Does happy baby massage your kidneys?

Here's another yoga teacher question that I recently recieved:
"Does rocking side to side in happy baby pose massage your kidneys? Does it compress the kidneys, and when you release does it send them fresh blood? I am curious about this in regards to compression of the organs in floor bow as well! 'Fresh blood'- is that a thing?"

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Can we compress or massage the kidneys?

Well, I guess the first question that we need to answer is can we actually massage or compress the kidneys in ananda balasana (happy baby pose). First, when we take a look at someone with normal anatomy, we'll see that the kidney are in the back and roughly half of them are covered by ribs as in the picture to the left. In addition to ribs, if we can imagine slicing through a body at about the middle of the kidneys and looking up at it, we would see that there are some more things that cover the kidneys from behind, mostly muscles. We can get this view from a MRI or CT scan. The CT image below is a slice taken right at about the middle of the kidneys (the 2 lighter gray round things near the bottom of the picture). This view is like imagining a yogi in happy baby with an invisible bottom half, you could look up from the bottom, and the kidneys would look like the CT scan. You can see here that the kidneys are pretty close to the back, but there is a good bit of cushion between them and the floor. These structures include the transversus abdominus, quadratus lumborum and lumbar multifidus muscles adding up to around 1.5 inches of thickness plus any more cushion from fascia and fat. To massage the kidneys, you'll need to get through these layers of muscles.

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Second, when we look at the body in the pose, your weight is also going to be distributed to your upper and mid back, not letting much pressure concentrate to the kidney area (that soft area on your back between the ribs and pelvis). When you rock side to side in ananda balasana, you might be able to press the kidney areas into the floor a little, but you can't really focus much pressure there. The natural curve of your back and body will also make it difficult to focus pressure on the kidneys. As for compression from the inside, there is some weight coming from your abdominal organs on top of the kidneys while laying on your back. Your kidneys also get pushed down from you lungs and diaphragm when you breath in, so a combination of having organs on top of  the kidneys and the diaphragm pushing down may cause a little squeeze on the kidneys.

So what's the conclusion?

You might be able to give the kidneys some gentle stimulation in ananda balasana. I don't know that you could compress them that much more than normal since there is not a lot of weight coming down on them from the front of your body, and you can't press them that well into the ground. If you can get some compression, then you might be able to cause a temporary increase of blood flow to them just like anything else you compress in the body. Read my article on twisting for more information on compression, reactive hyperemia, and "fresh blood!" So, does happy baby massage or compress your kidneys and bring fresh blood to them?! Maybe... but probably not much. No worries though, asana practice is completely awesome for getting your blood flowing everywhere, kidneys and all. Throw in a few standing poses before happy baby, and all will be well! I hope that's helpful. Thanks for the question!

Namasté

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Kidney anatomy image from Clinically Oriented Anatomy by Moore. Kidney CT image from http://www.lumen.luc.edu/. Ananda balasana image from yogajournal.com.