Muscles increase in strength and quickness and endurance by quick changes between work and rest. One should therefore be capable of completely relaxing or slackening the muscles, either all at once, when the body rests, or during a particular movement; slacken all those that are not in use while the movement is in progress.
Sit on a chair, letting the left arm hang quite limp by the side. Then feel its muscles with the fingers of the right hand, and convince yourself that they are quite soft. Now take hold of the left wrist and lift the left arm up to shoulder height. Be careful, that you really lift the whole weight of the left arm with the right, as the left arm must not help itself to be raised, and must of course not resist. Suddenly release your grip, and let the arm fall. It should then dangle to and fro before coming to rest in vertical position. Repeat same exercise with relaxed right arm. In a like manner then lift a leg with both and let it drop; or lie down on the floor and ask a friend to lift and release the legs, one after the other. The neck can be relaxed in the same manner., although it is harder to relax, but be careful that the head drops on to a soft cushion. The abdominal muscles are best relaxed in a sitting position, leaning well back, or when lying in bed. The best time for carrying out these exercises is, then, just before going to sleep.
Convince yourself that the whole body and every limb rests on its particular part of the bed with whole of its weight; in other words, try to make yourself as heavy as you can. Then you will be more sure to get healthy and refreshing sleep.