Fins are a favorite with most competitive swimmers. Author very much included.
Especially when it comes to faster underwater dolphin kicking, where they can help us work undulation, improve hip drive, and simply… go lightning-fast.
The added surface area on fins also makes them a natural choice for power work.
But the impact of fins isn’t as simple as “big fins = more power.”
A lot of the speed boost we get from using fins comes from making each kick more effective, not simply making our legs produce more force.
Here’s a look at how swimmers can use fins to boost dolphin kick power when the fins come off.
Swim fins are one of the essentials for swimmers looking to improve in the water. To learn which fins work best for which type of swimmer, read my complete guide to the best swim fins for faster kicking and swimming.
The Effect of Fins on Dolphin Kick Power
A study by Wang et al. (2025) took a group of 17 swimmers and had them do a bunch of underwater dolphin kick sprints with and without fins (FINIS Zoomers, in this case).
Swimmers then did a series of semi-tethered UDK efforts with progressively increasing loads, from 21 to 93 N.
This allowed researchers to build a load-velocity profile—they could better see how swimmers maintained speed and power as resistance went up.
The big findings:
Fins increased estimated UDK power by about 26%. Swimmers increased power output from 91 W without fins to 115 W with fins. This wasn’t measured directly at the muscles but was modeled off each swimmer’s load-velocity chart.
Fins made each kick more effective. The larger surface area on fins—the fins added about 44% effective propulsive foot area—meant swimmers turned more of each kicking motion into forward propulsion. In other words, they didn’t suddenly become “26% stronger” when they put fins on.
This is a subtle difference but important because swimmers tend to think that:
Big fins = more force = more boom-boom (power).
It’s more like:
More surface area with fins = more of each kick gets turned into forward motion.
I know it probably feels like we are splitting (chlorinated) hairs a little bit, but fins improved how well swimmers applied each kicking motion more than they increased force production itself.
Fins help swimmers go faster. Your “water is wet” finding—with fins on swimmers went much faster, averaging 1.46m/s without fins and 1.70m/s with fins. A solid increase of around 16%.
Fins increased distance per kick. Kick tempo stayed relatively similar, but swimmers kicked an extra 20% further with each kick cycle with fins on.
Fins allowed swimmers to handle more resistance. The real training benefit of fins showed up as resistance increased. Swimmers maintained 10-22% more velocity with fins as load went up. Basically, fins mean we can overload the dolphin kick without sacrificing as much speed.
More Power Doesn’t Mean the Same Kick
A note of caution before you haul butt down to the pool, fins and drag chute in hand. Fins change the way you move through the water, so it’s key to mix in regular dolphin kick with this type of work.
Especially because fins can change technique and body position.
A study compared freestyle sprinting with and without fins and found that those little flippy-floppers added more “catch-up” to stroke coordination, and also reduced kick amplitude, kick depth, and stroke rate (De Matos et al., 2022).
And in the case of dolphin kicking, each kick carries a lot further down the pool—sending us an additional 20% with each kick cycle. The added speed narrows kick amplitude, too.
So the kick we do with fins on isn’t exactly the same as the one we use on race day.
If all your max and power work is done with fins, you end up awesome at fin-assisted kick without rehearsing the tempo, amplitude, and feel required for race day.
How to Program Fins for UDK Power
The key is pairing that extra overload and speed with race-specific reps without fins on.
The fins do the overloading work and the barefoot reps immediately after are where the adaptation lands into your actual race movement.
For example:
- 4 rounds:
- 2x15m UDK with fins + medium resistance (small-to-medium drag chute), fast
- 2x15m UDK barefoot no resistance, max effort
- Rest: 60-90s between reps, 100 easy swim between rounds to reset
Keep the resisted reps fast enough that the dolphin kick still looks and feels like your real dolphin kick, and not like you are wrestling the chute underwater.
Then attack the barefoot reps with the goal of carrying over that same speed, pressure, and crispiness.
Wrapping Things Up
Fins are a powerful tool for developing a stronger underwater dolphin kick… when used properly. The goal isn’t just to strap them on and go fast up and down the pool, although that can be fun in its own right.
Use them to overload the kick while maintaining speed, and then reinforce that work and make the adaptations land into your regular dolphin kick. That way, you are training the race-day tempo, amplitude, and feel for the water.
Happy kicking!
