Tiring is good though, it means you can reach a maximum of energy expenditure. There’s a trade off with how big to make the fins though, similar to gears on a b

Tiring is good though, it means you can reach a maximum of energy expenditure. There’s a trade off with how big to make the fins though, similar to gears on a bike. Too small and you get bigger losses, I assume. Also depends a lot what you optimize for. For underwater swimming, especially scuba, you want to optimize for saving air, meaning minimize the total energy expenditure and keeping heart rate low (the mammalian dive reflex helps here too). In water, that means moving very slowly and with longer strokes, for the same reason container ships move slowly to conserve fuel. It looks really inefficient to pedal fast because all that water around your knees needs to be pushed back and forth for no gain.