Just finished watching this
video. Watching this, I had an idea as to how the muscular contractions that have their origins in the mind can be relieved if the mind experience which is causing the muscle contraction can be experienced consciously. As long as the experience remains subconscious, some muscular contractions remain and keep on causing suffering. If it comes to the conscious part of the brain, then it stops causing the muscular contraction and the suffering goes away.
This process seems almost parallel to how meditation works. It brings to awareness what causes upheaval in mind and once that is seen through, it no longer does.
Also, practices such as yoga which involve stretching can release certain emotional states and it is believed that if kundalini rises suddenly, it can be dangerous. I think it might also have to do with being unable to process difficult emotions which come to the surface doing advanced yogic postures.
In my own experience, I have found that more stuff that I process through doing different practices, the more relaxed my body becomes. I have also read (have mentioned this before on DhO as well) that enlightenment/awakening can be considered as having progressive state of relaxation.
After my first Goenka Vipassana course, I had a very relaxed body and gained the insight that some emotional events cause the body to tighten up and if those don't occur, then my body will remain relaxed and I won't suffer.