The chair is one of the most important parts of the workstation; therefore, a properly designed and properly adjusted chair, along with appropriate posture, is important to help reduce or prevent back stress, restricted circulation, irritation and fatigue, and other distractions caused by the discomfort of an inappropriate posture. Remember, you may not always realize that your discomfort could be a result of inappropriate posture, and may constantly try to adjust their seating position to remain comfortable.

Your chair should promote proper working posture and avoid pressure on sensitive parts of the body. You should have the chair adjusted to where:

• Your feet are flat on the floor, with knees at an angle of 90 degrees or slightly more. If the chair is too high, pressure under the thighs reduces circulation to the lower legs. Sitting in a chair that is too low can result in lower back pain.

• The chair’s backrest supports the natural inward curve of the lumbar area, or lower spine. The backrest should either be small enough to fit into the small of the back, clearing the pelvis and back of the rib cage (thoracic region), or curved to provide adequate support. Inadequate lumbar support places excess pressure on the spine.

• The backrest angle is set so that your hip-torso angle is 90 degrees or slightly greater. Leaning forward too much compresses the internal organs and disks of the back. Many people prefer to lean back slightly while working at a computer. Don’t lean back too far, though, or you’ll have to extend your arms too much to reach the keyboard and flex your neck forward to see the monitor.

• If your chair has a backrest that moves back and forth with you, adjust the backrest tension to give adequate support for your weight.

• Back of the knees are 2-3 inches forward of the chairs front edge. This eliminates any pressure in the popliteal area (back of the knee) which contains blood vessels and nerves. Excessive pressure in this area should be avoided. Some backrests adjust to effectively shorten the seat pan. If enough popliteal clearance does not exist and the chair does not adjust, then another chair with a shorter seat pan should be acquired.

• Where armrests are used, elbows and lower arms should rest lightly so as not to cause circulatory or nerve problems. Shoulders need to be relaxed, not hunched up. Arms should be close to the body and not required to make frequent, far reaches, or be held away from the body. This can occur if the chair has armrests that do not allow the worker to sit in close to the table. Armrests can also get in the way if they are too high for the user. Where problems occur, lower or remove the armrests, or obtain a different chair.

• Change your position occasionally during the day by raising or lowering your chair a little, adjusting the back angle slightly or "unlocking" the backrest, if possible, to let it move with you.

Note: The seat and backrest should support a comfortable posture that permits frequent variations in the sitting position through slight body shifts and/or chair adjustments.