It may sound hackneyed, but remember what your parents told you: Don't slouch. "If you're slouching, that puts stress on your lower back, you overuse those muscles and then you become fatigued and have soreness and discomfort," says Charles Kopin, ergonomic specialist for Industrial Health Care in Waterbury, Conn.

Your head should be directly over your shoulders, back should be straight and resting against the chair back (ideally with support in the lower curve of the back, or lumbar), knees should be slightly higher than the hips, and feet should be able to rest on the floor.

"That (posture) gives the spine a tremendous amount of strength," says Scott Bautch, chiropractor in Wausau, Wisc. "It keeps the pressure on the bony part of the spine, which is meant to carry weight, and keeps it off the disc," which can only take pressure for short intervals, he says.

Too much load on discs can cause the fluid inside them to seep out and become brittle, says Bautch, who is also president of the American Chiropractic Association's Council on Occupational Health. "It speeds up the degeneration of the back tremendously."

Since every body has different dimensions, the more adjustments that a chair can make, the better, particularly to height and placement of the lumbar curve, says Kopin. For those with short legs, footrests can also help.

Just as important as proper positioning, experts say, is getting up and walking every 20 to 30 minutes for about five minutes. Movement increases blood flow and oxygen to muscles that have been holding the body in one position and helps refresh them.