HR zone inconsistency

I’m expecting the response to this to be ‘Go see a doctor, sharpish!’, but thought I’d check to see if anyone else has had similar issues, or can offer some Coachful Wisdom.

I did a 400k ride yesterday, and my heart rate went all funky on me. See the attached png (assuming I’ve done this right). For the first 100k or so, it’s all good - hit a climb, rises up to zone 4 or 5 without any issues, recovers well.
Then, it starts struggling to get to zone 4, slowly getting worse and worse until in the last 100k it never got out of zone 2, no matter what I was doing.

Typically, my average heart rate on a long ride is around 148 - it’s 130 here. The result is that my muscles aren’t getting enough oxygen pumped through, and I just lose all ability to push hard. I even have to stop halfway up climbs to recover (which is unheard of for me, for the sort of climbs I’m doing here)

This happened once before - on a 300k ride a month ago. I’d just recovered from a cold, but was feeling ok. After that, I took about a week to recover, and did a few hard hill-training rides in the following weeks, with no issues at all - but those were around 100k, so it seems to only kick in after that amount of time.

Sideline question - my nutrition approach on these rides has changed a bit, as alluded to in the ‘fuel your rides’ thread recently. I’ve been trying out Tailwind as liquid nutrition, instead of more energy bars & lucozade. Could it just be that I’m not getting enough energy in, and the heart rate is the effect, rather than the cause?

Did you feel ok overall? My HRM does some VERY funny things with my heart rate when the battery is on it’s last gasp.

However you mention you had to stop on the climbs which isn’t normal. So i guess you could be:

  • more fatigued than you realise
  • suffering from low energy availability or Red-S. Could you be seriously over training and under eating?
  • incubating some sort of bug/virus
  • be dehydrated
  • have an issue and should really get checked out

Am nkt sure a change in nutrition is the cause unless what you’re intaking is preventing fluid absorption from the gut to your bloodstream, in which case you could be seriously dehydrated. Tailwind is suppossed to bw really good for avoiding that tho…:thinking:

1 Like

OK - aside from “go see the doctor” I’ll take a stab:

Your HR chart from your 300k looks like a season of overtraining in microcosm. That “last bit” where your HR doesn’t want to leave z2 is…not great. Depressed HR is a classic sign of overtraining.

Lots of factors here - your age and fitness levels, mainly, but what kind of annual mileage do you do to support this level of effort? How much base butt-in-the-seat FTP training do you do to build towards your past month. Just saying that seems like a lot of mileage that could quickly lead to overtraining if you don’t have the base (and nutrition) to support it. Are you at all bradycardic? Do you track RHR?

And age-wise, I’m mid-50’s and still I’m starting to find that one-week of recovery isn’t enough sometimes. Seems to me like you’re (admirably) pushing yourself really hard - maybe too hard.

Take a nap, man. Oh, and see your Dr. :smirk:

(not a coach or an MD, but I’m guessing there’s nothing wrong w your heart!)


Have you noticed any change in resting heart rate or HRV, assuming you track them.

As noted by @DameLisa, HR monitors can act strangely. Usually, if the cause is not a low battery, the readings get more realistic as the ride progresses.


Exactly this. And I would argue with this volume of training (and age, etc. etc.) - you should absolutely be watching RHR (and HRV if you can manage it) for early indicators of overtraining/burnout.

My two cents, but I seriously doubt this is a hardware issue w the HRM. In my experience when the device or battery starts to go you’ll see inconsistent readings and dropouts. @nicktick 's chart looks to me like normal operation.


I agree, but in these situations you have to make sure your measuring device is correct. Coincidentally, I did a ride today and it took 9 minutes for the HRM monitor to record correctly.

1 Like

Sure, I’ve had similar issues with the contacts picking up HR. But once it does have the cardiac rhythm, it records normally - like in @nicktick’s graph. Very different problems…


