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Struggling with Garmin’s lactate threshold test

Okay, I just finished my Garmin lactate threshold test and I am a bit surprised. My score today is the same as my score on January 17. I am struggling to believe that.

I definitely ran further today than in January. To be able to compare my scores, I always run the same course. Okay, the wind and temperature isn’t always the same, but for the rest there is no difference. Besides, I run a loop, so I have headwind and tailwind.


Heart rate zones

The Garmin lactate threshold test is a program in my Garmin Fenix watch. I warm-up for more or less 10 minutes, click a button and my watch tells me to run a couple of minutes within a certain heart rate zone. I don’t know the zones from the top of my head, but every 4 minutes the zone I have to run in, is a bit higher.

There are 5 intervals I have to do. Four of 4 minutes, one of 3 minutes. According to Garmin their watch: ‘uses your user profile information from the initial setup and your VO2 max. estimate to estimate your lactate threshold. The device will automatically detect your lactate threshold during runs at a steady, high intensity with heart rate.’


Different data, same result

That’s all fine to me, but how can the results of 2 tests be the same, if my data is so different? I mean, this is the data of January and today for each interval:

  1. 4 minutes: 660 meters – 141 bpm vs. 690 meters – 139 bpm
  2. 4 minutes: 620 meters – 146 bpm vs. 670 meters – 142 bpm
  3. 4 minutes: 700 meters – 150 bpm vs. 740 meters – 152 bpm
  4. 4 minutes: 760 meters – 161 bpm vs. 810 meters – 161 bpm
  5. 3 minutes: 620 meters – 170 bpm vs. 680 meters – 170 bpm


So today I ran further in every interval. I ran in total 30 + 50 + 40 + 50 + 60 = 230 meters further. Also my average heart rate was in my first 2 intervals today lower then in January. In interval 3 it was 2 beats per minute higher, yet I ran 40 meters more in that interval. Interval 4 and 5 my heart rate was the same as in January, but I did run 50 meters and 60 meters more. Still, my overall result is the same.


Different feeling, same result

It also felt different this time. I remember in January I had to push to get into the higher heart rate zones and it felt hard to finish that last interval. This time it went easy. I could have kept the pace of the last interval, 4 minutes and 26 seconds per kilometer, for a lot longer. Still Garmin tells me my lactate threshold is the same as in January; 167 beats per minute or a pace of 4 minutes and 58 seconds.

I know it’s just a number. It doesn’t say that much, yet it’s a test I do on a regular basis to see if my stamina is improving. I feel it is. Strava says it is. Since my test in January I ran the Houffa Trail, a 23,5 kilometers race in the Ardennes, the Ommerland trail, a 44,5 kilometers race and an ultra in Sussex. And I’m not even talking about all the training I’ve done. That’s why I am struggling to believe Garmin.

I will admit, I’ve been lazy. I’ve been trusting my Garmin. I’ve got another Lactate Threshold test – the one on this website – I can use. It requires a bit of calculation and a bit more time, but I do think it’s a lot more secure. So let’s start using that one. Starting next week, when I will make Sara do one.

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