Cannot get my heart rate above threshold

First a little background on myself, as I am a new user here ;):

My activity level has gone up and down over the years. As a teenager a did a lot of biking on the road. During university years, it was more partying than sporting though. Then I started mountainbiking, did that a lot, participated in mountainbike marathons, up to 120km/5000hm on one day. Then family+kids came, and my activities dropped again. A couple of years ago I started running, mainly trailrunning. I think about 20-30km per week. Last year I almost did not run though, for various reasons, but mainly lack of motivation. A few months ago I got a new watch (Garmin Forerunner 245) and this watch gave me a motivation boost. In the past I had used heart rate watches, but always only very simple ones. But this Garmin watch has so many features, navigation, health statistics, etc. Somehow this watch gave me the motivation to start running again. Now I am 51 years old, and running about 30km/week.

One of the features that I like on my Garmin watch is the recommended workout. My runs are usually slow long runs, but my watch once in a while suggests to do a threshold run or a vo2max run. I actually enjoy these variations in training a lot, and I guess they are good for me, so I have started to follow the recommendations. But I have trouble with the vo2max runs.

Threshold runs, where I am supposed to run with heart rate just below threshold, are fine. The typical workout is 22 minutes @155bpm. Not easy, but I can do that and maintain that heart rate during the whole workout. I have to admit that I do not know my LT heart rate exactly. I had it measured 20 years ago, it was 164 at that time, but I suppose it has dropped over the years. Based on I how I feel during the the threshold runs, I guess it is now just below 160 or so.

But when I do a vo2max run, where my heart rate is supposed to go quite a bit above threshold, I just cannot do it. Just today I did a 8x2min interval @165 bpm, at least that is what Garmin suggested me to do. ;) But my heart rate just does not go that high. Typically, during one section of 2 minutes, my heart rate steadily goes up to about 150, then starts flattening and usually never goes above 156-157. I am exhausted after two minutes. One week ago I had a 5x3min session, and I did not even manage to finish the 3minutes each time out of fatigue. Still my heart rate never went higher than about 157.

How is this possible? How can I run for 22 minutes with a 155 HR average, but if try to run faster, my HR just does not go higher than that, but I am exhausted after two minutes?

I guess it is all related to the fact that I have not done these kind of hard intervals for a long time, and my body is just not used to perform at this level. Has anybody else experienced this? And what would be your advice to me?


    If you don't use a chest strap you will not get accurate HR readings from your Garmin.   Optical HR's are only accurate at rest.   Use a chest strap, do a max HR test and then you will know what HRs you should be running at.

    this isn't for your model of Garmin but applies to all wrist based HRM's and will be in the manual somewhere

    About wrist HR accuracy... (Garmin response) - fēnix 6 series - Wearables - Garmin Forums
  • But I do use a chest trap when I am running.
    peter - in that case you need to do a max HR test so you can calculate your heart rates for training.    Your Garmin has no idea what your max is or your VO2.   If you google LT tests you can do that too and record your HR and that will give you a current LT pace too.
  • Yeah, I guess that makes sense. But regardless of my max heart rate, I am still wondering why my heart rate just does not go higher than the rate that I am able to run for twenty minutes.
    peter - that's why I thought you weren't using a chest strap.   You have turned the optical function off on your Garmin?   Maybe check battery in chest strap, if that's failed I think your Garmin will default to wrist reading.   Definitely some dodgy readings there.  But you're definitely running too fast or trying to, your LT threshold will have dropped from when you were younger/fitter but LT threshold pace you should be able to hold for about 60 minutes.   

    My MHR is 160, I do all my base training at 70-75% MHR, not WHR.   I'd run a marathon at roughly 85% MHR.
  • My base trainings are around 130, I can do that for hours without problems. I have only recently started trying these threshold and v02max trainings. I have entered a best guess for my zones, it could be true that I have guessed too high and the watch wants me to do things I am not able to do. Will look into good LT tests.

    The readings are at least consistent over the couple of runs I did at higher rates, but I will see what happens if I disable the optical function.
    Let us know how you get on.
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