Really high heart rates... is this normal?

I posted on here a while ago asking about very high HR during MTBing (vs gravel/road). I’ve now done 4 races (3 long events - 2 70 mile races, 1 45 mile and 1 shorter event of 15 miles). During these events my average HR over 7-8 hours has been close to 90% and during the 90 minute race it was 93%! All the events have been compounded by either screwing up nutrition or super hot/humid temps. I even ended up in the ER on a cardiac monitor and needed IV K and Mg after the 8 hour race… Anyway… does this happen to anyone else? What is going on here? Am I taking years off my life with undo cardiac stress doing this?

I have a master’s in Exercise Science and did numerous VO2 max tests about 20 years ago and my max HR back then (with an RER >1) was 185. The highest I’ve seen in the last year is 183 so I’m pretty sure I’m not just off by 10 bpm for my max. Screenshot of my HR during the shorter race. The avg isn’t just being driven by some outliers - its sustained close to 90-99% the entire time.

ETA: I do have a cardiology follow up - in September. The ER was due to dehydration. This was meant more of asking if anyone generally has what seems like higher than should-be-possible-for-long-durations HRs.

What does your doctor say? Stimulating the Heart IMO might add years to your life but your doc may (or may not) say other wise, take his advice not a random internet stranger. Personally, Ive only been over 90% for an hour in a long TT and just below it on average (88% max) for a 2h TT, but we are all different.

ER? 90% for 7 hours? Sounds horrible and I’d make some changes.

Read the second paragraph in the first post.

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That graph doesn’t look totally unreasonable for a 90min race, especially in warm temperatures.

However I’d say if you are pegged at 90% for 8 hours…something is amiss. I’m not a doctor and won’t try to speak to any of that but if you ended up in the ER from one of those then I’d say whatever was going on is not “normal”.

It is reasonable to see higher than normal HR when racing MTB, especially in hot temps, but your experience is definitely not what you should be expecting.

@Lorichka6, after my stay at a Holiday Inn Express last night I feel uniquely qualified to answer this question! HAVE AT IT BOSS, FULL SEND!!!

Seriously though, PLEASE take the advice of many others here in that YOU should talk to YOUR doctor about it. He/she is the only person with your complete medical history. I understand reaching out to like minded people to get their opinion (we’ve all done it), but even if someone here has gone through EXACTLY what you are going through and their doctor says it’s ok to press on, it doesn’t mean YOUR doctor will.

Whatever direction you choose, best of luck to you and I hope things work out!


Hard to say if it’s normal or not - HR is highly variable by person.

But, generally, running at 90% of MHR for hours on end isn’t normal.

Do you have any symptoms that indicate other problems? Arrhythmia, AFIB, etc? Do you recover normally after the races? How do the race efforts compare to training efforts?

If you’re overheated and dehydrated, that could explain some of it. But, I’d ask why you get overheated and dehydrated at these events (but not gravel/road races)? Either way, trips to the ER and IV treatment isn’t normal for anybody.

I can push a pretty high % of max for 1.5 hours. Had one XCO this year that I did 180 bpm for 1.5 hours. Max HR is around 196, age 36. My resting HR is not particularly low either for a 4 w/kg athlete you would think my resting hr would be lower than 60 bpm…

In the last year my highest 20 minute hr is 188.

My take on the ER visit is that is not related to HR, but hydration, which can certainly impact HR. That said, I am not a DR.

I did talk to my doctor - he told me to see an exercise physiologist but wasn’t overly concerned. My heart rhythm normalized as soon as the Mag and K were on board. The ER visit was secondary to dehydration - I was hypokalemic. 9L of CHO/electoroyte drink during (and 1 L before the race) wasn’t enough for that 8 hour miserable race.

No other symptoms. Resting HR is upper 40s. I recover fine. The race efforts are harder and I never ride for as long as those races during training. The shorter race was definitely “race pace”. The 3 other longer rides were just challenging because of the elevation profile - 8k and 5.5k vertical respectively over 70 and 55 miles. I never mimic anything like that in training. The ER visit was dehydration - the conditions were horrendous.

The heat definitely plays a role and I am realizing now how profound of an impact it has. I’ve been tracking temperature more closely and equivalent rides are close to 15 bpm on average higher in the 90 degree/humid weather we’ve been having this summer vs cooler temps.

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How do you feel at those HRs? There will be times I look down and am at 85% HR and I am having a conversation… not easily but easier than I’d think I should be.

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This just sounds impossible. For me, this is VO2max power for 5 minutes after which I soon fall apart.

Rather than calling your doctor immediately, my first thought is that your HR monitor is suspect.

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I dont look at HR in race, and only look at power when I know I got in over my head with the lead group.

As a whole, how do I feel about those HR numbers? It is good to know i can push my body that hard, is it good for me? Idk

Interesting observation. I wonder if all of this comes from a baggy mtb jersey flapping against the hrm whereas on non mtb rides he’s wearing a tighter fitting kit that isn’t causing the issue

Not to say you should ignore the readings, but worth checking

My guess is a wrist based monitor or some other lower quality HR monitor. Or maybe the monitor just doesn’t like the constant buzz of off road riding? It just seems completely impossible to ride for 7 hours at 90% of HRmax. People do VO2max workouts and it’s tough to spend 15-30 minutes at 90% of HRmax.

Or, the OP doesn’t really know his true HRmax.

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Yes. If your data seem unbelievable, consider the way they were acquired. If he showed up in my office with this concern, my first question would be what HR monitor was used.

Hypovolemia will cause a higher HR. Hard to say much else without knowing what the rhythm was…

Talk to a cardiologist and no one on this forum that says otherwise.

That fact that you ended up in the ER needing K says you either depleted the shit out yourself and were massively dehydrated or there’s something wrong. Either way, I’d stick to nothing above low z2, if anything, until you’ve got a cardiologist to check off on it. Either way, potassium imbalances are nothing to ignore, it can kill you. Your heart kinda needs it… like… a lot

Nah, I’ve mountain biked for years and the HR monitor works fine (assuming it works fine of pavement).

You say they are compounded by nutrition and/or heat, but those both could be the primary reasons, right?

I don’t ride more than 4 hours often, but I’ve had lots of rides of 2+ hours that, when I look at my data after have me at 80-90% threshold zone and above (avg HR approaching 90% of HRmax), but not quite as high as your examples. But, I’m averaging a few beats below my LTHR, so it works out to be like long over/unders.

Something like 2 hrs in Z4 and 30 minutes Z5 in a 3 our ride. I did that Saturday, and it was hot and humid, and I was on a terribly overgrown singletrack trail with lots of punchy climbs, so I was going slow, lost about 3 lbs sweating, but didn’t feel fatigued really but the heat was the definitely making a difference. I also have some routes on sandy, flat forest roads (not much opportunity for recovery) that I like to push the pace on in the cooler months, but I’m probably walking the line between fueling enough to maintain really close (over and under) to LTHR and blowing up, because it’s obvious when I get home that I could/should have fueled more, and will see similar high avg heart rate that surprises me. The supra-threshold portions of the rides usually come in thick sugar sand stretches. I don’t have much luck riding z2 outside, because I like to push speed.

I guess I have no proof the HR monitor is giving good data but I feel like it would be a pretty big coincidence that it only gives very high values on MTB rides. I am a female wearing a sports bra so the strap is under the bra. My husband has a HRM as well, I suppose wearing that one during the next stupidly hot day just to confirm is easy enough to do.