Dhyāna means absorption. It is the art of self study, reflection, keen observation or the search for the infinite within. It is the observation of the physical process of the body, study of mental state and profound contemplation. It means looking inwards to one's innermost being, dynāna is the discover of the inner you. The practitioner becomes vibrant, alert and poised, his vision reflects his true self like a well polished mirror.
One of the most well known meditation tradition taught by the Buddha is "Ānāpānasati", meaning mindfulness of breathing. Ānāpānasati means to feel the sensations caused by the movements of the breath in the body, to simply watch the breath if the breath is long, to notice that the breath is long, if the breath is short, to notice that the breath is short.
Similarly, in the Ashtanga Yoga tradition one of the three focus point is the breath (ujjayi). To simply watch the breath going in and out the body, while performing the difference stages of yoga postures and their transitions. With time, the practitioner experiences a focused attention meditation in motion. It has been scientifically demonstrated that ujjayi and ānāpānasati slows down the natural aging process of the brain, lessening of emotionally reactive and automatic responding behavior.
Consistence practice of ujjayi, moves the diaphragm and activates the vertebrae that are connected to the SNS's neurons and by this brings it to action. SNS is in turn connected to homeostasis and to "flight or fights response" which liberate the nutrients like fat and glucose for muscular action. The muscles becomes toned, and the body becomes light and slim.