practice Vajrasattva purification, and practice guru yoga. Physical exercises There are also auxiliary physical exercises (trül khor) which use various postures (asanas) and movements. There are different traditions of these physical exercises with different sets of exercises. Jey Sherab Gyatso states that some schools practice a set of six exercises, while "The Pakmo Drupa and Drikung Kagyu schools both maintain a tradition of 108 exercises." The commonly taught "six exercises" are outlined in Phagmo Drukpa's Verses on the Path Technology: A Supplement (Tib. Thabs lam tshigs bead ma'i lhan thabs) as follows:There are six exercises for purifying the body: filling like a vase; circling like a wheel; hooking like a hook; showing the mudra of vajra binding, lifting upward toward the sky, and then pressing downward; straightening like an arrow, and then forcefully re-leasing the air in the manner of a dog heaving; and, in order to energize the passageways and blood in the body, shaking the head and entire body and flexing the muscles. These are the six.The first exercise is particularly important, as it is a kumbhaka (vase breathing) breath retention practice, in which one breathes deeply into the navel and holds the breath there for as long as one can. This breath hold technique is also applied in tummo. According to Tsongkhapa, these six are to be done in conjunction with the hollow body contemplation. This practice will allow one to feel much joy, and also will help prevent any injury which might arise from the changing flow of the vital winds resulting from the practice of the six yogas. A related practice is the visualization on the body as being hollow: "here the body and the energy channels (nadis) are to be seen as completely transparent and radiant". This technique releases tension and gives suppleness to the subtle energy channels. Tsongkhapa describes this practice as follows:One commences as before with the practice of visualizing oneself as the mandala deity. The special application here is to concentrate on the body, from the tip of the head to the soles of the feet, as being utterly empty of material substance, like an empty transparent balloon filled with light...Here the body is to be envisioned as being entirely without substance, appearing in the mind like a rainbow in the sky. Inner heat Inner heat (gtum mo, skt. chandali, literally meaning "fierce, hot or savage woman") practice is the foundation