Fast underwaters are an essential skill for swimmers.
So it’s no surprise that Bob Bowman, coach of Michael Phelps, Leon Marchand, Regan Smith, Hubert Kos, Summer McIntosh, and countless others makes them an absolute priority in practice.
“We spend quite a bit of time trying to develop this skill,” says Bowman.
Here’s what that looks like.
Explore the kicking motion
Underwater dolphin kicking is really hard for a variety of reasons, from breathing constraints to the fact that it’s significantly more taxing than full-stroke swimming (Segovia-SanBenito et al., 2026).
But learning the movement is the hardest part of all:
- Phase timing between the trunk, hips, knees, and feet.
- Feeling the water on your feet.
- Allowing enough time for vortices to develop.
- Maintaining a good body line.
- Kicking smoothly through the transitions.
To master this movement, it is essential to explore the kicking motion in a variety of ways.
Bowman:
“I like to do a lot of kicking on their side in a streamline, I like to do kicking on their back, we do vertical kicking, so our athletes are going through a large menu of things that will help them develop that feel for what the real dolphining motion is.”
Amplitude, tempo, and range of undulation all vary by swimmer. Exploring the kick from different positions helps you find what works best for your body.
Lock in kick counts
Kick counts—pick a number of kicks you are going to do off each wall and do them on every turn and push-off—are essential for swimmers looking to build smoother and faster underwaters.
Kick counts make every wall deliberate—no more winging it, no focusing on your UDK when you “feel like it.”
Every wall, a bunch of kicks and opportunities for improvement.
“Virtually anything we do has a specified number of kicks,” he says.
Of some of his current swimmers:
- Leon Marchand: “He never doesn’t do 7 kicks on any set. Threshold, everything.”
- Regan Smith: 6-7 kicks on backstroke sets, 8 for butterfly sets. “She does it [the kick count] all the time.”
Pick a number of kicks. Hit it every wall. Make it automatic.
Often we avoid working on the things that need to be worked because we want perfect conditions or we push it down the chlorinated road.
Kick counts call your bluff and force you to kick more.
Overload the kick vertically
One massive constraint with underwater dolphin kicking? Breathing.
Vertical kicking solves that challenge—giving you more opportunities to stack reps. It also offers opportunities for overloading the kick. Resistance/load can easily be adjusted per swimmer’s ability.
Loaded vertical dolphin kicking can improve knee extensor strength—important for kicking (Suciu and Popovici, 2014). An intervention with vertical freestyle kick done over several months led to significantly improved kicking speed and better distance per kick.
Getting vertical with your dolphin kick:
- Improves body line.
- Forces swimmers to kick powerfully in both directions, improving symmetry (Thompson et al., 2026).
- Allows swimmers to work kick frequency for longer periods of time.
Michael Phelps lived on a steady diet of vertical kicking in the run-up to the Beijing Olympics and beyond.
“Some of the most effective work in the pool comes with vertical kicking,” said Phelps.
Think finning, not pushing
The underwater dolphin kick is “a finning motion, not a pushing motion” says Bowman.
Finning is another way of saying that undulation drives the movement. Initiate from the trunk and drive with the hips.
Research (Tsunokawa et al., 2025) with swimmers shows that when the hips initiate changes in direction within the kick—instead of the knees—they kick faster.
When swimmers “push” they are primarily kicking with the knees. Knee-led dolphin kicking breaks undulation, disrupts the body wave, and shatters vortices before they can really form and generate propulsion.
When you fin, you use your whole body and you kick faster through the water. (Ideal.)
Rockets
A fan favorite for developing an explosive dolphin kick—rockets!
Head over to the deeper end of the pool, sink to the bottom, push off the pool floor in a clean streamline, and vertical dolphin kick straight up like a Trident missile shooting out of the water.
Awesome for:
- Working body line
- Hyper-tight streamline
- High-tempo kicking
And just pure joy—training faster underwaters can be a lot of fun, and rockets check that box.
Progress smartly
Bowman emphasizes progression and starting where the athlete is and building up from there.
No sense trying to hold an Olympic swimmer’s kick count and crashing out halfway through warm-up.
For example, in the early 2000s, long before Michael Phelps’ huge golden run at the Beijing Olympics, Bowman and Phelps realized that the dolphin kick could become a significant advantage on race day. To improve it, they steadily increased kickout distance.
Methodically. Progressively.
“During the summer of 2002, Bob and I resolved to work that dolphin kick into my training, into my IM sets,” said Phelps. “If we did ten 400 IMs, for instance, I would dolphin kick [to 15m] on the last two, from breast to free; then work my way up to four, six, eight, and finally, ten.”
Start small:
- Use your kick count—it’ll give you a baseline to work with
- 1-2 kicks per wall (if that’s what it takes)
- Build consistency (build a streak)
- Level up as you get better (add one more kick)
Consistency and habit matter more than performance at this point.
The Bottom Line
Improvement with underwaters can feel hard, because there is a lot to improve:
- Kick technique
- Breath management/CO2 tolerance
- Leg power
- Leg endurance
- Trunk/hip/ankle mobility
- Body line control
- Streamline
And so on.
To get better, attack it from multiple angles. Work it consistently. Be intentional about kicking lots. Learn the movement.
And then, with practice and enough reps…
You’ll unleash PB-smashing underwaters in competition.
ABOUT THE AUTHOR
Olivier Poirier-Leroy is a former national-level swimmer, 2x Olympic Trials qualifier, and author of several books for swimmers, including The Dolphin Kick Manual: The Swimmer’s Ultimate Guide to a Fast Underwater Dolphin Kick.
The book is a beastly 240+ pages of actionable insights and research into elite dolphin kicking technique and performance. It details everything from mastering undulation to vortex recapturing to structuring a dryland program for dolphin kicking success.
The Dolphin Kick Manual combines evidence-based insights with a collection of 20 ready-to-go sets and a 6-week Action Plan to help swimmers set a course for dolphin kicking success.
Train smarter and kick faster.
👉👉👉 Learn more about The Dolphin Kick Manual
I don’t understand how Marchand can do 7 kicks off of every wall. Like how can you do that when descending 500s? Are his lungs just bigger than everyone else’s?
All of the articles written by this guy are good and informative but they read exactly like AI
Olivier has been writing this way since before ChatGPT was even a glimmer in Sam Altman’s eye.
I feel monifin in a long course pool is great for developing the feel of finning in both directions for symmetry
Consistent kick counts off the wall in fly can help zero in your stroke to hit the next wall perfectly every time. It takes a lot of race reps to perfect, but I found in college racing the 100 that counting kicks off the start and all three walls translated to hitting the next turn and finish in phase.
“Here comes Marchand with the big underwater – OH HE CLOSED THE GAP. LOOK AT THAT! THE FRENCH HAVE COME ALIVE” 🗣️