respect...

i usually listen to the same thing half of the times on the way to beach or an upbeat music... definitelly not techno though... also a good set of fast funky breakbeats works a treat...
In fact, i'm sure that there is a medical/biological explanation behind it, as heavy music 100% makes impact when it comes to any physical activity, and gives you easily 50% more adrenalin, and energy. Especially if it has strong, catchy upbeat feel that makes you get into it as soon as you hear it, because it increases your heart rate, and makes you want to move more and harder.
Now, the ideal thing would be to find a waterproof set of ipod and headphones.