How to Develop an Awesome Underwater Dolphin Kick

A fast underwater dolphin kick is a blend of technique, mobility, ankle strength, and smart training. This comprehensive guide covers all four.

For swimmers who feel like their dolphin kick is stuck in first gear, or who are fed up with losing ground on each wall, what follows will improve your underwater dolphin kick. And more importantly—the times you swim on race day.

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Improve Your Underwater Dolphin Kick

Building a faster underwater dolphin kick comes down to four areas that all go hand in hand:

• Technique. Getting your dolphin kick technique right is the big first step to faster underwaters. Better kick mechanics leverages the training to come and reduces wasted effort and speed.
• Mobility/Flexibility. Improve your mobility and your ankles can generate more propulsion with every kick.
• Ankle strength. Build ankle strength for better foot positioning through the kick, and propulsion becomes more powerful and consistent.
• Training. Train it the right way and it stops being something you work on occasionally and becomes a weapon you deploy every single race.

The best underwater dolphin kickers master all four.

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The Technique Behind a Powerful Dolphin Kick

Good dolphin kick mechanics looks like a smooth, powerful, full-body movement.

The kick starts in the core, drives through the hips, and finishes with a sharp ankle snap. Technique is where most swimmers have the most to gain.

All those meters and hours of underwater kicking are only as effective as the mechanics behind it.

Early Vertical Ankle

A big ah-ha moment a lot of swimmers have is when they understand that they shouldn’t be just kicking up and down, but that they should be kicking backwards.

Water should be getting displaced horizontally and not just vertically.

This is where the concept of Early Vertical Ankle (EVA) steps in. In the same way that freestylers want an early vertical forearm (EVF) during the catch, the goal with the kick is get your ankle into a vertical position early–so that it “catches” and displaces more water for propulsion.

A more flexible ankle makes this easier, which is why the mobility work later in this guide matters as much as it does.

Remember: The feet are the main source of propulsion when kicking. The thighs, knees and hips are driving them, but it is your feet that actually are solely responsible for moving you through the water.

Finding your kick amplitude

Kick amplitude–the vertical range of the kick from the bottom of the downkick to the top of the upkick–is best done in a compact way for generating propulsion and minimizing drag.

A wider kick creates more drag, and until you have the strength and body control to generate enough propulsion to overcome that drag, a compact kick is the more effective option.

But the picture gets more nuanced at the elite level. Caeleb Dressel and Gretchen Walsh—two of the fastest underwater swimmers on the planet—both use considerably larger kick amplitudes than most swimmers.

What separates their kicks isn’t just raw power—it’s the exceptional body control and core strength that allows them to generate propulsion that outpaces the additional drag.

Your optimal kick amplitude is already built in. A meta-analysis of underwater dolphin kick studies (Veiga et al., 2022) showed that competitive swimmers consistently kick with an amplitude of 0.2 to 0.3 times their body length—the same ratio observed in fish. Rather than chasing a specific kick size, focus on building the technique and strength that lets your body find its natural range.

Kick amplitude is unique to each swimmer’s strengths, so experiment with different ranges in practice. For example:

• 25 dolphin kick with extra narrow amplitude
• 25 dolphin kick with extra wide amplitude
• 25 dolphin kick fast

The kick you use when going fast will tell you more than any blanket prescription can.

Remember: Kick amplitude isn’t one-size-fits-all. Start compact, build strength and control, and let your optimal amplitude reveal itself through testing rather than assumption.

Improve undulation

Mastering the underwater dolphin kick is frustrating for a lot of swimmers because they are not undulating properly. Instead, they kick from the knees, leading to a clunky and slow leg action that goes nowhere.

The dolphin kick is a full body wave.

