Or really any other body part that is not your lungs. I remember being confused about this one when I first began yoga. On one level, it makes a lot of sense, but if you really think about it for too long, you realize it makes zero literal sense. You breathe into your lungs and not other body parts or organs, and we yogis should know this! Right? Ok, here is the translation, which many of you already deduced without my explanation:
"Breathe deeply and therefore stretch safely". The idea being that the calming, opening effect breathing deeply has can be transferred to various parts of your body. A more accurate way to say this is "imagine breathing into your quadriceps".This can be referring to the relaxation response that is caused by deep breathing and which is useful in deep stretching.
Another, more literal use of this imagery is something like "imagine your breath swirling around in those tight muscles and opening them up". While the air we breathe in doesn't exactly go to the muscles, swirl around, and open them, it does contribute to the stretching and strengthening processes in a really profound way. When we inhale, oxygen is transferred through tiny sacs in the lungs called alveoli into the blood stream and then the blood flows throughout the body, bringing oxygen to various sites. Oxygen is a necessary part of the healthy functioning of all tissues in the body, including the muscles! So in this way, the statement is true.
And in any case, it seems to be useful imagery and I plan to keep using it.
Thanks for the response on this series, friends! If you think of other phrases we use in yoga that you want to discuss, let me know!