Yoga philosophy sees human anatomy as not only physical, but as energetic. Mudrā-s and bandha-s are some of the most potent tools that can work on this energetic level and create positive shifts in our body-mind. Mudrā-s and bandha-s are ancient yogic tools, emblematic of the power that yoga can wield.
These are a few touch points on mudrā-s and bandha-s, to give a sense of the breadth and subtlety of these tools of yoga.
3 aspects of mudrā-s: prāṇa, kleśa-s, jatharāgni
Mudrā-s are defined as that which facilitates the movement of prāṇa, or life force. According to the yogic system, we are healthy when prāṇa flows smoothly is inside the body, unhealthy when the prāṇa is outside the body. Mudrā-s are also defined as a set of practices that burn the kleśa-s, or psycho-spiritual obstacles. Finally, a mudrā is defined as a tool that makes the jatharāgni (metabolic fire) healthier.
jatharāgni: metabolic fire
According to the yogic system, the jatharāgni (metabolic fire located just above the navel) is related to our immune system. Our metabolic fire deals with how we take in and process food--as well as experiences. If our metabolic fire is healthy, we can process the food so that the energy can nourish every part of our body, and our immune system stays strong. If our jatharagni is unhealthy the food cannot be digested and we become susceptible to disease.
On the energetic or psychological level, when our jatharagni is healthy we can process experiences and emotions in a way that does not leave residue. For example, if something occurs that makes us angry, does the anger linger or are we able to process the anger so that we learn from the experience? Any experience can nourish the mind as long as we are learning.
bandha-s: a type of mudrā
Bandha-s are a subset of mudrā-s. Bandha-s are defined as (1) binding the body in a posture in such a way that the prāṇa is unbound and (2) that which frees all the vāsanā-s (past impressions) that have bound us.
role of teacher
Mudrā-s and bandha-s have a special place in a hatha yoga. As tools, they are specifically meant to nourish our inner fire (agni) and our life energy (prāṇa). Like a very fine blade, these practices can have positive uses if you know how to intelligently adapt them to an individual; if you don't, they can be harmful. It is important to work with a competent teacher, so that the practices remain beneficial and the student stays safe. Finding a competent teacher is not only an analytical process, it is also trusting your intuition and feelings about someone you might work with. Then both teacher and student make a commitment to the unfolding process of yoga.
examples of mudrā and bandha
Some āsana-s such as jatharaparivrtti (lying twist with straight legs) become a mudrā when done as a stay posture with certain prānāyāma ratios and possibly bandha-s. The same holds true for viparita karāni, a modified shoulderstand with a bend at the hips, legs slightly lowered, and hands under hips. Ultimately, the practice of mudrā-s and bandha-s is a mental practice as well as a physical practice because the mind must be steady to practice them.
For example, jihva-bandha is a bandha in which the tongue is folded back when the mouth is closed. Its purposes are to improve the metabolism (and therefore the immune system), vitalize the senses, prepare the system for subtler experiences, make the mind more silent (mind becomes calmer so perception becomes better), and reduces the "temptations of the tongue", food and talking. The practice of jihva-bandha brings control to the tongue so it's not wagging too much (easy on the gossip), and we only eat what is appropriate.
find a trained teacher
But again, although I can describe the benefits of jihva-bandha, special emphasis is placed on experiencing the effects through the guidance of a well-learned teacher. This cannot be emphasized enough as these tools are quite potent and we want to make sure the effect is beneficial. We want these tools to make our inner fire balanced and healthy, so that we can process that which we take in, so that our food and experiences nourish our body, mind and heart, making our body strong and our heart-mind resilient.