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When you use a custom workout in Apple Watch (such as the dynamic run sets coming to Training Today any day now), you can receive various alerts to keep you at the right effort throughout your workout.

The available alerts vary depending on the type of workout you are doing.

For example, running outdoors gives you pace, heart rate, cadence, and power.

And for outdoor cycling, you get Speed, Heart Rate, Cadence, Power

However, for indoor running, you only get heart rate, which gave us a particular problem when designing our dynamic workout plans that need to work everywhere.

It went further than that. When discussing how to build dynamic sets, one thing Ade was keen to do, if possible, was use RPE as the alert. RPE stands for Rating of Perceived Exertion and is a purely subjective scale of 1-10, where one is very easy, and ten is all out. The benefit is that it is simple for any athlete to use this without prior data or knowledge because you can easily judge your maximum effort and work back from there.

Moreover, RPE, by its essence, incorporates your physiology into how you are feeling, and it is not reliant on a data set that could be wrong. It’s you understanding your body and how hard you can go.

However, the problem from an Apple Watch's point of view is that you can’t be alerted when you are not hitting your RPE range because how would it know?

So, there is no RPE “Alert” in Apple Watch custom workouts.

Without RPE being available, we have settled on using Heart Rate Zones for our dynamic sets because these are available for all workouts. (In the future, we will refine this to include other Alerts for specific types of workouts, such as Power in indoor cycling)

Rather than target specific heart rate numbers, Apple Watch sensibly targets heart rate zones instead.

HR zones can be calculated in many ways, and different approaches use different numbers of zones, from 5 (which Apple Watch uses) to 7 or even more in other approaches.

But let’s stick with what Apple Watch does. Here are the five zones, our explanation of each, and how they are calculated using a thing called HRR (Heart Rate Reserve)

Apple calculates your heart rate zones using the “Heart Rate Reserve” (HRR) method, which uses your Resting Heart Rate (RHR) and Maximum Heart Rate (MHR).

RHR and MHR are updated at the start of each month based on the figures collected by Apple Watch from the previous month; your Heart Rate Reserve (HRR) is then calculated by subtracting RHR from MHR, and your zones are automatically adjusted based on the table above.

So if your MHR is 168 and your RHR is 50, then your Heart Rate Reserve is 168-50 = 118, and your zones are now calculated as a percentage of that reserve plus your resting heart rate. But you don’t need to do the maths; you can see the calculation result in the Watch app on your iPhone in Workout > Heart Rate Zones.

There are some things to be careful of with how Apple Watch calculates your HR zones. For example, Apple has decided to calculate your RHR and MHR on the first of every month. I find this strange - why not use a rolling 30-day period? This decision could impact your zone calculations.

As far as I can see, Apple has not published how they calculate your RHR or MHR either, making it hard to understand if not wearing an Apple Watch overnight could impact it, for example.

So my concerns:

The best way to measure whether these zones are accurate is to relate them to your RPE. Over to Ade for a more technical description and some guidelines you can use:

Heart rate zones are a good tool for judging intensity levels and there are many different models, all variations on a similar theme. Still, they work on the same basis - that your heart rate is a good indicator of which energy system your body prioritises to produce energy in your cells.

The problem is, unless you have regular access to lab testing of lactate thresholds, etc., they represent a broad guide derived from studying a large cohort of athletes, and as we well know, individuals have their individual physiology.

So, using a simple HR zone scale to try and make accurate judgements of, for instance, when an athlete has tipped into anaerobic respiration is not very specific to that athlete.

The RPE scale has a lot going for it!

But we can also use other cues to determine which zone we are really in. Based on the Apple watch model of five HR zones you can judge them using how able you are to hold a conversation.

Zone 1: You would have no difficulty chatting to a friend in this zone while enjoying a brisk walk.

Zone 2: if you can hold a normal conversation with your running partner, you are probably in zone 2.

Zone 3: When you enter zone 3, you should be able to speak a full sentence without gasping for oxygen, but not easily manage a longer conversation.

Zone 4: In this zone the odd word or two is probably all you can manage.

Zone 5: it's probably best to stay quiet! 

I’d summarise this for me as z1 is a nice chat on a brisk walk; z2 is a conversation while running, maybe enjoying the scenery; z3 is a sentence here and there, probably something like “How much longer do you think this hill goes on for?”, z4 is more challenging and could be “Tough? yes-it-is!”, z5 is thinking don’t even look to me, please, let alone talk!

If you are following a custom workout such as one from Training Today and feel your HR zones are not aligned with what you are experiencing, you can adjust the Apple Watch HR Zones to be better aligned. You can only have exactly 5 zones.

First calculate what you think your HR Zones should be based on the discussion above. You can then adjust the zones on either Apple Watch or iPhone (they will sync across) and the custom workouts will alert you around these new zones.

On Apple Watch: Settings > Workout > Heart Rate Zones > Manual, then enter the HR ranges for each zone.

On iPhone : Watch App > Workout > Heart Rate Zones > Manual, then enter the HR ranges for each zone.

Here is what I have set mine to:

Hope that all makes sense!

As always let us know if you have any comments or questions in the comments to this post of via support@trainingtodayapp.com

Cheers!

Training Today Team

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