Relaxation generally stands for a release of tension with a return to equilibrium, the practice of relaxing the muscles of the body will bring rest to the body and to the mind also, relaxation is naturally done by all during sleep.
People who know the science of relaxation do not waste any energy.
There are various exercises in relaxation for the particular muscles of a particular part of the body: you can relax the head, the shoulders, the arms, forearms, wrist, etc.
The practice of yoga involve a thorough relaxation, the various relaxation exercises lead to a state in which there is a mental picture of calmness and strength. Relaxation reduce levels of pain, anxiety, stress or anger, so relaxation techniques are often employed in stress management programs and can decrease muscle tension, lower the blood pressure and slow heart and breath rates, among other health benefits.