7. Backrest angle adjustment
- Many chairs have backrests that are fixed and do not allow for the angle to be adjusted.
- When the back rest angle is not adjustable, employees may end up being forced to hunch over their desks when the angle is too far forward, or more commonly, have to slouch to allow their backs to rest on the back rest that is angled too far back.
- The backrest must be adjustable in angle (90-110˚ is the recommended angle).
8. Backrest angle adjustment with lock
- Sometimes chairs have backrests that “free float” and cannot be locked in place.
- When the back rest does not lock, employees may suffer back discomfort from being unable to rest their backs in an upright position. The back needs the option for stability and lumbar support for prolonged sitting.
- The backrest must lock in place.
3. Height adjustment range
- Many chairs do not lower enough to accommodate employees with shorter than average legs.
- When the chair’s seat pan does not lower enough, the employee cannot keep his/her knees at 90˚ of flexion with his/her feet flat on the floor. This is the optimal posture for the back and the legs. In this posture the back is the correct biomechanical position reducing back strain and the legs are relieved of the pressure that would be present should the feet not be supported on the floor.
- The seat pan should lower to 18” above the floor or lower.
4. Backrest height
- Some chairs have backrests with a small surface area.
- Too small of a backrest does not support the employee’s upper back. This can cause an increase in muscle tension, possibly resulting in overuse of the muscles and consequent upper back discomfort.
- The backrest should be at least 24” high.
To have an ergonomically-friendly office chair, there are many essential features that need to be present before the chair can be called “ergonomic”. After performing Ergonomic Evaluations for 17 years, I have learned a great deal about recommending ergonomic chairs. I have come across people of many shapes and sizes who don’t fit into just any office chair. Because of this, when I make my ergonomic report recommendations, I need to recommend a fully adjustable ergonomic office chair right off the bat. If I don’t the employee will be unhappy because they will continue to be in discomfort and their employer will be unhappy if the chair I recommend has to be returned. Therefore it’s best to get it right the first time!
The following posts will cover the 22 features I have found to be essential when recommending a chair and the reasons why.
1. Seat pan depth
- Many chairs have seat pans that are too long for employees with shorter than average legs. There is also the occasion of the employees with longer legs whose legs are not fully supported by their seat pan.
- When the seat pan depth is too deep, pressure is placed on the back of the employee’s knees causing discomfort. As a result, the employee sits forward in their chair in a “perched” position to avoid the pressure. This results in the employee not being able to use their back rest for support. If the back musculature does not have support, there will be continuous muscle tension resulting in overuse of the muscles which commonly causes back discomfort and possible injury. Additionally pressure points may also cause reduced blood flow and nerve conduction.
- The seat pan should be 19” or shorter in depth, and a seat pan slider should be present so the optimal depth can be achieved for any employee.
2. Seat pan width
- Many chairs have seat pans that are too small for larger size people and too big for smaller size people.
- When the seat pan width is too small, larger size people can’t fit comfortably into their chairs. When the seat pain width is too large, smaller size people find the contouring uncomfortable causing pressure points that reduce blood flow.
- The seat pan should come in several different sizes to accommodate all employees.
The wrists are another part of the body that easily adopt awkward postures throughout the day. Consider some occupations such as computer users, dentists and dental hygienists, surgeons, mechanics, farmers, and musicians – all of these workers assume awkward wrist postures through wrist flexion (hand flexes down), extension (hand extends upwards), ulnar deviation (hand moves sideways on thumb side) and radial deviation (hand moves sideways on pinky side). When you combine awkward posture with other ergonomic risk factors such as force, static posture, contact stress, and repetition; you may end up with some pretty sore wrists, hands, fingers, arms, and elbows (problems with the wrist can extend out to other parts of the arm). Here are some tips:
- Try to keep the wrists as straight as possible during the day – For computer users, this means raising or lowering the keyboard so your wrists don’t flex or extend. For other occupations, this means making sure your work level is neither too high or too low to promote wrist flexion or extension.
- Try not to deviate wrists (bend sideways) – For computer users, this means considering a split-angle keyboard to keep wrists in line. For other workers, it means adjusting posture or using different tools to avoid deviation, (e.g. knives with a 90 degree angle, pliers with bent handles)
- Take frequent breaks – Especially in the case of musicians who can not change their postures easily. 5 minute breaks every half-hour are recommended.
- Stretch and strengthen wrists – To lengthen tight muscles and tendons and to increase force output with less strain.
- Avoid contact stress – Don’t let your wrists rest on any sharp surfaces.
- Rotate tasks – Try to change tasks frequently to give your wrists a break. This allows the blood to flow freely through muscles and tissues, and with luck, repair any damage.