By Olivier Poirier-Leroy on SwimSwam
Elite underwaters aren’t just the result of kicking hard—it’s in the hips. Here’s why you should UDK from the hips, not the knees.
Fast dolphin kicking is our golden ticket to faster starts and turns… and speedier results on the clock.
And for many swimmers, once they decide to develop their underwater dolphin kick, next steps are usually:
Kick faster! Move the feet super fast! Be more dolphin, less potato!And sure, those things will help, but here’s something a little more actionable.
A recent study (Tsunokawa et al., 2025) looked at a group of competitive swimmers doing all-out dolphin kicking underwater. Researchers examined how the joints worked together and how this impacted frequency.
The swimmers who kicked more dolphin-y and less potato-y did two things with their hips that slower kickers didn’t:
The hips changed direction first
Fast kickers didn’t rely on the knees to drive and change kick direction.
Instead:
The hips initiated each change of direction The knees followed just after This timing is especially important during the transition between down-kick and up-kickThe hips first and knees second timing creates a smooth, powerful wave instead of a herky jerky, stop-start kick that crushes speed.
The hips dominate throughout the kick
Fast kickers started each kick with the hips—but the hips also remained in a leadership role throughout the movement.
In simpler terms: the hips drove the movement, not just initiated it. When the knees take over, either to try and start or to drive the kick, coordination breaks down and frequency collapses.
Downward toe speed doesn’t matter without this timing
The whole “kick faster and harder” thing is half the answer—moving the toes and feet fast is obviously necessary.
Other studies with national-level swimmers show that vertical toe speed—particularly in the upkick—is a strong indicator of fast dolphin kicking speeds (Atkinson et al., 2014).
But only when you have the right timing.
You can have “fast toes” kicking from the knees, but you won’t have a fast kick. Combining powerful drive from the hips with quick toes is what develops legendary thrust.
Get the timing right first, and the feet take care of themselves.
Practical Ways to Dolphin Kick with the Hips
Instead of trying to muscle through the kick with the knees or slicing the water with your toes, work that hip-knee timing with:
Vertical kicking – Do slow vertical kicking, emphasizing sequencing hips > knees > ankles. Dolphin kicking underwater presents a natural constraint—breath holding—which can make it more challenging to get the time and reps required to really focus on timing. Vertical kicking removes this limitation so that you can work on hip timing without running out of breath. Dolphin kicking on your side (fish kick) — Fish kicking is one of the best dolphin kick drills there is—it forces more undulation and better hip timing. Throw on a monofin to really highlight efficient timing. Fish kicks are a technique tool and also a propulsive aid—a study (Collard et al., 2008) showed that national-level swimmers kicked faster on their side versus on their front. “Flick” the hips at each part of the kick – At each phase of the kick, when the downkick starts or the upkick takes over, start the movement with a flick of the hips/pelvis to reinforce the proper timing. Dryland exercises like kettlebell swings and hip thrusts can build the hip drive for this motion.The Bottom Line
Fast dolphin kicking is such a challenge because swimmers can’t just muscle through it.
There’s a smooth and precise sequencing that needs to happen to allow vortices to form, the body wave to roll down the body, and for thrust to explode off the feet.
So if your underwaters feel:
Clunky and knee-driven Powerful but like you aren’t displacing any water Gasses you out fast without meaningful speedIt’s likely not a power or strength problem…
But a coordination problem.
So work those hips (they don’t lie).
Faster underwaters await.
Level Up Your Underwater Dolphin Kick
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
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