Well I think I understand, now.
Over the past few months, I've gotten into rugby. I like it. It's tough. It's aggressive. It's different. It allows me to run side to side, as well as straight forward.
Trouble is, I'm finding it pretty difficult to achieve my definition of "training," which is working hard enough that I feel like I've been hit by a train. I've been lifting weights and doing aerobic endurance workouts and doing sprints and running agility drills and practicing my passing. Now that I think about it, I don't do a lot of tackling practice, and that might help with the whole "hit by a train" sensation.
But I understand now the urge to, say, run in the morning, swim at lunch, and finish the day off with bootcamp. When you are a ridiculously fit individual, it's hard to find the exercise--or, more probably, combination of exercises--that will make you sore. So you do lots.
Help me. I'm becoming an exercise junky.