If you determine your zone according to heartrate, you do not have to recalculate anything: you'll go slower with the same heartrate.

Where I live, my morning long runs are around 70° and 85% humidity for most of the warmer months. When the initial transition hits, it probably costs me about 15 seconds/mile from my routine pace until I acclimate (about a month). If I just slow a little, I have no problem running 120 minutes. But, when I am on vacation in Florida and attempt to run at mid- to high-70s and 90% humidity, I will routinely flame out after an hour, even when I slow down. It would probably take me a few weeks to acclimate to that.

I generally still use HR but give myself a few extra beats at the upper end of the zone when I'm not used to the heat. I also recommend slowing way down and adding walk breaks to keep your HR lower too. After a few weeks of doing that in warmer weather and your HR should be more normal on long runs.

You could try using a pace-adjustment calculator, like this: https://runnersconnect.net/...perature-calculator/ -- but this doesn't account for BMI or running economy or whether you're running in sun or shade. Lighter runners with better economy will have much less pace slowdown in hot and humid conditions. Or, as longtrousers says, you can just slow down more. If you think you cannot continue running and hold Z2 heart rates, then you can always take walking breaks until your HR recovers and then start jogging again.

Re: 1) My understanding is that the training stress in hot/humid conditions is going more towards cardiovascular adaptation than towards activity-specific muscular adaptation. Specifically, your heart works harder because it's trying to pump blood not only to the other working muscles, but also through many capillaries close to your skin to dump excess heat more efficiently. This is not a loss; the additional cardio adaptation can help performance. I feel anecdotally that I tend to see a fall boost in performance after summer running blocks spent in similar conditions to what exxxviii mentions (usually 70ish and humid).

There is an additional wrinkle to this which is that if your heart is working harder, it could trigger metabolic adaptations -- so an easy-paced run with a high heart rate can deplete much more glycogen than an easy-paced run with a low heart rate. I am not aware of evidence on this besides anecdotal experience of myself and others (particularly from hitting the wall in marathons run in hot conditions) and so would welcome any support or refutation!

Re: 2) Adapt your training location, time, and attire. Run during the coolest part of day, in the shade, with as little clothing as possible. If you want the physiological effect of a long and easy effort that trains muscular endurance and fat metabolism, and you cannot make the running effort easy enough, stack the run after a Z1/Z2 bike ride or other aerobic activity.

I learned this a few years ago:

If it's a Saturday afternoon in August ...

If you go for a run around noontime ...

If buzzards follow you ... As you go past the cornfield ...

You might want to back it off, just a little bit

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"What's your claim?" - Ben Gravy
"Your best work is the work you're excited about" - Rick Rubin

1. Well, it depends. Dehydration will impair performance at high and low intensities. At low intensity this is primarily through pacing via increased perceived exertion. Based on a central governor theory this pacing alteration would be to prevent your core temperature from rising too high and would happen prior to the onset of dehydration / hyperthermia.

There is a balance of systemic training load and training load on your cardiovascular system, legs, etc. For example: If you weight lift both squats and bench-press, and do 5 sets of each, then you have "10 sets" of training load for your whole body, but only 5 sets worth of adaptation for your legs.

All this is to say that yes, exercising in the heat increases the strain on your body, but the signal for adaptation of your running muscles / cardiovascular system is not 1:1 with that strain.

2. You are not looking to train heart-rate. Heart rate is only a proxy for exercise intensity. It is imperfect in that it is a proxy for many other things as well. Your blood feeds your working muscles, the harder they work, the more blood they need. The more blood they need the faster the heart beats.

When you get dehydrated (*Simple explanation ahead*), you lose blood volume. Instead of 5L of blood, you lose some of the water component and you're done to 4.5L of blood. But, you still need to fill 5L worth of blood vessels and so your heart beats faster when you're dehydrated to make up.

When you get hot, your body wants hot blood on the surface of the skin to transfer heat to the environment. You "vasodilate" (open up) more blood vessels near your skin. Suddenly the volume in your vascular system goes up (above the 5L in the example above), but you still have only 5L of blood (or maybe less because you're dehydrated). Now you have a vascular system that wants 5.5L of blood, but you only have 4.5L of blood and soo.... your heart rate increases.

