top of page
  • Writer's picturecoachmk

#WWCMKD: Hot Race Day Edition

Updated: Jul 21, 2021

Situation: Your race is tomorrow, and you’ve seen a ‘heat advisory’ notification from the weather app on your phone. WADOIDOO???

Please start with this document, not with Google! You may ask the wrong question. If you Google "how to hydrate in heat" you are going to get terrific advice for running in the Sahara, where temps regularly exceed 101. Chances are pretty good that you are not *actually* running through the desert, so let’s step back a little.

We’ve been training for 20 weeks. Race day looks to be hotter than expected. How hot is hot? What does that mean? What precautions do we take, what do we do differently, how do we adjust race-day expectations?

Rule #1 of running in heat: it can, and likely will, slow you down.

It is more effort to cool down than to warm up, so in hot weather higher heart rates will yield slower paces. Those A paces that felt comfortably hard in the EAT may feel damn near impossible on race day. Trying to push pace isn't a good idea, you have to respect your effort levels; 170bpm will still feel like 170bpm even if the pace on your watch doesn't look that bad twenty minutes into a race.

Now, we need to talk about ‘hot’. On the surface, the term seems relative; what I consider to be ‘hot’ living in Denver may seem insanely wussy to someone living in Florida….when we are debating whether to eat inside the restaurant or on the patio. We can’t think about absolute temperatures, but rather how they impact core temperatures

Core temps explain why you sweat during hard workouts even on cold days and why you continue to sweat even after the shower following a hard workout.

Rule #2: Heat means we have to worry about core temperatures rising more quickly than usual, impacting our ability to sustain effort.

Generally speaking, anything at or above 70 for events that will require an hour of hard work or more is considered ‘hot’ for an endurance runner, as that’s the point past which your core temperature will rise exponentially (increasing at an increasing rate).

Rule #3: Temperature alone doesn’t tell us much, we need context to grasp the big picture.

Generally speaking, if you are running on a road, you won’t have a lot of shade. So you will be in direct sunlight for most, if not all, of your race (survivalists and ultrarunners call this ‘exposure[1]’). We need to consider the following data points:

· What time the sun rises

· What time the race/your corral starts

· Temperature (will it be hot?)

· What time you expect to finish (how long will you be eating the UV Sandwich?)

· Cloud cover, yes or no? (will you be exposed for the duration of the event?)

· The dew point (how humid it feels)

· Relative Humidity (how much fluid you can expect to lose per hour)

· The heat index (how uncomfortable all this shit would feel even if you weren’t racing)

Ok, That’s a LOT. Does #allofthis really matter?

We need sunrise vs start time and general idea of your predicted finish time to calculate how long you can expect to be ‘exposed’.

Sunlight radiates off asphalt so if you’re exposed you have rays from the sun bearing down on you as well as radiating up from the ground, making YOU the meat in a UV sandwich. You will feel hotter than the predicted heat index. This will increase at an increasing rate after your first hour of exposure.

When it’s humid too that sunlight will be radiating off the asphalt to heat you up AND heating the humid air around you, the air that you are breathing. This is why we care about relative humidity. The more humid it is, when you are hot, working hard, and breathing hot air, the harder it will be to cool off. Your core temps will rise uncontrollably, which will cause you to sweat more, and this chain reaction will force you into the electric fence sooner than you would normally expect.

When a race is expected to be hot, or is in a place like Miami or Maui where hot and humid is the norm, we prefer races that start before the sun rises. The earlier the better (less exposure).

A simpler question is to look for ‘worry points’. Here are the benchmark figures that should get your attention:

· Actual Temperature: 75

· Dew Point Temperature: 60+

· Relative Humidity: 65%+

· Heat Index: absolute value of 75, or 5+ degrees higher than the actual temperature

Real-Life Examples (from a call with a client running Miami Marathon)

Q. The forecast for my race tomorrow is a high of 72.

A. That doesn’t tell me anything.

Q. The sun is expected to rise at 6:40am tomorrow, my race starts at 7am, my wave should be released at 7:05, the dew point will be 70 and temps 65 by 9am, partly cloudy all day. I expect to finish my race in roughly 1:30, so around 9am. I don’t understand the other numbers, but the heat index before 9am is 82.

A. Woah, Heat Index of 82 is HIGH, yo. The good news is that the day will be partly cloudy, so no direct heat from the sun, YAY! Unfortunately, despite that, it’s still going to be hella muggy out there (a 12-degree difference between dew point and heat index is huge; it’s only 70 degrees but will feel considerably hotter due to the moisture in the air. Even if you are local and used to this weather it still may be hard to breathe) and you won’t get to start until an hour after the sun has risen, which means you will be running around the time the Heat Index, and therefore the mugginess, starts to kick in. You may be on the cool side in the corral and feel like you want to strip down to your skivvies by the time you start, then sweating profusely by the 5k mark. This whole race will feel like WORK, no matter how you slice it. This was never your A-race, so let’s consider a new strategy, I am genuinely concerned about heatstroke. That can, and absolutely will, f*ck with your May A-race.

Rule #4: Preparation starts as soon as possible

Rule #5: Food slows the rate of water absorption

Rule #6: You are not a camel, more than 4 cups of water per hour is more than your kidneys can filter

Rule #7: You don’t need as much water as you think you do while your body is at work

Next, we discuss how to prepare. Specifically, how to ‘hydrate’.


If you know that your race is likely to be hot and humid due to geography, you need to start hydrating 2 weeks prior, working with Ellie. If the heat is a night-before shock and a bummer, drink up tonight and have an extra Nuun before bed, then another one 2 hours before your race begins (if you plan on having breakfast, drink your Nuun THEN WAIT at least ten minutes to eat. Water is absorbed within 5 minutes on an empty stomach; when combined with food it can take up to 120). During the race itself, more than 4 cups of water per hour isn't a great idea.

During the race

1. you are not actually in a desert. You don't need to grab water just because you pass it on the course.

2. when you do take water, remember to take sips. Volunteers just fill the cups as instructed, it's not like anyone put serious thought into how much you need.

3. Each cup will have about 3-4 oz of liquid. There are 13 water stations, and 4x13=52. Your body can absorb 34 oz of liquid per hour....BUT ONLY in the most extreme heat and humidity, and ONLY when it is at rest. Again, we are not actually in a desert, we are running a marathon.

3b. If you don’t think you are going to win this marathon, and aren’t counting on that money to pay your mortgage, you need to seriously ask yourself WTF you aren’t DNF-ing. Because YOUR COACH WILL.

4. Your kidneys are the limiting factor: they can only filter so much water per hour (0.26 gallons or 4 cups to be precise), and most of the energy in your body is being directed to your muscles. Trying to consume more than 4 cups of water per hour is pushing the upper limit of what your body can reasonably be expected to do.

5. Water will sit in your belly while it waits for its turn to be filtered, so if you are consuming more than 4 cups of water per hour, you will be able to feel the water sloshing around like a water balloon. It's a very good way to vomit, which will definitely dehydrate you. Let's not do that.

It's going to be fine, because you are #coachedandloved #andwinningatlife

[1] Don’t believe me on exposure? Talk to a boy scout. Watch any episode of Naked & Afraid. THE FIRST thing you do in an emergency situation is smear mud all over any exposed skin THEN build a shelter to protect you from ‘the elements’…because THE most dangerous element is sunlight.

Coach MK Fleming is the founder ofFitness Protection, LLCwhere she coaches all kinds of runners for $29 per month and gives marathon plans away for free. Click here to download her most popular training plan, Tenacious AF!

10 views0 comments

Recent Posts

See All


bottom of page