Learn the underwater dolphin kick: streamline, upbeat and the 15-metre rule. With evidence-based figures, breath-hold safety and a side-on video check.
The underwater dolphin kick is the fast way to move in streamline right after the start or turn: arms stretched, head between the arms, the wave running through the whole body. The honest answer to "How much does it really give me?": a lot – but you may only use a limited amount of it. In freestyle, backstroke and butterfly your head must break the surface at the latest at 15 metres after the start or turn [1].
Why it's worth it: in 14 butterfly sprinters, mean underwater velocity was closely related to the time over the first 15 metres (correlation −0.70 at the start, −0.95 after the turn) [2]. Among finalists in 100 m and 200 m races, the underwater profile was the main determinant of a fast start [9]. And it can be improved: computer simulations of five Olympic-level swimmers gave propulsive efficiencies of 11 to 29 percent, versus about 56 percent for a dolphin [6] – so there is room above.
Honestly: which measure determines your speed is unclear. A systematic review found inconsistent results, partly because the measures were defined differently [5]. That's why you learn a technique with principles here rather than a magic number. Be realistic: until the wave runs smoothly, you usually need several weeks of regular sessions (rule of thumb, not a study value).
Push off and glide for two seconds: arms stretched, head between the arms, back straight. This is the foundation; without it the kick does nothing. Milestone: you glide five times without your arms coming apart.
Push off, do three small, quick kicks and glide again. The wave starts in the chest and hips and runs down to the feet; maximum chest flexion was related to speed in one study [3]. Milestone: you recognise the wave in the body rather than only in the knee.
The downbeat feels stronger, but the upbeat decides. In a 15-metre study with 15 swimmers, speed was strongly related to the upkick [3], and in a seven-week training study with young swimmers, the improvement came mainly from the upbeat [4]. Milestone: you feel the pull upward as clearly as the one downward.
There is no universal rhythm: in sprint butterfly swimmers, kick frequency was not related to underwater velocity [2]. Test two or three frequencies over 8 metres each and time them. Milestone: you know your fastest frequency.
Build in steps: 5, 8, 10 metres, always with a partner. The 15-metre mark is an upper limit, not a goal [1]. Milestone (practice benchmark): you manage 8 metres in streamline without breathlessness.
When you surface, you go straight into the first arm stroke. In butterfly, you are additionally allowed only one arm pull underwater [1]. Milestone: you break through without losing pace.
Film yourself from the side underwater and count the kicks from the wall to the 10-metre mark. With low-cost underwater technology you can evaluate kick length, frequency and amplitude yourself today [5]. Compare two frequencies back to back – the stopwatch is more honest than your feeling. And plan your breathing too: surfacing too early gives away speed, surfacing too late is a fight for air. Agree with your partner on the number of kicks at which you arrive comfortably.
Up to 15 metres after the start or turn at most – then your head must break the surface in freestyle, backstroke and butterfly [1].
No. Hyperventilating before a long breath-hold can lead to loss of consciousness underwater [7]. The DLRG allows at most four breaths before diving exercises [8].
That is not clearly settled. A review found inconsistent results [5], and in butterfly sprinters frequency was not related to underwater velocity [2]. Test your frequency yourself.
Only one: after the start or turn, one downward dolphin kick is permitted before the first breaststroke kick [1].
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