Pushing, pulling and lifting are the three important activities in which the body forces are applied. All five principles of body mechanics have to be taken into consideration while performing these activities.
To push near the top of the back of a heavy chair to move it is more effective for tipping it over than for moving it along the floor. If the force of the push is to be effective it must be applied at the level of the center of gravity of the object and in the direction the object is to move. To do this one should crouch before the effort and then apply the force for the push while coming out of the crouch. This will insure that the major part of the force will come from the large and strong muscles of the thighs and legs as they come out of the large crouch. This will relieve and protect from injury of the smaller and weaker muscles of the back.
The person exerts the required force with the least possible muscular effort. Forces exerted by the hands and forearm originates from a right-angled bend at the elbow. Force exerted downward from the elbow joint rather than upwards or sidewise. For moving heavy weights, force exerted at or near the center of gravity of the weight. For lifting heavy weights, force is exerted as near as possible to the center of gravity of the worker’s body. Force exerted from a stable position of the worker’s body. Force for moving heavy objects exerted by the large, strong muscles of the legs and thighs when straightening out from a crouch rather than by the muscles of a straightened arm or the small muscles of the back.
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