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:


7 Effective Strategies to get you back to your swimming post-COVID: lessons learnt in Perth

 A sad sight: many swimming pools all around the world have been closed now for nearly 12 months - hopefully, an end is now in sight!

It seems like an age ago since we posted this video describing how much swim fitness you could expect to lose during the first wave of lockdowns due to the coronavirus pandemic. In fact, it was almost precisely 12 months to the day since we did. Back on the 15th March 2020, here in Perth, we’d been instructed that the wonderful Claremont Swimming Pool would be closed for a period of 4 weeks, and given that many parts of the world also had that similar mindset at that entirely uncertain time, it seemed prudent then that a video about how much swim specific fitness you might lose in a month was probably about right. How wrong we were! 

Whilst the technicalities and physiology of detraining mentioned in the above video still hold value, for many of you, the magnitude of time proved to be way off the mark. However, with the various vaccines around the world now starting to see some positive results and pools in many parts of places like the UK looking set to re-open in April, a return to the pool for many of you is now imminent. 

That all being said, if we have learned anything here in Perth about how our swimmers were initially anxious about their return to the pool (which for us, as mentioned in this blog last month about how fortunate we’ve been here, was June 8th, 2020), we are sure that the following points are likely to be going through your head as you contemplate kicking off your swimming afresh:

  • “How will I feel? Will I be even able to 'feel the water' at all?”
  • “Will all my fitness be completely gone?”
  • “Booking a lane for 45 minutes seems like such a stress and takes the fun out of relaxing into my swim!”
  • “What if I really don’t enjoy the experience?”
  • “Is it still too early? Am I physically at risk?”
  • “What if this just confirms that I’ve found a new affinity for open water swimming - or another sport - and really don’t relish a pool swim any longer?”
  • “What if this is just a temporary re-opening - will I just be wasting my time, effort, and money with so much uncertainty abound?”
  • “How exactly should I get started again?”
  • “What if I injure myself in my first few sessions back?”
  • “With no events on the horizon, is it worth me building up for anything anyway?”

These points were all echoed by our squad here in Perth, and whilst this was now 9 months ago, we hope that the benefit of foresight on how our swimmers over here dealt with these challenges will help you address some of these perspectives yourself as you venture back to the pool.

Loss of feel for the water:

Let’s start off with the aspect of loss of technical skill in the water.

One of our very earliest blogs here at Swim Smooth dating back to September 2009 was “Six is a Magic Number” - which was a short post about how, when getting back into swimming after a period of absence, it will typically take you about six sessions to regain some degree of “feel” and affinity for the water. Usually the first session feels surprisingly good as you will ordinarily place little pressure on yourself to perform well. Just experiencing being back in the water and being grateful to return to the thing that you love will carry you through.

However session two often feels a little worse due to some residual fatigue and maybe the expectation of wanting to achieve something. Then, with a good mental approach, a little tenacity and a commitment to consistency, sessions 3 to 6 will all start to improve. Coach Paul explains this very scenario from back in 2010 when he returned to swimming after a 16 month lay-off as a new parent, in our blog entitled “Dreading Getting Back to the Water?

Loss of swim specific fitness:

Let’s move on to the elephant in the room - swim-specific fitness, and perceived lack thereof.

Back in June 2018 we conducted a little experiment with the Perth Squad entitled "(Project) Going backwards in order to go forwards!” which essentially involved slowing everyone in the Squad down by 2 seconds per 100m on their current CSS times. A few thought this was a silly idea, “why slow us down when we’re already going well?” to which we simply replied, “sometimes, the positive benefit of being able to confidently hit your target times - even if it means you finish a session thinking I have more in the tank - can be highly beneficial as a line in the sand and a place to bounce back from!” 

The experiment worked really well and we were able to bring everyone’s swimming back up to a great point within just 3 or 4 weeks. Chances are you won’t have any idea where your CSS pace currently is upon returning to the pool after such a long hiatus, so the advice here is to be ultra conservative. Say you were at 1:40 per 100m for CSS prior to your lockdown, and that was 12 months ago, be really audaciously cautious and aim for some target paces of say 1:50, or 1:56 or even 2:00 per 100m in sessions 3 to 6 of your Magic Six. It might prove to be way too slow, but if it does, it’s given you a little structure, a little focus and something to start back from. Don’t be in a rush to build back too quick, take your time and use it as a chance to dial in some perfect pacing - that swim specific fitness will come back before you know it!

45 minutes is just too stressful to arrange:

So, what about the perceived stress of 45-minute individual pool bookings being too difficult to organise and not worth it? This did prove to be a bit of a sore spot for many of the swimmers here in Perth, especially as the automated booking system proved to be technically challenging for some. Those that did persist though often had the wonderful opportunity of a whole lane to themselves, and whilst this might be a rather lonely experience initially, we’d encourage you to immerse yourself in this and see it as a chance to see what it feels like for many an elite swimmer on a daily basis. 

You’ll be surprised by what you can fit in within 45 minutes with a well-structured program too. In the new version of the platform, it’s now possible to scale every one of our 1,000+ sessions to a time frame that suits your allotted pool booking spot. The system doesn’t just chop off the start and finish, it intelligently scales the entire session to give you a mini version of what you would do if you had the luxury of a typical 60-90 minute session:

Concerns about enjoyment factors:

First and foremost, COVID has taught many of us to reprioritise things in our lives and to focus on doing what we love above all else. If you are a triathlete, chances are swimming has been your weakest discipline and potentially this has meant that, at times, swimming hasn’t always been as enjoyable as say a ride in the hills with your mates or a run in the park with your dog. It’s very normal therefore that, with a forced hiatus, you might be questioning how much you’re going to enjoy this return to your swimming and whether or not it might be a bit of a letdown.

