Hand held tools

Selection the model of the tool should be suitable to the task and also the posture adopted during the work, as the correct handing handling will achieve the task with minimum stresses. The shape of the hand gripes must have a diameter of approximately 3 cm and a length of approximately 10 cm

10 CM 3 CM

The hand must be somewhat convex to increase the contact surface with the hand. Gloves are not recommended. Bending the wrist in flexion direction should be prevented by correct locating the handgrips on a tool or using curved tools. Hand held tools must not be heavy, if the tool cannot rest on a surface and is normally used with one hand, its weight should not exceed 2 kg.

CORRECTINCORRECT

CORRECTINCORRECT

If the tool is heavy and rested on a surface and need to be lifted, it can be suspended on a counterweight and the subject should avoid lifting this heavy weight Motorized hand held tools can reduce the body stresses, noise and vibration.

The position of the hands and the elbow should be well below the shoulder level during carrying out the task. When the subject needs to work in a level above the shoulder level, the duration of the work must be limited and regular breaks must be taken Also working with the hands behind the body should be avoided

CORRECTINCORRECT

Posture at workplace Sitting down is better for any subject to perform a fine manipulative task. It describe as natural human posture. It has also many advantages 1- the overall static muscular workload required to lock the joints of foots,knees, hips and spine is reduced. 2- energy consumption is greatly reduced during sitting

3- sitting is better than standing in circulation. 4- it is more stabile posture which might help to carry out tasks requiring fine or precise motion. The sitting drawbacks 1- restriction of subject mobility 2- it is to difficult to perform a job which requires the hands or arms to operate with large forces 3- assuming sitting for long period of time will lead to many health problems. Like postures, LBP,……

N.B The standing is anatomical position, The keys to good posture are proper body mechanics, exercises, self awareness, and proper design of tools and working equipments The spine anatomy and its normal curves. This natural shape is the one which produce both optimum pressure distributions over the cervical discs and the optimum level of static load on the intervertebral muscles.

Good posture is achieved by 1- Proper body mechanics : by assuming proper postural alignment and keeping the natural curvature of the spine. Mechanically there is always balance between internal muscular forces and external gravitational pull.

This balance is achieved in proper postural alignment and produced optimum pressure distribution over the spinal structures and intervertebral discs. It also produce optimum level of static load on the muscles

2- proper work place design : work place design includes the machine, tools and environment. if the subject sits on a chair with 90 degrees backrest inclination, the trunk will move anterior, the subject will lean the trunk forward and that increase the thoracic kyphosis and cause flattening of the lumbar curve

In addition to this distortion to normal curvature of the spine, the muscular load will increase as follow : The line of gravity will shift slightly anterior to the lumbar spine and the moment arm of the force exerted by the weight of the trunk will increase so the torque on the lumbar increases and also the torque required by the back muscles increases. The load on the intervertebral disc increases to 140%-200%