I’m not going to say that everything is fine for sure (as you would need to check in with a cardiologist to confirm that), but it is quite normal during ultra-distance efforts that if you push hard early (Zone 4 & Zone 5 effort in the early hours) that you will likely see a drop in heart rate - both average and peak - later in the event. This is often simply due to the accumulated fatigue and reduction of output. Even if you’re sustaining the same power output (very unlikely), that your heart rate will be lower later in an ultra event.
Nearly 20 years ago, I raced the 24-Hour of Moab mountain bike world championships in the solo category. As you can see, my lap times for the first couple of laps were closer to 1.5 hours, and 12+ hours later the fastest I could go was about 1.8 hours (20% slower, so at least 20% less power output - though I wasn’t measuring power back then).
In my earliest laps, my average HR was about 150 (max into the 170s) and by the end my average HR was closer to 120 (max 145) for a lap of the same course.
Even comparing two similar time/duration laps - Lap 5 (1:48:30) and Lap 11 (1:51:00) that were 12-hours apart, my average HR on Lap 5 was 135 (max 158) and on Lap 6 was 120 (max 145) even though my speed (and therefore power output) was nearly the same.
If you completely regulate your effort early (avoid Zone 4 and 5 completely), its common to see a lesser drop in heart rate over an ultra distance event…as well as better maintenance of power/speed.
Hope that makes sense!


This is fascinating and makes absolute sense. Basically as your stamina wanes thru an ultra event, HR and Power capacity both decline as well. Aka fueling aside, you’re just tired.

1 Like

I’ve had 3 things happen when my battery starts to wane.

  • the odd random dropouts, have had this happen once on a dying battery
  • HR spikes, also had this once on a dying battery
  • most frequently, I get numbers that are consistently inconsitent, sort of like when a PM isn’t calibrated. They’re either too high. Or too low. Consistently. And then HR dies entirely. Is annoying. Particularly when I was having cardiac issues and I assumed it was an aging battery, but no, I really was pushing 220bpm.


1 Like

Thanks for all the comments. Really useful.

My HRM does some VERY funny things with my heart rate when the battery is on it’s last gasp.

It’s a reasonably new HRM, and the battery is registering as 60%, so I think it’s ok. I also did the ol’ count your pulse and compare to the HRM test a few times just to be sure, so I think it’s working ok. I have had issues with them before, though, so I know what you mean

you could be seriously dehydrated

I’m usually pretty good at taking on liquid, and I do the ‘colour test’ to monitor it. Think that’s ok.

Lots of factors here - your age and fitness levels, mainly, but what kind of annual mileage do you do to support this level of effort? How much base butt-in-the-seat FTP training do you do to build towards your past month. Just saying that seems like a lot of mileage that could quickly lead to overtraining if you don’t have the base (and nutrition) to support it. Are you at all bradycardic? Do you track RHR?

This is pretty much my standard routine (or half-way through it, rather) - I do Sufferfest stuff to build FTP and MAP over the winter, and then do a 100mile ride to get the legs going, usually early March. Then I fit in a Super Randonneur series (200km, 300, 400, 600) doing one ride a month, before a big event (last year 1500km in five days, this year 1650 in six, but with a bit more climbing). annual mileage is around 10,000km. The only differences are:

  • I’ve started a bit earlier this year, because my event is in June, not August
  • I’m more focused on hills this year due to the nature of the event.

So it’s been harder work, and perhaps I didn’t have enough of a break over winter. But it’s not like I’m hitting 50% or 100% more than usual - it’s just an incremental step up.

I don’t track RHR, or HRV. I don’t have a power meter on my outdoor bike, and even the heart rate monitor is slightly new - my previous one gave up the ghost before I started doing the real long distance stuff. I always just used to ride by feel. And this feels wrong - and different: I’ve done loads of endurance riding, and know what it feels like to get tired and slow at the end of the day, but this feels worse than that. And it starts way too early in the day.

And age-wise, I’m mid-50’s and still I’m starting to find that one-week of recovery isn’t enough sometimes. Seems to me like you’re (admirably) pushing yourself really hard - maybe too hard.

Late 40’s here. Damn, I’ve always felt young and invincible. I was born to suffer, not born to age!
But yes - perhaps it is just fatigue. I had my 600km ride planned for a month’s time - I’m going to try taking it really easy for a few weeks and see how things go for that. And maybe tone down the ride itself…

1 Like

Years of experience, with dropping heart rate during exercise, two things:

  1. Your heart rate WILL drop if your glycogen stores are depleted. It’s called the dreaded “bonk”. You might feel ok but your heart can’t keep up. Good thing is it is temporary.
  2. You are overtraining. That’s really serious. Why? Your body cannot produce enough glycogen to even start. You run out of glycogen stores and your body cannot make any more. You’ll finish but your body is taking the brunt of it. There’s a way your body consumes itself to make energy and that’s never desired. The real problem is that it will take months to recover.
    So, which is the case? Take a day rest. What happens to your RHR? Did it return to normal? You just overdid it. If it doesn’t or it takes several rest/recovery days, you are overtrained and need to back down for an extended period of time.

