gail o riley's blogs says:
(i have no clue who he is but i like the idea)
The theory behind mudras is that each area of your hand has a reflex reaction in a specific part of the brain. A mudra locks and guides energy flow and reflexes to the brain. One of the most common and recognizable mudra is holding the tips of your thumb and pointer finger together in a circular form. You may have seen this hand position being held while someone is meditating.
I really find one mudra in particular very helpful for my breathing. In this mudra the tip of my thumb and pinky finger are touching together. I hold them gently in position as I sway my arms back and forth as I normally do while I am running. I feel deeper, easier breathing, which enhances my running rhythm and efficiency.