Anyway to not get to Max HR when trying for a mile PR?

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If you're doing a PR and the thing you are doing is only 6 minutes or so, who cares. I average above 180 for 30 minutes on my runs on the summer. That's also why I swap a run for a bike once a week in the summer to feel more breeze

Don't worry about it, most likely an equipment error. I always tell people to not trust HR monitors (I don't know what you're using, but it doesn't matter) to be accurate at any time, but most especially when their HR gets to either extremes....really fast or really slow.

Learn how to take your own pulse with you fingers on your wrist and compare that to what your HR monitor is saying. But also to second what some others have said, listen to your body too. If you were in a dangerous cardiac situation you would know it, were you lightheaded? Dizzy? Vision problems? Nausea? Any numbness, tingling, cold sensation? Trouble breathing(not rapid breathing, obviously you'd be breathing fast, but I'm referring to a feeling of being strangled or drowning)?

Even at 31, if you really did have a HR of 193, that's not too concerning if you're pushing yourself towards your max.

As and unnecessary aside: **I'm a critical care nurse, so that means when I'm at work and I have patients, they are continuously monitored with 5 lead EKG monitors at the bedside. There's other monitoring equipment too, like pulse oximetry, blood pressure monitoring equipment, etc, but the cardiac stuff is the most important and useful to us. When one gets into nursing, critical care or other areas, they are always taught to "Never trust the equipment" and what that means is don't trust the numbers that the equipment is showing you, if something looks off with your patient you go assess the patient first and verify that the equipment is functioning properly, and you use your own senses to assess their physical state, instead of jumping to conclusions based off of an equipment error. You can do the same for yourself as an athlete with a radial pulse check.

I have a Garmin Forerunner 255. It matches my Polar chest strap by +/-1. So I don't wear the chest strap anymore.

You big dummy