Hi, I have this strange behaviour when I run in Zone 2, my heart rate goes up too much. I feel I’m running easy, I can talk and not tired at all, but the heart rate is much higher compared when I’m really pushing myself to the limits. I’m attaching my last 10km run, at 4:48 /km pace with average HR 139 bpm, and my last 14km run at 5:47 /km pace and average HR 156 bpm. I think this influences my plan negativity, because the sw understand I’m pushing hard but the reality I’m not!
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Hey,
My first question of course:
Are you using chest strap ?
Second:
Are you anxious about keeping your heart rate low?
Anything that changes between those training sessions?
Is this one off thing or you’ve noticed this regularly?
MJ
Are you using chest strap ?
No, only my Garmin Fenix 5
Are you anxious about keeping your heart rate low?
Absolutely not!
Anything that changes between those training sessions?
No, I did hundreds of training sessions in Zone 2 with same HR or even higher
Is this one off thing or you’ve noticed this regularly?
Regularity. In the last 3-4 years I’m not able to keep my HR low when I run Zone2.
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Hey @mlanzi
I highly recommend you to buy yourself a chest strap as optical hr measurements are notoriously inaccurate. There are several validity studies done over the years (and of course the watch companies won’t disclose these) but when comparing with chest strap, optical wrist based measurements can differ.
At lower intensities like walking, the optical HR measurement units seem to be able to keep up, but when intensity increases, they seem to loose track of the heart beat (and likely detect our gait/stride characteristics and blend those signals together and go a bit crazy).
I would assume your lower zone 2 may be more accurate but the higher intensity HR is actually the faulty measurement, but hard to know.
To eliminate the frustration and confusion, I would warmly recommend purchasing a chest strap and see if you can see a change there. 
Happy holidays,
MJ
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I can confirm what Marjaana says, although optical is inconsistent.
I’ve found they can be bang on compared to the chest or all over the place and way off. That’s the big issue. I’ve moved back to using a Polar chest strap and also using an armband for my Whoop.
The arm band would most probably not work for the Fenix!
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