Extremely high heart rate on a 36er

I’ve been observing a very curious effect for a while. When riding a 36er, I can easily pump up to an extremely high heart rate and have it sustained, but without a heavy panting.

Take this recent 27km ride as an example. The average speed was 17km/h. On a mostly flat road. About half the time, my HR was in zone 5, i.e. >166bpm. If I were running or biking under such a HR, I woundn’t be lasting 5 minutes before I need to take a break. But apparently on a unicycle I don’t feel the urge to have a rest at all. I don’t pant for breath, don’t sweat crazily; I don’t even need to drink a lot. This is truly intriguing to me. Every time Garmin tells me I’ve done a great job on anaerobic training, I feel like I was cheating.

The 36er I ride is an Oracle 36 by the way, with 118mm cranks, no gears.

This totally contradicts with my knowledge of how metabolism works. Theoretically as my HR goes rocket, my muscles should be craving for Oxygen, and I should be breathing heavily, right? When the HR goes beyond zone 5, there should be a lot of anaerobic metabolism going on and I should get sour and exhausted very quickly, right? No, it’s just not the case.

So here are my questions:

  • have any of you folks experienced the same, err, symptoms?
  • is it a good thing or a bad thing, to have a high heart rate for extended time?
  • what’s going on here?

My first thing to check would be anything that could affect the HR sensor while you are on the 36". I assume you are using the optical sensor on your wrist? If you were wearing the watch strap looser than you would in other activities? Or is it resting on your handlebar setup in a different way?


No it’s not looser comparing to other activities, I wear the watch every day in a consistent way.

I also updated the watch from a Garmin Fenix 6 to a 7S this year (which reportedly has an improved HR sensor). On both watches I observed the same phenomenon.

But I do think you made a great point! On a 36er I would put much more weight on the handlebar, would that confuse the HR sensor?

Just a guess that your numbers don’t fit into the normal parameters of the heart rate algorithm causing the results to be skewed.

Riding a 36er is just that thrilling. Sets your heart racing.

Nearly 10 years ago I developed some software for pebble watch to do step counting and fall detection, and I know how tricky it is. For HR estimation, signal noise has to be removed and typically the prediction is based on an assumption about the activity (e.g. running or cycling), as well as the expected HR. These assumptions may be based on your input, or GPS and accelerometer readings. It would be 100% certain that their algorithm was not tested on unicycling.

Your gut feeling will be correct.

For what its worth, following are 3 snippets from reviews and scientific journal articles:

“As soon as we picked up the pace for intervals and track sessions, we started to see some erratically high maximum heart rate readings compared to a Wahoo Tickr X chest strap monitor.”

“Several studies have demonstrated that HR measurements from wearable devices are often less accurate during physical activity or cyclic wrist motions.8,11,35,38,39 Several research groups and manufacturers have identified that cyclical motion can affect accuracy of HR in wearable sensors.9,10,15 The cyclical motion challenge has been described as a “signal crossover” effect wherein the optical HR sensors on wearables tend to lock on to the periodic signal stemming from the repetitive motion (e.g., walking and jogging) and mistake that motion as the cardiovascular cycle.40 )”

“Clinicians have cited motion artifacts in pulse oximetry as the most common cause of false alarms, loss of signal, and inaccurate readings [10]. During physical activities, MA contamination in PPG signals seriously interferes with HR estimation. The MAs are mainly caused by ambient light leaking into the gap between the PPG sensor surface and skin surface. In addition, the change in blood flow due to movements is another MA source [11]. In practice, MAs are difficult to remove because they do not have a predefined narrow frequency band and their spectrum often overlaps with that of the desired signal [12]. Consequently, development of algorithms capable of reconstructing the corrupted signal and removing artifacts is challenging [1]”


I use the garmin fenix 6 watch and I haven’t seen any problems like this.

I know that Garmin determines the heart rate zones automatically, do you think they are relatively well defined for you? Did you check your pulse?

The maximum heart rate is not necessarily the same from one activity to another, but the variation is relatively small and cannot explain such a difference.

It must be an algorithm problem as @gocup suggested.

In my experience, I’ve noticed that the heart rate is higher if I start an activity. When I ride my unicycle without starting an activity, the heart rate displayed on my watch is always lower (I’d say about 20 bpm lower).

What’s more, if I ride a unicycle without starting an activity, the AI will think I’m cycling if I put my hands on the handlebars or swimming if I have my arms in the air (indoor training or freewheeling).

