. >> reporter: chris mccarron is one of the most winning jockeys, and the founder of the school.ockey? >> it is the ability to stay out of the horse's way, to a great degree. >> reporter: staying out of the horse's way so much that it barely feels you on its back. >> the horse is not going to be able to perform at the best peak if it is carrying 100 pounds. >> reporter: so the size is considered more important than the riding experience, you better weigh under 112 pounds. body expectations are far more rigid than more athletes, and on par with the lowest fat rates to even survive. >> the typical male jockey has the fat range that ranges between 3 and 7. >> reporter: oh, my gosh! >> yeah, and the girls are between 8 and 12. >> reporter: that is incredible. compare that to average body fat percentages, around 25% for women, 18% for men. vanessa is a gifted, slim rider, but still struggles. >> well, i stopped eating so much chocolate. >> reporter: no more chocolate? >> no, no more chocolate, and trying not to go over 1500 calories a day. >> reporter: it is pressure like this that ca