Propulsive forces are generated by a wave that starts at the core and travels down the body, increasing in amplitude and power as it passes each body segment:

• The core starts the undulation, creating the wave
• The hips amplify the wave
• The knees “push” the wave down to the feet
• And the ankle and feet receive that wave and turn it into thrust

This body wave travels 2 to 2.8 times your forward speed through the water–the faster that wave travels relative to your swimming speed, the more efficiently your body is turning energy into propulsion (Veiga et al., 2022).

Stiff or clunky undulation disrupts that wave and steals potential propulsion.

Research backs this up. West et al. (2022) examined the relationship of different kinematic factors and elite dolphin kicking and found that faster swimmers moved their trunk nearly six times more than slower swimmers during the downkick.

This increased undulation meant more powerful vortices, with that movement flowing through the rest of the body. The slower swimmers, kicking from the knee, never got the wave started in the first place.

To improve dolphin kick undulation, try:

• Fish kicking — Kicking on your side naturally opens up the hips and kick, promoting more undulation.

• Experiment with amplitudes — Building on the previous point, exaggerating and minimizing the kick can help you find that faster middle with optimal undulation

• Dolphin kick on your back, arms at side — Remove the constraint of having your arms interlocked overhead and let undulation move freely.

Picture a whip when you are kicking– the handle is your core, the tail of the whip your feet.

Kick in front of you

When setting up your kick, remember that the extension of the kick should be completed in front of your body.

Russell Mark, formerly the USA Swimming National Team High Performance Manager and now high-performance consultant at ASCA, has spent considerable time researching underwater dolphin kick mechanics.

His two key focus points for developing a more powerful kick include:

• Bend your knees so that the kick takes place in front of the body.
• Follow through with your toes in front of the body too.

The following image shows what Mark means when he says that:

Notice that in all three cases that the swimmers’ respective kicks complete the down (or up, in the case of the backstroker) kick well in front of their body.

Doing so allows the swimmer to use the strength and power of their quadriceps in delivering the kick.

Remember: Most of the propulsion in the dolphin kick happens during the downkick. The execution and follow-through of the kick should take place in front of your body.

Increase toe speed

Fast dolphin kicking uses power to generate propulsion—but speed of movement is also essential.

The toes and ankles should snap up and down quickly and continuously. No pausing at the bottom or top of the kick. Just a smooth, bubbly blur.

Research with elite kickers consistently shows greater vertical toe velocity in both the upkick and downkick phases compared to slower swimmers (Veiga et al., 2022).

The downkick creates most of the propulsion in the dolphin kick, so swimmers naturally ease off and decelerate during the upkick.

But this is a mistake—increased toe velocity in the upkick is one of the strongest predictors of elite kick speeds (Atkinson et al., 2014).

Practically, increasing toe speed in the upkick closes the propulsive gap between kick phases and increases the amount of time spent generating meaningful propulsion.

The hips largely drive this early upkick peak in speed—so a strong posterior chain is essential. Back extensions, deadlifts, kettlebell swings, and Supermans are worth adding to your dryland training to build a more powerful upkick.

Kick fast in both directions

Using your up-kick takes concentration and work, especially if you have never used it before. Although the up-kick serves as a set-up motion for the down-kick, it can also serve as a means for creating propulsion.

Gary Hall Sr. is a two-time Olympic medalist, flag bearer, and founder of the legendary Race Club. He’s worked some of the fastest underwater swimmers alive, including Olympic champions Maggie Mac Neill, Nathan Adrian, and Roland Schoeman.

His assessment of what most swimmers get wrong with the UDK:

“With respect to improving underwater dolphin kick, the two most important elements missing in most swimmers are the tendency to kick from the knees, rather than undulate from the hips, and the absence of a forceful upkick.”

Research supports the propulsive case for the upkick (Hochstein and Blickhan, 2011).

Swimmers who transition quickly from downkick to upkick can reuse energy from the vortices generated during the downkick (“vortex recapture”), adding propulsion and boosting efficiency.

