Cardiac Drift on Turbo

Hi All

Two mornings a week I do a 5.45am fasted cardio session lasting two hours. I use the erg mode on my turbo set at 160-165 watts. My ‘ftp’, (based on a 3 min max effort - 20 mins rest - 20 mins max effort on an indoor turbo) is 243w, (so 256w before the 5% reduction).

The other days a week I do one 1-2 x VO2 sessions, (either one VO2 session and one base session, or, two VO2 sessions if I feel strong). On a Sunday I do a 3-4 hour ride which is base zone with hills which I push harder on.

This morning I set the bike at 165 watts and my heart rate slowly increased from 138w after 5 minutes to 153w at the end of the 2 hours.

I use a fan and have the door wide open to help with cooling. I naturally run hot so sweat a lot and I get through two 750ml bottles of water on the ride.

So my question is this - Does cardiac drift mean much indoors? In an ideal world I guess my heart rate should end up pretty close to the stating heart rate but with heat build up in any indoor setting, should I pay attention to this cardiac drift?
If I should, is the solution to reduce watts until my heart rate sticks to a given % of the starting heart rate?

Thanks for all your input.


Assuming you meant 138bpm rising to 153bpm.

Is this your first baseline?

I throw out the first 15-30 minutes of HR data due to warmup.

20mins rest would replenish my aerobic energy and I think make FTP slightly too high to be sustainable in a longer session. That aside though, I don’t think I’d modify my FTP though to manage cardiac drift. Rather let my hr adapt to a sustainable power.

How does this compare to your other endurance rides? Or that 3 hour Saturday ride? It seems like a lot of drift to me but if you are getting really hot on these rides then that could account for some of it.


When outside I don’t have a power meter on my winter bike so I try to keep my heart rate as close to 145-150bpm by altering my speed.
My summer bike, which I will switch to soon, has a power meter and I can then check that. I live in an area with lots of small hills so we are always going up and down. Not sure how easy it will be to keep power constant but have never tried it.


This is the first time I’ve thought about checking. I have been doing these rides for about 3 months now and if I am at a slightly lower wattage, my HR stays much closer when comparing my 20 min HR and my 115 min HR. As in, without 5bpm.

Maybe it’s a matter of dropping my wattage back down to maintain a constant HR?

I was just thinking if I push a little more watts then my legs would get stronger and eventually my HR would drop back down again but now I am thinking that may be a false dawn.

This gets into coaching. Personally if its later in base (or beyond), then if HR is stable at say 150W for 2 hours (and target events are 2 hours or less), then its time to begin focusing on progressing power. In other words, I’d stick with 2 hours at 165W. But other people/coaches will have different opinions.

(and FWIW I’d still fuel these rides, and perhaps delay eating until 45-60 minutes in)

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With only a single fan, the drift is expected

Even that can be somewhat personal and can change over time, dependent on how well you are heat adapted. For example in 2019 I took 2-3 months off due to an injury, and then a 2+ week trip to Europe in August. Came home completely detrained however had been spending a lot of time outside in high heat all summer. To my surprise after getting back on the bike/trainer for only a couple weeks I was seeing low cardiac drift on 2+ hour endurance (Warren, Gibbs from TR’s traditional base) workouts in a 75-82F garage with only two modest fans for cooling. And I naturally run hot (wife calls me ‘the human briquette’ :fire:) and need 2-3 water bottles on a ride like that. First fan on the floor in front of wheel, and the second fan on top of a toolchest and pointed at the back of my head.

YMMV as they say.

I get that. I follow Francis Cade on YouTube and he has quoted research saying you need up to 9 fans to equate to the outdoor coming effect. He didn’t mention all the variable that would obviously affect that statement, (temperature, fan strength, fan position, person body temperature etc).
I know a single fan is likely to lead to overheating but wasn’t sure how significant that would be in a ventilated room early in the morning before the outdoor temperature rises.
So is your thought that the cardiac drift I experience completely normal?

I found after 90 mins my heart rate started creeping, (6 watts until that point) and in the last 15 minutes it increased again (another 5 watts).
This is why I wonder if it is body temperature or cardio fitness. My background, (from decades ago) was as a competitive gymnast for over a decade. Gymnasts don’t exactly need a great base engine and to do the sport for that long, you have to have the natural attributes of a gymnast. On the flip side, I have no natural cardio fitness on the bike…I’m better at building muscle.
I had a max test done on the bike years ago and the physiologist told me I had a ‘bloody awful base’ which was why I have been focusing on trying to improve that…and why I was looking at cardio drift as a sign of fitness when we can’t have an actual test done in Britain due to lockdown restrictions.

