[Skywalker]

this could get an interesting thread. I for myself would say that a lot of pros do hyperventilation as well but as well in somewhat "controled" forms. I for myself think it is somekind of technique without competetive freediving might be barely where it is now. Hyperventilating prolonges the start of urge to breathe and that urge does a good part in using up oxygen in form of contractions or general uneasiness. I would not recommend hyperventilating on non competetive dives and also with a good buddy while on training.

Robert