The transition phases are also where frontal drag spikes when dolphin kicking (Cohen et al., 2012), which is another reason to make those transitions snappy:

To improve the upkick:

• Resisted kicking — Adding drag helps isolate the dead spots in the kick cycle. Use DragSox, resistance tubing, a drag chute to highlight the deceleration in the upkick.

• Fish kicking — Kicking on your side requires a balanced kick, otherwise you will kick off into the lane rope (not ideal). Alternate 25 on either side to build a more active upkick.

Remember: The up-kick isn’t just for setting up your next big dolphin kick, it can also be used to generate a little more propulsion through the water and reducing drag.

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Ankle and Foot Mobility

Ankle flexibility is important for fast dolphin kicking—especially for beginners or swimmers with naturally stiff feet.

Multiple studies on both dolphin kicking and freestyle kicking show that increased ankle range of motion powers faster kicking speeds:

• A study with NCAA Division I and recreational swimmers showed that ankle plantar flexion showed a significant moderate correlation with flutter kicking speed. Notably, neither body size nor vertical jump power predicted kicking speed (McCullough et al., 2009).
• Restricting ankle range of motion by 30% produced a 19% decrease in kick speed (Willems et al., 2014) .
• Restricting it by just 10% caused swimmers to bend their knees more to compensate—creating drag and dropping speed by 5.8% (Kuhn & Legerlotz, 2022)
• Greater ankle extension was positively correlated with faster dolphin kicking velocity in a study of 41 experienced swimmers (Wadrzyk et al., 2019)

More flexible ankles allow swimmers to catch and displace more water, reduce excess drag, and even help mitigate excess knee bend in the kick.

Mel Stewart, the 1992 Olympic butterfly champion, made ankle flexibility a daily non-negotiable:

“Something that always gave my dolphin kick an edge was ankle flexibility. I stretched my ankles every day, before practice, at home watching TV. If you saw me out on a Saturday night, and I was standing there talking to friends, eventually you’d see me curl my foot over and stretch my ankles. I did it nonstop.”

Forefoot rotation

Swimmers typically focus on plantar flexion — the ability to point the toes straight ahead — as the key mobility target. That’s mostly right, but the forefoot plays a bigger role than most swimmers realize.

In a study by Shimojo et al. (2019), 17 national-level swimmers had their ankles taped to restrict plantar flexion before performing dolphin kick sprints.

They kicked slower—but when researchers looked at why, the answer was surprising. The tape reduced plantar flexion on land by 4%, but hydrodynamic forces in the water meant ankle angles remained largely unaffected. Swimmers kicked through the restriction.

So what caused the speed drop? The tape actually limited the ability of the forefoot to rotate inward—not toe pointing itself.

It’s a reminder that ankle mobility for dolphin kicking is more complex than simply stretching the calf and pointing the foot.

The best mobility work is kicking itself

There are lots of ways to work ankle flexibility, but simply kicking more is the best one. Every kick against the water gently pushes the feet beyond their natural range of motion.

This is as specific and functional of a stretch that you can ask for–it stretches and strengthens in the precise range of movement that matters for the dolphin kick (Willems et al., 2014).

Additional mobility drills can be used to unlock those stiff ankles:

• Lacrosse ball to the bottom of the foot. Place a lacrosse ball under the arch of your foot and apply pressure via body weight. A single 3-minute session per foot has been shown to improve ankle flexibility and lumbar mobility significantly, particularly in swimmers with poor baseline mobility (Russo et al., 2023).

• Foam roll the calf. Roll the full length of the calf, both sides, for around 45 seconds per leg.

• Ankle rotations. Using your big toe as a pointer, draw 15-20 circles in each direction. Can be paired with foam rolling.

• Wall lean stretch. This is a classic stretch, and one that you have mistaken for being an exclusively calf-stretching posture. Facing a wall, plant your foot so that your toes are pointing upwards, heel on the ground, and lean forward.

• Ankle rollers. The money maker. Sit on your ankles and slowly rock backward until your knees lift off the ground. Hold for 1-2 minutes. Daily practice produces noticeable improvements within one to two weeks.

