Not directly related to rationality, but this approach should help with exercise akrasia (the post is about yoga, but generalizes to other forms of exercise), and that's always on topic.
Doing yoga improved my rationality skills. If I were rewriting optimal exercise I'd add a section titled Retraining your Broken CNS.
You would probably like this blog.
I like this a lot, especially the beginning. Concise, clear and true. And the bit about the difficulty of following subtle gradients is particularly well put.
I'd like you to flesh this out more, especially because the title "manifesto" leads readers to expect more substance. Maybe add examples, or thoughts on group vs. solitary practice, or considerations about yoga for kids and yoga for seniors, and in each case make very clear what you think isn't helpful and what you think is.
I sort of take pride in having written a post called "manifesto" which is not at all like a manifesto :) One point I'm trying to make is that there is no "right way" to do things here, so of course the advice ends up rather open-ended.