But even if I did this session outside, I sweat buckets so could experience overheating on a warm day so it’s hard to know just how much focus to give this. The theory makes sense, I’m not sure on the practicality of it.

I am not a competitive rider but do do sportive etc. I was planning on doing Le Etape last year but it got cancelled. I have a few century rides this year planned so my riding time can be 4 hours+ of moderate intensity (as opposed to 1-2 hour vigorous effort).

Some cardiac drift would be expected yes, as there is additional overhead imposed by cooling you.

In the attached screenshot was a test I did keeping heart rate at about the same level, and letting power decline. The green is core temperature. You can see at the same heart rate, power continues to drop and core temp rises.

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Oh, hello fellow ex-gymnast :metal: :wink:

Honestly so much drift for an endurance ride is a lot. BUT - this is one try and you definitely should not draw conclusions from one ride. Being in your shoes, I would start to keep an eye on it.
PRO tip - register to - after upload, you will see the cardiac drift calculated in an intelligent way - it takes the warm-up and cool down out and takes a comparable time slot (you can influence it) - this is so much more easy!

At the other hand, if you already know that your base is weak, this drift it totaly possible. And honestly, don´t get misunderstood - traditional “base” plan on TR carries this name, but the focus is on the Sweetspot with aim to push your ftp higher. But you do not train that long steady endurance tempo, so you don´t get that much better in it… in the words of @ambermalika you are what you train for :slight_smile:
To build a very good stable base, you simply have to spend hours in the low zone and your body - rather quickly - adapts. In my case, I sacrified a few years ago something like 8 weeks in the spring and I was just ticking miles with a friends with one goal. At least 150km and brething by the nose. After 2 000km like this, I went to the lactate test and it proved a magnificent progress in that sense - I could actualy ride endlessely in my endurance zone without any cardio drift and super stable blood lactate. At the other hand, as soon as it ramped up, my lactate sky rocketed and I failed quickly the ramp test :slight_smile: - predictably
That year, it was my plan - I build a super base like that and than did hard rides in the hills and it got me nicely through the Oetztaler Radmarathon (my first race)

Today, I wouldn´t be so strict, I don´t have any ultra endurance in sight, but in your case, I think this would be good to actualy add some really easy rides and focus on that side as a plus to the SS work

Besides, think very well about the total work load - if I read well your numbers, 165W is Z2 for you. So this is actualy not “that” easy - but that depends if you can handle the added stress. Longer Z1 rides are really a safe bet and a super way how to train easily your cardio system without risk of overload, if you have harder SS/VO2Max trainings other days…

Disclaimer - I am not a coach, nor a physio, just talking from my experiences and knowledge :wink:

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To give you a glimpse on the - here is what you get as a calculation of the cardio drift - you can see it takes into account only the portion of the ride that is similiar in the first part and in the second part (violet dots are the 1st part, red are the 2nd part) and you can modify that manualy easily with the blue scroll bar…

Not easy to have a constant power, you will see :wink:
BUT - you can do a test…warm up for 15-20 min and than choose a lap (for a nice portion of time) and use a strategy - for example you set up a constant watt goal (sustainable) and you pedal systematicaly on that power goal and stop pedalling on the downhill. Hit lap button after the first lap and pedal in the same way the second lap - than you have a direct comparison how your heart works on the same watts for longer period of time…

That’s a lot of drift at that intensity IMO, regardless of whether you’re riding indoors or not. You may or may not care depending on your training goals. But if you keep doing that same 2 hour workout for a couple weeks you will see that come down a lot, I bet.

Just keep doing that same 2hr workout every week. You’ll see HR normalize.

Hi there

I did read on this forum that there isn’t a huge difference in adaptation between cycling in a low zone 2 and a high zone 2. If I drop my watts by 10-15w my heart rate drops significantly and stays more stable.
I will repeat my afore mentioned workout a few times of the next few weeks and monitor the drift to get a better overview and then change my intensity so this doesn’t happen. Dropping my watts by 10 watts still keep me in zone 2!

Maybe I should stick to the high bar? It was so much simpler than all this physiology I don’t understand. Mind you - the release and re-grasps started to scare me just before I gave up so cycling is probably less daunting lol