Weak legs & HR spike during hard interval

Does anyone know if a Garmin 830 captures heart-related data other than just heart rate? I was doing 30-second power intervals last week. I normally do three sets of ten, but on the eighth effort of the first set, my legs felt too weak to continue. I looked down and my HR was 199. It would normally peak around 170. In the graph, HR is the red line and power is the purple line. I continued riding at a moderate pace for another hour and felt totally normal. My doctor asked if I took my pulse when this happened (I didn’t). He was looking for unevenness (I guess HRV). I was using a Polar H10 chest strap with a Garmin 830. The Polar H10 tracks HRV, but I don’t know if my Garmin is recording it or how to go about accessing it. I have an appointment with a cardiologist next week. I feel perfectly fine and I’ve ridden regularly since this incident, but I’m not letting my heart rate go past the mid-150s. I’m 53 and fairly lean. I’ve been racing and riding consistently for 8 years. Never smoked or been overweight. I ride around 9 hours a week, including one or two e-MTB rides that are social/zone 1, so I don’t think I’m overtrained. Any input on the technical side or in general would be appreciated.

I don’t know that HRV is going to tell you much (as in, I really don’t know).

If it happens again, def take a manual HR count. And go see a cardiologist, not just a GP.

Could be the HR strap flaking out, but given you also felt different, I could also be your heart.

I had an arrhythmia back in 2015. It was an SVT that would occur under high load, during intervals or racing. It slowly got more common so I had to treated. Not all arrhythmias are deadly-bad, but they all should be diagnosed/treated by a doctor. With mine, I’d have a small drop in power, and feel “butterflies” (like an adrenaline rush), but otherwise fine.


HRV will depend on your HR strap, my Polar H10 in conjunction with the 1030 will but only a stationary reading but I agree with @AlistairSH it probably won’t tell you much and your better to seek medical help as you are doing.

Garmin straps don’t do HRV to my knowledge. If you want that functionality you need a Polar. As others said, HRV isn’t going to tell you anything about this incident.

I’ve seen HR spikes like this happen on monitors all the time, and that wouldn’t concern me by itself… but the fact that there was a performance issue at the same time and you FELT something else, yeah, go see the doc. Good call.

This is exactly what just started happening to me. I’m doing all the test currently for the cardiologist but damn it I hope it nothing like it was for you.
Obviously the doctor will tell me what’s required (it anything) for my issue but what was the treatment for yours?

Yes they do. Comparable to Polar H10 according to Polar testing.


Maybe it’s not as accurate. I know Marco Altini didn’t endorse it a while ago. Perhaps that’s changed.

IMHO like debating 86% vs 88% is upper tempo. Whatever. Go look it up if you think it matters, I’ve posted links to Polar’s study. It’s on the forum.

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I had an SVT. Basically, as the signal to beat passed through my heart, there was a pathway to cause an extra beat in my left atrium. Thankfully, it wasn’t VT, which involves the ventricle and is often the type of arrhythmia that causes athletes to pass out (and sometimes die) mid-race.

We tried anti-arrhythmia meds, but they also tend to lower your HR overall and with a resting HR of 35, we couldn’t get the dose high enough to resolve the problem without risking fainting.

So the next step was ablation. They run a couple electrodes up a vein into your heart and zap the tissue that’s letting the extra signal propagate. It’s not open heart - just a hole in your leg or arm vein (or artery) big enough for a small tube. Usually out-patient and heals enough to resume exercise in a week or two.

All very stressful, but could have been much worse.

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Thanks for sharing. All of that sounds incredibly familiar right down to the very low resting HR (mines 37). Hopefully mine is nothing too crazy like yours. Just got to wait to get all these tests done.

IME that’s exactly what arrhythmias during hard exercise are like: heart rate goes sky high, with bpms possibly greater than you’ve ever experienced (plus can feel strange - fluttery - although not always noticeable in hard exercise), and your legs lose power, while they too feel strange and jelly-like compared to normal.

That’s not to say that’s what you experienced, but it seems possible.

FWIW since I began trading, a couple of years ago, some intensity for more easy endurance, these incidents have become rare for me (as in can’t remember the last one), whereas previously they occurred every few months or more. No idea if the changed intensity distribution was the reason, but very welcome.

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@bmcd70 if that happened to me first thing I would do is change the HRM battery. When the battery starts to go that’s the type of behaviour I’d expect to see.

Wasn’t arguing, man. Simply saying what I recall. I haven’t dug into the HRV stuff in a while because I think it’s of limited utility for most people. Altini is the guy who does all the research on it and as of last look, it was Polar, Oura, HRV4Training and cameras, etc. Maybe Garmin has passed his check… maybe he never looked at Garmin. I honestly don’t know.

You’re probably right, and it probably doesn’t matter THAT much either way and maybe Garmin has upgraded their stuff. As I said, I just wasn’t aware of it.

That was my initial thought, but he also had a performance issue and feeling coincident. I’d do both - change battery AND see the doc based on what he wrote.

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I bet! :smiley: First time that happened to me there was an immediate heart rate positive feedback loop.

I was lucky - it was very easy to trigger on the treadmill at the cardio’s office. So no need for the portable monitor and long-term diagnosis. From initial consult to ablation was about a month.

Consult (general cardiologist): “Well, ECG looks normal, it didn’t kill, so that’s good, come back for treadmill test.”

Later that week, treadmill test: 1 min increments in speed/inclide, had to get to 12* and 8 min/mile pace or something like that, basically an uphill sprint, and it triggered. Cardiologist #2 comes in, tells me there’s definitely an arrhythmia, and tells to come back to see electrophysiologist.

Next week: Electrophysiologist visit (same practice, just even more specialized MD). EP comes in grinning ear-to-ear “DO YOU KNOW WHAT YOUR HR WAS??? IT WAS 250BPM!!! AND YOU DIDN’T PASS OUT?!?!?!” Pretty funny reaction in retrospect - I guess he’s used to unhealthy people, not “young” athletes (I was mid-30s at the time).

Tried drugs for a week, didn’t work well. One week later was in for ablation. Normal daily stuff the next day (but took a few days off work just to be sure). Back on the bike after 2 weeks.

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