How To Perfect Your Bi-fin Technique For Freediving (+ Video Examples) 

Freediver | Blue Hole Dahab| Train Freediving

Finning is one of the most critical parts of freediving.

Better finning means shorter dive times, less energy spent entering your freefall, less CO2 production, less lactic acid, better body position, more relaxation...shall I go on?

Plus, it can make all of the normal challenges we face easier to deal with; less urge to breath, less hypoxia, easier equalisation, and more overall enjoyment of the sport.

In short, improving our finning technique is a straightforward way to enhance our overall freediving performance drastically.

But how do you improve your Bi-fin technique?

I call it a considerable positive impact on all aspects of our diving. 

This article is about bi-finning specifically, but the ‘big win’ value applies to all disciplines. 

Improving mono-fin, no-fins, and free-immersion technique(s) isn’t very demanding, but the rewards are great. The same can even be said about correct posture in static. It’s easy to work on, and the benefits are BIG.

The best part is, it doesn’t take years to develop a decent bi-finning technique. 

Depending on the problem, a good coach can fix most major issues within a pretty short time frame with sound cues, video analysis, and proper skill-oriented finning exercises. That alone can add many meters and seconds to our potential.   

And, if it’s simply a muscular issue that’s preventing proper technique, any squat-type exercises in the gym can quickly develop the strength and stamina needed to use and maintain correct form during a dive.

Three bi-fin mistakes to watch out for

Something that I’ve noticed is that most instructors and coaches (myself included, until recently) use the wrong ‘cues’ to teach proper finning technique for freediving. 

You’ll often hear; 

“Don’t bend your knee”, 

“Fin from the hip”, and 

“Use an amplitude similar to walking.”

While these phrases are of sound logic, intending to help students avoid bicycle kicking and promote a slow and relaxed kick, they are unfortunately wrong.

To fin correctly, we need to bend our knees. 

Cueing ‘fin from the hip’ promotes energy-wasting hip roll, and anywhere near your walking amplitude is wayyyyyy too wide for your bi fins to work correctly. 

I’ll explain why over the following few sections, but first, understanding how your fins work should help.

How your fins work & why it matters

Understanding how fins work can really help us zone in on how best to use them. 

Fins are “flexible foils”, and using fins to move is called “oscillating flexible foil propulsion”. If you’re interested, here’s a video illustrating just that:

How your fins work & why it matters

A simple way to describe this mechanic is: 

Freediving fins work (best) by bending in one direction and then quickly bending back equally in the other direction. 

This creates backwards-travelling vortices directly behind the fin, creating forward thrust... It makes you go forward.  

Sources of inefficiency in oscillating flexible foil propulsion (finning in this case) are when the blades don’t bend symmetrically or when the blades stall out. 

Symmetrical bending is simple enough. The front kick needs to be equal, in distance and power to the back kick to produce the most efficient forward propulsion, but what is stalling out? 

A flexible foil starts to stall when it reaches a maximum bend in one direction but is still being pushed through the water in that direction. This doesn’t create forward propulsion, and it creates forces perpendicular to your direction of movement. 

In simple terms, doing DYNb and finning too wide means the widest part of the kicks just propel the diver towards the bottom of the pool or to the surface, and not forward. Any energy not put towards the ‘direction of travel’ is a big waste.

The second type of stall is when the blades move through the water at an angle or with a twisting motion. To maximise, efficiency, the blades need to be as straight as possible. Any type of tilting to the side is once again a big waste of energy. 

Using the ideal fin-mechanics happens by improving and using technique to achieve them. 

The three common phrases used for teaching finning work against this goal. 

While they successfully cue against “horrible’ technique, they only improve it slightly to just ‘bad’ technique, which won’t allow you to develop the most efficient technique for travel. 

A word on body mechanics

Whether we like it or not, our bodies aren’t designed for swimming or finning. 

Unlike a dolphin or a fish whose body from head to tail is made up of vertebrae which can flex equally in both directions, we have legs. We evolved as land animals. 

This means a ‘push’ bias, or being much stronger in extension than in flexion. 

Our glutes (hips), quads (knee), and calves (ankle) are much bigger and stronger than their opposite muscles; hip-flexors, hamstrings, and shins. 

Also, the corresponding joints have a greater range of motion in the ‘pull’ direction than in the ‘push’ one. All of this is great for standing, walking, and lifting things up.. but not great for finning.

We need to use our ‘poor’ anatomy as best as we can for finning, and this means taking advantage of our limited range of motion in the ‘push’ direction, and using our strongest muscles to move our fins. 

This means mostly hip and ankle extension using the glutes and calves, and for the front kick, mostly knee extension us for the back kicking the quadriceps. That’s the best we can do with what we have available to us. 

The problem with “Don’t bend your knee”, “Fin from the hip”, and “Use an amplitude similar to walking” is that they magnify our imbalances, not protect against them. This means using our fins inefficiently and using up our limited O2 stores at an unnecessarily fast rate.    