When pacing, in any situation, assess the following three things constantly and pay attention to the 2 that are reporting most similar.
1. Pace
2. Rating of perceived exertion (how hard does it feel)
3. Heart rate.

Let's pretend that you know the following to be true because you are in-tune with your running.
Base Pace: 8:00min / mile. RPE 3 of 10. HR 145bpm.

If you're running, and you're on pace, your RPE is correct but your heart rate is 150bpm, you're probably fine.
If you're running and your RPE is 2 / 10, Your Heart Rate is 140bpm, your base pace is probably faster than 8:00 now (yay fitness!)
If you're running and your RPE and 5/10, Your Heart rate is 155bpm, and your pace is 8:00, you should probably slow down.

At any given pace, when running in the heat, your HR is likely to be quite high and your RPE slightly high. Dial back your pace a little to balance Pace and RPE as your two indicators and understand that HR has a lot of other stressors at the moment.

Drink well during activity to mitigate any dehydration induced HR increases.
Try something like Skratch's Hyperhydration to keep a little extra water on-board.

Weigh yourself before and after exercise, aim for 2-4% weight loss to ensure that you are not overhydrating.

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I talk a lot - Give it a listen: http://www.fasttalklabs.com/category/fast-talk
I also give Training Advice via http://www.ForeverEndurance.com

The above poster has eschewed traditional employment and is currently undertaking the ill-conceived task of launching his own hardgoods company. Statements are not made on behalf of nor reflective of anything in any manner... unless they're good, then they count.
http://www.AGNCYINNOVATION.com

This is exactly the approach that I follow.

I live in Texas. Yesterday, I did 1:40 outside following this plan. You just gotta slow down, and drink. My 10min avg HR during the early part of the run was within 2bpm of my last 10min of the run and pace was within 2s/mi for the same regions (no cardiac drift). I lost 5 lbs out of 145. Including the belly full of water I left with, I drank 6 lbs of water.

My pace@RPE is about 15-20s slow. My HR@RPE is about 10bpm high. My HR@pace is about 15-20 bpm high.

As others have mentioned, when your HR is higher you are more working your cardio system. You can still build good fitness but your muscles aren't use to the stressors.
I moved to Florida 4 months ago and I typically am very poor in heat. I have been running 50-75miles/week and my most often pace is 8:00-8:30/mile for long runs and haven't been doing speed work much.
A few days ago despite not having run faster than 7:00/mile in 2 months, I did a treadmill workout where I spent a combined 40min/90min at 6:00/mile and I felt in control and could have done more if required.

I could barely walk for 3 days after that workout. Despite stressing my body regularly and building fitness, my muscles were not used to that kind of pounding. My cardio system clearly could handle more than my skeletal system. This is why most recommend that if you are in a hot climate, still try and do your speed work when cool or on a treadmill so you can still push your skeletal system.

Heat acclimatization is tough. Many think running outside 2-3x a week will do it but in reality, you need 5-7x a week to get good heat adaption skills. Try cycling without a fan or going into the sauna after a swim and you will notice your runs get much easier.

Last point that a lot of people miss. As you get use to the heat your body begins to sweat more. You have sweat 2L/hr normally but that may jump up to 2.5-3/hr when acclimated thus if you are not aware, that can be your limiting factor. I am a champion sweater and last summer I did a strict heat protocol for 10 weeks and by the end I was sweating 4L/hr running. This meant that although I felt comfortable running in Florida midday heat/humidity, unless I had a constant supply of water, I would get dehydrated very quickly so keep that in mind as summer goes on. I will often run with a few bottles and do 8km loops around my house and refill each lap.

I live in west Houston, so I "get" to run/cycle in high heat and humidity for several months in the year.

Today was 90f, 72%hum, "Feels like temp" of 106f, wind S15-18mph during my run - and it's not hot yet.

I'm not fast by most everyone else on this forum. My fastest 1/2marathon was 10:55 in Feb (i'm 60yo). I've been running since Jan 2015 and now cycling since Dec (trying to do my first HIM sometime whenever we get to race again).

I ran an "easy-moderate" 4 miles today at 13min/mi. HR was @147, my max is 177. HR is 10bpm higher than in the winter, but I expect that. On my long days I do a loop, like someone else previously mentioned, where I run by my house as I do two laps or three (around 4 mile loop) and stop to drink when I get to my house. When I run <=6 miles, I don't take anything with me and slow down as necessary, including walking.

