Yoga Guide: I've often heard yoga teachers say that twists like Ardha Matsyendrasana "wring out" and cleanse the internal organs. Is there any truth to this? Would it even be desirable?
Amy Matthews: There are a number of ways that a statement like “twists wring out the organs” is inaccurate and incomplete if we are looking at the anatomy and physiology of the visceral organs (the organs in the thoracic, abdominal and pelvic cavities).
First, there is a difference between moving the visceral organs around in the spaces they occupy and actually "wringing" the organs out. The term for moving the organs around in relation to each other is mobility. The term for movement within an organ – like the beating of the heart or the contractions of the stomach – is motility. Each organ has an optimal range of mobility and of motility, and it varies from organ to organ. Too much movement in the organs (whether it is mobility or motility) can be as unhealthy as too little movement in the organs – for example, more mobility in the heart could actually make the heart less efficient!
Any movement that changes the shape of the thoracic, abdominal and pelvic cavities can move the organs in relation to each other – this includes any movement of the spine, ribcage, abdominal wall or pelvic floor (including breathing). If a twist is done in such a way that it actually articulates the spine (as opposed to just articulating in the hip joints and shoulder girdle), it will mobilize some organs in one plane in space. All the other movements of the spine – flexion, extension, lateral flexion and axial extension - also mobilize the organs in other planes, if the movement is done in a way that actually articulates the spine.
The organs are positioned in the body in such a way that each organ moves in a different plane in space, and no single movement – twisting, flexing/extending, side bending – will mobilize every organ.
The motility of the organs is affected by a wide variety of factors, including signals from the nervous system and the endocrine system. Finding more mobility in the organs might also help make more motility available in an organ, but the two do not necessarily go together (even if more motility would actually be desirable in the organ). Every organ does need a supply of blood, and increasing mobility in the organs can increase blood flow, which brings in nutrients and oxygen and takes away by-products. To a degree, increased circulation can help each organ function at its best – though again, balance is more important than constantly increasing blood flow, and at some point too much circulation is not helpful.
Yoga Guide: Along the same lines, twists are often touted as aids to digestion. Is this correct?
Amy Matthews: In the case of the stomach, small intestine and large intestine, to some degree increasing their mobility also does have a direct effect on their motility. This is in part because the function of these digestive organs is to transport their contents from one opening in the body (the mouth) to the opening at the other end (the anus), along the way extracting water and nutrients. The more mobility there is in the intestines in particular, the more easily the contents can move through. And if by "improved digestion" we actually mean less constipation, twists that mobilize the abdomen might indeed be helpful with "moving things along." (If "improved digestion" means better absorption, not necessarily.)
Yoga Guide: Inversions seem to inspire a lot of anatomical claims. Can they cause retrograde menstruation during your period?
Amy Matthews:We are constantly in relationship to gravity, and when we change our relationship to gravity it has an effect on our body, definitely.
Our bodies are constantly adapting to changes in our external environment and in our internal environment and seeking a dynamic and shifting state of balance, called homeostasis. While the events of the menstrual cycle are in many ways highly evident, we are constantly dealing with all kinds of factors that affect our balance. More important than coming up with proscriptions for every condition (like not inverting during menstruation) is learning to listen to our bodies and not imposing ideas – either about doing something everyday, or forbidding something on certain days.
Chances are good that different women’s bodies will respond differently to inverting during menstruation, and for some women it will feel balancing and for some women it will throw things out of balance. Nothing is true for all women, just as nothing is true for all people.
Yoga Guide: Can inversions increase the blood flow or oxygen flow to the brain? Improve circulation?
Amy Matthews: The purpose of the circulatory system is to insure that there is an appropriate amount of blood flowing to each tissue in the body – so if the circulatory system is functioning well, there will be just enough blood flowing to the brain, and an inversion will not have any effect on that blood flow, in a positive or negative sense. (More blood flow to the brain is NOT a better thing.)
A healthy circulatory system is an adaptable one – one that is able to increase and decrease blood pressure as needed. So any activity that invites the circulatory system to adapt is one that will "improve" it, in some way.
Yoga Guide: When backbending, it's often said that you shouldn't hug your knees into your chest between backbends. Is there an anatomical reason for this warning?
Amy Matthews: Nope, no anatomical reason that flexion following extension is better or worse for the spine than twisting or anything else.
If you do a survey of styles of yoga, some will follow back bending with flexion, some with twisting, some with returning to neutral. (And sometimes in the same class a teacher will lead a sun salute with Upward Facing Dog followed by Downward Facing Dog but later will say after a Wheel pose not to bend the knees into the chest – both are backbends followed by forward bends.) A more important point of focus would be making sure that movement is distributed throughout the spine, so that the same joints in the spine are not doing all the movement all the time. If the movement of extension in a backbend is localized in the lumbar vertebrae and what follows is a twist that also focuses the movement in the lumbar vertebrae, those lumbar vertebrae are in danger of being over-mobilized, and the other parts of the spine might not be learning about how to move at all.
Yoga Guide: I have covered my skepticism about "sweating out the toxins" before, but I'm interested on hearing your opinion on this.
Amy Matthews: As you might imagine, I’m skeptical – while sweat is one of the body’s ways of processing and dispensing with toxins, so is peeing and exhaling. So if we sweat more, pee more and exhale more, great. But then we also need to inhale more and drink more clean stuff, too – balance is the key.