Finning is one of the most important parts of our freediving.

Better finning means shorter dive times, less energy spent entering your freefall, less CO2 build-up, less lactic acid, better body position, more relaxation, and the list goes on. 

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

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

I call it, ‘big-win training’. It’s not very hard to improve our technique, but when we do it makes a big-positive impact to 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 decent finning technique. 

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

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.

3 mistakes to watch out for

Something that I’ve noticed is that most instructors & 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”

The thing is, while these phrases are of sound logic, with the aim of helping students avoid bicycle kicking and to 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 to wide for your bi fins to work properly. 

I’ll explain why over the next few sections, but this is the first thing to take in is that, These common cues are wrong.

How your fins work & why it matters

Understanding a little about 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:

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 backward-traveling 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 stops bending in direction and is still being pushed through the water. This doesn’t create forward propulsion, it creates forces that are perpendicular to your direction of movement. 

In simple terms, doing DYN 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, not where they want to go. 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 maximize 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 in my opinion just isn’t right.

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 & 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. 

For the back kick, this means mostly hip and ankle extension using the glutes and calves, and for the front kick, mostly knee extension using 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.

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 take power off the back kicks by letting our ankles collapse, meaning less efficiency and less symmetry. 
  3. We need to hold a lot of tension in the core to maintain stability, meaning more discomfort during our dives. 

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 ‘roll’.  

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 without 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 problems here once again lie 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 propulsive force, and any non-propulsive force is a waste.

A walking amplitude

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

Correct amplitude is what 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 normally 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 switch directions immediately, and this 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, both sized divers would have roughly the same distance between the front and back kick.

Alexey 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 too, as there’s a distinct loss of balance as his finning gets wider and wider.

Recommendations for Perfect 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 though 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.    

A great example of proper 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 near-perfectly even power forward and backward. Even with arms-up, she hardly rotates at all while finning and has no ankle bend.

So there you have it

A good coach and 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 over time, make the small modifications that are needed to suit your body type and equipment. 

Fin stiffness, leg length, weighting, strength, stamina… can all play a role in the ideal finning for you. Find that ideal finning, it won’t necessarily take a long time to achieve. 

Remember, finning is a big-win technique. Train is as much as possible and you will not regret it.

Need any help with your finning?

A ‘Video Analysis’ from my shop might be the right choice for you.

Send me a video of your diving. I will take a look and identify the changes and improvements that you can make. You’ll receive; an explanation of what needs to be improved on, why it might be affecting you, and a few key exercises to help fix they particular issues.