Using Heatmaps To Improve Your Swimming

Our new digital platform at includes some very special new features to improve your swimming. One of which is the ability to monitor your stroke technique just by wearing an Apple Watch as you swim:

Two years in development, we call this new patent-pending system "Stroke Insights" and it's set to cause a revolution in swim coaching. No only can the system detect faults in your stroke technique but it can predict the time saving you will gain by improving your stroke and help you monitor your improvements over time.

Introducing Heatmaps

During an average swim session you are likely to swim around 1000 strokes with each arm. Using your Apple Watch, the Swim Smooth app records every rotation and acceleration of the watch on your wrist 50 times per second as you swim. Using our special algorithms developed by Swim Smooth's Adam Young, we can track every single stroke you take in three dimensions. You might know Adam as a swim coach but he also has a background in maths and engineering which has made this stroke tracking technology possible.

Using these algorithms, combined with a bio-mechanical model of the human body, we can accurately show you your stroke position at key areas of stroke technique. For instance Perth squad swimmer Phip pulls wide on her left side:

Here's her Stroke Insight for her left side pull through from the Swim Smooth platform:

Notice the dots on the heatmap. Every dot represents a single stroke, so you can see the variation in your stroke technique. There's 300m of data on that heatmap (approx 150 left arm strokes).

Note that the heatmap dots don't show the position of the watch, instead we've calculated the position of the centre of your palm and shown that instead. That's much more interesting from a coaching perspective.

The rendering of the swimmer behind the heatmap shows the most common position in the heatmap, together with a green "target zone" which you should be hitting. Those swimmer images make it easy to interpret but don't ignore the heatmap - very often you can glean extra information from it as we'll discuss below.

Heatmap Spread

The great thing about a heatmap is that it gives you an idea of the variability in your stroke. Very experienced swimmers tend to have tight heatmaps as their stroke is very repeatable:

But if you are new to swimming you are likely to have much more variability from stroke to stroke and so will see a bigger spread in the datapoints:

Pay attention to that in your own heatmaps, many of your strokes may sit within the target zone but others may fall outside - this could happen as you get tired or on a breathing stroke.

The Impact Of Breathing

If you've been following Swim Smooth for a while you will know that breathing can have a huge effect on your stroke technique. In fact we often say If something is going to go wrong in your stroke, it will happen when you breathe. With heatmaps you can see this change in your stroke really clearly, particularly on your arm recovery and pull-through underwater.

For example here's Myffy's data, who has two really distinct clusters in her pull-through heatmap. The higher cluster is on a normal stroke and is sometimes a little close to her body. The lower cluster is when breathing as her arm collapses downwards giving a deep pull through:

It's clear to see the same thing from her video footage:

It's normally obvious which is the breathing cluster as it shows as a deterioration in technique, typically becoming deeper or wider on the pull through. 

With arm recovery most swimmers rotate their body more when they breathe, bringing their hand higher and possibly more inboard. So clusters representing breathing strokes are normally higher and likely closer to the centre line: 

How Far Should You Swim?

The Swim Smooth app on your Apple Watch collects motion data for up to 90 minutes of swimming so we normally suggest you simply record your entire swim session in full and see the results afterwards. That said, you can record data from a single length of the pool and see a small heatmap for it.

To get data from both sides of your stroke simply swim on one side (we suggest at minimum of 100m but ideally at least 400m) then undo the strap, move to the other wrist and continue swimming. Don't touch any settings, just move it and start swimming again. The watch will detect the wrist change automatically.

Quick tip: Stick to freestyle when swimming on your "opposite" wrist as stroke type detection is less accurate than on your normal wrist.

For further information on how to best use your Apple Watch sign up for a free account at and watch all our introductory videos here:

Here's the system's crossover detection:

Trial Insights Completely For Free

Keen to discover your own heatmaps? Signup for a free trial of our new platform at (there's also an iPhone app here) and we'll analyse three of your swims completely for free to test things out and get you started.

At the moment this technology is only available for Apple Watch users but we hope to be able to bring to other smart watches in the future. You can use any Apple Watch from series 2 onwards (there is no difference in accuracy between devices).

What If I Don't Have An Apple Watch?

Although you need an Apple Watch to get Stroke Insights, the rest of the swim analysis platform (including our extensive training plans) are fully compatible with Garmin.

In fact, you can use Swim Smooth without wearing a watch at all, just tick off training sessions as you go and start to receive coaching feedback from how you are training.

Swim Smooth!

Have a question on Stroke Insights / Heatmaps? Post it in the blog comments here:



Anonymous said...

I just bought an Apple watch specifically for Insights. At the moment I'm skeptical about the results as I've been typed as a swinger and I'm definitely a smoothy. But, I've not swapped hands yet - AND - I mix up the session with IM work; so I'm not being fair to the tech atm. Still, what it offers is awesome and once I'm fully versed with it's capabilities I'll use it with my swimmers (I'm a Masters coach).

I have to say that this article is invaluable. Along with the video on SS it is very, very useful. Thank you SS for providing this swim education.

I'm excited to continue using the watch (especially as I shelled out a blimmin fortune for it), and do more front crawl specific swims to evaluate more objectively than I currently have; this article has encouraged me to do that.

Thank you SwimSmooth.

Stephen Jackson said...

... and for non apple users? For example, Garmin?

Anonymous said...

Pity you signed with apple. There are by far much more Garmin swimmers...

Unknown said...

yes it seems a real game-changer for all swimmers but as Stephen told you what about all triathletes that are all using Garmin watches !
All my bets to you SwimSmooth !

jolaca01 said...

Hi, I will also love to see a Garmin watch version of your app. It has gyroscope sensors as well so I can't see why you could not implement your app for Garmin watches. Apple watch is too fragile and exposed (beware pool walls!)

Walid said...

Great app! The only problem I see is that some swims do not get synched from iPhone to swimsmooth app.

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