In the Professional and home world, we spend most of our time sitting. Yet the seated position is not suitable for human morphology at all. The first reason is that it imposes on us the maintenance of small muscular contractions over long periods, the second because it deformed the natural curvature of our spine.
In the sitting position, the curvatures of the spine are not respected. The comparison below highlights the fact that, the tilting basin backwards, the pressures between each vertebra are unevenly distributed on the discs, where, in standing position, we have a uniform distribution. In the long term, this finding leads to the deterioration of intervertebral discs, lumbago, sciatica or herniated disk.
The head and the screen
The neck should stand upright, in the extension of the spine, and the head, slightly inclined forward. For the wearers of glasses with focus, this posture is possible provided you position the screen a little lower.
The distance between the eyes and the screen depends on our view and our age, as well as the resolution of it. It is recommended to have a minimum distance of 60 cm and a maximum of 90cm. It is advisable to put it at a distance of arm.
The top of the computer screen must be at the same level as the horizontal line that passes through our eyes when standing upright. It is always possible to adjust the height of the screen, putting it on dictionaries if necessary.
The screen should be tilted slightly backwards to put in our look to be well perpendicular to the screen. The eye must be up to 20 ° downward without tilting the neck.
Regarding the brightness, it is necessary to avoid glare, differences of brightness and contrast between the environment and the screen, the sources of direct lighting. In addition, Piece lighting is recommended between 300 and 500 lux, which is less for a Position requiring document or other reading. It is also recommended to pose about every hour to avoid visual fatigue and head words.
The back and the Chair
It is essential to have a fully adjustable chair (height and inclination) to adapt it to the need and its morphology. There must also be a lumbar support adjustable in height and depth, with elbow supports and 5 rollers adapted to the surface of the floor.
- Adjust the height so that the thighs are horizontal when the feet are flat.
- Check that there are about 5 cm between the front of the seat and the back of the calves
- The seat inclination must be zero or very slightly forward (approx. 5 °).
- The height of the backrest and its inclination are determined according to the curvature of the backrest: the Shape must mould the curvature of the back at the lumbar level to serve as support to the shoulder blades.
- The depth adjustment at the lumbar level should ensure that the torso is slightly backward. An angle of about 110 ° is recommended between the legs and the back.
The arms are held in a comfortable position where the forearms are almost horizontal (90 to 135 °), in the axis of the shoulders or inward. The shoulders are released.
If the chair has armrests, they are adjusted as follows: ARM at 90 ° and elbow in support, the shoulders must be slightly loosened.
The legs are placed in an angle greater than 90 degrees, allowing the feet to rest flat on the floor.
Arm and hand with mouse and computer keyboard
Prolonged use of the mouse or keyboard in bad conditions can cause pain to the fingers, wrists, arms and shoulders. Some important features are to be taken into account for choice and position:
- Size of the mouse: it must be adjusted by hand.
- Buttons: The pressure to click the buttons should not tire the fingers.
- The mouse or keyboard must be in the extension of the forearm in a straight line.
- Handle the mouse with the wrist at the height of it and not in support of the work surface.
- For the keyboard, the principle is the same, the wrist must be at the height of the keys and not below.
- Ideally, the mouse should be in front of us and not on the side. So it’s best to choose keyboards with digital pavers that come off so you can better center the mouse.
- It is generally recommended to use the keyboard more than the mouse. So it is necessary to properly retain the keyboard shortcuts many features to avoid using the mouse.
The best keyboard is the ergonomically molded keyboard with an integrated control in the center this one. It will allow not to use a mouse (very restrictive), to eliminate the deflection of the wrist and to reduce the pronation of the forearms.
If we can not do without mice, the best system is the touchpad, which allows to have a use of the same type as the pen.
Worksafe (2010) – Ergonomics Guide: work at the Office
S. Montreuil (2012) – Office work with visualization screen
J. Nolen (1989) – Computer Automated process planning for World Class Manufacturing