I always take my phone so I can call my wife to come get me if necessary (needed it once last summer).

I guess the point is you will be slower, will have a higher HR (just don't get above about 85% max HR), drink throughout the day and realize that even walking out there will help you adjust to the heat and humidity where you'll gain acclimation to the heat.

Don't focus on your pace, focus on your time on your feet. Of course, stay tuned to your body.

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Not a coach. Not a FOP Tri/swimmer/biker/runner. Barely a MOP AGer.
But I'm learning and making progress.

I'm running in Florida and lately the Feels Like is 102-106°. I hate running in the morning humidity so I choose the mid day/after work heat. For long runs, my wife rides next to me with water and electrolytes in different bottles. I don't wear a shirt because it holds water/sweat and doesn't let the skin breath and cool. It will actually trap your body heat in the shirt. Try to find shady routes. Start easy and if you're running by HR then just go slower. You should have no problem running a 13,14 or 15 minute pace if need be. It's called the Ironman Shuffle. You'll acclimate soon. Worse case, STOP, take a break in the shade for 10 minutes to recover them start again. Another option is a morning 45-60 minute run and an afternoon 45-60 minute run. Stay on top of electrolytes and water before but mostly drink water and electrolytes after.

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http://www.sfuelsgolonger.com

This is the reason I bought a Stryd. I’m in NC and the humidity is demoralizing. I’d throw in a few walk breaks here and there once your HR starts to sky rocket past your RPE for the effort.

I'm continually surprised by how often people overthink such a simple sport.

As Pat Clohessy would say "It's just running". Sometimes it really is as simple as that, even for the best in the world.

Yeah, I'll never understand why people come to a forum to ask questions about others experiences<pink>.

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http://www.sfuelsgolonger.com

And sometimes it’s not that simple, like running in extreme heat. Glad to hear you have it all figured out. This forum probably isn’t for you. For the rest of us, we enjoy sharing experiences and tips to better ourselves.

Thanks for all the replies. Lots of good info here. One of the things I've struggled with, is figuring out how to run slower. For some reason it's hard for me to run more than 30 sec/mi slower than my usual Zone 1 pace. It's like it's almost painful and I just feel clunky. That probably means I just need to work on it and practice running even slower than is comfortable.

For example on Sunday when it was scorching, I would normally have tackled that run at 8:15-8:30 pace. But because of the conditions, I slowed it down as much as I could, and I ended up averaging around 9:00 min/mi pace. But my HR was still super high and my RPE was probably around 7 or 8 (rather than 2 or 3) out of 10. I tried to go even slower as that seemed needed, but it was painful (in a different way) - hurts my knees and hips and almost *feels* harder. Guess I just need to practice that. Maybe that would be something useful to try on a treadmill where I can more precisely control my pace and try to keep my cadence the same as I lower the speed.

I completely understand. Yes, I think running super-slow is a skill. I don't know if its a valuable one, except as needed to be able to handle the heat. But, it definitely takes practice...and, uses (different) muscles differently...hence, the soreness even when already adapted to running lots. I try to mix TM and outdoor running during this part of the year for that reason:

1. TM running for speed.
2. Outdoor running for heat-acclimation.

I have no qualms about dividing a run either into a two-a-day (one outdoor, one indoor), or split where I do part of a outside and finish inside. I try to get 45-60 minutes outdoors in the heat most days (5+ out of 7). But, any runs where the focus is PACE (tempo, threshold, speed), move to the treadmill.

On the plus side, the adaptations from heat typically result in a small boost in VO2max, so indoor paces bump by a good bit (20-30s/mi). I try to take advantage of that with the indoor pace work.

I'm a cyclist that runs. A full week I'll run probably 8 to 12 miles. To qualify anything I say.

I don't own a TM but have a smart trainer for the bike. I'm finding in the heat here I'm doing my running outdoors in hopes to heat adapt and doing my bike workouts indoors when it is hot (or going super early).

Reason is since bike is my priority and run is kind of a "well rounded" thing to do, I prioritize more "power" indoors in the cooler environment on the bike.

