Isn't it interesting that one person's experience is so different than another's!
Is legs up the wall safe? The answer is yes! Well, no! Well, maybe? As always, it depends! It depends upon your unique biology and biography. While legs up the wall is wonderful for most people, there will be a few people for whom this is not a good idea. The danger is extrapolating that contraindication for one person into a contraindication for everybody.
I can easily visualize that for some people with severe heart conditions leaving the legs up the wall for a while may put too much of a strain on their heart, but certainly this is not the case for the majority of people. But, don't worry about the theory-what happens when you do it! What is your experience? Does it work for you or does it make you feel worse?
Beware of dogmatic assertions. Check it out. Does it work for you (or your students)?
Okay...having said all that, it is nice to know what the science does predict. I found this study
interesting: it showed that even with the “king of inversions,, headstand, blood pressure did not increase! (Indeed, heart rate variability improves during the headstand.) However, the subjects in this study were basically healthy and people with high blood pressure were deliberately not included. So, if headstand did not put extra load on the heart, I suspect legs up the wall will not make the heart work harder.
(Consider this logic for a moment: yes - in an inversion the heart has to pump blood to the feet, which it does not have to do when we are standing because gravity pulls the blood down when we are upright. But, while standing, something has to pump the blood from the feet back to the heart agains the pull of gravity! In an inversion, gravity brings the blood back to the heart. So, does the heart really have to work harder during an inversion? During an inversion, the heart is pumping blood up to the feet, but when standing the heart does help to return blood from the feet back up to the heart. (It is not just the heart making this happen, however, it is much more complicated than that.) The same amount of work has to be done by the body to move the blood around the circulatory system. And, that is what the study showed: blood pressure did not increase during an inversion, so we could assume that the heart was not working harder, at least in healthy people.)
To be sure, let us ask someone who has considered this concern in more detail.
Here is a quotation from an article called Inversions and Cardiovascular Problems
- ...[Regarding] legs-up-the-wall pose. Technically, it's not an inversion at all, since no part of the spine is inverted, but it's worth discussing. Yes, the heart has to work harder to bring blood to the feet in this pose than when standing or sitting, but not all that much harder because the torso is not inverted. Also, there's no thoracic compression. So the pose is fine for [cardiovascular problems]. (If you put a cushion under the pelvis, or if you want to be extra careful, place a cushion under the student's head to avoid raising blood pressure in the head.)
So, given all the above, I would say that legs up the wall is safe for the vast majority of students. But, no pose is safe for everybody and it is still important to teach every student how to pay attention so that they can check for themselves that they are safe.