If I were you, I’d try riding my unicycle and:

  • monitoring the heart rate displayed without starting any activity
  • starting another type of activity (like running)
  • try measuring your heart rate by taking your pulse.

Personally, even when I give it my all on my G36, most of the time I reach zone 4 without ever reaching zone 5.

EDIT: my bad, I just checked how the 5 zones were set on my watch, and the max heart rate was set at least 7 bpm above my real max heart rate (192 instead of 185 or lower). By default, the zones are set from the max heart rate (90%/80%/70%/60%). You need to be at least sure that the max heart rate is correct. That explains why I almost never reached zone 5. :sweat_smile:


My experience with my Fitbit Charge 5 is that the heart rate is completely unreliable. I wore a chest strap monitor for years when I was doing a lot of bike racing, and got to the point where I could tell you my HR within a few beats, without even looking. The Fitbit would be wildly off. 180 bpm when I was hardly working (I never hit 180 in a race), 150 when I was killing myself in an interval, etc.

I tried moving it up and down my arm, wearing it tighter or looser, cleaning the sensors, no help. I couldn’t even get a sleep score with it because it would tell me it couldn’t get good HR data.

I finally gave it to Mrs Impossible. She thinks it works OK.

Anyway I can’t give you anything like the technical explanations above, but I think it’s probably just wrong!


To me it sounds like a measurement error.

In my case, I cycled and mountain biked a lot with older Polar heart rate monitors back when there were only chest straps and know pretty well how my HR reacts to which activities (running HR and threshold are much higher than in cycling or unicycling: while running HR is about 7-10 beats higher concerning LT and subjective exersion feel: I can do sustained running sprints over 170 for a bit without going all out while on the unicycle peaks above 170 are very strenuous and mean I can’t continue at that level much longer).

About 2 years ago I got a Garmin Instinct Solar which I really like. But I quickly upgraded to a chest strap, as the HR reading with the wrist strap were so off. Based on my experience (compared to both my chest strap and to an arm blood pressure measuring device that also shows HR), the resting HR from the wrist sensor is relatively accurate. Thus, it works well in tracking my resting HR at night (years ago I would wake each morning and while moving as little as possible put on my chest strap and take my resting HR).

But for activities it is often so wrong, sometimes showing values to 60 or 80 as I am doung high effort near LT threshold (over 160). Just last weekend at the Elsbet 4-day Muni event in Switzerland: on the first 2 days I didn’t wear my chest strap as I thought we were doing only downhill shuttles. Then riding a steep 20% uphill with 110mm cranks on my 29 I look down at the watch and see 59 BPM (would be nice!!), but obviously wrong. The last 2 days I wore the chest strap and then had the expected 150-170 bpm doing strenuous uphill.

If you are really interested in training with the HRM, I would add a chest strap. Mine was something like €20 accessory.

Concerning the 36: When I ride the 36, even in road races with 100mm cranks (I’m not that good in road), I can’t get my HR much over my LT in the mid 160 range (while running my average for a 10k will be over 160). On the 36 in the flats my limit is cadence, not my HR (sustained uphill is of course different).

There are averages and heuristics like max HR 220-age and percentages for zones. But in the end each person is difference.

The absolute maximum heart rate is irrelevant. What matters most are:

  1. high range between max and min (as max is genetic and decreases with age, having a low resting HR is GOOD). Mine is currently 42 BPM
  2. having quick recovery is good: I.e. unicycling uphill with a 170 pulse, it is a very good sign if your pulse returns to say 130 within 1 minute of stopping
  3. doing high work at the given HR is important (if one individual has a 180 average for a 10km ride that doesn’t really matter if another rider is faster with a 150 average).
  4. and being able to do sustained high effort at or just above LT is good (requires lots of training).

Read about lactate threshold (goes by lots of names), but this is the HR below which you are primarily using aerobic energy stores and thus sustainable as long as you get fluids and energy. Above LT is anaerobic where other energy stores are used that take days to replenish and cause other effects that make continued effort increasingly difficult.

The main effects of training are 1) decreased resting HR, 2) ability to do longer duration at or near LT, 3) fast recovery (in minutes) and 4) higher strength/force output at given HR.

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You are basically correct that if you are in zone 5 you should be anaerobic and should be limited to about 20mins… but is that correct. You heart rate zone will change for different sports. Even if if you do an FTP test on your unicycle, you need to work out your other zones, do not trust the garmins assumptions.

