Tummo, also know as the Inner Heat Yoga or Psychic Heat Yoga, is one of 6 Yogas of Naropa. Monks in Tibet practice Tummo and they are famous for drying wet sheet on their bodies in the middle of the snow with this method of yoga.
Tummo or Inner Heat Yoga focuses on harnessing the body’s uncontrolled energies and turning them into heat. Tummo is a more advanced yoga and participants must go through years of basic yoga before they can achieve the control over their bodies that is required.
Mentally, a person must be able to focus and clear their mind very thoroughly, and part of the practice is to harness all of the uncontrolled thoughts and dreams and turn them into heat in the body. The mental training is done by visualization and meditation techniques. The students visualize themselves as deity beings and their physical bodies as being vacuous, thus clearing the mind of wasteful, ego fueled thoughts and dreams.
Once the students master the clearing of their minds, they are taught further visualizations of esoteric patterns that relate to energy centers and channels that produce heat in the human body. These esoteric patterns and visualization are very complex and relate to the body’s functions on a very deep level.
After achieving the focus and in-depth understanding of the necessary parts of their inner selves students start training on the breath. Heat takes energy and breath is one of the main ingredients that fuels the body’s heat energy. One of the breath techniques used is called bellows because it is similar to the bellows used to stock a fire and it forces strong air into the channels that produce heat in the body.
These breathing practices require massive amounts of energy and the body must be trained to handle this kind of work. The body must also be expanded through years of yoga so the lungs can work at this volume and the channels in the body are open enough for this kind of force to circulate.
The practice of Tummo, or Inner Heat Yoga, is used in some of the Tibetan monasteries. The popularity probably stems from the severe cold weather and cold living conditions in the monasteries. Most of the monasteries in Tibet are stone and there is not that much wood or fuel to burn as heat so being able to control your body’s heat is probably a much-desired skill in those settings. However, I am sure the most valuable benefits are with the mind and body control and the greater depth of self-awareness that practice can give the student.
Monks have spend lifetimes studying these patterns and techniques and passing the knowledge down to other monks that have also spent lifetimes adding to these accumulations of knowledge in the hopes of passing it down to another generation. These yoga techniques are very advanced. Be very skeptical of people who try to market yoga lessons as advanced as these and who claim to have these kinds of skills and knowledge. A few key questions about their training regimen and the length of time they have practiced yoga should give you some insight to the truth of their claims. Monks spend full days for years training, and decades to achieve these skills and it is highly doubtful that westerners with 40 hour a week jobs and busy lifestyles have the time to learn theses extremely advance skills.