Yoga does not consist in sitting cross-legged for six hours or stopping the beatings of the heart or getting oneself buried underneath the ground for a week or a month. These are all physical feats only. Indeed yoga transmutes the unregenerate nature and increases energy, vitality, vigor, and bestows longevity and a high standard of health. Most importantly yoga is the science that teaches you the method of uniting the individual will with the Cosmic Will.
Yoga is integration between thoughts, words and deeds, or integration between head, heart and hands.
Swami Sivananda