My fondness memory of training is when I was training for racing, arenacross, it is a shorter course in smaller arenas hence the name arenacross ha, around 15 minute races, it is a full blown sprint race, the track gives you no areas to take a break unlike supercross or outdoor tracks. I was doing crazy sprint drills and pushed so hard I passed out a few times. There is something weird that I liked the fact I would push myself so hard, that the next thing I know I am picking myself off the ground dazed and confused. In the gym I don't push as hard because I don't want to get injured, but when it comes to cardio I go until I can't anymore.