Now, let’s take a look at each of the common finning methods taught in more detail.

Forget “Don’t bend your knee”

Reality check: It isn’t possible to fin forward and back equally, without using knee bend. 

Remember, our leg joints aren’t designed to bend symmetrically. If we don’t bend the knee, we’re asking our hips to do something they aren’t designed for: push (back kick) and pull (front kick) with equal force. 

Not bending the knee means that we would have to accept a combination of 3 things. 

1. Our shoulders will twist, pushed forward by our stronger back kicks. 

2. We need to compensate for asymmetric power by collapsing and bending our ankles (this happens subconsciously and a motor-reflex to imbalances)

3. We need to hold a lot of tension in the core to maintain stability, meaning stronger urge to breath, and more difficulty equalizing. 

This video (starting at 6:30) is a great example of a no-knee bend kick. Thanks to the very slow frequency of finning we can clearly see the tendency to have shoulder rotation, and the ‘hand-paddling’ to remove some of the roll.  

Ignore “Fin from the hip”

The second cue works closely with the first. In order to get students to avoid the knee-bend, instructors will often say to fin with the hip.

What this does is promote ‘hip roll’,  along a similar radius to a soccer kick.

Why, because the hip flexors are too weak to do this movement alone, we need to help them out by twisting our bodies with our abdominals.

The problem here is that at the widest part of the kicks, our femurs will be angled with the hip, and therefore the fin(s) will also be angled in the water. To be efficient, flexible foils need to move straight back and forth along an axis, not in semi-circles around a radius, which is what happens with hip-roll.

The problem here once again lies in creating tension and of course, inefficient use of the fin.

Here’s a great video illustrating leading with the hip, which causes lots of body twisting, and very clear ankle bend. Remember, any rotational force isn't a propulsive force, and any non-propulsive force is a waste.

Stop using “a walking amplitude”

Proper amplitude ties everything together. It prevents; our fins from stalling, rotational forces, bicycle kicking, and uneven power biases. 

Correct amplitude allows us to use knee extension to our advantage in the front kick, and stay within the power range of our muscles on the back kick. 

Amplitude is key, and most get it wrong. 

Think small. We almost ALL fin too wide. 

It’s the way we usually create power on land. 

How do you jump higher? Bigger extension. 

How do you run faster? Longer strides. 

But fins are fins, and to work properly, bigger isn’t better. 

Once the fin stops bending, it needs to immediately switch directions, which requires a pretty small amplitude. 

Anything more than 2/3s of our walking stride is probably too much. 

Yes there are going to be exceptions, but too wide is too wide. 

Tall divers probably need longer fins or a smaller amplitude. Their long stride can easily stall-out their fins, where a short diver could get away with ‘bigger’ strides. Objectively, measuring only the distance travelled by the fin(s), both sized divers should have roughly the same amplitude finning. 

Alexey Molchonov has the tendency to fin too wide. 

What’s great about this video is that his amplitude gradually increases over around 4-6 kick-cycles and then he resets and repeats. This makes the problems of ‘width’ easier to see, as there’s a distinct loss of balance (more shoulder rotation and spinning around the line) as his finning gets wider and wider.

Recommendations for perfect bi-finning

Any or all of the three problems mentioned above waste energy and oxygen by creating imbalances between the front and back kicks in our finning cycle.

We can either twist inefficiently through the water, push ourselves into the line/floor, or allow our ankles to bend and collapse and compensate for this uneven front-back power bais. One way or another, these problems will cost meters in your performance and make our diving feel harder than it has to.  

We can to avoid them by cueing, teaching, and training the correct movements;

1. Power the front kick with knee extension.

2. Keep your toes pointed for the back kick.

3. Use a small amplitude. 

Once the ability to perform a front and back kick is mastered, all that’s left to play with is amplitude. This is easy to coach and can quickly lead divers down the path to proper finning technique.   


An example of great form is Alenka Artnik’s 85m CWT-b dive. 

She has the best bi-finning that I can find online. 

Notice how she fins with a small amplitude, drives the front kick with knee extension, and supplies almost perfectly symmetrical power forward and backwards. Even with arms-up, she hardly rotates at all while finning and has no ankle bend.

So there you have it

A good coach can help you analyse and improve your finning, but only if they understand how to do it properly themselves. 

We need to bend our knees. 

We cannot fin from our hips. 

Big, near walking amplitudes, are bad. 

Keep those things in mind and try to avoid these common mistakes in your own training. 

My advice would be to try and copy Alenka’s finning and make the small modifications needed to suit your body type and equipment over time. 

Fin stiffness, leg length, weighting, strength, stamina… can all play a role in the ideal finning for you. Play around with it until you get it right.

Remember, finning is a big-win technique, so master it to make the rest of your diving much, much easier.

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