http://swissbaync5d7ykaz7dh7v4qjrb4gmen5aj3bogxrcgbb43ij34bjuyd.onion/pdf/Books/Survival/Medicine/oddsnends.htm
There are four main categories of breath-hold diving, and only the first three are
recognized as a sport for world competition: totally unassisted; constant ballast, whereby the diver descends with the aid of a weight belt and ascends
still carrying the belt. variable ballast, whereby the diver descends with a weight belt, then drops the belt and
ascends under his own power; and "no-limit" breath-hold diving To reach such fantastic depths (and come back...