BASS PRO MIDWEEK MOTIVATION - When is it Too Hot to Run Outside

Hello runner friends!

Welcome back to the Bass Pro Fitness Series

MIDWEEK M😊TIVATI😊N blog!

Now let's get started by talking about the obvious... it's hot outside. REALLY hot! So hot in fact that ultrarunner Dena Carr posted this after her morning run yesterday, "What does humidity above 90% look like for a run? I’m dripping wet from sweat and my daughter asked me how I was so wet without it raining. She thought I jumped in water somewhere along my run. Not sure if you can see the sweat dripping or that my blue shorts look grey (no filter) from being soaking wet." Yikes right??

And Nathan Toliver posted this, "Got up this morning to enjoy a cool morning run for once, but the heat index was 90 with 99% humidity at 4:45 in the morning. That run sucked. I promise never to complain about cold weather runs ever again…." Okay, so that picture is not Nathan but I'm sure that's how he felt after that run. I don't know about you but I'm ready for some cold weather runs too…and please remind me that I said this when I'm blogging about the cold this January. 

So this poses a question since the heat index is supposed to be 120 degrees or higher today through Friday here in the Midwest... When is it too hot to run outside? 

The answer, according to Marathon Handbook, is likely not as simple as you might think. There isn’t a single cutoff temperature that is universally agreed upon as being too hot to run outside. Moreover, when discussing running in the heat, there is more than just temperature to consider, as humidity plays a major role in the resultant “real feel“ or how hot it actually feels outside. We will discuss the heat index, which is a measure that takes into consideration both the air temperature and the humidity, later on.

However, if you’re looking for a general guideline for how hot is too hot to run outside, according to the Road Runners Club of America (RRCA), you should avoid running outside if the heat is above 98.6 degrees Fahrenheit and the humidity is above 70-80%.

The Risks Of Running In The Heat

The reason that it could be dangerous to run in the heat is that the core temperature of the body rises too high, increasing the risk of heat illnesses like heat exhaustion and heat stroke.

Your body does have natural thermoregulatory mechanisms to help cool down your core body temperature when you exercise, such as sweating and increasing circulation to the surface of your skin to move blood further away from the core of your body.

However, these mechanisms are often insufficient for running in extremely hot and humid conditions.

When deciding how hot is too hot to run outdoors, you need to pay attention to not only the air temperature on the thermometer but also the humidity. Humidity makes running in hot temperatures even more taxing on the body because when the moisture content of the air is higher, it feels hotter.

The Heat Index combines the air temperature with the relative humidity, so the metric measures the apparent temperature or the “real feel” outside. The humidity doesn’t really cause any appreciable increase in the Heat Index or how hot it actually feels outside at or below 40% humidity.

However, above 40%, humidity rapidly increases the Heat Index. Essentially, the reason that it is pretty difficult to assign a particular air temperature and humidity value to when it is too hot to run outdoors is that the thermal strain of running in the heat increases exponentially—rather than linearly—with an increase in humidity.

For example, when it’s 88° F (31° C) out with 40% humidity, it will still feel like 88° F, but when it’s 88° F with 70% humidity, it will feel like 100° F (38° C).

When the humidity rises to 85% at the same temperature, the Heat Index jumps to 110° F (43° C).

For this reason, it’s not easy to calculate the heat index on your own.

However, there are plenty of online calculators, such as the one here, that can help you determine the real feel of the heat out there.

The reason that paying attention to the heat index is particularly important is that the body is much less effective at cooling down your core temperature when running in the heat and humidity versus running in dry heat.

When you run in the humidity, the moisture content in the air prevents sweat from evaporating readily.

Essentially, because the moisture content of the humid air is so high, sweat will not evaporate readily, which means that the heat energy stays trapped in your body without getting released.

In this way, running in the humidity causes heat to build up in your body, which in turn, increases the risk of heat illnesses like heat exhaustion and heat stroke.

So there you have it friends. Determining if it's too hot to run outside is up to the individual. But if you decide to go for it rather than taking it to the treadmill, be smart. Take water or electrolytes with you, check the hourly forecast and run at the coolest time, dress appropriately, wear sunscreen, slow your pace down a bit, and wait for the weekend to do your long run when this crazy heat advisory goes away. Believe it or not, fall is just around the corner and so is the Bass Pro Marathon and Half as well as the Dogwood Canyon Trail Runs. So train smart and be patient. Cool weather is on the way. 

Happy Running!