Having had a few days to think, and see what happens with my body, I think it’s a combination of both nutrition and overtraining.
On the nutrition side, my stomach wasn’t feeling quite right for the last few hours - bloated, gassy, not nauseous, but no desire to eat. And in the days that followed, it’s been pretty clear something wasn’t right. I’m going to blame Tailwind and try going back to my previous regimen (flawed as it was, at least it worked, and I know how to work around the potential issues). I didn’t feel like I was bonking, but it could just be that the Tailwind was taking the edge off so I was able to keep a base level of function, but not anything above that.

On the training side - I think the delayed scheduling of the Wahoolimabob Tour (and the fact that I was a bit of an arse about it and took umbrage at the low intensity, pushing harder than I should have), combined with the earlier start of my normal outdoor training is the issue.

I’ve taken my RHR a couple of times since then, and it’s at 60, which I think is about the lowest I’ve ever measured it (which is not regularly). I’m going to take things easy for a couple of weeks, see how I feel on a 100k ride, and then judge how to take it from there.

Thanks again for the help - really good to get some quality advice.


Helps that you appear to know what you’re doing and are on top of things!

Best of luck going forward.

When you focus on nutrition, do not forget the post-ride fueling as well. You need the glycogen there (among the other protein and nutrients you need) as well for recovery.

1 Like

Something im experimenting with is using beet juice extract. I used it yesterday and my HR was consistently beliw zone. Today, i didn’t use it and my heart rate was at the top of the zone. I think i fiund a solution for longer rides

1 Like

No personal experience but I’ve seen David Weir (GB para-athlete) talk about beetroot several times. And he did ok…

You obviously just weren’t suffering enough!

I’ll chime in, as much because of the Tailwind connection as the dropping HR issue. Maybe several things that piqued my interest, actually.
I’ve done HammerGel for somewhere around 2 decades, I think. No plan to change that, honestly. I’m 65, mountain biker since about mid-30’s and got back into road biking around 40, when I started a little mtb racing too.
So a few weeks ago, talking to a fellow rider in our area who does a longer race about every year (266 miles mtb, I think it is), said to me as we were talking about my struggles with declining power, “You should try Tailwind. That Hammer stuff is pretty old school.”
Can’t argue with him, but at my age, most things are “old school.” :slight_smile:

(I stayed with 26" wheels LONG after 29" was standard, rode my '98 and '99 model Klein Mantras into the ground, and when frame fails were finally FINAL, I relented and upgraded to a carbon fiber Trek Fuel EX 29. 7 years later, it’s still my joy on the trails.
Similarly moved to a 2020 Domane SLR6 summer of 2019 and am loving bigger, softer tires and comfort geometry. It fits my older body well, and I can still go fairly fast uphill, and can rip downhills better than ever before.)

SO, I wasn’t easily convinced about Tailwind. I researched some, still not convinced. Simple sugars led to stomach upset issues in my earliest mtb racing, and when HammerGel came along, it seemed to stop the problems. I’m not well disciplined at getting the food IN as soon as I should, and that is PROBABLY the biggest reason I sometimes have been running out of power during rides. (I have had some serious health issues last fall that lasted into early this year, but am finally seeing most all metrics getting back close to where they were. I’ll leave that out of discussion here.)
The friend’s perspective is that Tailwind works for him, and he said something like, “You just have to keep feeding it to avoid the bonk.”
I’m not likely to be successful with that, I’m afraid.
So I’ve STAYED with HammerGel AND (more importantly and more effectively) Hammer Perpetuem in my drink, along with their FIZZ electrolytes tablets in the drink bottles. I do NOT ride the distances @nicktick has been doing, but I probably do more annual miles, 7,000-8,000 miles per year last 3 years, including some mtb in those miles. My LONG rides, though, are century rides, and longest ever 111 miles. Elevation is significant, just did 100 miler 2 days ago with just under 8,000 feet of climbing.
I’ve found that I need to START OUT with 1 serving of Perpetuem and 1 FIZZ in each 23oz water bottle if the ride is going to be 3hrs or longer, maybe even 2.5hrs is a better target. For me, that’s around 45miles or more. There’s ALWAYS elevation here, so I probably average 15-16mph most rides, and down into 14’s occasionally if climbing is extreme. I pulled 15.1mph a couple days ago on that century. Solo, some wind, and a long stretch of low power after a tough 5.5mile climb that I bonked on the other side, and had a very gradual but very long ascent. I’d gotten into energy debt early in the ride and it caught up to me. I worked harder to get the Perpetuem in along with more HammerGel and I did eventually recover slightly, and the last miles were mostly downhill so I felt decent again and could make a little time up.

