Endurance right after HIT - too much stress due to cardiac drift?

Hi everyone,

This is my first post; I’ve been reading for a couple of days here and I’m amazed by the interesting content and knowledgeable people that are around here!

The “problem”: After a set of hard intervals (say 4x6’ hard-start L5, most of the time ~95% maxHR) I like to keep riding 1-2h in L2 just for standard endurance adaptations. However, especially at this time of year with little hard training under the belt, I have a lot of cardiac drift after these intervals (+25bpm, coming down slowly). Hence my standard endurance pace corresponds to tempo HR.

The question(s):

  • I feel like this elevated HR provides an extra stress on my body, but is this stress beneficial in terms of training?
  • What’s going on in my body?
  • Would it be better to keep the HIIT sessions short and add the “missing hours” to the endurance rides? (I’m training about 18h/week so that’s why I usually do at least 2.5h even when I do intervals but I could redestribute the hours and make the long rides longer.)

Btw my aerobic base is good and I have no cardiac drift during long endurance rides. It’s only intensity that makes my heart go crazy afterwards.

Thanks for your answers!

Best wishes from Switzerland,


I did vo2max session yesterday (5x5min); i felt good and was not empty after the intervals so i rode 1h z2 to finish the workout. It really depends on couple things for me; what time of the year it is, how much i have base, how fit i am, what are my goals etc… Sometimes i just feel horrible after intervals and there is no point to ride another one hour.

The main point of the HIIT sessions are the intervals, so maybe you should just keep those sessions short and add more hours for easy days. Or you could make your warm up longer and do the intervals later (i have done 3-4h workouts in the past when i did my vo2max intervals on the third or fourth hour).

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Anna, how much base do you have. Last year I found that intervals were killing me with fatigue. After 12 weeks of base miles, I was able to do intervals without getting overly fatigued.

So just slow down until your HR gets into the right zone. Do long slow distance rides by HR instead of power.


Base should be fine - I’m riding very consistently all year round, no HR drift on long rides, lately endurance block since end of December ~20h/week av., but only 1 HIT/week, so definitely not used to that yet. (Starting a more intense block now.)

Somehow during the season I never have the problem of such a severe drift (otherwise it would be impossible to race :wink: ). Now every time it’s happening I just don’t know if I should train through it - maybe even some beneficial effects (fatigue resistance)?

The last few times I’ve done what you said and rode in low zone 2 power so that my HR stayed in zone 2 as well.

Do you measure HRV? I wonder if it is telling you something, like you are tired? Or, maybe fighting off a seasonal virus.

Interesting idea. I measure HRV over the night (Oura ring) but have never measured it during a training.
I don’t think anything is wrong with me health-wise; I’ve had the same phenomenon every year when I started the intense sessions. I’m just curious what’s going on and how to optimize training :wink: .

I used to do this and I know a lot of the high volume workouts for the Build period are structured like this - but, there are other physiologists who question whether it’s even possible to stress both energy systems in the same workout. I think if you look into it, opinion is mixed between the camps.

For me, personally, I think better bang for buck is to try to hit extra intervals instead of inviting fatigue from some low volume stuff on a high intensity day. If I was doing 5 or 6 minute V02 intervals and was still feeling good after 5 or 6 of those, I’d try to tack on a 6th or 7th.

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Thanks for your answer - that’s the kind of thing I was wondering about!

Good idea regarding adding some intervals in case still alive. I think I’m perhaps too worried about “getting the hours in”.

I’s guess that if you’re doing really 18-20hrs a week of mostly LSD, you should try to work in at least 2 interval sessions a week of somewhere around 90% maxHR.

Chances are you have some available adaptations that shouldn’t be too hard to grab from high intensity work, whereas you might be really getting only marginal benefit from additional low, slow distance work.

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TR has these type of workouts planned in General Build. I’ve done them without issue. It’s usually 30 mins of z2.

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That’s the plan :wink: . I just did a few weeks of mainly sub-threshold work, now starting with more VO2max workouts.

I just meant to measure HRV in the morning as a gauge of how your body is handling the stress of training and life.

I’m not sure I’d agree with that - what you’re seeing is significant cardiac drift after hard efforts - which means your base is getting a little shaky when you challenge it. Can you share the cardiac drift numbers you see for a recent workout?

Unlike the comments from others in this thread, I see significant value in adding a large endurance block before or after my intervals. It helps establish consistency in duration of effort similar to my races as well as helps to train my body to deal with extra stress

As an example, yesterday I did Baird +6 and included an extended period of time at 75% FTP after the intervals. During the first 10 minutes post intervals I was at an average HR of 146, the next 10 was at 143, next 141, and the last 10 at 137. Today I did 25 minutes at 75% FTP as an extension to Brasstown and for those 25 minutes I averaged 134 BPM

It took me a solid 30 minutes for my HR to drift into the range I’d normally consider average at that power output, but it did get there eventually.

Thus, why I am asking about what type of cardiac drift you are actually seeing. It should take a while for your HR to come down, but given proper fueling, hydration, and base fitness, you should get back to the desired HR

For what its worth below is my cardiac drift numbers for the two rides I referenced above

Baird +6


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If done on the trainer, might be dehydration, or not enough ventilation?
It’s easy to over-heat inside. Heat drives HR up.

First 10’ after intervals: 130w, 143bpm - power is only 50% of outdoor FTP i.e. L1
An hour later: 155w, 137bpm - HR still a bit high but every day is different and at least I felt normal again
(I didn’t ride at constant power after the intervals, but rather upped the power into my normal L2 range once my HR came down.)

I guess the question really is whether riding with HR drift (i.e. keeping normal L2 power and accepting that HR will be in L3 for half an hour or so) is beneficial or detrimental.

Ah, well I cannot really answer that question scientifically - I don’t know the correct answer.

I can say that it does mirror what often happens in races, so that conditioning yourself to those types of conditions seems like it should be a helpful adaptation, but that is much more anecdotal than anything else

Agree that for race-specific prep it’s important to digest the intensity and keep riding (probably even higher than L2). But I’m not in that phase yet. At the moment my focus is L5 + L2 and later on I’m going to mix things up and throw in more race-like sessions, threshold under fatigue etc.

I guess I’m taking from this related discussion that I’ll be conservative in terms of the intensity of the L2 I add in the end and rather stay at the lower end of the spectrum (-> same benefits, less fatigue).