How much does heat and humidity affect running?

Summer is starting to heat up and if you live in a place like me here in Kansas City in the Midwest, along with that heat comes a lot of humidity. So, you may be wondering to yourself when going out for a run, how much does heat and humidity actually affect my running?
How much does heat and humidity affect running?

Summer is starting to heat up and if you live in a place like me here in Kansas City in the Midwest, along with that heat comes a lot of humidity. So, you may be wondering to yourself when going out for a run, how much does heat and humidity actually affect my running?

If you haven't been on this channel here before, you won't know me. I'm Jesse Funk. This series is called Runner's High, where we're talking about all the nitty-gritty details of being the best runner you can possibly be. So, if you want to know that, you want to be a great runner, you want to enjoy running, hit that subscribe button, stay around with me. I've got plenty of videos for you in the future. But today, you want to know how does heat and humidity actually affect your running when going out there to perform or going out for a long run.

The short version is you're going to go slower. Nothing crazy about that statement, right? You know that when it gets hotter you're going to go slower and you're like, okay, give me the obvious, give me the details. Well, with that, we have to think about what's going on with our body.

When we go out and run or when we workout, whatever we're doing we know that our body heats up, right again. Another almost Captain Obvious statement. But we have to think about when our body heats up, what's actually happening?

When that happens, it does a couple things. Number one, it’s going to spend energy on sweating. This is trying to cool you by transferring heat into water and letting it evaporate. And it's also going to move blood towards the surface of your skin so that he can dissipate into the air.

So, those two things are going on as our body heats up so we can try to maintain a better internal temperature. But part of what happens when it is hot and humid outside is your body has a harder time cooling off. And this is really because of the two factors involved.

Number one, when the air temperature is higher, it is harder for heat to dissipate from your blood to the air and cool that off by that mechanism. And when the humidity goes up, it makes it harder for that sweat to evaporate also kind of blocking that mechanism for your body to cool itself off. So, when you combine those two things together, heat and humidity rising, that means our bodies have an inability to cool themselves off.

Effectively what we're talking about here is that when your body cannot cool itself off, it's going to work harder to try to cool itself off because it needs to maintain that internal temperature. And by doing that, you're diverting resources namely, blood away from clearing all those kind of debris in the waste created when we're working out.

Meaning that those things that we've trained to do get our muscles to kind of react to certain loads, at certain speeds and our body will get rid of the waste so we can kind of operate in optimal level, cannot do at the same level because the energy is being spent on trying to keep us cool.

While we're trying to stay cool that kind of junk is building up, that’s a very non-scientific term, in our muscles. And from doing that, fatigue builds. When fatigue builds, then cardiac levels go up, cardiac drift. I did a whole video on that. If you wanna check that out, subscribe to the channel.

So, our heart rate goes up, our body's working even harder to try to cool us off. Fatigue is building, as fatigue builds, we slow down. Eventually, our heart rate reaches a level where it cannot go higher, it's working at maximum capacity, and you kind of just start to hit a wall at that point.

So, what are we talking about in terms of numbers here? Well, back in the 80s, legendary running coach Jeff Galloway put together this chart. This chart he put together to basically tell you what you should expect based on the temperature, how much you're going to slow down when you're running.

So, let’s get the chart out of the way. Now, if you use that chart, go back and just pause the video if you want to look at it. Use that chart to slow yourself down based on the temperature, you know that importantly as you pay attention to it, it is a nonlinear progression. Now, I know I'm getting mathy on you but stick with me.

What I mean by nonlinear progression is that it's not a nice straight line. As an example, it's not like every 10 degrees it's a 1% drop in performance. No, it's an even higher drop in performance the hotter the temperature goes. So, for example, when we go from 50 degrees to 70 degrees, we see about a 9% reduction in speed. But that same 20-degree jump when we go from 70 to 90, you're gonna see over 40% reduction in speed.

Okay. So, I'm interrupting myself here. After getting back from running in the heat and humidity, hence the red face, that I realized I did my mental math backwards. I won’t explain what I did wrong, but ignore the numbers I just told you.

When you're looking at that chart when you go from 50 to 70, it's a 7% increase in time, so you're slowing down 7%. But then when you go from 70 to 90, you're seeing like a 13 to maybe 15% additional decrease in time or increase, you're getting slower basically. The difference is larger as you go higher in the heat, but it's not as dramatic as I had said.

Again, I screwed my mental math. As always, kids, check your work so you don't do stupid stuff like that and have to interrupt yourself. Let's get back to the video, or the podcast, put together a research paper and petitioned USA triathlon to change how they do their national championship, a while back, both because of heat, and because of current conditions when the race is held in Cleveland.

So, if you want to check out my interview with him, I will link to it here at the end of the show.

The biggest thing to remember is that when it gets hotter, you're going to go slower, so just expect that. Accept that you're going to go slower. Don't try to push yourself beyond what you feel. I really kind of advocate for a rate of perceived exertion, which is keeping you in tune with how does your body feel at any given time or place and effort.

This kind of keeps you in tune with some of these changes that goes on, especially with heat and humidity, knowing that you're going to go slower. So, if you want to check out that interview with my friend Dr. Tom, that should be coming up on the screen here shortly. And I'll see you next time on the next episode of Runner's High.

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