So I just read this entire 214 page pdf today (quick, but amazing read) and it has completely opened my mind to all of the ins and outs of gesture drawing. There isn't a published book version and the editor has cleared it to be spread on the Internet, so consider this my gift to you. This brilliant book is by one of the Disney greats, Walt Stanchfield, and is composed of notes from his gesture drawing classes and compiled in this amazing reference. The link to the pdf is below. I HIGHLY recommend reading it. Enjoy!