chair ergonomics

Ergonomic Considerations for Purchasing an Office Chair



A safe and supportive computer work station is essential for health and production. Occupational therapists use ergonomic assessment as an evaluation tool to recommend equipment design for both work and home. Studies done by the British Chiropractic Association found that 59 percent of the working population sits all day at work, and 56 percent of chiropractors view office workers as vulnerable to back pain. Therefore, proper chair design and adjustment may prevent or reduce health issues related to improper posture and position.


Ergonomics is the science of design, which is intended to maximize productivity in the workplace. Proper design reduces fatigue and discomfort. Since many jobs require long hours sitting in a chair, reducing physical discomfort logically increases efficiency. Along with occupational therapy, proper ergonomics decreases error rates and overuse injuries. The need for occupational therapists performing ergonomic assessments proves that one size does NOT fit all.


Since providing every employee a custom designed chair is not feasible, providing them with a fully adjustable chair covers a large range of people. According to the Canadian Centre for Occupational Health and Safety, proper chair seat height is 25 to 30 centimeters below the work surface. A seat that is too high forces a person to work with feet unsupported or the body too far forward on the chair. A low seat will put excess pressure on the buttocks of taller users. Feet should be flat on the floor and knees should form a 90 degree angle with the hips.
The size of the seat pan should be at least 43 centimeters wide, leaving 5 to 10 centimeters of space between the seat and the back of the chair. The seat pan should support the thighs, without permitting knee back to contact the front of the seat pan. If needed, a footrest raises knee height to relieve pressures on the back of the leg.


Back pain and fatigue occur when poor chair conditions allow inadequate back support and uncomfortable postures. A person’s chair needs fitted lumbar support, which means the backrest fits closely into the curve at the small of the lower back. Correct support will maintain the natural S curvature of the spine. Backrest height adjustments allow proper alignment of chair lumbar support with a person’s size. To enable the body trunk to stay within a recommended 30 degrees from upright, a reclining backrest tilt adjustment needs to be present. Also, moving the backrest forward and backward allows shorter or taller people proper adjustments for leg length on the seat pan.


Using armrests is optional, but if used should be adjustable with padding for comfort. Low armrests may cause a person to lean to one side for resting, distorting posture. High armrests cause raised shoulders, and muscle tension in neck and shoulders. Armrests too wide or too close cause additional fatigue. Also, if they interfere with desk to chair placement, the chair may be too far from the desk for correct posture. If armrests are not adjustable remove them. Otherwise, adjust them to support the lower arms with shoulders relaxed.


The base of a chair needs at least five strong legs. Otherwise, the chair has inadequate support and is prone to tipping. Casters must be appropriate for the type of flooring. A chair without casters or improper casters increases reaching and bending, which leads to muscle strain.

armrest, ergonomic, Occupational Therapist, Occupational therapy, office chair