Heart rate shown while blaze in pocket

[Perza]

Blaze was in my shorts pocket while playing beach volley (so that sand does not get to it). In other words it was not in my wrist.

I wasnt expecting to see any hearth rate readings after the workout, but only steps and active minutes and so on.

Why does it show the heart rate graph and how does it know what the heart rate was?

Is there other calculations going on in stead of pure measurement data?
HR

[Perza]

Please Fitbit, could you give an understandable or any answer?

This goes to the reliability of the heart rate readings.
How did the Blaze find heart rate readings while in the pocket? (without any bad jokes)

[bbarrera]

optical sensors attempt to estimate your heart rate by indirectly detecting blood flow under the wrist. The wrist is not the best place to do that, and a lot of factors can prevent it from working:

- sunlight

- clenching wrist as when lifting dumbbells or barbells

- sweat

- non-rhythmic movement

- locking on to a stronger "signal" such as your running pace

so your Blaze's LED sensors were madly trying to find a signal that looked like a heart rate, and you got what you got.

You can turn off HR when putting into your pocket. If your goal is more accuracy, then the gold standard chest strap is the answer. Even a chest strap can have temporary issues depending on the moisture level of your skin - happens to me once or twice a year, and I wear chest strap 5 days a week for ~50 weeks a year (workaround is to use a little electrode gel, or ignore first 5-10 minutes).

[Perza]

Thanks for the answer about optical sensor. That makes perfect sense now.
So I should have set heart rate tracking to 'off' before putting Blaze into pocket. 

[bbarrera]

Yes. Reliability while on the wrist is another topic. The simple conclusion is - if you are doing intervals or HIIT or heart rate training - use a chest strap if you care about accuracy.