Outdoors? I've noticed it going from about 75 or 80 deg F to upper 80's to lower 90's that I've lost an entire 45 seconds per mile staying upper Z2 really low Z3 on a run. It's killed me. I'm not a full time "runner", so it probably hurts me more.

My cooler pace on really hill stuff around the house is like 8:30. I've been back into the 9's lately in the heat.

You need about an hour a day of heat exposure to fully stimulate heat acclimation. So, 1-2 hours a week isn't going to do much. Its not that you're not a "full time runner"...you just aren't heat training enough.

Btw, the stimulus has nothing to do with exercise. Its simply elevated core temperature. So, sitting in a hot sauna is just as effective as running at mid-day. A corollary to this is the fact that cycling (except maybe uphill) isn't a great stimulus. The much greater airflow helps keep the core temp down.

Its interesting that you say you cycle indoors to get better "power" because of the heat. I never see heat related degradation in power until the temps outside approach 100*. In fact, I used to do my weekly threshold intervals from 5-6pm May-September. There have only been a few days when I bagged it due to heat (inability to hit/hold power targets, HR climbing without bound).

Actually, you covered most of it quite well in your post.

• moderate your pace
• choose your time of day
• run in shade if possible
• dress appropriately (light colours, suitable fabric, don't overdress)
• hydrate adequately
• cool body down with water/ice if possible (head, neck, etc)
• acclimatise
• sun protection

It's a simple sport.

I could overcomplicate it by saying I ran 18km, last Tuesday when and it was 34 to 39C that morning, averaging 4:54/km, with a HR of 135, max of 169.

But really, what's the point? There's SFA edifying in those numbers.

I added some meaningless numbers in my previous post. Can I be one of the club now?

I'm sorry if you didn't like the tip in my initial post, but hey, I'm only sharing my experience too.

It really is a simple sport. So many overthink or over analyse it.

It's more of the supra-threshold and VO2 stuff. Zones less than that on the bike outside don't bother me. But doing 3x3's at 320 to 350w in 90 deg heat the power just ain't there after the third rep. I also don't have the time to ride Z1 for like 30min between sets to really cool down. I have to "get it in".

Running wise, I do intentionally try to make the runs one hour long uninterrupted. Also, I spend a ton of time out in the back yard during the weekends and at home after work doing yard work out in the heat. Weekends I'm usually outdoors in the heat a few hours per day.

But, I hear what you're saying though. It probably does take a good amount of time. Almost like an outdoor laborer like lawn care or construction.

I agree its a simple sport. But, sometimes people need some context or magnitude...or even an "excuse" / permission to slow down the needed amount. So, numbers sometimes are useful to provide some concept for what's expected or normal. Of course, ultimately the answer is slow-down how ever much it takes. Lots of people want to only slow down "some" of that amount...and they still see their RPE or HR grow without bound.

I agree your numbers above are useless. What's more useful is the CHANGE in those numbers from cooler conditions. So, knowing that 45s - 1:00 mpm slow down is perfectly normal seems to be helpful. Knowing that your HR WILL be elevated by 10-20 bpm at the same RPE seems to be helpful. Also, knowing that as you acclimate..about half of that slow-down / elevated HR may come back as they acclimate...also seems to be helpful....to enable people to "just do it" and be patient.

I drop my son off for practice at 3:30 and then do a little run around Spring Valley (W Houston) everyday. It was 112 heat index yesterday. My run was a run walk. My pace was marathon pace +2 Min. It was, in a word, terrible. But in ways I cannot quite explain, I am simply addicted to the challenge that running in extreme environments provides.

One thing I caution people is that if you go too hard in the heat you can really put yourself in a hole. I did a some half mile repeats last week when it was merely 95 and have paid the consequences since. Because I expected it to be hard, I didn't calibrate properly. Hard was probably more like as hard as I possibly could have gone. Which is always dumb in the middle to the week.

I, too, like to run in the heat. I'd much better run/ride in 100+ "feels like" versus <50. I don't live in Wyoming for a reason :)

I had a meeting yesterday and didn't get my ride in until 7:30pm. "Feels like" had dropped to 106.

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Not a coach. Not a FOP Tri/swimmer/biker/runner. Barely a MOP AGer.
But I'm learning and making progress.