One of the hardest sports I participated in. Was a State back stroke swimmer. Our coach was one of the premier world elite swimmers. World record gold medalist multiple times. Jim killed us. Our practices were 3 miles per day of swimming (dual practices per day). I have complete respect for athletes of his caliber. Swimmers are probably the most fit athletes in the world .
PS none of us could ever beat Jim. He even gave us a pool length head start! LOL