Bottoms Up!

May 22, 2002

COLLEGE STATION -- An assistant professor in the Ergonomics Center of the Texas Engineering Experiment Station (TEES), Gordon Vos studied pressures on the posterior while people sit in chairs. Vos' 2001 doctoral analysis of buttock/thigh pressure and a dozen top ergonomic chairs also looked at the importance of armrests and posture. "Chair construction was the most significant factor in lowering peak pressure. Armrests and posture didn't make much difference when compared to the chair design," said Vos, who noted nearly 75 percent of all work in industrial countries is done while seated. Vos also found that men experience more pressure on their bottoms when sitting in chairs than females. He added that while more research was needed to determine why, he thought it was probably due to weight. Contoured chair pans with 3-D knitted fabric were found to be the best for reducing peak pressures on test subjects. Vos said he suspects the knitted fabric allows the seat's foam padding to cushion better. The contour likely distributes weight more evenly. The research also found the memory foam chairs didn't perform any better than regular foam in chairs. Memory foam is a pressure and temperature sensitive material that's supposed to automatically adjust to a person's unique dimensions. Vos came up with the idea of doing research on sitting in chairs while working on his master's degree at Texas A&M University. He was writing a paper while seated in an old wooden school chair. "I remember thinking 'this has got to be one of the most uncomfortable chairs I've ever sat in,'" Vos said. For his study, he took 12 top office chairs, 12 men and 12 women and set up nearly 300 different configurations with them. Vos also built a synthetic model to test on the chairs. The contoured seat pan finding suggests more research is needed on the depth, width and curve of seat pans, Vos said. Not surprisingly, some of the most expensive chairs were found to be the best in reducing pressure in the end. However, the top-selling chair did not have the best performance, meaning it likely sells because of aesthetic and advertising appeal rather than ergonomic design, Vos said. Vos added that other chair construction factors contribute to the overall ergonomic quality of a chair. The ability for height and back adjustments are critical while armrests and backrests serve other ergonomic goals, he noted. Noting that not everyone can afford a premier chair, Vos had some bottom-line advice for chair shoppers. "The big three items in any chair are height adjustment, lumbar support and adjustable back rest," Vos said. "Plus, find one that fits your size and look for a contoured seat. If it has 3-D knitted fabric, it'll be advertised." The Ergonomics Center is funded in part by the National Science Foundation. TEES is the engineering research agency of Texas and member of the Texas A&M University System.

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