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In Search of the Ultimate Seat
By: Jeff Wilcox

Seating solutions have evolved over the centuries, as our forefathers discovered they could increase seating comfort by contouring the wooden seat. This type of seat is now usually reserved for rockers and dining chairs. While they are more comfortable than a flat surface, they do little for long-term seating comfort.

Enhancing seating comfort from a flat surface to a contoured seating surface was one of the steady progressions that seating has made over the decades. The objective has been to improve the comfort through technology and available materials. The advancement in seating comfort came to the present solutions over numerous developments, some forced by mechanized products and the need for an increase in user stability. The current solutions in mechanized equipment basically date back to the early years of the 20th century. Henry Ford used spring suspension in the automotive seats for added user stability and comfort.

While development in seating has been prolific over the past several decades, the outcome of those developments has resulted in contoured seat pans with foam, contoured foam, or a flexible material covered support with foam configuration. Some manufacturers have incorporated the popular memory foam (visco-elastic polyurethane) to give the user increased seating comfort.

What seat designers and marketers have known is that the purchasing decisions are made based upon costs, the visual comfort read, and the initial sit, not necessarily long-term seating comfort.

Some of the latest developments in seating are mesh seats. While they afford the user air movement, they do not improve the important elements of seating comfort. These elements are proper ischial support, lumbar position, and pressure reduction on the gluteus maximus muscle tissue along with soft tissue. The advent of the memory foam, or visco-elastic polyurethane foam, helps reduce the pressure on the gluteus tissue.

There are important design considerations for properly designed seats. Not only should the seat be able to handle the force placed upon them, they should be ergonomically dynamic. No individual is just a weight; they are actively dynamic when sitting, so their seat should be actively dynamic.

Current Analogy to Seating Comfort
* 1905 - There are relatively few styles of seats in use to date starting with the two main types of seats: bench seats and bucket seats. A bucket seat is a separated seat for one person. Although we think of them as relatively new, it is interesting to note that Henry Ford's first model had bucket seats. From that time to the present, the challenge has been to increase comfort. This has been accomplished to date by innovations to the foam or improvements to the inner seat construction with the addition of springs.

* "Flat-springs" have been used for comfort since the early days of automotive seats. These pieces of wire bent into a zigzag pattern increased comfort. One drawback to this type of support was that it created a sling effect, which, over a very short time, becomes uncomfortable because this design does not properly support the ischia and pelvic region.

* Newer concepts use an elastomeric mesh (fabric mesh with elastic material woven into the fabric) used for support as a replacement to the flat springs.

* To assist with seating comfort, manufacturers have utilized various materials to improve the seating comfort. Foam has long been used for this purpose. Additional foam developments utilize the viso-elastic foam developed for NASA and later used for handicapped seats. This foam helps distribute the load.

The object for seat manufacturers has been to make the seat look and initially feel very comfortable (what could be referred to as "eye-appeal"). Our eyes perceive that the seat looks comfortable, so our mind goes along with that perception.

How many times have you looked at a chair or seat and it looked comfortable and when you sat in the seat initially it felt comfortable only to find out that, in a short period of time, the seat was uncomfortable?

Normal seat cushion construction utilizes foam over a substrate that is plywood, plastic or metal. All of these solutions rely on the foam to distribute the seating load.

Some seats, while appearing comfortable and initially sitting comfortable, sometimes demonstrate their ineffectiveness to provide proper long-term seating comfort in actual use. Improper cushion support will most likely result in back fatigue and soreness.

Redefining Seating Comfort
There are many important elements to seating comfort that go beyond the looks and beyond the initial sitting characteristics. The real issues with seating comfort are the reduction or elimination of pressure points created from normal sitting, proper ischia support and lumbar position.

Reduction of pressure points along with reduction of pelvic rotation improves long-term seating comfort while still utilizing current foam technology.

By supporting the gluteus properly, hydrostatic capillary pressure is reduced, which reduces the symptomatic sensory indications of pain and discomfort. Discomfort and fatigue are normally due to the lack of ergonomic seating dynamics.

The key to proper seating comfort is to make sure that the ischia are in proper alignment with the pelvis and the seating surface while counter-balancing the ischial tuberosities pressure. The more you can keep your hips and pelvis perpendicular to the seating surface, the less rotation of the lower spine, resulting in better lower back support. Contour and comfort are symbiotic and need to be an integral part of the seat construction; coupled with proper inner suspension (counter-balance), this will noticeably increase comfort.

When evaluating seats, any sit tests conducted should include a range of ages from young adults to seniors; the age ranges are very important. You are no doubt very aware of your members and their age ranges. It seems younger users have a greater tolerance for discomfort, while older users know very soon if something is comfortable or not.

Any comfort evaluation testing should include some long-term (more than a few seconds) sitting in the seat types with the application in a static position. Another evaluation should include actual use conditions for each seat being evaluated.

We know from experience that the cushion can look good (what we referred to earlier as "eye-appeal") and still not be comfortable. Airline seats are good examples of this situation. The seat can look very plush and comfortable. The initial sit impression seems comfortable; however, within a few minutes, you realize that the seat is not as comfortable as it looked.

The real key to seating comfort is proper weight distribution. The more uniformly your weight is distributed, the less blood flow impingement you have. This reduces or eliminates discomfort, giving the user greater comfort. Greater comfort translates to the ability to sit in one position longer without discomfort.

Jeff Wilcox is senior project engineer for JP Moll Company, www.jpmoll.com. He can be reached at wilcoxjsw1@comcast.net.









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