Lactate threshold heartrate cycling vs.running

I wonder How running lactate threshold heart rate (rLTHR) and cycling lactate threshold heart rate (cLTHR) usually compare. Last week I finished an initial testing week for one of the duathlon training plans on the SYSTM app. While I was quite satisfied with the Full Frontal results, I cannot get my head around the result of the 5K running pace test. Full Frontal resulted in a cLTHR of 167 bpm which is very much what I would have expected from previous training and testing. However, the 5K running pace test results in a rLTHR of only 154. Although I only run casually, I would have expected that number to be roughly in the same ballpark as the cLTHR or even higher than cLTHR. What do you experience when comparing cLTHR and rLTHR? What’s the coache’s take on this?

Just looked at the instructions for the 5k test and they don’t make much sense, if you run the 5k in less than 20m, you’d be including the warm up in the HR calculation, which would give an artificially low value.

I’m not even a casual runner, I only run 5-10km a week at Z2 pace to add some extra volume and maintain bone density with some weight bearing exercise. I ran my first and only 5K race in Spring 2022 having only ever run in Z2 ( based on my SYSTM cycling HR zones) I paced my race effort on my cLTHR of 172bpm and could definitely have run faster or longer (i.e a full hour at threshold)

Are you using a fitness watch to measure your pace/HR on runs, depending on the platform you’ll probably get better zone information from there?

I’m way too slow to have that as an issue :wink: Anyway, to me the instruction was quite clear, that the 5K test needs to be clocked separately and I was following the prescribed warm-up routine so my HR was already in “working mode” when starting the test.

I am using a Garmin watch (Venu) which does the job quite good. However, since I do feed Garmin Connect and only with the data from the SYSTM-prescribed activities I have no other test at hand to figure out any other reliable numbers.
The only reason I am asking my question here, was that I was under the impression that rLTHR should tend to be higher than cLTHR. But maybe I am mistaken or my running skills are even worse than expected.

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What do you use for your cycling HR? Do you also using your Garmin watch, or do you use a chest strap?

I use the chest strap for cycling and running.


LT will be different in both sports… there’s much more muscles getting used in running, and much more Lactate getting used to power the running… remember Lactate is a fuel, but when you’re producing more than you’re using the biproducts of this excess (Hydrogen ions?) causes fatigue to increase quickly.