I find it amazing how much my mind and body are so active during my freestyle workouts in the pool. The structure of my workout is a Warm up, Build up (Drills), Core (main set), then Warm down. During the workout I am focusing on so many things to help me become a more efficient swimmer.
I am thinking about having proper:
arm catch and high elbows,
having a strong flutter like kick moving from the hips,
stream line body position so that I am as slippery in the water as possible,
and becoming like a fish with shoulder and hip rotating as one.
Not to mention I'm trying to keep track of the 10 x 100 yard repeats in my head while swimming in a 25 yard pool.
Oh, did I just finish my 6th set or 7th set? I was chatting too long with the guy in the lane next to me and now I lost track. Anyway, I go with 6 and continue focusing on having proper bio-mechanical positioning in the water but then I'm thinking, oh no, I have to go pee...
If you like multi-tasking like I do then you'll find swimming is so much fun.