So, I have been looking a lot at the "Natural Method", a somewhat radical physical education philosophy that permeates a lot of what Parkour is all about. It all comes from one man, Georges Hébert, a pioneer in French physical education around the beginning of the 2oth century. He trained military fighters, sailors, school children and olympic athletes, wrote theoretical and practical books and essays about physical education and had an exceptional understanding of physical activity in general.
I stumbled upon one of his early books on google books and spent most of my spring, summer and fall translating it into English, with tremendous help from Gregg of Hawaii PK. There is a ton of great information in there for traceurs and other athletes as well as anyone interested in basic fitness. It's about a hundred years old, and yet most of it is still extremely relevant and applicable to modern sports and fitness. Yes, there are pictures of men with funny mustaches. And massive muscles too, so don't laugh too much unless you can measure up to their fitness scale.
Mr. Hébert, chapeau bas and thank you.