Garmin Training Readiness – Not Accurate – Here’s Why

Sources of Inaccuracy

There are potentially many sources of inaccuracy ranging from the quality of the input to the correctness of the calculations and through to how you use the device.

Garmin’s latest Elevate 5 sensor is found on the Epix 2 Pro/Fenix 7 Pro and will be on most future, higher-end Garmin devices and this new generation sensor is more accurate than the previous generation. The likes of dcrainmaker have found it to be accurate during a variety of endurance sports and Fit Gear Hunter is impressed with the accuracy during gym/X-Fit activities. The Quantified Scientist is less convinced stating that the improvement over Gen 4 is modest and that deep sleep correlations are not great.

Q: Does any of that matter?

A: Yes. Mostly

Your acute training load (ATL) is a short(ish) term measurement of the load placed on your body by exercise. Its data will come from either a power meter or your heart rate monitor. So long as your optical sensor is ‘about right’ and your power meter calibrated then the ATL will be ‘correct enough’ in my experience.

Next, we look at your HRV which is a measurement of how your body is handling stress in its widest sense ie including exercise stress and general daily stress. Garmin takes this data from its optical sensor and the key measurement is based on the average of your night’s sleep. Broadly speaking this IS a scientifically correct method to use. There are quite a few factors that can make this reading incorrect, however:

• Latency – how long do you take to get to sleep? How accurate are the start sleep and end sleep points that Garmin uses to delimit the averaging period? If you lie in bed reading for an hour Garmin may well assume you are asleep… that’s really your fault and not Garmins, in my opinion! I DO expect Garmin to be accurate but I don’t expect them to perform miracles.
• Skewing of HRV – your late evening activities do impact HRV more in the first few hours of sleep. This could be from drinking alcohol or simply eating late; in both those cases and other cases your nightly HRV average will be impacted (lowered). Latency and skewing can both be reduced or even eliminated if you take a 1-3 minute manual reading every morning with a chest strap and a proper tool like HRV4Training, however, Garmin has the advantage of fully automating the data collection process overnight and, for most people, that is practical. In any case, it is also accepted as a scientifically accurate averaging method for the purposes of HRV.
• Incorrect determinations in sleep stages – The Quantified Scientists analysis against a polysomnograph (PSG, below) tool raises concerns that Garmin is much less reliable at accurately recording HRV during Deep Sleep. This is the physical regenerative phase of sleep and so I would assume it is the most important one to get right. Note that I’m not talking here about Garmin incorrectly identifying Deep Sleep, it’s more that in that period as defined externally by PSG, Garmin is less accurate. I’ve not seen any analyses that show how impactful the calculations made in deep sleep are on the overall average, I would imagine it’s quite important and I believe that WHOOP used to focus its data gathering more on those periods of sleep before changing to a similar method as Oura/Eight Sleep.
• HRV algorithms – Garmin uses widely accepted algorithms where its nightly HRV average is assessed against a multi-week moving average (your baseline range)

Then we have the tinkering in the daytime. Garmin appears to use HRV readings from during the day to potentially boost or degrade readiness. My understanding is that this is somewhat of a made-up concept and has not been widely tested. It’s wrong! Although to get an alert that you might be recovering faster is also useful.

Then we come to the single-digit assessment of your entire training readiness. It’s great that it’s a simple percentage number. Everyone can understand that. However, I would challenge Garmin and all the other tech vendors to show the science behind how they add together all these disparate measures. AFAIK they are not additive. It’s wrong.

I think Garmin has also missed a trick by excluding ‘feel’. At the end of every workout on most high-end Garmins, you can now assign your RPE and FEEL to each workout. Garmin could use a similar approach to assess your feel when you wake and add that to the readiness score. But then, of course, it’s just yet another factor that can’t really be combined with the others!

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A Mis-Interpretation of One Reading

OK, I showed you this image at the top and the corresponding one below comes out of Connect both places give you the breakdown.

I think that Garmin’s algorithms are working as intended when this is produced. However, you would have thought that this is basically saying ‘Stay in bed’. The readiness of “1” is starkly clear, right? Well, no. It means that I shouldn’t train hard and I would say that is a correct reflection of what I should avoid today. If you look at the HRV Status then you will see it is ‘High’ or within my normal range (which it is). I am specifically trying to overload my body at the moment to elicit a certain endurance training response and today is the end of a hard training block. Thus, as my body is coping, I’m going to do something similar again today.

Or as Garmin say…

If you are using a block-based training model, then a lower training readiness score during a deliberate overload period likely echoes that work. Against that background, you should still check to see which factors are driving that lower score. Higher than normal acute training loads and longer recovery time estimates can be expected during block training. Reduced readiness caused by other factors (e.g., sleep history or high stress) might be a reason to re-evaluate your approach.[Garmin]

I would thus argue that the simple Garmin number is also misleading, adding to other sources of inaccuracy. Perhaps there needs to be a ‘Readiness to train AT ALL’ number and a ‘READINESS to train HARD’ number. I am TOTALLY ready to train today but, in agreement with Garmin to a degree, I am absolutely not ready to train hard.

As a counter-example, HRV4Training clearly and correctly (IMHO) tells me to stick to the plan…

I think Garmin has the presentation and interpretation wrong. Although I’m pretty sure they do understand the data they work with.

Tip: If you want to ‘just train’ check your HRV score

Tip: If you are following a plan and have low readiness on an intense day…replan

Take Out

Hopefully, the information above gives you an idea of why your Garmin readiness reading might be incorrect and/or confusing.

Readiness may well turn out to be useful for you so keep using it if that’s the case. FWIW, I would say that Garmin Readiness is useful to me but that it is not definitively correct and I treat it with caution.

I do use Garmin readiness each day but I also have other HRV/readiness tools including WHOOP, Oura, HRV4Training, Athlytic (Apple Watch) and Eight Sleep. They’re all pretty good and, in my opinion, even better when they all agree with each other 😉 WHOOP and Oura are more easily worn and HRV4Trainign is probably the most correct. I especially like Eight Sleep as it gives scientifically validated nightly HRV averages and adjusts bed temperatures to boost HRV and recovery

Fit Gear Hunter

Quantified Scientist