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Strong Ankles

Ankle flexibility a lot of attention, but all that range of movement needs something behind it to create meaningful thrust. And that means ankle strength.

Strong feet are especially important when you consider that:

• Most propulsive force is generated at the feet in the dolphin kick (Nakashima et al., 2009)
• Ankle and knee motion explain 93.3% of kick velocity (Connaboy et al., 2015)
• The lower leg muscles active the longest through the kick cycle (Yamakwa et al., 2016).

Two specific muscle groups do the heavy lifting at different points of the kick:

Dorsiflexors maintain foot position and tension against the water during the upkick. Internal rotators angle the feet during the downkick for maximum propulsion.

Both were significantly correlated with faster dolphin kick velocity in a group of 26 competitive swimmers (Willems et al., 2014).

As we kick faster, the demand on these muscles also rises sharply. In a study tracking a male Olympian during high-speed dolphin kicking, ankle joint torque increased by 64.5% as kick velocity increased (Chen et al., 2022).

That’s a lot of load on a muscle group we don’t specifically train!

How to build ankle strength for faster dolphin kicking:

• Calf raises – Balls of the feet on a step, lower the heels down slowly, then drive up onto your toes. Full range mirrors what the kick demands. Progress to single-leg or add load as strength improves.

• Jump rope – Beyond raw ankle strength, skipping improves reactive strength (Trecroci et al., 2015)—perfect for faster transitions between kick phases.

• Toe raises – Strengthens the tibialis anterior, which controls dorsiflexion and maintains foot position during the upkick. Stand flat-footed and lift your toes as high as possible, heels planted.

The ankles generate most of the thrust in the dolphin kick and work harder than any other segment through the kick cycle. A few minutes of targeted work, several times per week, strengths and protects your feet, leading to faster kicking.

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Training the Dolphin Kick

Alrighty then..

We’ve talked about improving technique, flexibility, and strength. Now, to put it all together. It’s time to put this knowledge to work and actually implement it into your training.

Start here:

Kick counts

Using a kick count for your dolphin kicks at practice is essential. Elite underwaters aren’t a guess or an accident.

“I am constantly counting in practice.” – Gretchen Walsh

Set a baseline kick count for every push-off at practice—i.e. two kicks per wall—and stick to it. This removes the mental back and forth and very rapidly increases the volume of dolphin kicks being performance in training.

Pick a starting point that is doable—the goal is consistency when starting—and steadily increase over time. The beauty of the kick counting habit is that you’ll do lots of dolphin kicks in a wide variety of conditions in training, giving you automatic underwaters on race day.

“If you don’t apply it [the kick count] every time, it won’t pay off.” – Ryan Murphy

Resisted kicking

The most direct way to build a faster dolphin kick is to use resistance.

A study by Sengoku et al. (2020) had 32 elite collegiate swimmers add a short resisted dolphin kick protocol to their weekly training sessions. Both kick velocity and kick frequency improved significantly.

These were already elite kickers, meaning that resisted kicking can even find room for improvement at the top level.

Resisted kicking is so powerful because it forces higher muscular output through every part of the kick cycle. Transitions are more crisp, the upkick has to work harder, and force application goes up. Adding load simply forces the kick to work harder and organize in a way that is more efficient.

In-water resistance training consistently outperforms traditional dryland training for swim-specific performance (Guo et al., 2022). A study by Amara et al. (2022) combined in-water resisted kicking (using a drag chute) and strength training in the gym and saw big jumps in kicking performance (+6%).

Resisted kicking works best after warm-up when you are still fresh—max power output is the goal with this type of set—and can be done a couple of times per week with progressively increasing resistance.

Core training

The legs and feet create the thrust, but the core is the engine behind the dolphin kick. It starts the body wave, regulates undulation size, stabilizes the streamline, and coordinates energy transfer for propulsion.

Research by Chen et al. (2022) saw that increased core activity boosted ankle force by a whopping 25% during dolphin kicking.

