There are many opportunities for people's hands to engage in all kinds of labor, so the projection area of their hands in the corresponding representative parts of the motor area of the cerebral cortex is relatively large. According to the principle of neural functional structure, this is called growth-related law.

Scientists have proved that if the front part of the motor area of the cerebral cortex is injured, it will not cause paralysis and paralysis of the tested limb, but the movements of the contralateral hand are not so flexible and the coordination between the fingers is not so coordinated, which shows that a certain part of the motor area of the cerebral cortex is closely related to the hand.

The opportunities for elderly people to work by hand are relatively reduced, and their hand movements are gradually slow and inflexible. And fitness ball sports just meet the conditions of the elderly. In China, there has been a folk sport of fitness ball for a long time. The elderly keep rolling metal balls in the palm of their hands to stimulate the nerves of the palm and arouse the excitement of the sensory area of the cerebral cortex. Then the excitement is transmitted to the sports area. This rhythmic and moderate-intensity stimulation is very suitable for hand movements of the elderly.

Insisting on exercise can make hand movements sensitive, accurate and coordinated. In housework, there are also many jobs that can exercise the hands of the elderly, such as kneading flour and corn with both hands, which can make them flexible and agile.