So, the think I want to avoid most is bonking, but equally important is that upset stomach that just about STOPS me from eating. That’s been a thing of the past since I started using HammerGel, UNLESS I just ignore the need to eat for so long that I may as well have not brought the gel along. I’ve done that more than a few times. But I really never do that anymore, I just let myself get “a little” in debt and then start having warnings and try to make up ground, and ease off the gas pedal if necessary. I DO think that the complex carbs and BCAA works best for me, and ESPECIALLY the Perpetuem on long rides. I LOVE doing long rides, seeing more countryside, climbing more mountains, etc. So I tend to overdo it. I’m slowly learning that I need rest days or at least easier and yes, SHORTER days.
Whatever it’s worth, I suspect that the introduction of Tailwind to your routine should at least be considered as a possible piece of your puzzle. What have you done before that? What part of the old methods (assuming they worked?) are missing now? Is Tailwind okay but you also need something else? I can’t help there, but I know what works for me… I just need to be more disciplined about keeping the right stuff going IN, not just carrying it along with me! I’m embarrassed at how many times I have HAULED THE WEIGHT of all that needed for long rides, but FAILED TO EAT IT! :roll_eyes:

As for the HR dropping, I recently started what was to be a moderate 40 miler or so, but turned back at about 5 miles because the only 2 hills I’d encountered to that point showed my HR steadily DROP as I climbed these small hills. I should have gone up into 130’s or so, but went down into the 70’s bpm and then the 60’s on the second one, steeper than the first one. I wasn’t hammering but I was working. I rolled back down and then checked my pulse by hand, saw it close to what both the Edge and Fenix were showing, and decided to roll back home.
Took a look at data, couldn’t figure out any problems, and my own experience with failing batteries in these HR straps (Garmin HRM Dual) was that they tended to go HIGH on last 2 or 3 rides before any obvious fail or just dropping out.
It was a Friday and I actually scheduled an appointment with my doc the following week to get checked out. But talking with a buddy that evening and looking at data more, he saw that I had dropouts showing on that ride. I’d missed them but they were there.
Ended up canceling the Dr. appointment and checking things out with the HRM. The battery TESTED at 3volts, which SHOULD be no problem for good readings. But I put a new battery in (3.34volts, which is pretty typical for a new CR2032 coincell) and things seemed to be fine. Did a ride inside that night, and HR acted as it should with the ride workout. Also used an OLDER HRM Dual and it did fine, HR looked on target.
That was about 3 weeks ago. I’ve since noticed more dropouts, not all throughout rides or for very long stretches, but there, nonetheless, with that same HRM device. The OLD one has actually become my dependable one and seems to not show ANY dropouts, so I think the one that is less than a year old is actually defective, but it will show what appears to be accurate, realistic data for almost the entire ride, but close examination usually shows some dropouts of HR, so I can’t trust it, I’m afraid.
Whether you have a similar issue, I have no idea, but I was surprised to see this with mine. You might look close for dropouts (I think you maybe already said you did that) and you might check your pulse manually a couple times or more on a ride to see if it agrees with what’s showing on devices. Not easy to do very accurately, I’m afraid, if it means stopping and trying to count what is likely a moving target at that time. And it isn’t certain to catch a discrepancy that MIGHT only happen when the transmitter and receiving devices are “under load?” I don’t know how that process works, actually, and whether the devices draw more power from the battery when HR is faster?? Seems possible but I don’t know.

Best of luck figuring things out. I would NOT DISCOUNT the possibility that there is a problem with something that you need to get checked out. We ALL felt indestructible once upon a time…:grinning: And we ALL would LOVE TO FEEL THAT WAY AGAIN!
I have a friend who has always been very active, strong, fit, etc. And he began having a problem during a race and knew it wasn’t just a minor deal but had no idea what made him so powerless when stressed. Pretty sudden thing.
He went and got tested, had a 95% blockage of LAD (widowmaker) and had to can his vacation plan and go get open heart surgery.
Nobody who does the things we do thinks that could happen to them. Until.
So don’t fret, but don’t ignore if things are really different. I hope it will be a relief situation for you that things will go back to how they were, hopefully a diet thing, or the overtraining that has already been mentioned and makes a LOT of sense to us who don’t know the whole situation, but only you know how unusual things have been for you, or maybe NOT very unusual except for the Tailwind etc?
Trusting you’ll find some answers as you think it through.