When the practice of Thummo is properly done, then the body temperature goes up. In fact, there are experts in this system who are tested by their teachers, by placing wet cotton towels on their backs to dry them, as they sit down and practise the Thummo. And, the larger number of towels a practitioner dries, the higher up he is supposed to be in the hierarchy of Thummo practitioners.
But then, this is not the aim of the yogi who opts for spiritual development or whose mind is fixed on salvation.
Now, the followers of the Sri Vidya discipline of awakening the Kundalini, also worship the ‘Sri Yanthra’–the ‘Sri Chakra’ which is a diagram drawn to symbolise the infinite primordial energy as it permeates and pervades the entire universe. First, they worship the Sri Chakra or the Sri Yanthra externally and then they transfer it, by drawing the image within their minds, to the Anahatha chakra or the heart centre and offer mental worship to the Sri Chakra with the bijaksharas that are to be chanted until the Anahatha chakra activates and from there the Kundalini is led gradually to the Sahasrara chakra–the culmination of their spiritual practice.
However, there is a simple yogic practice by which the Kundalini may be awakened gradually and made to ascend to the Sahasrara chakra. It is better to practise it under instructions, personally from a teacher, but I don’t think there is any harm in giving the basic details of what it is.
“In fact, there are experts in this system who are tested by their teachers, by placing wet cotton towels on their backs to dry them, as they sit down and practise the Thummo.”