Does Max HR while dehydrated and overheated ... (Read 49 times)


    Does max HR measured while dehydrated and overheated mean the same thing physiologically as max HR measured under more "normal" conditions?


    Hi - A few months ago at the "sprinty" end of a 5K I hit my fastest HR ever, and have been using that as HRmax for various calculations that I mess with just for fun. I haven't hit within 10-15 BPM of that since then, and was beginning to wonder what the story was … was the watch wrong that day, am I just not pushing myself as hard as I did that day, etc.?


    Today I ran in weather that was 30-35 degrees Farenheit hotter than my recent runs (55 degrees and windy two nights ago; 90 degrees and strong sun today). It was a killer run (not in a good sense), and though I hydrated up well all day leading up to it I felt pulverized at the end, and even stopped a quarter mile shy of the end of my 5 mile course because "I just had to".


    Checking the HR trend during the run on Garmin I saw a steady increase up to the moment I stopped, and I was surprised to see that at the end of the run, when I was about to die, my HR was just about what that max HR was that I hit some months ago but that had been quite elusive since.


    So, I'm wondering - is a max HR of 178 BPM obtained while exhausted and dehydrated the same as a max HR of 178 BPM when feeling strong and sprinting at the end of a 5K - in terms of reflecting physiology?


    Thanks for any thoughts!

    Seattle prattle

      there's a bunch of things that effect heart rate including hydration level, how rested you are, humidity, etc. And then there's inaccuracies of most every heart rate monitor, some more than others...

      That said, heart rate training usually includes warnings regarding the caveats noted above. But for your purposes, heart rate is being used primarily for monitoring effort level (level of exertion). ANd it's done so as to modulate training and racing to yield the best results in conditioning and racing.

      So, here's the take away in the case you've noted: your effort on the hot day was in large part likely due to the heat, as you guessed, and it in fact drove your heart rate up with what amounted to a lot less effort than you did on the recent 5k done under less harsh conditions.And if we are after use that knowledge to further your training, we would note that the hot day training was not really a 100% effort of the kind you might want to use to gauge your maximum fitness and ability.

      Put another way, if you've done this for a while, you might expect that you aren't going to get the same performance on a very hot day, or a day when you are fatigued, or dehydrated, etc., and you would take that into consideration from the get-go, and certainly when interpreting your results (time/pace and HR).

      So, yeah, MHR means the same thing physiologically as max HR measured under more "normal" conditions, but for different reasons. ANd the reason is that your body has to work a whole lot harder under adverse conditions like extreme heat than it does under more favorable conditions. If you are trying to train at a certain level, those adverse conditions will drive your heart rate up more than under normal conditions, and you may not therefore be getting many of the adaptations that come with higher VO2 levels, running cadence, speed endurance, etc. that you would get if you trained at that heart rate under normal conditions.


        It also shows you that if you are running, or especially racing, on a hot or humid day, you'll need to slow down to keep the effort manageable. Going out at the pace you intended in those conditions will lead to serious crash and burn.