could produce different results.

Reference

Benden, Mark E.; Fink, Rainer; Congleton, Jerome, Content loaded within last 14 days An In Situ Study of the Habits of Users That Affect Office Chair Design and Testing, Human Factors, Volume 53, Number 1, February 2011, pp. 38-49(12). Last accessed on April 7, 2011 from http://www.ingentaconnect.com/content/hfes/hf/2011/00000053/00000001/art00004

This article originally appeared in The Ergonomics Report™ on 2011-04-07.