The core muscles don’t fire all at once. They fire in sequence across the kick cycle—abdominals and obliques through the transition, erector spinae and multifidus through the downkick, obliques and erector spinae again through the upkick (Matsuura et al., 2020).

Load up on core exercises, including planks, pot stirrers, back extensions and hip thrusts, bird dogs and dead bugs.

Vertical kicking

Vertical kicking is a simple and highly effective kick drill for faster underwaters. It trains technique and builds strength at the same time.

Swimmers battle against buoyancy, recruiting the core and initiating the kick from the hips and trunk. To avoid bobbing like a cork, swimmers need to kick smoothly and powerfully in both directions.

A five-month study with swimmers who added vertical kicking to their training improved 50m kick times by 4.56% and reduced kick count by 7.23%–they went faster and did so more efficiently (Mandzak et al., 2020).

Vertical kicking meets you where you are—start with hands lightly sculling to stabilize body position and float, progress to your hands out of the water, and as your dolphin kick gets stronger, add load via DragSox or a medicine ball.

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Dolphin Kick Sets

Understanding the mechanics of an elite underwater dolphin kick—sets and workouts specific to faster underwaters is another.

Here are three sets that target power, a balanced kick, and general volume. Everything the aspiring dolphin kicker needs to improve this skill.

Resisted Dolphin Kicking

This is the set used in the Sengoku et al. (2020) intervention that produced big gains in dolphin kick velocity and frequency with elite swimmers. Simple, short, and to the point:

• 200m dolphin kick, alternating 50 on your front, 50 on your back. Focus on undulation and leading the kick with the hips.
• 4×5 max-effort tethered dolphin kicks with short-resistance tubing. Take full rest between rounds (~60s).

Do this set 2-3x per week and you will find your kick phases melt together, power shoot up, and underwater prowess improve.

Vertical Dolphin Kicking

Vertical kicking is one of the most useful “drills” for dolphin kicking as it allows you to quickly increase kick volume. The vertical body position also isolates the kick, forcing you to kick powerfully in both directions.

For beginner/intermediate swimmers:

• 10 rounds of 20 seconds vertical dolphin kick with high tempo + 40 seconds rest

For more advanced swimmers:

• 20 rounds of 20 seconds vertical dolphin kick fast with DragSox + 40 seconds rest

Start with hands lightly sculling to maintain balance. Progress to arms out of the water to increase load and difficulty.

The Eddie Reese Dolphin Kick Set

Eddie Reese won 15 NCAA championships at Texas and coached a staggering number of elite butterflyers and underwater kickers. Joseph Schooling, Aaron Piersol, Neil Walker, and countless others.

This is his bread-and-butter dolphin kick set:

• 5×200 butterfly kick on back with fins, on 3:00
• 6 underwater dolphin kicks off each wall in a streamlined position
• Remainder of each length: butterfly kick on back, arms at side
• Kick fast!

Reese liked this set for his athletes because kicking on the back, with arms at the side “allows a greater range of motion so there is more involvement of the abs and the quadriceps.”

The 6-kick breakout off each wall builds your kick resilience, tolerance to CO₂ buildup, and gets you comfortable under the surface.

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Wrapping Things Up

A fast underwater dolphin kick doesn’t happen by accident. It’s built—wall by wall, rep by rep—through better mechanics, more mobile ankles, stronger feet, and training that’s deliberate rather than occasional.

The swimmers who own their underwaters aren’t more gifted. They’ve just put in the work on the right things.

This guide covered the essentials.

But if you want to go deeper—full mechanics, dryland training, core essentials, training programs, drill progressions, periodization, a whole bunch of sets, and everything else that goes into building a genuinely elite underwater dolphin kick—that’s what The Dolphin Kick Manual is for.

It’s the most comprehensive resource on underwater dolphin kicking available. Everything in one place, built for swimmers who are serious about making the underwater a weapon.

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