Weird Science – Wrist or Strap Heart Rate Monitor


OK we all think we know the answer but let’s get scientific…

1.0 Apparatus

x1 Garmin Vivoactive 3 for monitoring wrist based heart rate.

x1 Garmin Forerunner 235 paired with Garmin Dual Heart Rate Monitor Chest Strap.

x1 Heart. One owner.  43 years old.

x1 Workout.  Something to challenge the heart and the reactions of the monitors!

(for a thorough test I decided on a workout of – WU, 4x4min with 2min recovery into 4x1min with 1min recovery and finally 4x30sec with 30 sec recovery, CD)

The Apparatus

2.0 Method

  1. Upload the workout from Garmin Connect to both the Vivoactive and Forerunner Garmin watches.
  2. Pair the heart rate monitor strap with the Forerunner 235.
  3. Go outside. Establish satellite lock on both watches (one on each wrist ⌚). Start workout.
  4. Run to the beeps 🏃‍♂️.

3.0 Results

3.1 Strap Heart Rate Monitor

Pace v Heart rate (Strap)

Firstly, anyone else always see a spike in their heart rate during the first 10 minutes of an exercise before settling down? Or do I need to see a doctor? Nowadays I rarely use the strap for monitoring heart rate but always tend to find this ‘phantom spike‘ when I do. Or maybe I just need to shave my chest or wet the strap a bit more before I start?

Disregarding the early blip during the warm up phase heart rate and interval efforts are a good match. Even at the shorter sharper end of the scale recovery and effort are on track with the heart rate strap responding in ‘real time’ to exertion and recovery 👍.

3.2 Wrist Based Heart Rate Monitor

Pace v Heart Rate (Wrist)

The Garmin Vivoactive 3 was strapped to my left wrist (tightly) to monitor my heart rate for the same workout conducted at the same time as presented for the strap above. Happily, there is no phantom spike measured during the warm up and the data mirrored how I felt during the early phase of the warm up 😃.

Moving into the intervals heart rate and effort do not appear to track as well compared to the strap. The general trend is evident but not as defined compared to the strap.

4.0 Discussion

Let’s take a look at the 2 variables side by side;

Strap HR Monitor v Wrist Based HR Monitor

The above graph has been plotted 10 minutes into the workout to eliminate the ‘phantom spike’.

The tracking ‘isn’t too bad’ (scientific term), although I’m sure there must be some complex mathematics that could derive a relationship between the two lines and compute a percentage similarity. However, what is evident is that the largest discrepancies appear to be during the recovery phase, (see the dip in the blue line between 30 & 40 minutes v the orange line and similar as the workout progresses).

The wrist based monitor appears to lag v the strap monitor and does not adequately capture recovery before its time to go back to work again. Perhaps this is not surprising as the strap is closer to the beat it’s measuring and taking a direct measurement from source 🤔.

Exam Question (don’t worry it’s multiple choice)…

a). Strap Measured Heart Rate
b). Wrist Measured Heart Rate

OK now to see who has been paying attention…

Q. Considering the two graphs above (ignoring the first 10 minutes of data) which graph most accurately represents an interval workout of, 4x4min with 2min recovery into 4x1min with 1min recovery and finally 4x30sec with 30 sec recovery?

A. Graph a) or Graph b).

Obviously the answer is a) ✅. I think this is the most telling way of confirming that the strap has performed more accurately than the wrist based measure. Even without prior knowledge of the workout from graph a) it could be reasonably assumed. From considering graph b) alone determining the workout would be a challenge.

5.0 Conclusion

Ignoring the phantom spike the strap based measure is more accurate v the wrist based measure. But hell who cares, just go out and run off feel and you won’t be far away…..🏃‍♂️🏃‍♂️🏃‍♂️

Personally, I find the wrist based measure more than adequate, particularly when out for an easy run when you want to limit exertion, in this range of steady state running the wrist based measure is as accurate as the task demands – also saves you going out the door then remembering you’ve forgot to put the heart rate monitor on 🤣!!!

Note – I have conducted zero research into how these devices work to measure heart rate and the known technical pros and cons of each!

Author: Dr Neill A Weir