Also… conditions. Here is a ride I did a few years ago. Look at my heartrate drop at about 28km with no change in speed. Looks odd until you realise I changed direction and had a tail wind!


IMO, the Fitbit Charge 5 is not great from a HR and GPS standpoint. Not at all accurate. I love the lightweight form factor, but I don’t use it anymore.

Thanks to all you folks for your insights!

So today I took my old Garmin Fenix 6X along with the new 7S out for an experiment. I put the 7S on my left wrist and the 6X on the right one, and started a 5km test ride on my 36er. Here are the HR charts from both watches:

The 6X has missed the first few minutes, maybe a GPS issue, but their HR charts are definitely well-aligned.

At the end of the ride, when both watch reads at 165bpm (and dropping), I took a metrenome app and measured my HR manually. Turns out the watches are accurate enough!

So that rules out the measurement errors. I DO have extremely HR as it seems. So what now? Is it a bad thing? Should i quit 36ing?

Without formal training, certification, diagnostic testing and an in person evaluation I doubt that anyone here could really say what the best action is. See a cardiologist and do what they recommend.

Or you could do as I do, I don’t monitor my heart rate and don’t worry about it - I’m not a doctor.


Are you sure your max HR is set correctly? Age based formulas don’t work, you need to figure it out by doing some max HR test (plenty of options out there, generally a warmup-hard effort for 10 minutes or so-sprint finish, measure HR at the end).

Heart rate drift (heart rate increasing for the same effort) is normal over prolonged exercise, it’s one of the things that makes heartrate an imperfect measure of effort. So the part of it increasing towards the end is normal, especially in hot weather the HR increases to send blood around for cooling, but that doesn’t tell us anything about our oxygen intake.

From your description of perceived effort vs. measured HR description I would suspect your max heartrate being a bit higher than you have it set.


I’m 53 years old and your charts look almost the same as mine. I would suggest adjusting your heart rate zones. For Garmin Connect: Changing Heart Rate Zones in Garmin Connect | Garmin Customer Support

My predicted max 220-age=167 is really off. I’ve adjusted my zones and my max to 183.

There’s generally nothing wrong with having a high heart rate as long as it correlates to good performance. Actually, having a high heart rate is somewhat correlated with good aerobic performance (the more range between resting and max, the better). A younger cycling friend of mine had a max of like 230 or so. I encouraged him to start training with a heart rate monitor, and he sent me his chart from a race with an average of 214 for an hour race! He later became a semi-pro racer and won the East Coast region for about 3 years.

So numbers look fine to me, you just need to update your max and your zones to match you.


This is my HR chart from a Cross Country Muni race in Villanders Italy last year. I rode this on a 29+ with 110mm cranks and there are 3 big climbs (see elevation below in green), so my heart rate varies quite a bit. Note this is about 40 minutes effort compared to your under 20 minute effort.

Incidentally, I will be doing the race on the exact same course next weekend on June 2nd. My expectation is that my heart rate chart will look almost the same (hovering around my lactate threshold), but my hope is that I will be under 40 minutes (official 42:19 in 2023) meaning about 2-3 minutes faster, as my leg strength has improved (last year I was recovering from an ACL knee surgery and could only train about 80% max exertion).

I’m planning to pre-ride the course again this Saturday, then train the beginning of the week (at least one >1000m climbing ride) and then taper the 4 days before the race.


Here’s from my 10k race at the French Nationals fall of 2023 (I was slow as I was tired from the Muni races and I think trial the day before - and I’m not so good on the road anyway). This is on my 36 ungeared with 100mm cranks. (But obviously my max is higher than the predicted 167). The displayed max of 30km/h is unfortunately wrong.


I have a similar HR chart for 10K training on a 24er. But I was much slower. I’m 40 years old.

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Nice. Your zones look a bit low to me too: 25 minutes in zone 5 above LT is a lot!! unless that was your all out year best max effort and you felt like you were about to die (and you felt totally exhausted for multiple days), then I would raise your max/zone ranges maybe 4-5 beats. You can estimate the LT threshold subjectively (e.g. if you can’t talk in full sentences then you are above) and get pretty close although a lab lactate test is the “correct” way to determine it. I used to do one about every other year back when I was MTB racing. I haven’t done one in about 15 years but I don’t think mine has changed much (although my max has reduced with age) - LT used to be around 166/167 at age 35 (max 191), now age 53 about 165 (max approx 183).

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