First and foremost a chair must be comfortable and conform to the use for which it is intended. A working chair is going to be different than a read-the- paper or watch-the-news chair. It must allow some extended sitting: for a three-hour dinner, say, or a long night of cards, or for Handel's Messiah.

The ergonomic chair must encourage good posture. It must be flexible where you want it and give support where you need it.

A "good sit" requires good lumbar support and good proportions. It also respects the bones of your bottom and provides the correct angle of repose. I pay close attention to each of these four elements.

The most critical aspect in good chair design is ergonomic lumbar support. To attain this, I create an intentional tension with the sitting body. In the same way that a spring counterbalances a dropped weight, the chair backs that I make counter the forces they receive from the sitter.

I am not a back specialist myself, but I'm a good listener. My design approach takes into account thousands of conversations, comments and fittings with clients over many years. As a result, I've adapted and modified details of my chairs to make them more body-friendly. One upshot of this work is the contoured floating lumbar support - the "Floating Back" - that I first started developing in 1974 and have been improving and refining ever since. The Floating Back features taut yet contoured and bendable slats which deliver flexible pressure on a person's lower back while maintaining the spine's proper lumbar curve.

When it comes to the proportions of the chair, the two most critical elements are height from floor to seat and depth of the seat. Both can dramatically change an important feature of comfort: how the sitter's weight is distributed across the chair. Optimal distribution is usually attained when the seat depth supports almost the full length of the thigh - without being so deep that it cuts into the back of the knees - and when the height allows the sitter to plant his or her feet firmly on the floor.

The other dimensions I adjust are the width of the chair and the shape and height of the armrests (which can be a focus for some people); height of the arm; shape of the arm; and its relationship to the hand and fingers.

The position of the neck can be one of the most important features for people with neck problems. Here I find that wood is not the best solution. I work with an upholsterer to make adjustable neck rests of varying sizes and densities that can help many people find the comfort that can be so elusive.

When I'm custom sizing a chair to a specific client, I generally work in half-inch increments, as I've found that most people can feel and respond to this size change.

The angle of repose of a chair should match a person's preference - that magic tilt of comfort. Some like it further back, some like it more upright. By adjusting what I call the mouth of the chair - the angle between the seat and the back - I can tailor the chair's tilt to suit your needs.

We sit on our ischia, the bones that form the base of each half of the pelvis. Usually we don't notice how unyielding the rounded bases of these bones are until we sit on a hard flat surface for a while. To relieve this uncomfortable pressure, I gently sculpt each chair seat - the model here is the molded metal seat on old John Deere tractors.

Wood lends itself perfectly to this scooped seat design. Not only can it be carved with precision, but its texture and grain radiate warmth and aesthetic beauty. When people sit in these wood-seat chairs, I hear them express over and over again, "I love this wood, I feel good sitting in it."

For those who desire additional padding between their bones and the wood, I make chairs with upholstered seats. The base of the seat is a piece of Baltic birch plywood into which I cut a hole where the ischia will rest. Over the cutout I weave a support of Italian upholstery webbing. On top of that I place the seat pad, which I make by shaping latex rubber foam covered with a Dacron wrap. This process creates a substrate for the top layer: leather or fabric upholstery. In some of my chair designs, I've added a gentle S-curve to this upholstered platform which tucks the sitter into the chair back.

On the simplest level, a chair is just a place to sit. But it also can be a wonderful respite from a hard day's work, a ceremonial addition to a room and, if very successful, a piece of sculpture. I aspire to creating all of these in making the Ergonomic Chair.

"The inherent flexibility and customized contours of the Erickson design reduce static loading on the back by providing dynamic, active support. This allows the muscles of the back to relax while maintaining an upright, healthy sitting posture, thereby increasing blood flow and reducing fatigue." - Matt Zabel, industrial designer and ergonomist with Brooks Stevens, St. Paul, MN

"Erickson (makes) transcendentally comfortable rocking chairs." -Woodwork Magazine

"Perhaps the highest nexus of art and ergonomics is the Erickson chair." - The Atlantic Monthly

Erickson's chairs are in the permanent collections of the Smithsonian Museum of American Art, the Los Angeles County Museum, the Yale Art Gallery and Minnesota Museum of Art.