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?
  • Phelps now sometimes finishes with dolphin kicks in freestyle. What limits for how long is that the swimmer can't breathe while doing it. Maybe this is the clue. Dolphins are faster for many swimmers but oxygen debt limits its usage.
    – cvr
    Commented Sep 17, 2016 at 17:32
  • Freestyle with dolphins look like this. Frequency 100, no breathing - that's tough.
    – cvr
    Commented Sep 17, 2016 at 17:50

6 Answers 6


To be fair, David Berkoff didn’t quite invent the underwater swimming dilemma, but he had a large part in making it an enough of an issue that FINA had to institute the 15m rule.

Pre-dating Berkoff was a swimmer named Jesse Vassallo, who in 1976 was lined up against future Olympian John Naber. At a considerable height advantage, Vassallo figured he could do a bunch of dolphin kicks off the start to avoid the wash of the 6’5” Naber.

Berkoff brought it to a broader audience, that is for sure, but very few swimmers and coaches understood the best way to teach the underwater fly kick. For a long time it was considered a fringe aspect to swimming, something for outliers, something you had or didn’t.

Phelps, Australian Ian Thorpe, and most notably Neil Walker showed that the UDK would eventually need to be a part of every swimmer’s arsenal.

They showed that you could swim faster underwater than you could ever hope to swimming on the top of the water.

Because it hasn’t become an accepted and understood part of elite swimming until recently, it is only in the past couple years that we have seen the UDK being coached at an early age.

Where in past years swimmers with a powerful UDK was the exception, in the future we will see swimmers—across all disciplines—making use of it as it has become a part of the coaching curriculum.

See Also:


Within swimming circles, underwater dolphin kicks are sometimes called the 'fifth stroke' - they can be very useful for competitive swimmers, and all the top swimmers use them and use them well. Factors that can vary between swimmers include:

  1. Some people are better on underwater dolphins than others, just like some people are better at breaststroke or butterfly. You need to train and work on them just like anything else. If your technique isn't good, you won't get as much out of them so you will use them less.

  2. Some coaches have swimmers work more on them, or are better instructors. If the coach isn't emphasizing them, the swimmer won't learn.

  3. Some swimmers dedicate themselves to them. As I recall, Natalie Coughlin decided she would do 7 underwater dolphins off the start and each wall, and made herself train to do them. Others may not force themselves to work the technique and fitness required.

I'm not that good with underwaters - I swam HS/college before Berkoff, and have never spent the time required to learn them really well. Still, I use a few because they are faster. My daughter is much better, and it is really nice to watch her go into the wall even with someone, and pop up a body length ahead 10 meters off the wall.

Bottom line - if you are a competitive swimmer, you have to learn to use dolphin kicks. The better they are, the better your racing will be. It will take skill, dedication, and training, but that isn't any different than all the other things you have to learn to do right to go fast.

  • Thanks. 7 strokes will not be enough for 15 m including push off wall, I think. Since she did kicks at all, she considered kicks faster but could not keep doing them for the full 15 m. Something drove her to the surface. The need to breathe? But 15 m under water is not far for an Olympian. / Many say the kicks are the "fastest stroke". But I am not sure I agree if not even every guy in an Olympic final has the ability to do it to full 15 m. ;) Would be interesting to see measure of time over short distance compared to regular stroke.
    – cvr
    Commented Dec 7, 2014 at 1:33
  • Well, the fastest you will go on a lap is after your dive or coming off the wall on a turn. Breaking the surface of the water will only slow you down. So yes, there is a balance of staying down without oxygen, and milking the underwater portion for all its worth. That balance will depend on each individual and their abilities. And, you still need to work on the break out as well. Competitive swimming is all about doing lots of little things consistently and well.
    – Jon Custer
    Commented Dec 7, 2014 at 4:04
  • Why not time your daughter for 10 or 15 meters after a start in the water, comparing kicks and freestyle? / I am just a recreational swimmer who learnt by myself. Over a small, about 8-10 m pool I very roughly had 5.9 s freestyle and 7.8 s kicking under water. Starting both with a very soft kick off the wall. Only one try each and large error in my own timing :)
    – cvr
    Commented Dec 7, 2014 at 4:33
  • My daughter's reaction was somewhat predictable - she considers the underwaters a part of her race, not an end to themselves, and is intentionally balancing speed vs breath vs the particular race. I'll note that your 'soft kick' is probably nothing like a real turn where the racer is trying to keep that momentum going for as long as practical.
    – Jon Custer
    Commented Dec 18, 2014 at 0:10
  • I now watched the races on Youtube that I quoted in the question. Others have said the kicks gave big advantage. Phelps 200m freestyle finals Beijing: Phelps had considerable lead both before and after last turn. Influence of kicks uncertain. The only certain race is 100m backstroke Seoul: Berkoff & Suzuki gets significant lead. Berkoff even after poor start! But both are almost caught up in the end by 2 Soviet swimmers. They may have exhausted/oxygen depleted themselves under water? Maybe they could have swum that race in the surface too??
    – cvr
    Commented Dec 18, 2014 at 14:59

There are a few factors to take into account here. First of all, you'll note that this technique was never really used for freestyle events. That means that the ability to swim via underwater streamlining and kicking is not faster than swimming crawl stroke at the surface. For other events, it appears that the underwater streamline kick is faster.