Try turning this notion around to one of having the opportunity to start afresh with a clean slate and to focus on maybe new areas of your swimming that you haven’t done to date. A great example is developing your ability to breathe bilaterally. This is great for your symmetry and will drastically improve your versatility in the open water. We’ve seen many of our squad swimmers here in Perth do just this and have had fun setting themselves a relatively simple challenge (at least in concept!).

Now might be the perfect time to “carpe diem” for your swimming and turn those concerns into positive actions that you’ll reap rewards for down the line!

Your new-found love of open water swimming:

Last month, here at Swim Smooth, we spoke about how amazed we’ve been that so many of you have turned to the open water in these uncertain times when it might never have been on your radar to swim in icy-cold temperatures pre-pandemic. As a coaching program that focuses primarily on distance freestyle swimming for open water and triathlon events, we think this has been a brilliant outcome for the sport as a whole. But does this mean that swimming in the pool should suddenly be a thing of the past for you? No, we don’t think so, and here’s why - pool swimming:

  • makes it easier to structure a session
  • helps boost swim specific fitness*
  • can be quite meditative to follow the black line and have some simple targets to achieve (as discussed in this new podcast with Coach Paul)
  • complements the joy of swimming in the great outdoors
  • (eventually) makes it easier to meet with friends of varied ability and share the same session experience

* Every February and March here in Perth our 9.30am Squad on a Monday, Wednesday, and Friday get disrupted by a conflict with school carnivals being held at the pool. This can affect us for anywhere between 12 and 15 sessions and whilst the swimmers love the change of scenery generally, everyone typically reports a small decay in swim-specific fitness when they return to the pool. This year (for the first time since the 9.30am program began in 2004), we made sure to lock in our Friday 5km “Red Mist Endurance Session” at an alternative pool, which has allowed everyone to maintain their swim-specific fitness in a much better way. It’s not the perfect venue for everyone (as it’s a little further to travel) and the time is 1hr later than normal, but it’s working and that’s the key message here: some of your pool swims might make you feel like you’re missing your new-found open water swimming idylls like a long-lost love interest, but don’t fret, pool + open water = the best of both worlds.

Concerns about injury:

A study done in Australia on 80 of their elite swimmers aged 13-25 found that 91% of them were experiencing shoulder pain. When given an MRI, 69% of the swimmers showed inflammation of the tendon of the supraspinatus muscle. Empirically, 80% of the swimmers we take for 1-2-1 Video Analysis come to us to fix their shoulders. The majority of the research out there centres on managing the pain rather than correcting the underlying issue, which typically revolves around poor swimming technique. If you’ve had time out of the water, it’s natural to expect your technique to have deteriorated and to be concerned that this might see you back on the sidelines with an injury before you’ve even got truly started again. So, what do you need to watch out for:

  1. Entering into the water thumbs-first is one of the primary causes of shoulder pain in swimming due to excessive internal rotation of the shoulder joint.
  2. Crossing the centre line in front of your head (a "crossover") is also a big no-no, but highly common for the same reason as Point 1.
  3. Pulling through too deep/straight and even too wide during your propulsive phase can also aggravate the shoulder as well.

Here are some DO and DON’T images of that:



The challenge of course is to know if you’re doing these things and to what magnitude. If you have an Apple Watch, have a go trying our unique Stroke Insights feature within the new platform that flags these aspects of the stroke on a clever heat-map image using the gyroscopes and accelerometers built within the Apple Watch to give a visual depiction of your stroke in space - here are some examples of what that might look like if you’re prone to injury:

We can then make suggestions on how to refine these aspects of your swimming using dedicated drill sequences to address these before they become an issue.

A Program Worth Following:

Finally, the feeling of not knowing how to get started, of exactly what you are preparing for, and whether it might all be for naught if the pools have to close again, are all emotions our squad here in Perth expressed back in June. Know that our Certified Swim Smooth Coaches are absolutely chomping at the bit right around the world to help you identify some new goals and to show you how to get started.

It’s been a very frustrating time for them too, so you can only imagine how their passion and enthusiasm has been mounting up over the last 12 months ready to inspire you to new heights! We’ve certainly been humbled by the squad’s response and support here in Perth since June last year with record attendances at every session, and would highly encourage you to check out your local Swim Smooth Coach’s offerings as they’re all gearing their schedules up right now.

If you happen to live too far away from one our Coaches and want to target an event in the future or just aim to simply improve your swimming to go further, faster and smoother than you have before, you’ll be pleased to know that last week we released our brand new Dynamic Training Plans feature within the new platform. Just pick an event/goal, choose your event/goal distance, tell us when your event/goal is, tell us how many times per week you plan to swim and what your current level of ability is and we’ll construct you a bespoke Training Plan to get you back on track post-COVID! 

What’s super cool about these Training Plans is that they’ll adapt to your current state of fatigue and developing fitness and as such, you may see changes to your program when they’re delivered each weekend accordingly. What’s more, you can even edit how many sessions you can slot in per week should your (or your pool’s) situation change as you progress forwards. 

Give it a try! The first 3 swims are on us! You don’t need an Apple Watch or wearable of any sort for this aspect of the platform (though we do recommend one!) - to check it out, visit or find in the app store here:!

In summary:

Getting started again with your pool swimming can always be a bit daunting. With the right approach and expectation level, a bit of structure (but not too much in the very early days!), and the positive view of this being your golden opportunity to start from a blank slate to be the best version of your swimming self, you can achieve some wonderful things.

Take it from us, our squad over here in Perth has never collectively swum so well, despite everyone’s early reservations and apprehensions. We might have been fortunate to have been back a lot longer than you, but if nothing more, know that swimming “from the future” is a wonderful thing again and you too will soon be there! 

Keep us posted with your journey back.

Swim Smooth!

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