So I'm a bit of a fitness freak although I'm nowhere near ironman level but I was wondering whether setting the 2nd stage to the lowest setting (greatest effort required) would be a good way to give my lungs a workout assuming that I'm not task loaded underwater. It's probably not conclusive but I seem to be getting better mileage per tank now that I've found a new love for running plus I still work out with weights before going onto the treadmill for anything from 3 to 10km each time so perhaps I can continue this 'lung training' thing on dives as well?