Answer:
Physical parts? Im guessing you mean what do you have to do in barrels racing? Well for the rider- balance. This means that you can keep in the middle of your horse ( as much as people love sitting up when they barrel race its actually throwing your horse off) another part is leg pressure on your horse. Just dont use your reins- use your legs on the horse to emphisize the turn- it actually keeps the horses mouth healthier too! if anyone else has anything else to add please do!