I was watching this segment from a recent 60 Minutes (that's actually a rerun) about Olympic Gold Medal Swimmer Michael Phelps, who said that he spent literally thousands and thousands of hours, staring at a black line in a pool, swimming.
All I could think was, "Jeez. How boring!"
Now don't get me wrong. I think that swimming is a wonderful form of exercise - easy on the joints and great for cardiovascular fitness. But, as opposed to training for a marathon or biking long distance, or even track, when you train for swimming your head is stuck in the pool, for hours on end with nothing to distract you from...the water, other than the count of how many laps you've swum.
It seems to me that it would also be a little more interesting if they stuck you in a lake and told you to swim from one side to the other. But going up and back and up and back - I just don't see it.
When I was a student at YU, I actually used the pool every day after class. It was great excercise, and it even got me out of a gym requirement, and I lost twenty pounds without even trying. But it was boring as spit drying on a log. (And that's boring.) I finally asked Rav Schachter if I could review that day's gemara shiur in my head in the pool while I swam, even though I would not be wearing a kippah. He said "sure", and it helped a little.
But it didn't change the fact that swimming is still boring. Especially if you're going to do it for long stretches.