Running 101: Heat, Humidity & Hearts

Yes, Dan Perkins, Ironman extraordinaire, nailed it…..  I run way over my max target heart rate leading to over-exhaustion, complicated by heat and humidity exposure, resulting in performance issues during my runs. 

Dan suggested on my last Running 101 post that my issue of chills and running meltdown may be caused to my heart rate.  I had purchased a Nike Imara Women’s Heart Rate Monitor about a month ago and decided it was time to use it. 

The Fourth of July Firecracker 5K was my first opportunity to use the HRM. It wasn’t that hot out that morning and I was grateful. Temp was in the high 70’s / low 80’s, however, the humidity was well above 50%.  I strapped on my new piece of equipment all excited to see how well my heart performed!  WOW! The results were shocking, at least to me.  I was running in the high 190’s.  WOW!  And it climbed as I ran. Who knows how high it would have gone had I not been wearing the monitor and scared myself in to walking. Because at this point, I didn’t feel like quitting or walking and was not having any chills, etc. But as I finished out the race and I walked more and more to keep my heart rate within the MAX limit, I began to feel the slightest shiver.  I’m convinced I would have experienced the same chills and light-headedness had I not been wearing the monitor. So let’s talk about heart rate.

There are multiple ways to calculate your maximum heart rate.  There are simple methods and more complex ones. I used two different ones and averaged the results.  

      Method 1:   226-age = 187    Method 2 Women: 209-(0.7*age) = 182

Thus my maximum heart rate equalled 185.  The High Risk Zone or Redline Zone runs at 90% + of the maximum heart rate.   Meaning, that I am exerting maximum physical effort. I am breathless, my heart is pumping very hard, I can not sustain this level of activity for very long without possible serious side effects.  This is the zone you do not want to be running in for any long period of time.  This is a sprinters zone.  This is where I used to run, mind you for 100 to 400 meters, not for 5ks (at least not for me – some consider a 5k a sprint I’m sure!) The Anaerobic Zone is 80-90% and trains the body to metabolize lactic acid effectively.  I really couldn’t find any definitive answer on whether or not it was acceptable to run long distances in the 80% range of any length of time. But it seemed to be status quo that running in the 70% range was the healthiest. 

What does 75% of my maximum heart rate look like….   139.  Where was I running consistently by Mile 2…. 187+.  Hmmm…..  I didn’t feel bad, I was getting winded but not exhausted.

Now let’s look at the other two wicked elements I mentioned in my title:  heat and humidity.  They both have the same effect on our body and our heart rate.  Many people would probably not suspect humidity alone being such an evil-doer, but oh don’t let it fool you.  It is my nemesis and just may be yours too without you even suspecting it.   Here are the stats:

Heat: Temps between 60-75°F will increase HR by 2-4 beats/min. 75-90°F increase it up to 10 beats/min. 

Humidity: 50-90% humidity levels will increase HR by 10 beats/min.

Heat & Humidity:  Together the effect is magnified.

Why does this happen?  The heart’s oxygen output diverts blood flow to the skin to heat dissipation resulting in early exhaustion. Studies in Japan on ambient humidity result in the same effect because the humidity prevents sweat from evaporating. Sweating is the body’s method of keeping cool. When it is not functioning properly again the blood flow is diverted to the skin.  This study shows that hot, humid environment at sea level is as much incapacitating as is hypoxia at high altitude.*

You can’t control heat or humidity, what do you do to train?  The only thing you can do. The only thing that I should have been doing had I actually paid more attention to Jeff Galloway’s training lessons.  You control your pace and monitor your heart rate. 

This is one of the things that I am having the hardest time doing.  Because I run faster than I should. It actually physically pains me to run slower.  Does that make sense? SIDEBAR OPEN – I just started going to a boot camp ran by Bill Crutchfield, Crutchcamp, this week and he had us power walk.  Are you kidding me?  People do this? Ouch! Can’t I just run? – SIDEBAR CLOSED  What do you do? Practice.

I ran on Wednesday with my Nike HRM, on the treadmill to see if I could get a feel for what the correct pace would be for me. It was a great run! I slowed my pace to 12 min/miles, ran 4:1 intervals and could have kept going. I knocked out 3 miles like it was nothing.  This allowed me to max my HR around 160 or 86% and my walk interval would take it to the low 130s. This felt great!  I think I’m going to have to do this type of training for a while to really begin to understand what pace feels like and get comfortable with it.  

Thanks Dan Perkins for helping me find a solution sooner, rather than later.  This Saturday is my longest run to date – 5 Miles.  Yippy – Skippy!  I’m looking forward to the challenge. I feel prepared, not apprehensive. 

Does anyone else have any success stories they would like to share?  Any other concerns or questions?  I’m not an expert, but just like I did here a few posts back – if we share with each other, someone is bound to offer some great insight.  What’s your story this week? 

* Journal of Applied Physics, Vol. 40, Issue 2, 206-210


3 thoughts on “Running 101: Heat, Humidity & Hearts

  1. Amy, one of the great benefits of knowing this added with a stategic training plan is you’ll get faster! Joe Friel, coach extrodinaire, has made periodization a successful and standard means of training. Imagine a pyramid the bottom is your “base” the top your “peak”…base is meant to be slow, low HR miles. This increases your aerobic capacity to build upon. Since you’re just getting going stay smart and slow down to get fast. For more on how this works read Bill Wainright’s article on this at

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