Running in the heat: Heart rate skyrockets??

It is absolutely normal. It will change a little with adaptation to the heat, but even then not much.

I live in Tucson, Arizona, where running above 110 degrees in the sun is very common.

Basically, having been acclimated by living here 2.5 years, here is how I seem to go:

110 degrees and above: I redline at about 8:30-9:00/mile. I can't go faster for any lenght of time and I have to carry a frozen bottle to go beyond 4 miles even.

100-110. I can cruise at 8:30, and my heart rate comes in at a very high, race-pace like average, even though this is far from lower temperature "race pace" for me.

90-100. I'm well acclimated to this. 90 is the new 80. I can tick off 7:00's and 7:30's up to about 6 miles.

Below 85 degrees: New PR territory. Anything is possible.

I live in vegas and I'm sort of in the same ballpark...

To the OP, I tend to slow and keep my HR in the right zones, but also go a little more by RPE.  If my HR is up but I don't feel like I'm going that hard, I will maybe up a zone (Z3 instead of Z2) and not worry too much.

I kind of hope I'm getting some kind of overload training benefit from running in the heat. I don't know this to be the case at all... I just hope for it.

One thing I do know, when I go to an event back in the world and it is 85 degrees and humid that means nothing to me now.

Thanks guys.

I will admit, it kind of freaked me out at first, but then once I slowed down/began to walk it got better.

I probably should be doing more to acclimate.

Yup. My HR skyrockets as well, and usually the heat takes a LOT out of me, especially the run. Biking, I don't have that much of an issue.  Last week, I thought it was a little bit cooler enough for me to go out (100 degrees? Like Kido, I live in Vegas), and I did, and I was about a min/mile or so SLOWER, and HR was touching Zone 4, even though the RPE was much lower.

Expect that your HR will be higher, and go by RPE as well. If you feel like you're going a little too hard, back off a bit. It's OKAY. I think I've read somewhere that your min/mi will be slower by a min per 5 degrees above what you "normally" run in. I would LOVE to have 95 degree days...but that can be a little TOO hot for some folks. 

I wouldn't fret about it.  I think you can accumulate to the heat if you can tolerate it. My limit is 100 for the run. Any higher, I suck, and I become a grumpy runner, but other people can do it with no problems. 

I saw a difference with humidity as well.  While I am a slow runner (9 minute per mile +), I recently went to South Alabama for a trip.  Here in AZ at an elevation of 3500 feet, I can run my normal pace and keep my heart rate below 140 for 5 miles or so in temps up to 100, except for uphill.  I ran at 105 Sunday and slowed down about 30 sec/mile.

While at the beach in AL, I ran 5 miles in 100 degree heat with high humidity.  Elevation was close to sea level.  My pace was the same, but my heart rate kept jumping to around 160.  I felt fine muscle-wise, but the heart rate worried me.  The rest of my runs were done at 5:00 am and 80 degrees (and on the beach, so I didn't even worry about pace).

I also had trouble cooling down.  I'm used to sweating, but in AL, I just dripped.  Here it evaporates and cools the body.  One last thing is water.  I go through a liter or so in 5 miles in AZ, but in AL, I needed very little water during the run.  I still drank before and after, but my throat did not dry like it does in low humidity.  It was nice to not have to carry my camelbak while running.

You'll get used to it, happens to me all the time.  I am working on ultra endurance running right now, and so I will not go above Z2, even if that means I have to walk.  This is hard in the heat, because my heart rate is a lot higher, but I am not doing myself or my training any favors by going into a higher zone.  

You'll acclimatize!  

I train primarily by heart rate and sometimes have to slow down to a walk to stay in Z2 if I run in the Florida heat after work.

On  a few occasions I've just packed it in and walked home if it was too hot.

Avoiding the afternoon heat is one of the incentives for me to get up early and run.  I can't always escape the humidity, but at least the temperatures are more tolerable.

Mark     

This is my theory for running in FL as well.  I'll go out when it's 90 with a heat index of 105 and pound out 5 grueling miles hoping that it'll make me fly when I'm racing in below 85 weather...

I have no data to support this theory

But to the OP, yes.  My HR skyrockets when it gets really hot.