Heart rate monitor lag or Aerobic system not enough developed

I coach a 26 years old girl that is quite new to cycling. She is cycling since 2020. She has a lot of volume (17000km in 2021, 11 500 already this year).
She follows structured training and works with a power meter since the end of 2021. It’s been a successful year so far (finished 10th in her road race nationals championships) .
The girl is struggling with steady state Z5 workout. So we changed it to tabata 30/30 40/20 format, and it’s working better (Thanks to your great intervals videos) .

The thing is that her heart rate is either turning on or turning off even on tempo, sweetspot intervals. Her heart rate takes sometimes 5minutes to turn on.

On the internet, the reviews are all saying it is accurate.

So do you think that this lag in her heart rate is down to aerobic system that should be developed or down to a inaccurate armband heart rate monitor ?
See the graphs below for exemple, they really shows that massive lag.
What can I improve ? Classic heart rate monitor or anything special in her training for erasing that ?

Thanks fast talk for fantastic content and helping me to improve the girl training

Technical issue. Get a Polar H10. (unless she is from another planet :slight_smile: )


I wouldn’t trust any heart rate band for the arm or wrist for accurate measuring.


Wearable ECG monitor — Movesense Medical or Polar H10.

I have each of them and I prefer the Movesense MD because of the accuracy of the cardiac wave form. However, note the following article by Bruce Rogers MD

I agree completely with the prior comments.


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If you go by Dr. Seilers ‘session intent’ (high or low intensity) you don’t even need to measure anything to steer your training.

The results of you training efforts will become visible during a test or race.

But, measuring every structured training with accurate equipement is a great way to monitor your progress with high frequency.

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