The great French acting teacher and theorist Jacques Lecoq has spent a lifetime investigating the dramatic possibilities of human motion and the body.  He sums up his work in the book The Moving Body, which I recommend highly for any serious student of body language and public speaking. 

Lecoq began as a physical education instructor, and he made a study of virtually every form of dramatic theatre that involves the body – from mime to commedia del arte to Greek tragedy.  For Lecoq, movement must always have meaning; gesture must always be justified. 

His central insight is that meaningful movement can have 3 ways of justifying itself:  indication, actions, or states.  Indications are gestures like pointing out a moving object, or a sign.  An action is just like it sounds, doing something to carry out some purpose:  find an object, catch a train, stop someone from leaving.  States are the physical manifestations of attitudes, such as emotions or feelings. 

If you’re a public speaker, these categories are very useful ways of thinking about your movement.  If you’re not doing one of these three, then your movement will be purely mechanical – it won’t be justified.  From Lecoq’s point of view, that means it won’t be interesting.  Public speakers who keep these categories in mind, and analyze their own movements from this point of view, will eliminate a good deal of unnecessary gesture and greatly increase the interest, and therefore the charisma, of their body language. 

Lecoq’s insights are not based on science, but rather on deep observation of human movement from the point of view of finding the drama in it.  As such, Lecoq has much to teach the public speaker. 

Indicate, act, or state.  Do one of the three.  Eliminate everything else.