Underwater dolphin kicks are often considered "the fastest way of swimming".
Dave Berkoff introduced underwater swimming and won Olympic golds in 1988. Rules were changed and now only allow for 15 m underwater after start/turns.
Michael Phelps is considered a master of underwater swimming and his gold on 200 m freestyle in Beijing was, according to many, secured by his underwater kicks after the last turn.
It may appear like a simple relation. - Swim under water and gain time. But some facts make the relation complicated, I believe.
Many were impressed by Ryan Lochte swimming 50 m under water on 20.8 s at a clinic. It is fantastic but probably not very much faster than Lochte can do in regular freestyle. Swimming without breathing will also accumulate lactic acid.
Many say Michael Phelps achieved a considerable distance advantage by underwater work in one turn only (as described above). To get this advantage, the speed must be considerably higher than Lochte had, recording 20.8/50 m.
And all swimmers do not make full use of the allowed 15 m swim under water. (Some say Phelps' large and supple feet make him more suited for underwater swim.)
So to me there are simple questions about this matter that have not been answered. Questions like:
- How much faster is underwater swimming after a start/turn?
- Why don't all swimmers make use of the maximally allowed 15 m under water?
- How useful is underwater swimming for competitive swimmers?