Posture

Posture
Prolonged work in the same position, whether seated or standing, can cause discomfort. Where possible, movement should be incorporated into the task to prevent discomfort and fatigue.

Standing
Here are some guidelines for optimum posture for standing jobs:

Avoid having operators stand still in one place for unduly long periods of time. The activity of the leg muscles acts as a pump and assists the veins in returning blood to the heart. Prolonged standing stops this pumping action and this causes swelling of the lower extremities.

Provide a rubber or padded mat where prolonged standing cannot be avoided. This should reduce fatigue and improve comfort.

Sitting
A well-designed chair for the operator is one of the most important parts of a work station. It can favorably affect posture, circulation, the amount of effort required to maintain a position, and the amount of pressure on the spine.

The following recommendations should be followed:

• The seat should adapt to the user, not vice versa.
• Chairs should be stable and fully and easily adjustable from the seated position.
• Seat pans and backrests should be upholstered and covered in a material which absorbs perspiration. A 20mm compression is about firm enough.
• Seat pan height should be adjustable and should transfer the user's weight through the buttocks, not the thighs.
• Backrests should adjust up/down and backward/forward or flex with body movement for good lumbar support. A forward tilt of the seat pan may relieve body stress in certain applications since it allows the backrest to follow the person when performing varied tasks.
• Where mobility is required, wheels or casters should be fitted to the chair (hard casters for soft floors and soft casters for hard floors). Special consideration should be given in certain cases, for example, where a slippery floor makes it difficult to keep the chair in the desired position. Where wheels or casters are fitted, chairs should preferably have five legs. This offers improved stability and reduces the risk of tipping over.
• The front of the seat should be of a "waterfall" design in order to provide sufficient clearance for the flesh of the thigh and to prevent reduction of blood circulation.
• For tasks requiring frequent lateral movements, seats should swivel.
• Holding the same seated position for long periods of time causes fatigue. The diagram on seat posture illustrates what has been normally accepted as the best posture for sitting for long periods. However, individual preferences must be permitted, and it is therefore important that chairs be well designed and adjustable.
• In order to achieve satisfactory posture it may be necessary to adjust the work station height. This is the reason that typewriters and computer terminals are often placed on a lower work surface at secretarial work stations.
• Footrests should be provided where chair or work station height adjustments cannot be made sufficiently to allow the relief of pressure under the thigh from the seat. These should be angled and covered with a non-slip surface to provide comfortable support for the feet.
• Headrests should be considered for operators where the head must be tilted forward or backward for prolonged periods. A common application is the use of optical viewing tools such as microscopes. The head is relatively heavy. If the head is not kept straight, the pull of gravity will cause stress and strain in the muscles of the neck.
• Handrests should be provided for intricate tasks such as fine assembly or inspection. With the weight of the arm supported, the hand is stabilized improving hand dexterity and comfort.
• Armrests should be provided when tasks require the arm to be held away from the body. The further the arm is held away from the body, the greater the fatigue and subsequent decrease in manual control. Armrests should be padded and covered with an absorbent non-slip material.
• Work stations should be designed to avoid unnatural postures. Operators should not have to lean forward or backward unnecessarily. The use of a device to incline the workpiece freely in any direction (a gimbal) can often help in complicated assembly jobs. Rotary platforms similar to lazy Susan may also be utilized to access the far side of a workpiece and thereby eliminate bending and extended reaching.
• Work stations should be designed in such a way that all objects and tools which require frequent access are located within acceptable reach distances. The design should account for individual variations (anthropometrics).

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