FEDEC (the European Federation of Professional Circus Schools) has published a new instructional manual for circus tutors and trainers to join the series currently available on its website.
This new one is titled Theory, Guidance & Good Practice for Training [PDF] and gives an introductory overview to the topic divided approximately into three sections: the skeletal, muscle and nervous systems; biomechanics; and devising/planning a conditioning session.
It's probably the only place you'll see Newton's Second Law of Motion demonstrated by an aerial cradle diagram, if nothing else.