free diving
 

does anybody know any free-diving exersizes/training for the lungs?

I have seen a lot of people pass out during breathholding excercises. Be extremely careful, and never do them alone.

Aside from actual breathholding excercises, running is probably the best thing you can do.

Also remember that your body uses oxygen differently at depth (increase in partial pressure) and while you may only feel slightly 'out of breath' at thirty feet, you may well pass out as you ascend.