Or were you thinking more specifically?
Maybe the original question was about respiratory efficiency ? Pilots are not advised to go rapidly from one pressure extreme to another, for example by deep scuba diving immediately prior to operating at a normal cruising cabin altitude. As I understand it, spearfishing is traditionally done without the luxury of scuba gear and the like, and involves some pretty lengthy breatholding !
To be honest, I'm not really sure what I would advise on this if asked. Anyone else any ideas ?