Issue 01 · The truth about fins

Inverkeithing Competitive Amateur Swimmers (InCAS)
Apr 29
3 min read

ISSUE NO. 01 · FOR THE CURIOUS SWIMMER · APRIL 2026

EQUIPMENT · THE TRUTH ABOUT FINS

Do fins really make you a better kicker?

Most swimmers think bigger fins mean bigger power. The science says something different — and once you understand it, you will train with fins a lot smarter.

The science

Scientists tested how much extra power swimmers got from their underwater dolphin kick (UDK) when they wore fins. With small fins, swimmers got about 26% more power. That sounds great.

But here is the catch. Those small fins added 44% more surface to each foot. So the fins were a lot bigger, but the power went up by less.

A different test used really long fins. They added 360% more surface. The power only went up by 36%. Ten times more fin. Almost the same power.

Why? Two reasons. Your legs do not get ten times stronger just because your fins are bigger. And fins make you kick slower and longer than you do without them. That is a different kick. Not your race kick.

+44% more foot area with small fins · +26% more kick power produced

What it means for you

Fins are still useful. But not for the reason most swimmers think. Fins are not a magic power button. The power you build with fins on is power for kicking with fins. It does not fully carry over to racing without them.

What fins are good for: feeling the wave through your body, sensing the upkick (the part most swimmers ignore), and spotting which leg is weaker.

The smart play

Use fins to feel the kick. Not to chase fast times.
After fin reps, do barefoot reps straight away. That locks the lesson into your race kick.
Match your fin tempo to your barefoot tempo. Do not slow down just because the fins are on.
The goal: use fins so you can kick faster without them.

Take it to the pool — Worksheet 01

Know it

True or false? Fins make your legs ten times stronger when the fin surface is ten times bigger.

☐ True ☐ False

Why do you think that? Talk it through with a teammate or your coach.

Feel it

Count your kicks. Next session, push off and dolphin kick to the 15m mark. First with fins, then without. Count your kicks each time.

With fins: _____ · Barefoot: _____

What changed? Tempo, length, or both?

Train it

Contrast set. Four rounds of:

2 × 15m underwater dolphin kick (UDK) with fins, light drag
2 × 15m UDK barefoot, max effort
Sixty to ninety seconds rest between reps
One hundred easy swim between rounds

Fins overload the kick. Barefoot reps lock the lesson into your race movement.

Swim words — acronyms & terms to know

UDK · Underwater Dolphin Kick. The kick you do off the wall before you break the surface. Same dolphin shape as butterfly, but underwater.

Upkick · The part of the kick where your feet move up. Most swimmers only push down hard. Good kickers push hard both ways.

15m Rule · After a start or turn, your head must break the surface within 15 metres. Applies to freestyle, backstroke, and butterfly. Breaststroke has its own underwater rules.

Printable PDF: the worksheet version of this issue will be linked here once uploaded. Designed for poolside or print use.

Got a question about this issue? Ask your coach poolside.

Under the Surface · A coaching education series · InCAS 2026 · JC Squad