Friday, March 19, 2021

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 a 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 track 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.

Combined with a bio-mechanical model of the human body, we can accurately show you your stroke positions at key parts of your stroke. For instance Perth squad swimmer Phip pulls wide on her left side:

And her Stroke Insight for her pull through:

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 picture of the swimmer shows the average position the heatmap represents, together with a green "target zone" which you should be hitting. That makes 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:

If you are new to swimming you are likely to have much more variability from stroke to stroke:

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, who has two really distinct clusters in her pull-through heatmap. The cluster in the target zone is on a normal stroke, the wider cluster is when breathing as ## presses out on the water to support her head whilst breathing:

It's normally easy to work out which is the breathing cluster as it shows as a deterioration in technique, typically either deeper (as with Myffy) very wide or deeper pull. 

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

Stroke Insights collects data for up to 90 minutes of swimming and we recommend you swim for at least 400m with the watch to get a full picture of your stroke over time. That said, you can see data from a single length of the pool.

To get data from both sides of your stroke simply swim for 400m on one side, then undo the strap and move to the other wrist. Don't touch any settings, just move it and start swimming again. The watch will detect the wrist change.

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

Trial Completely For Free

Keen to give this a go? Signup for a free trial at (there's also an iPhone app here). We'll analyse three of your swims completely for free!

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).

Have a question on Stroke Insights / Heatmaps and how they work? Post in the blog comments here: #add link#

What If I Don't Have An Apple Watch?

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

In fact, you can use the system 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!

* You might know Adam as a swim coach but he also has a previous career in maths and engineering which has made developing Stroke Insights possible.