Heat, Humidity, and HR | 80/20 Endurance

Heat, Humidity, and HR

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    I’m in the Southeastern US and we’re at the point in the year that it’s not possible to run outdoors and not experience high “real feel” or dewpoint temps no matter what time of day you run. You can get a bit acclimated to it, but that only goes so far. At least for me as I seem to suffer inordinately to the warmer conditions and my HR is always higher for given efforts.

    How best to adjust for this in 8020? Previously I’ve just slowed down in the summer, keeping my HR in zone even if this means a 60-90sec per mile adjustment of pace. But if I stick with a power zone then that will mean HR of 10-25bpm higher than similar efforts in colder temps. In particular, after a hard workout in the middle of a run, it’s almost impossible to get HR “back down” afterwards during the “cooldown” without resorting to walking.

    What’s the best approach to this with regard to 8020? Not worry about the HR aspect or keep HR in check. I typically have used HR & power in my workouts – for example letting power lead me into a particular interval but then holding HR once it flattened out in zone. But that’s hard to do with the conditions. Appreciate any discussion and guidance, thanks.


    Hey Brian,

    Great question! I live near Fort Worth (TX), so I understand exactly where you’re coming from. When it comes to training in the heat, you need to consider both the effects of the heat AND cardiac drift. At any given pace, hotter weather will make the effort more difficult. At the same time, even when you’re keeping your effort the same as in cooler weather, cardiac drift will probably still elevate your heart rate. However, cardiac drift shouldn’t make the run feel more difficult.

    I hope I don’t get in trouble for posting an outside article on this, but I found this to be really helpful in explaining how cardiac drift works.

    Why cardiac drift is important for runners who train by heart rate

    To me, the best approach will take both of these variables into consideration. Adjusting your pace / power so that the overall effort is about the same, but also realizing that you’ll probably still end up with a higher heart rate. Make sense?

    If you’re on Facebook, Steve Palladino has a page for power based runners. He created a calculator that will adjust for variables such as heat and elevation. This is really helpful.

    However, I might consider retesting in the hotter weather. It’ll probably lower your CP a little, but not as much as if you tried to keep your heart rate at the same level. Another possibility would be going by perceived effort and not worrying about your heart rate. Again, this will probably slow you down some, but not as much as if you ran by heart rate. I hope this helps!

    Matt Fitzgerald

    Great advice, Alan. Couldn’t have said it better myself. Because I don’t train by zones, my own approach would be to adjust entirely based on perception, which is totally doable. If I did train by zones, I would create retest and use summer-specific zones. But even there you need to fine-tune by feel.


    Argh, so you’re telling me I need to gauge how I feel? But I spent all this money on these gadgets?

    Kidding, well only partly, to be honest.

    I’ve learned to *not* trust myself and how I feel when I workout/race…too many times burned in a race by going out too fast I guess. Or perhaps just the “once bitten, many times shy” scenario extended out to infinitum.

    And admittedly I’m not great at self-evaluation, often “gutting out” harder efforts and saying to myself they don’t “feel that bad.” Thus seeking out some objective measures like HR, or lately, power zones.

    But training runs aren’t races and my HR isn’t getting *that* high, just routinely into the “x” or “y” zone that 8020 zones says to avoid.

    I guess the big risk is that I’ll overcook myself if I ignore HR in hot weather and let it go into x/3/y zones when Pace/Power are more zone 1/2?

    Matt Fitzgerald

    It’s a huge problem. Training gadgets are systematically robbing athletes of the ability to feel their own bodies. I’ve become quite interested in/alarmed by this phenomenon of late, as have others. Here’s an article I wrote recently about a study on device overdependance in runners:

    Breaking Free From Device Dependence

    I’m even working on a book and a new set of training plans that are intended to combat this scourge!


    Races are generally a different matter. Excitement / adrenaline can really mess with your perception. For races, I’ll use my power target as a point not to exceed. At least early on. However, if it feels more difficult than it should, I’ll back off to what feels right and try to hold it there.

    With workouts, you might consider still checking your stats after the fact. If your heart rate is a few beats higher, no big deal. But if it’s in the stratosphere, maybe back off next time. It took me a few runs to dial this in. But now it’s really dependable. The rare times when my heart rate is really high, I find that I was ignoring my better judgment and pushing too hard.


    Thanks for the feedback guys. Part of this is I’m coming from a long period where I experimented with MAF training, then transitioned into the UphillAthlete methodology which is alot like MAF – both of these have huge emphasis on training below the Aerobic threshold…as defined by HR (moreso MAF than UA which gives more flexibility on zoning but I have been using HRMs for over 10 years now so I am fully indoctrinated for better/worse).

    HR generally works pretty well for me…except in those special instances like excitement, certain medication, etc…with heat/humidity being an annual factor that comes into play.

    What I worry about it is overdoing and it not realizing until my poorly-developed intuition picks up on by which it will be too late. So I guess what I need to realize that heat-induced HR is not going to over-cook my week of training the same way it would if it was effort-induced right? So it’s like an inflation situation?

    I have my long run in the morning, it’s on trails so pace isn’t a great indicator – but I can experiment with keeping an eye on power but ignore HR and see how I feel instead.

    Matt Fitzgerald

    Lean on power. A watt is a watt is a watt. If you adjust your power zones for the conditions and make power your primary cue in the runs that really count, you’ll be safe.


    Thanks Matt. Saturday’s trail long run experimenting with RPE was a bit of a disaster. Probably the problem was the fact it’s a group run and I always have trouble judging effort in a group setting, tending to go much harder than I would on my own. This group in particular tends to hammer uphills and then coast downhills and while I’m a pretty good climbing runner these repeated spikes tend to “bake” me eventually and on this extremely hot/humid run I totally blew up, needing to walk/run the final 30minutes of the 2.5 hour run.

    I’ll try backing off of watts (Stryd has a race calculator that lets you estimate power based on heat/humidity) and see if that helps next time around.


    RPE on a group run can be more difficult. Especially if you’re more competitive. If it’s just me, keeping the intensity at the appropriate level is rarely a problem. But if it’s a group run, it helps to use pace or power to make sure I’m not pushing too hard. At least initially. I’ll set a top end for my intensity. For example, I might want to keep it at or below 250 watts. As long as I’m in a good rhythm and it falls within these parameters, I’m good. But if my natural effort is above 250 watts, I’ll dial it back. When I pull back, I’ll pay attention to what RPE is and try to hold it there. Then, I’ll check periodically to make sure I’m more or less on target.


    Yep, triathlon coach Joe Friel says these group runs are susceptible for falling into the “happy hard” zone. Just hard enough for you to feel like you did something, but not hard enough to make any gains, but too hard to recover properly. It’s part of why I started training with HR/power gadgets, but it’s still tough in a group run to let the rest pull away even if it’s just on uphills.

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