Higher Heart Rate in Later Intervals

Having done Antelope this morning (disgusting), I noticed that my heart rate for the later intervals was higher, even than those of the same target power earlier in the workout. My question is, and it may be a very silly one, but is this a sign that my aerobic base is not sufficient, or is this simply what happens over time throughout a workout naturally?

Thanks guys, great product.

Yep, natural. Known as “cardiac drift”’.

Depending on the degree of the HR increase I later intervals it could be an indication of an insufficient base but within maybe 5 or so BPM this is to be expected.

It’s usually called HR drift. And it is basically caused by you fatiguing you’re faster twitch muscle fibers earlier in the workout and causing you to use a greater number of muscle fibers to get the work done.

How much higher is significant. Years ago I was using virtual power only with a dumb trainer whose resistance (I found out later) was increasing over the course of a workout. My HR increase over those workouts was significant (I thought it was normal) because in fact the early intervals were too easy and the late intervals were too hard.

I don’t think it’s too significant, but I was curious. The last interval was 3% lower in power and my heart rate was 7bpm higher. So, as the replies above have discussed (thanks for replying) it seems it may simply be a symptom of expected fatigue.

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Sometimes it’s a symptom of having a flat tire and not realizing it

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Relatively normal. Sometimes a result of dehydration, but also related to base fitness.

Nothing to really worry about.

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A symptom of fatigue is not being able to reach a high HR, so your workout response looks normal to me.