The 15-metre underwater phase is often faster than swimming: a tight streamline, a body wave from the hips, smart oxygen management and a timed breakout.
## Introduction The underwater dolphin is not called the fifth stroke for nothing: after the start and each turn you may stay submerged up to 15 metres, and for good backstrokers this phase is often faster than over-water swimming. Straight talk: surface after five metres and in every 100 you give away up to 60 metres of potential top speed.
The propulsion does not come from the legs in the narrow sense but from a body wave running from the hips over the knees into the feet. On your back the powerful kick points upward, the body whips like a lash — tight, fast, from the trunk.
This guide turns your underwater phase into a weapon: streamline, wave mechanics, amplitude and frequency, plus honest oxygen management and the perfectly timed breakout just before the 15-metre mark.
## What You Need - Resilient trunk and hip mobility for a clean undulation. - A watertight tight streamline (hands stacked, arms firmly by the ears). - Good breathing economy — the underwater phase is a balancing act with oxygen. - Optional a monofin or short fins for isolated wave training. - Knowledge of the rule: 15 metres maximum, then the head must surface.
## Step by Step ### 1. The streamline first Without a tight streamline every kick fizzles. Stack the hands, interlock the thumbs, press the arms firmly by the ears and tense the whole body into an arrow. Every millimetre of open angle is drag — and drag dominates your energy cost underwater even more than at the surface.
### 2. Start the wave from the hips The undulation begins in the trunk, not the knees: the hips initiate, the wave runs over the knees into the feet. Think of a whip — the handle (trunk) moves little, the tip (feet) a lot. Kick from the knees only and you make lots of motion and little propulsion.
### 3. Calibrate amplitude and frequency On your back the upward kick is the powerful one. Keep the wave tight and fast rather than big and slow — too large an amplitude brakes and pulls you out of the streamline. Find the frequency at which you noticeably accelerate without the form falling apart.
### 4. Manage oxygen honestly The underwater phase is fast but expensive: it runs on oxygen debt. Do not go to the absolute limit — if the form falls apart or you gasp in panic, you were down too long. Better 12 clean metres than 15 falling apart.
### 5. The breakout just before the mark Place your first over-water stroke so it catches at full speed before the head must surface at 15 metres at the latest. The transition from wave to first stroke must have no glide pause — otherwise the whole speed gain fizzles right at the seam. Practise this one transition until it sits without thinking: it is the moment where most metres are lost.
## Common Mistakes - Kick from the knees: lots of motion, little propulsion. Fix: wave from the hips over the knees into the feet. - Amplitude too large: brakes and opens the streamline. Fix: undulate tight and fast. - Open streamline: drag eats the kick. Fix: hands stacked, arms by the ears. - Breakout too early: wasting the fastest phase. Fix: hold the wave toward the 15-metre mark. - Diving too long: oxygen debt and a rule breach past 15 m. Fix: time the breakout clearly before the mark.
## Safety Notes Underwater training deliberately runs on oxygen debt — the risk is called shallow-water blackout (hypoxia from holding your breath too long, sometimes after hyperventilation). Never hold deep and fast on purpose beforehand to dive longer, and practise long underwater stretches only under supervision, never alone. With dizziness, tingling or vision disturbance, surface immediately. Build distance and repetitions cautiously and keep generous rests between hard underwater sets.
## Pro Tip Train the underwater phase with a floor mark at 10 to 12 metres and the goal of still arriving accelerating there, instead of rolling out. Most people lose not at the start of the wave but at the end, when amplitude and frequency collapse. Count your kicks per dive and keep the last wave as powerful as the first. This turns the fifth stroke into your secret best-time machine — exactly the section that separates the performance levels in backstroke. Backstroke races are decided underwater.
## FAQ ### How far may I stay underwater in backstroke? Up to a maximum of 15 metres after the start and after each turn, then the head must have broken the surface. With a clean dolphin wave this phase is often faster than over-water swimming — exploiting it fully but surfacing before the mark is one of the biggest time levers in backstroke.
### Where does the propulsion of the underwater wave come from? From a body wave that starts at the hips and runs over the knees into the feet — not from pure knee extension. Think of a whip: the trunk moves little, the feet a lot. On your back the upward kick is the powerful one, and the tight streamline keeps drag low.
### Why is the underwater phase often faster than swimming? Because at the surface you fight wave drag that you partly avoid a little deeper — and because a tight, continuously undulating streamline propels very efficiently. That is exactly why the start and underwater sections are among the determinants of backstroke performance. The art is not to overdraw the speed advantage on oxygen debt.
### How do I avoid a blackout in underwater training? Never hyperventilate beforehand, never go to the absolute limit and never practise long underwater stretches alone. Shallow-water blackout often comes without warning. Build distance cautiously, surface immediately at the smallest warning signs like dizziness or tingling, and keep generous rests — speed is worthless if safety is missing.
Learn Backstroke: Relax Onto Your Back