Chairs can be a crucial factor in preventing back pain as well as in improving employee performance in office work. As the majority of office workers spend most of their time sitting, a properly designed and adjustable chair for comfort, efficiency, and for the task being performed is critical. All adjustments should easily be made from the seated position. A good chair provides necessary support to the back, legs, buttocks, and arms, while reducing exposures to awkward postures, contact stress, and forceful exertions.
Importance of an ergonomic chair
When an employee spends six to eight hours in the chair, the height of the chair and the work surface are critical. The chair height is correct when the entire sole of the foot can rest on the floor or a footrest and the back of the knee is slightly higher than the seat of the chair. This allows the blood to circulate freely in the legs and feet.
Poor back support and inappropriate postures may result from inadequate backrest size, material, positioning, or use. Working in these postures may lead to back pain and fatigue. Backrests should support the entire back, including the lower region, and conform to the natural curvature of the spine.
Using a chair with a seat that is too high may force the user to work with the feet unsupported or encourage the user to move forward in the chair to a point where the back is unsupported making it more difficult to maintain the S-shape of the spine. These awkward postures can lead to fatigue, restricted circulation, swelling, numbness, and pain.
An inappropriately sized seat pan can be uncomfortable, provide inadequate support to the legs, and restrict movement. One that is too short can place excess pressure on the buttocks of taller users; one that is too long can place excess pressure on the knee area of shorter users and minimize back support. A seat pan that is too small can restrict movement and provide inadequate support. Prolonged use can restrict blood flow to the legs and create irritation and pain.
Armrests that are not adjustable, or those that have not been properly adjusted, may expose you to awkward postures or fail to provide adequate support.
Armrests that are too low may cause the user to lean over to the side to rest one forearm. This can result in uneven and awkward postures, fatiguing the neck, shoulders, and back.
Armrests that are too high may cause the user to maintain raised shoulders, which can result in muscle tension and fatigue in the neck and shoulders.
When the armrests are too wide the users is likely to reach with the elbow and bend forward for support. Reaching pulls the arm from the body and can result in muscle fatigue in the shoulders and neck.
Armrests that are too close to the body can restrict movement in and out of the chair.
Large or inappropriately placed armrests may interfere with the positioning of the chair. If the chair cannot be placed close enough to the keyboard, the user may need to reach and lean forward in the chair. This can fatigue and strain the lower back, arm, and shoulder.
Armrests that are made of hard materials or that have sharp corners can irritate the nerves and blood vessels located in the forearm. This irritation can create pain or tingling in the fingers, hand, and arm.
Armrests, if provided, should be soft and allow the user's shoulders to relax and elbows to stay close to the body. They should be adjusted so they just make contact with the lower arms when the lower arms are positioned comfortably at the users' sides.
Possible solutions for chairs
If the seat cannot be lowered (for example, it would make the keyboard or monitor too high), use a footrest to provide stable support for the feet.
Provide a chair with a seat pan that is adjustable and large enough to provide support in a variety of seated postures. It is recommended that the seat should be:
Height adjustable, especially when shared by a number of users. The chair height is appropriate when the entire sole of the foot can rest on the floor with the back of the knee slightly higher than the seat of the chair.
Padded and have a rounded, "waterfall" edge.
Wide enough to accommodate the majority of hip sizes. Chairs with oversize seat pans should be provided for larger users.