I recently completely Open 120, and it’s really obvious that cardiac drift set in at around 90 minutes. Power was very constant, but heart rate definitely crept up although still remained in zone 2. It got me thinking though, if I had had an even longer ride planned, should I have been reducing power to keep heart rate in zone 2, or keeping power the same and accept the cardiac drift? And to make improvements to the aerobic engine, should we be trying to do endurance rides long enough to cause the cardiac drift or stopping at the point cardiac drift occurs?
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Accept that you are going to drift up and keep power steady in Zone 2. You might want to lower the amount if you are going into Zone 4 HR though…
I have just done open 120 and my HR went from 104 to 110 bpm (Zone 2 for me is 95 to 117) by the end of the whole 2 hours. It would take a lot more effort than 65% ftp to get me to go into zone 3
You’ve a better aerobic engine than me then! If you ride zone 2 long enough then cardiac drift will happen. It can also go with poor fuelling, hydration and cooling too, but even with those controlled you will experience it if you ride long enough, but when is individual and can be altered with training.
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I’m kinda glad you can do this. Folks who are post COVID can see much different results. The key is that your heart rate should increase over a period of time, unless you are well trained or a super human. I would see a difference of about five BPM over an hour for a Z2 ride on the trainer. A recovery (Z1) ride would see very little difference and maybe a decrease in BPM.
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Regarding the contribution of (de)hydration to cardiac drift, there is a mention of that in this episode of the Knowledge podcast.
I think I’d be inclined to accept the drift and maintain constant power.
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I have a 3 hour Zone 2 coming up this week on my TT plan (not looking forward to it though!) will see how that goes and whether I drift into zone 3. I will get back with the results
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Just finished my 3 hour Zone2 endurance ride. For me Zone 2 is (95-117 BPM). The workout varies in 10 minute sections between 55-65% FTP but I increased that for me to 60-70% of my FTP. I started at 104 BPM and during the 60% efforts I maxed out at 107-108 BPM and with the 70% efforts it was 109-110BPM and it kept stable throughout, no drifting anywhere near zone 3. My max was 113 and that was during eating and drinking then it dropped back down to those other figures a few seconds after.
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As long as heart rate remains within Zone 2 then keep the intensity power wise the same throughout. If the heart rate increases beyond that then reduce the power a bit as the physiological stress you will be experiencing will have increased. Be that from heat, hydration, fuelling, or aerobic conditioning
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Thanks @Coach.Andy.T. From an aerobic conditioning perspective is it worth trying to ride until we experience cardiac drift in an effort to improve it, or will that come regardless with better aerobic fitness? I appreciate it might be hard to always know when cardiac drift is only down to conditioning rather than any of the other factors that might come into play.
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Cardiac drift can happen under most circumstances, but one thing that will definitely bring it on in a hurry is elevated core temperatures. I will see a low level of it riding in a 10C room (and that’s supposed to be optimal for indoor training). Move the temperature to 20C (or higher) and I see drift after 30 minutes and it will increase as time passes OR the temperature increases by as little as two degrees. That is even if I have a big and powerful fan is blowing.
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So cardiac drift is generally a way of determining if you are staying below Lactate threshold 1, the turn point for when lactate starts being generated quicker than it is cleared. On a lactate graph it is the first noticeable increase in Black before the sharp shift which is LT2 or can signal MLSS/FTP/CP and various descriptors for aerobic threshold.
Anyway, all thresholds are variable day to day and also during a ride due to conditions. As you ride more, maybe your substrate availability decreases, temp increase, and your LT1 essentially decreases. This is why HR starts to increase relative to watts as your body is trying to clear the buildup of metabolites and probably wanting to burn more carbs as well due to increased oxygen demand to assist with clearance of byproducts.
For the athletes I coach, for sticking to Z2 I look for maintaining Z2 HR, there is likely still a bit of drift, but if HR remains in Z2 and the drift is <5% then I see that as acceptable. If they are training for heat or we’re intentionally trying to see fatigue resistance, then I want them to experience cardiac drift. Need to be careful how we measure it though. Say your ride finishes in a town, with stop start traffic. Power goes to zero, but HR remains maybe 100 BPM even when stopped or coasting, so that gives the impression of cardiac drift. Turbo is the best way to monitor it. Stopping mid-ride can also exacerbate it, or efforts/surges throughout.
Sorry, very wordy answer. But long story short, aim to keep HR in Z2 when doing Z2 training, and cardiac drift within 5%
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I tried to do heat acclimatisation for the Tour of Portugal last year. Turbo, no fan, winter kit, and SS efforts. Z2 the HR kept going up to 150 (SS HR), then in SS HR went to 180 (near max) and recovery was at 160. Heat plays a huge factor
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Thanks for taking the time to reply @Coach.Andy.T I appreciate the wordy answer!
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