I just bought a Magene C406 pro and it measured what I show in the image. Does that makes sense? It was a strenuous ride, but everything felt in order, sustained, and the whole ride lasted 20 minutes (in which I seemingly averaged 175bpm).
Is this measurement OK, or is the Magene just bad quality?
It is hard to tell without knowing your physical condition/training status (and the actual workout done) but not totally unrealistic for a human being. Seems a bit high, depending on what you did as exercise...
I'm pretty sure I never hit more than 175 bpm as maximum HR in 10+ years of sports with HRM belts. That doesn't apply to any other person since heart rates are an individual thing, but anyway, as suggested in False hrm results, I'd try to check the following points:
If the readings turn out to be consistent, I would suggest to verify against a secondary source and see if it matches up - I'm not saying it has to be a condition and you have to take a ECG under load but if you have no experience with your heart rate and just started (structured) training, there is no harm in consulting your doctor, there's no harm in knowing how your body behaves and knowing that you actually are a "high-pulser". In structured training, you should know and trust your zones.
Also, as Weiwen mentioned: We don't know what the background of above's workout was, but from experience with training apps like Zwift, you hardly ever go into a hard effort without warm-up to avoid injury. Assuming your true max. heart rate is 210-215, you went into a 15+ minute zone 3 effort with a little zone 4-5 in the end. When you do this on a typical short Zwift workout, there's at least 5 minute warmup before you go through any hard blocks.
It is not that difficult to check the readings of an HR monitor with an independent source. The start is really to put a finger on one of your big veins and feel the beats. Care must be taken not to overcount due to the beats in the fingers themselves but it usually works quite reasonably. It is not that difficult. It is not simple to do during the activity but it is simple enough to do it right after the end of a sprint or some other activity. Or even just for the rest heart rate. Then you just look at your watch and count the beats in 1/4 minute or in 1 minute or similar. You should get a very reasonable estimate of the true heart rate.
I do own a Magene heart strap but I haven't used it for several years because optical sensors on watches got much better than what they used to be. Id did have spurious results from time to time as I did with other optical sensors in other circumstances. It can happen.
If you can get a hold of such a watch, even if just borrow from a friend for a short time, that is also a good way to check the correctness of the strap. Even more accurate are the optical sensors in pulse oxymeters where you even see can see the curve on the display together with the current HR.
As mentioned in other answers, your indicated HR is high, but not impossibly so. But conspicuously high for sure.
One estimate of the average max HR for a given age is 220-age. This is not your own max HR, it’s the average max HR, and there are slightly better formulae than 220-age, but it is a start. And we can note that if your HR on this ride topped out at 212, your actual max HR is probably higher. An average of 175 is also seemingly high. So those values seem a bit unlikely. But you could just have a high heart rate!
However, as already said, heart rates are a very individual thing. I assume this is your first HRM, so you have no baseline. One thing you can do is warm up, take your pulse manually, then maybe do an interval and take your pulse again. Compare it to the HRM readings. Or borrow a friend’s smartwatch.
In general, I warm up for my threshold intervals. Actually, I always warm up, and most people should probably warm up rather than jump right into a hard 20 min effort. Perhaps you are young and you can get away with this for now, though! The ramp up from your starting HR seems fast, but my HR pretty quickly rises and stabilizes during my threshold or sweet spot intervals. Here is one example session. Of course, and not to rub this in, but I was starting each interval from a warmed up state.
In general, HRMs are an established technology. Magene is a mainland China brand with some credibility. It’s likely that Magenes in general aren’t bad. It’s possible you got a dud, or something is interfering with the wireless signal. Wahoo's TICKRs have seemingly (from anecdotal reports from forums I'm on) had a number of duds. Polar is generally regarded well, but I heard one person report they had a dud from this company.
