I got Broad's yoga book and read it yesterday, I skimmed here and there but read most of it. I thought it was interesting. I think I have read some of the studies on yoga that were not maybe the most scientifically stringent so I liked that he tried to sift through some of the people that are telling falsehoods or with sketchy degrees. I feel like he could have mentioned more of the good studies in depth though, even if they were smaller groups, good science is good science. I have read some interesting things about yoga and blood pressure, but his main point on hypertension seemed to dance around that and talk about inversions rather than an overall positive effect. I have borderline blood pressure but am safely low enough to just treat with lifestyle, and it runs in my family so it is of particular interest to me since I try to watch all the possible ways to keep it low enough to avoid medication. Once you eat healthy, keep a good weight, avoid salt and excess alcohol, I feel like it's nice to turn to yoga and exercise as well since I kind of hate taking medicine if I don't have to take it. It is somewhat in keeping with his summary of research that yoga can slow the body down, but I know my style of yoga is slightly cardio at times too, although I do tell my students that I recommend other cardio besides yoga, even if it's just brisk walking or the elliptical. Running is great, but it gives me headaches, to me exercise has to be something that makes you feel good, so follow your bliss!
Also as a Registered Yoga Teacher through YogaFit, I feel that I had a good, comprehensive, and safe 200 hours of training from a variety of teachers and backed by a board made up of various health experts. He sort of poo poos YogaFit as yoga with sit ups but we do a lot of things that make yoga safer for EVERY body type. I personally do not recommend headstands, although I like shoulder stand okay, and I show my class wheel but we don't do it all the time. I believe that the intense poses are not something to do frequently or for prolonged periods, or if you don't have the strength in supporting muscles. It does concern me that someone could get hurt in class so I always mention modifications, but sometimes people try things that their body is not ready for and I cannot necessarily stop them. I do have yoga insurance and have an info sheet for everyone so if they have a major injury or health condition I can tell them ideas for modification. I would be horrified if someone in my class was injured, so I think that is why I often mention modifications and don't adjust people physically unless they ask, for the most part.
I agree with his summary that yoga has anti-depressive qualities and it can't hurt creativity to literally get the blood flowing, he also has an entire chapter on sex as well as a thread about it running throughout the book which is a discussion for another day. I personally think yoga is good for the immune system, endocrine system, and organs because many of the twists and other poses wring out or put gentle pressure on these systems, which could force the blood away for a moment, but when it rushes back in I think that is a good thing, blood has a lot of beneficial molecules! (totally my own opinion there everyone after practicing regularly for 9 years). I also think that his final statements of uncertainty were important. It is interesting that he has practiced yoga himself for 34 years, he obviously thinks it's good for him with more reward than risk. Even with my science background, it annoys me that we sometimes only want to trust science "studies" rather than realize that something like yoga which can be social and spiritual as well as physically focused may be hard to quantify at times.
In a way, yoga is my connection to spirituality. I grew up Catholic but eventually felt a lot of the beliefs were too strict and rigid for me personally, and downright against some of my world views. I know a lot of people ignore or maybe just don't think about the parts they don't like of a religion (eg. take birth control although the church says no, the condemnation of gays) but my mind is sort of purist in that sense, if I'm going to go spend time somewhere, I want to truly believe and feel comfortable with everything my group professes. I like the Unitarians a lot, wish there was a church like that closer to us here. I feel pretty comfortable and resonate with the philosophies of yoga, like the yamas and niyamas which Broad doesn't even mention, sadly. I do think yoga can be a support of any religion and does not need to be a threat to anyone of a certain belief system, if anything, it can enhance the mind spiritually.
I do hope there are bigger studies of larger groups on the benefits of yoga, I would participate! I've done yoga regularly since 2003 and I am sure I would not be as healthy, mentally, spiritually, or physically if I had not found yoga. Like everyone of course, I am a work in progress. Yoga got me through a lot of hard days of teaching teenagers, some with incredibly chaotic and negative energy. To me, yoga is a great way to keep my energy healthy, hard to quantify that. I think a key is also to keep your ego in check. That's hard as both a teacher and student, but 100% in line with what yoga teaches us as we let go of competition and judgement. If your ego rules you, you're more likely to suffer an injury, I'm sure of that. I'm in life for the long haul (my grandma is 99 and I hope I got a few of those genes) so my yoga motto could be summarized as, "de todo un poco, everything in moderation, variety is the spice of life".
If you read the book, I would love to hear your opinions as well.