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After trying the local "Hill" I was surprised to see my heart rate dropped substantially despite subjectively putting in a lot of effort. How can I maintain constant cardiovascular effort to all the way to the top of the hill?

I'm a moderately fit, mid-forties man. I'm in my local running club, I parkrun 5k in 23min etc. I ride to work daily (about 4miles along a disused railway path). While I'm furloughed, I've been trying to maintain fitness on my bike by doing some longer rides and up the local Hill, nicknamed "The Wall" on Ashdown forest, Sussex, about 1.5km with a gradient between 8 and 10. I monitor my HR with a Polar 200 watch.

And I've found it pretty tough!

That wasn't a big surprise, but I was surprised to see that my heart rate dropped substantially during the climb from about 140 to about 90-95 on the second (steeper) section of the climb. A HR of 95 would normally be "brisk walk" level of effort. But subjectively it felt "very hard" with burning legs and heavy breathing. I found it necessary to drop right down to the lowest gear to keep going.

Is this drop in HR expected? What should I be doing to ensure that I am able to push consistently all the way to the top?

My ultimate goal would be "build CV health", but my medium-term motivational goal is "get up The Wall as quickly as possible."

The research I've done such as https://www.cyclingweekly.com/fitness/training/improve-your-climbing-353501 mostly focusses on "how to lower your heart rate while climbing".

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    Hi James. Welcome to Bicycles SE. We can't offer (human) medical opinions. See a doctor/cardiologist for this sort of question. It be might your normal pattern or it might be a problem. But as an intermediate answer, listen to your body not the tech. – Warren Burton Apr 13 at 12:52
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    What is your cadence? If your legs are burning I suspect you've let your cadence drop below 60. You likely need to gear down and pedal faster. – Daniel R Hicks Apr 13 at 13:20
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    90 or 95 and heavy breathing are a strange combination. I would first question the HR measurement. Did you try to get the HR the traditional way at the top? Or at least did you feel any fas or slow hearth beats? – Vladimir F Apr 13 at 13:35
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    @JamesK When my heart rate shows strange values the time has come change the battery of the chest strap as it may skip 1 beat in three. – Carel Apr 13 at 14:41
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    Did you stand up while climbing? Polar 200 measures heart rate from wrist with an optical sensor, and those are very sensitive to changes in hand position. For best results, you should have the watch a couple of centimeters above the end of ulna (the bump on your wrist) and just tight enough to leave a mark to skin when you remove it. If the readings are still strange, I'd double check with chest strap sensor before going to doctor. – ojs Apr 13 at 15:04
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I have seen this effect with several different optical based wrist HRM's. Your HR is not 90, but likely closer to 180. Optical HRM's generally have a longer lag to track changes in the heart rate and sudden jumps can be interpreted by the software as drops rather than increases.

I've found that for long sustained efforts, the HRM eventually tracks back to the correct value, but can be wildly off for shorter efforts. There is also the physiological lag in HR vs effort. Early on in a workout, your HR doesn't track your effort particularly well.

Many of the coaching/training blogs I follow are suggesting that perceived effort should always trump HR based training, particularly as HRM's struggle to track correctly at high heart rates. If you're breathing heavy and think you're working hard, you're working hard regardless of what the HRM says.

For a recreational athlete I'd suggest just living with it. I find the convenience of wrist based optical sensors far outweighs the occasional data inaccuracy. Most professional bike riders still use electrical chest based straps for this reason, but they also all use power meters to gauge their efforts during training.

If you want to learn more about the limitations of your device, I recommend searching for reviews on DCRainmaker.

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  • Concur - double check your heart rate by counting heartbeats for 10 seconds while on a straight and simple section of the climb, while watching your headunit or simply count ~15 full pedal revolutions (that would be 10 seconds at 90 RPM) – Criggie Apr 13 at 20:55
  • I've also had issue with chest straps losing contact and giving absurdly low numbers, so they're not a guaranteed fix. This gets worse as they get older. In the gym, cleaning and tightening can often make the difference if they start playing up, but halfway up a hill that's not a useful option. I wouldn't (@Criggie) try to measure heart rate with respect to cadence unless using a cadence sensor with live readout - it's too subjective in a way that's linked to fatigue and perceived exertion – Chris H Apr 14 at 9:06
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    Another thought is skin conductivity. If I rode with my monitor dry, it didn't really start working reliably till I got a sweat on. Had to dampen the rear of the chest sensor to get it working from start. – Criggie Apr 14 at 14:06
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    @Criggie absolutely, and saliva works better than tap water – Chris H Apr 14 at 14:42
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    @Criggie, Going one further, when it's heading to winter here and the air is very dry I use a water based personal lubricant to wet the pads. This then gets displaced by sweat as you warm up and the chest strap readings are accurate from the start. Also washes off strap and person easily! – Byron Ross Apr 14 at 23:11
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I'll offer a few observations from personal experience.

Firstly, I have a Fitbit Alta HR which also has an optical HR sensor. I find it's pretty accurate running, but fails abysmally on a bike. It tends to synchronize to my pedaling cadence, rather than my heart. All optical HR sensors have heuristics to compensate for motion, and this means they may be accurate in some activities and not others.

Secondly, when I was first starting to cycle seriously, although not new to athletic pursuits, I did often find I couldn't get my heart rate up to its maximum no matter how hard I tried. Even if you already have a good cardiovascular system, it takes some time to adapt to be able to recruit 100% of that performance to cycling.

For example, here are two personal records up Hawk Hill. The first is on Dec 17 when I was just starting to get seriously into road cycling:

enter image description here

I attack the hill aggressively, and give it all I've got up all the way to the top. I try at the end to wring out every ounce of effort, yet my heart rate barely goes up.

Now another on Feb 25, after a little more than two months of serious cycling:

enter image description here

Note the two rides use different means of calculating power, on two different bikes, so don't directly compare them. But they both used the same head unit and chest strap.

This time I get near the top, and I'm actually able to recruit more performance and get my heart rate up to 191. 192 is the highest I've ever recorded.

So, is it an inaccurate sensor or a legitimate phenomenon? Guess you'll have to do it again and check your pulse manually with a stopwatch. 😁🚲

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    James reported not that he couldn't get his HR up, but that it dropped from 140 bpm to 90-95 bpm during a high effort attempt. That's probably not a lack of physiological response and is more likely a sensor issue. – R. Chung Apr 14 at 3:35
  • @R.Chung I'm sure you're right, but I've had efforts when my legs couldn't take any more despite having the CV ability to push on. At that point I tend to slow down a lot, dropping gears almost unconsciously. My breathing then comes down. I'm similar in age and possibly overall fitness to the OP (he's faster on foot, I ride more) but don't have the competitive spirit to push lactate-filled legs. – Chris H Apr 14 at 9:17

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