When I'm running I tend to get focused on training-related topics and think them through ad nauseum, in between focusing on traffic to make sure I don't get run over. Also, lately I have a constant soundtrack of kids songs running through my head as a result of all the noisemaking baby toys in our house.

On the trainer I try to watch TV shows or documentaries that don't require much thought so I can loosely pay attention but focus on the effort when I need to.

Same on the treadmill, but I mostly end up thinking about what a strange form of self-inflicted torture it is and counting the tenths of miles and/or seconds until I'm done.

I'm not swimming much at the moment but when I do, I'm bad enough at it that I'm pretty much constantly focused on my form, breathing, etc. Unless I see a band-aid or a big hair in the pool, then I spend the next 10 minutes trying to block out the fact that I'm swallowing copious amounts of pool water that is contaminated by whatever disgusting thing I just saw.