The kicking underwater has advantages over surface swimming -

1) surface turbulence. Wakes and general turbulence are more at the surface, since that's where the dives and most disruptive stroke propulsion happens. Staying deeper means you don't have to fight through that turbulence. I regards to your question about starts and turns, in those situations you have a combination of (a) maximum propulsion from pushing off the blocks and acceleration due to gravity on the start and pushing off the wall on turns, and (b) maximum surface turbulence, so the streamlined kick to both get past the turbulence while avoiding it and maintaining as much of that maximum momentum makes this technique universally effective at starts and turns, for all strokes and athletes.

2) Surface tension - water molecules, because of hydrogen bonding, want to stick together. That's why water pools into droplets when you spill it. When the water is able to flow smoothly, uninterrupted over the body, it creates the least resistance. Stroking at the surface is constantly breaking that surface tension and is disrupting that flow.

3) Maximum propulsion - while the water offers resistance, it's that resistance that propels the body forward when you push against it. Kicking in the water, only, gives more propulsion than kicking, partially, against the air.

The physics of the fastest swim strokes - Science Friday


I have been in the swimming world since 1978. Swimming competitively at all levels minus Olympics/Worlds. I have coached world champions and country club only athletes. What everyone has to realize is ALL swimmers are different. Sometimes you have to realize you can't teach certain things to certain people. Because they are genetically unable to do what you are asking. Let's take Hypoxia into consideration. Working with 2 different athletes both female, both starting at 10, both ending training at age 14 with this group. The training sets for UDK and Hypoxic training are done routinely and made to extend both distance, as well as increase propulsion. At the end of 4 years of the same training, 1 swimmer can push the 15-meter mark quickly off any wall, and stay in any race 200m or less. While the other still barely breaks 6-meters, and loses so much from staying under that she is better off coming up. Both athletes compete at a very high level. Just 2 different swimmers that are genetically different.

Also, take into consideration the type and distance of the race when deploying your UDK, if Caleb Dressel goes 15-meter under the water there is no way his 50 is that fast.


Reading the informative answers and comments here and watching various Youtube videos, I propose the following.

Swimming under water is faster for many swimmers but to make use of the full allowed 15 meters you must have a very good tolerance for lactic acid/oxygen debt.

The lower body including feet is more important when doing dolphin kicks since the arms do not move in this stroke. A swimmer like Michael Phelps has size 14, supple feet. He also displays excellent technique and other positive factors that can make him use the underwater advantage longer.

Who chooses to swim under water and for how far is based on tolerance to oxygen debt (also vital/total capacity for lungs), anatomical aspects, technique and probably more factors.

Addition Sep 28, 2016:
Swimming under water may be faster for a large part of top swimmers, but the "wear" (like oxygen debt) is so strong that the rest of the race will suffer too much, if they swim too far under water.


The point no one has made clear is that underwater dolphin kicks (UDK) isn't faster than surface swimming. It's used to help maintain the high speed of the start or turn where the speed is greatest from push off the blocks or wall. They make slowing down, slower. As long as a swimmer can maintain the higher speed off a turn with UDK's, that is, as long as they can maintain a speed greater than their surface speed, then they are effective. Dolphin kicking does provide thrust at a greater speed than flutter kicking since it engages the entire core from the abs to the ankles.

As the OP's answer correctly noted however, hypoxia will quickly become a limiting parameter the longer you stay underwater. A properly streamlined person does have a lower drag in a streamlined underwater position than they do on the surface. That's why submarines are so much faster underwater than on the surface. They aren't making waves. Your legs are also a relatively inefficient means of propulsion, so the oxygen demand is high while you are unable to breathe. Therefore UDK is most useful for swimmers who have excess lung capacity, allowing them to stay submerged for a long period of time, who have large, flexible feet and ankles, and who have a superior streamlined position underwater. But the bottom line is that it should only be used when it's a benefit to your overall speed off the start or turns, before you run out of air and before you make it to the 15m mark.

  • It IS faster for backstroke. Long after wall or start momentum was gone, the underwater specialists would stay under. For as long as the possibly could. Why? Because it was faster, which is why they changed the rules to limit how far they could use that technique. Commented Apr 17, 2023 at 19:51

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