Body & mind age with time and so become tense & stressed. If we breathe deeply & slowly and watch breath with keen mental attention, we will get peace & rejuvenation. Also we should give auto-suggestion to all parts of body starting from tuft or crown & ending with toes and then in reverse way from toes to tuft.
There is a relation between breath & mental state and also between body & mind. Relaxed muscles will make mind peaceful.