A major use of modern fitness trackers like the Fitbit Charge 3 or sport watches like the Polar Vantage V is in their daily tracking of steps/activity, heart rate, sleep…
This constant tracking allows you to know how active you have been outside of training, in your everyday life. How much you slept (and increasingly, how). If your resting heart rate is changing, which can point to a beginning health issue.
Being active in daily life – living an active life – is a major influence on fitness, maybe more so than sports training, so this matters.
Increasingly, such trackers also work with HRV (heart rate variability) measurements or SpO2 sensors for blood oxygenation measurement.
Charge 3 SpO2 – Still Unused
The Charge 3 famously includes an SpO2 sensor, has been supposed to use it only (but, at least) for recognizing sleep apnoe… and the Charge 3 still does not use its SpO2 sensor.
Vantage V HRV – Only with HR Belt
Similarly, the Polar Vantage V only measures HRV for its orthostatic test, for which it requires a heart rate chest strap such as the Polar H10 (or one of their earlier models). This test is used in the Recovery Pro function which indicates whether (according to HRV measurement) one is recovered and ready for the next training session.
I wore both devices, the Polar Vantage V and the Fitbit Charge 3, on opposite wrists, not the same, to avoid that source of potential confusion.
(Wearing multiple trackers on the same wrist puts them into different positions from where they would normally be worn, potentially changing the oHR (optical heart rate) results. And if they bump against each other, that can change e.g. the step count.)
Both Fitbit Charge 3 and Polar Vantage V ask for a setting of whether they are being worn on left or right wrist / dominant or non-dominant arm. That should at least help reduce the number of arm movements wrongly counted as steps.
The steps recorded by Fitbit Charge 3 vs. Polar Vantage V show some discrepancies.
On active days with 10,000-20,000 steps, there is an average deviation from the mean of 2500 steps. The trend lines, at least, do indicate very similar levels of activity.
The major differences here, where the Polar Vantage V counted many more steps, only result from training sessions for which I wore the Vantage, but not the Charge 3.
So, it would be more indicative of the daily tracking of steps to leave those training days out of the graph. Here you go:
This nicely shows how similar the two curves tend to be – and how different the actual values still come out to be.
You are active and/or train enough, you should better recover. Sleep. Perchance get data on it, apparently…
Tracking sleep, Polar Vantage V and Fitbit Charge 3 again agree on the trends, but produce rather divergent values.
This time, it is the Polar Vantage V that gives the higher numbers rather than the Fitbit Charge 3 (which gave a higher step count). And the difference easily amounts to 20-60 minutes.
As happens so often with such data, it is difficult to decide which result to trust.
Looking at the times the apps give me for when the devices think I fell asleep and woke up, I find them quite believable. Unfortunately, I find both quite believable…
You don’t have to be highly active, you only have to be alive to ‘burn’ calories. And thus, we get to the calculation of calorie consumption (energy expenditure) in the course of a day, given by fitness trackers and sports watches…
Calorie burn rises with activity, as measured by steps, of course. That actually makes for a simple test of logic regarding the data:
What we get from the look at the two devices’ calorie ‘measurements’ are, of course, very similar lines to those from the step count.
This actually shows the best on those days where I recorded training sessions with the Polar Vantage V, but not the Fitbit Charge 3. Again, we find a rather high discrepancy between the actual values given, anyways. And again, there are values that look similar – or rather, trends that look fitting.
Resting Heart Rate
Optical heart rate measurement is not just getting to be everywhere because it is more convenient (and to many people, feels better) than use of a chest strap. An oHR sensor also makes it possible – and here, the convenience really matters* – to measure heart rate 24/7.
(*In training, that convenience is paid for by heart rate data that is of dubious quality. This was visible in some blog posts already and will be a topic again, soon.)
What various devices, such as the Fitbit Charge 3 and Polar Vantage V, produce from that is graphs showing the heart rate throughout the day. And data about resting heart rate.
What Exactly is RHR (Resting Heart Rate)?
Funnily, though you may find an entry for resting heart rate in many apps, it is not entirely clear what they actually measure as that: Is it the lowest heart rate reached during the day? The lowest heart rate maintained for a certain amount of time?
The Polar Vantage V makes it quite obvious that it shows and differentiates between the lowest (resting) heart rate during the day and while asleep. This is rather good, but I regularly see my lowest daily HR during the time I am falling asleep or just after waking up (or what the watch thought was my waking-up time).
Looking at the trend lines, it looks like my RHR went up slightly right after the training days, which makes sense.
That I should see a difference of 10 bpm between my resting heart rate as given by Polar Vantage vs. Charge 3, though, shows that different measurements or different algorithms are at work. It seems like RHR should be a straightforward value, but it clearly isn’t.
Looking at the data here, I would tend to trust the Fitbit with its smoother trend line rather more, at least for interpreting the trend.
What to Interpret from RHR
After all, the best use of resting heart rate is to observe if it’s going up. If it is, there is a good chance that either training has been (a bit too) intense, or you are coming down with something.
The greater fluctuations that the Polar Vantage V gives (for the lowest heart rate during the day) make me fear that it was influenced by some measurement errors.
Of course, it could also be that those values are actually closer to the truth, just weren’t averaged over a certain time span. Or does the Fitbit average heart rate over too long a time to get to the RHR it gives?
Either way, the differences between the two devices are odd. Still, the trend lines from the Fitbit Charge 3 and from the Polar Vantage V’s lowest heart rate during sleep look sensible and useful.
At least when it comes to the trends, the results of the 24/7-tracking for these basic data appear believable.
They should make it possible to learn from them – and to learn the same things from Fitbit Charge 3 or Polar Vantage V.
I would not count on either device to be absolutely exact, though…
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