This post is sponsored by our friends at Aqua Knuckles! Use code MYSWIMPRO for 15% off your order.

Is it better to keep your hands cupped and fingers together when you swim, or let your fingers spread apart? We’re putting on our swim nerd hats and diving deep into science to teach you how to swim faster with your fingers open!

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The Key to Fast Swimming

When it comes to fast swimming, there are 2 areas you’ll want to focus on:

  • Decrease your resistance: Reduce drag by improving your body position. This is the easiest way to get faster.
  • Increase propulsion: Pull more water with each stroke. Dryland training helps a lot with this, but you can also work on aspects of your stroke technique to maximize force production. In this post, we’re focusing on boosting propulsion.

Related: How to Swim Freestyle with Perfect Technique

Early Vertical Forearm

The first step to increasing propulsion is to work on your catch. A proper catch starts with a solid Early Vertical Forearm (EVF), which increases the surface area you use to pull water. This essentially turns the area from your fingertips to your elbows into a large paddle!

When you combine a perfect catch with proper hand position, you’ll be unstoppable.  

Related: What is Early Vertical Forearm?

Physics 101

So, why is it faster to swim with your fingers slightly apart? It comes down to 3 physics principles:

  1. As your hand moves through the water, the layer of water around your hands and between your fingers moves as well.
  2. This “sticky” layer of water surrounding your fingers increases the surface area of your hand.
  3. The force of the water will slightly flatten the skin on the fingers, creating a webbed effect, similar to a duck or a frog.

Numerous studies have proven this to be true. A study published in the Journal of Theoretical Biology found that a hand with fingers spread slightly exerts a 5-10% greater force than a hand with fingers held tightly together. This study also found that when compared to fingers spread wide, a slight spread between fingers produced a 5-10% greater force.

So, what does that mean? Keeping your fingers just a few millimeters apart — but not too far apart — will help you increase propulsion and swim faster!

Related: Analyzing Katie Ledecky’s Freestyle Technique

In fact, researchers at the American Physical Society Division of Fluid Dynamics concluded that a finger spread of just 10 degrees (5-10mm) could boost a swimmer’s speed by 2.5% compared to swimming with fingers held together. For example, if you swim a 25-second 50-meter freestyle, you could drop a full ½ second by implementing this finger spread technique. Here’s the math:

25 Second 50 FREE * (1-2.5%) = 24.375

The Cylinder Model

For even more scientific proof, let’s look at the Cylinder Model. Think of each finger as a cylinder placed in the crossflow of the water. To determine the hand position that creates the best frontal area, we have to plug some numbers into a formula.

  • Option A = Fingers spread 5-10mm apart
  • Option B = Fingers held together
  • Option C = Fingers spread 10+mm apart

To calculate the frontal area of each of these hand positions, we’ll work with the following formula:

Frontal Area = CYL ½ pV2

  • C = Depends on calculating the Reynolds number
  • Y = Total distance across all cylinders
  • P = Fluid density
  • L = Cylinder length
  • V = Hyperbola’s velocity at infinity

After quite a bit of math, you’ll find that Option A (the 5-10mm spread) creates the ideal frontal area. 

Now you may be thinking: “This is great to know, but how do I apply this to my swim training?” We’re glad you asked!

Open Finger Training with Aqua Knuckles

Use code MYSWIMPRO for 15% off your order of Aqua Knuckles!

Some of the world’s fastest swimmers — such as Michael Phelps and Katie Ledecky — train and compete with their fingers slightly spread. And if that’s not enough reason for you to give open finger training a try, the science doesn’t lie. When you’re ready to implement open finger training, Aqua Knuckles can help!

Aqua Knuckles’ DUBL WIDE will help you train your body to default to open finger technique. Wearing the DUBL WIDE as little as a few times per week will help you get a feel for proper finger separation. Simply slip it on your middle and ring fingers and swim your workout as normal!

Each pair of DUBL WIDE Aqua Knuckles creates a 5mm spread between your fingers, making your human paddles a whole lot bigger and developing muscle memory for future workouts and races. They come in 6 sizes (based on American ring sizes) to ensure you get the perfect fit. 

More Open Finger Training Tools

Try incorporating these options to further enhance your open-finger training: 

  • Fist Drill: Swim with your hands in fists for a 25 or 50 and focus on a solid EVF and catch. Then, open up your hands and swim with open fingers. Your hands will feel huge!
  • Paddles: Paddles can help you simulate increased force production that comes with spread fingers. Don’t rely on these too much, though, because you can’t use paddles in a competition!

Have you tried Aqua Knuckles or open finger training? What do you think? Let us know below! Use code MYSWIMPRO for 15% off your order of Aqua Knuckles!



  1. Great video. ! Learned a lot. I will order the aqua knuckles. I’m up to 100 laps freestyle 25 yard pool in 56 minutes. I hope this makes me faster ( I’m a 57 year old female )

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