Heart rate drift after efforts over threshold

I did The Trick today for the first time. I’m not great at AC so it was really hard. After the first 1-minute set I noticed my heart rate would not go back to z1 even with a 6-minute recovery. It would just stay mid-z2 and didn’t go any lower. For the 15-minute sub-threshold section my heart rate stayed constantly around LTHR.
This constrasts with what I see happens in workouts that stay sub-threshold or around threshold. For example, at the end of on location videos my heart rate always goes back to z1.
I’ve noticed the same thing when running. Any effort over threshold and my heart rate can’t go down even with extensive recoveries.
What’s the science behind this? I don’t think it’s dehydration or the typical drift that you experience in long efforts such as 3-hour runs or very long rides. It looks like my heart rate finds a different basal state after I go far above threshold or close to my aerobic capacity. I wonder if the coaches can offer some information on the subject. Thanks!


While the specifics of everyone’s HR responses will be different if course, this sound normal to me and is my own experience.
Most especially if intervals have taken me above the threshold HR that SUF measure during 4DP tests.

Then it takes a long long time to get to Z1. Which I think is pretty normal (so even if the workouts show Z1 that’s just an algorithm remember - because the power target becomes Z1 most of the workouts aren’t adapted (some are though) to show HR any different.

Some people have tried to measure this and say HR will drop by ‘n’ beats per minute … not sure how reliable that is as again everyone’s different (down to the time of day, sleep state, fatigue state, stress state etc)

I am also the same if I’m starting below, and starting below threshold, then everything’s good :+1:

Not a cardiologist myself but from past reading I’ve gone with it’s fine to be in Z2 even after what we perceive to be decent rest intervals.

My worry is - if this is a heart concern - then of course a doctor / cardio person is the best place for advice.


Agreed. Overloaded AC efforts push my upper-end much harder, and I usually find my recoveries are nowhere near to the level I get from less intense efforts.


Take a look at some of the rides. What was Z1 HR is now a Z2 after efforts. Yes, your efforts SHOULD affect your recoveries.


Yes, definitely normal. If I do a straight 15-30 minute Z1 recovery ride and that’s it then my HR typically stays in Z1.

However, if I do a hard SUF workout - especially with MAP/AC efforts - and then do a 15-30 minute Z1 recovery ride, my HR may never get down to Z1 - or if it does, only for a couple minutes.


yeah it’s totally normal. As Martin said, for the most part hte HR target seems to match the power target and it doesn’t necessarily mean your HR should hit that zone or that it’s a problem if it doesn’t.

one potential explanation for this: It is pretty well established that your brain recruits motor units to meet force demands by starting with the smallest ones, they call this the size principle. Impulse comes via CNS, tells motor units sufficient to meet the impulse to fire, then all muscle fibers within that motor unit fire as one. As the force demands increase (e.g. you click up a few gears), the impulse is stronger and more motor units are recruited, including more bigger ones. You also start recruiting more motor units as the initially-recruited motor units fatigue.

When you do the max 1-min efforts in the trick, you are basically recruiting ALL of the motor units your CNS is going to be able to recruit (based on both force demands and fatigue progression) and you are GASSING them. You are using all of the itntramuscular ATP, all of the phosphocreatine, and a good chunk of the glycogen.

After you’re done with the interval, all that good stuff needs to be repleted, which means cellular respiration, which means oxygen. So even though you’re pedaling at zone 1 and only using the smaller motor units again, those bigger motor units are recovering and they need oxygen, so means higher heart rate. Also because those bigger motor units are not used as often as the smallest (you’re using the smallest ones all the time every day), they don’t have the same mitochondrial mass and so it takes a while.

So, totally normal. And you should also see this after sub-threshold or threshold intervals, it’ll just take a lot longer to get there. Like, if you’re doing 10 min threshold intervals, you may not see any meaningful drift until the last few intervals. but if you do a 60 minute threshold interval, you’ll most likely see hr stay elevated afterwards.

Also, just to note, if your HR is let’s say zone 3, it doesn’t mean your recoveries count as tempo work. I don’t think it works that way.

Also ETA, OP noted that they did n’t think this drift was the “typical drift” that you see during longer rides or runs. that’s partially true and partially not, because recruitment of progressively larger and less efficient motor units as the initlaly recruited ones fatigue IS actually part of the reason you’ll see HR drift during longer rides or runs. So this mechanism applies in both cases just to different degrees.


@devolikewhoa Perfect Response!


Thanks to all for the replies! This really covers all the questions I had


Fantastic response @devolikewhoa! I would give more than one like if I could :smile:


Lol y’all are nice to me!

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@devolikewhoa You have a gift of expressing things in ways that help relatively uninformed folks (like me!) grasp more of the picture, and connect more of the dots!
I appreciate the time you put into this!