canklecat

There are several articles with guidelines for estimating and using heart rates. This one is pretty comprehensive.

Your maximum HR will depend on your age, physical condition, medications, certain supplements, intake of alcohol or stimulants such as caffeine, tobacco, whether you're well rested or fatigued or otherwise stressed during the test, etc. When in doubt, repeat the test two or three times. It'll probably change a bit over time anyway.

While the 220 minus age estimate is sometimes dismissed as inaccurate, it works for me. I'm 61. My peak HR setting up my Wahoo Tickr a few months ago was 173. That isn't sustainable for me under any circumstances, just the maximum I could wring out pushing myself to the point of nearly passing out. And I did the test indoors for safety, and the temp was in the high 70s with the a/c off. That's down a bit from my 177 peak a couple of years ago.

Guesstimating for real world conditions including summer heat/humidity, I figured my maximum HR that would be sustainable for maybe 30 seconds would be around 160. I figured my sustainable average HR over the course of a 20-60 mile ride would be 150+ for up to around 30 minutes, and 140-145 over the entire ride on a good day. And it's turned out that way consistently per Wahoo Fitness and Strava. I've done several tests on a handy nearby 5-mile training loop with a short, steep punchy climb on one side and a 1-mile continuous 2% climb on the other, using the bike computer monitor on the handlebar to check HR, cadence, speed, etc (I don't normally ride with that stuff, just a Tickr and phone in my pocket).

But there are some complications I have to account for. My thyroid and whole endocrine system are screwed up by an auto-immune disorder, and I take a thyroid supplement -- the endocrinologist is still tweaking the dosage, so every few weeks I have to adapt. The main effect I've noticed is my heat adaptation has suffered this year, so I'm not doing as well in summer heat as I had before the illness. But I'm fine when the temp is closer to 80 or cooler, so I do most of my harder workout rides at night or cooler than usual mornings/evenings.

I take antihistamines pretty much every day and generic Zyrtec doesn't seem to cause any problems. But occasionally I need Sudafed for congestion. That spikes my HR and BP, so I need to be more careful on those days.

And for years I've had severe headaches that respond pretty well to as-needed doses of blood pressure and heart regulatory meds, especially metoprolol and lisinopril. They make me sluggish and depress my heart rate. So I need to remind myself to deduct at least 10 points, preferably 15-20, from my usual HR. So if on a normal day my temp pace HR is 140, I need to keep it closer to 120-125 for a couple of days after taking BP meds.

Occasionally I'll forget and push myself too hard, including Sunday. I was listening to my app for 5-minute updates on my HR, and when I heard 140 I figured I was okay. On a short, steep climb that I usually sprint up my HR will be around 160-165; but Sunday it peaked at 150 with the same effort. My average for the 40 mile ride was 130, where it would normally be 140-145 on the same route at the same effort. I neglected to account for the effect of the meds. So I was pretty wiped out the rest of the day. Ideally I should do a heart rate test in conjunction with the BP meds to set a separate baseline.

So take into account all those possible variables when estimating your own heart rate.

BTW, this doesn't have anything to do with speed. I'm a little faster now, a little stronger on climbs, than I was a couple of years ago. My conditioning is a little better despite some health setbacks. But I'm not anticipating any significant further improvements. After a certain age we hit some fairly hard limits.