Over the last few weeks, I've had at least a couple of evenings a week where I got home a little later than usual, and therefore had to prepare and eat dinner a little later than usual (i.e. after 8 p.m.). As many of you out there know, what this means in terms of the practice is that I wake up the next morning feeling a bit heavier than usual. What this also means is that it is a bit harder to make myself move my bowels before starting practice, because... because, well, probably because the food from last night hasn't had time to digest... honestly, I'm not entirely sure if the bowels that one moves on a given morning actually consists of waste matter from the food from the previous evening, or if they consist of waste matter from food eaten more than one evening ago (this is where my knowledge of biology is not so good); if the latter is the case, then the feeling of lightness that many Ashtangis reportedly get from moving their bowels may be more psychological than real, since if moving your bowels does not actually get rid of the waste matter from last night's food, and it is last night's food that is causing one to feel heavy, then moving the bowels won't probably do very much to relieve any feelings of heaviness. Simple logic, right? ;-)
But the question of what waste matter is actually being moved by which bowel movement is probably a purely academic question, as is the question of whether the resulting (unbearable?) lightness of being is psychological or real in nature. What matters, as far as the practice is concerned, is that one preferably gets to move one's bowels before practice, and that such movement results in a good feeling of lightness, leaving one ready to take on the rigors of practice without being distracted by the heaviness in one's innards.
But what if, as happened to me this morning, one finds oneself unable to move one's bowels before starting practice? You could, of course, keep sitting on the toilet till the bowels (or Kingdom) come. But this is very likely not a productive (no pun intended) way to go about things. As anybody who has ever experienced constipation knows, trying to take a shit is very much like trying to go to sleep; the more one tries to "will" it to come, the more it stays away. It comes when it comes. Period.
So what is a good Ashtangi to do in this situation? Well, here's something that has worked for me. I just get on the mat and start practicing. When I get to Surya B, there is something about doing Uttanasana immediately after Utkasana (a.k.a. Ekam and Dwe positions in Surya B) that gets the bowels moving for me. For the last few weeks, if I have been unable to move the bowels before practice, I would feel the bowels stirring in these two positions within the first or second Surya B. Every single time. Without fail. And then I would have to either hold in the poop (which might be good for extra bandha strength training, but not so good for the body in general, because what has to go, has to go) or walk/trot/run to the bathroom to get the stuff out of the system. I always pick the latter. Yeah, it breaks the rhythm of practice, but again, what has to go, has to go (a.k.a. there's more space outside than inside).
So yeah, I guess what I'm saying is that it seems that Surya B (more particularly, the first two positions of Surya B) seems to have a laxative effect on my system. Come to think of it, I actually suspect that everybody probably has a "laxative pose" or two out there (i.e. the pose that will get you to go to the bathroom when all else fails); they just have to discover what those poses are, since every body--and presumably, every bowel--is different.
But all this is just me talking about my own very particular experience of the relationship between practice and moving the bowels. Does this resemble your own experience at all? Or is your experience very different? Feel free to share, if you are not averse to talking about such matters of the bowels.