3 Ground Rules for Running in the Heat

3 Ground Rules for Running in the Heat

Just drink plenty of water and you’ll be fine. Right? Not exactly. Anyone that has run in the heat and ran face first into “the wall” can tell you that sometimes figuring out what enough means can be complicated. With summer training comes the heat and humidity, two of Mother Natures tougher foes for endurance athletes. 

If you don’t have access to a coach or a lab, how do you figure out how best to hydrate so you don’t end up crawling along the sidewalk?

There are a couple simple rules of thumb that should keep you safe and running. 


What’s going on?

The higher the heat and humidity, the more you are likely to sweat. Sweating will make you dehydrated which reduces your blood volume, which makes your heart work harder. You can see where this is going, right? And it doesn’t take that long either. Just a few percent dehydration will slow you down, hit 4 or 5% and you’re likely to end up in the medical tent.

The simplest way to determine if you’re hydrated and ready to train is the pee test. Aim for pale yellow before you head out on that run.

If you are doing longer endurance events that will have you doing runs of two hours or more, you should also do a sweat test so you know approximately how much fluids you should be taking in while running. Weigh yourself before an easy 60 minute run (without clothes). And then weigh yourself after (before taking in any fluids). Every pound you lose is 16 ounces of liquid you need to replace.


Runs up to 60 minutes

Too many runners over do it. They go for a jog and then grab a sports drink. Unless you are going really hard, you don’t need to the extra sugar and calories. You just need water, especially at lower intensities. If you didn’t calculate your sweat rate, a simple rule of thumb is 3 to 6 ounces every 20 minutes.

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Up to 90 minutes

This is where you need to start paying attention to electrolytes, especially if you are a salty sweater (it stings your eyes is a good test). Electrolytes, like sodium, potassium, and magnesium, help keep you hydrated by regulating the flow of water in the body and keeping those nerve endings firing (i.e., warding off fatigue). 

You’ll need to supplement your regular water intake on longer, sweaty runs with additional electrolytes, typically from a sports drink or salt tabs. Most sports drinks are actually a little light in electrolytes. Check the label. A good rule of thumb to aim for is 750 ml per liter. If you need more carry some extra salt tabs.



Over 90 minutes

At this point just staying hydrated and keeping your electrolytes up isn’t enough. You’re also going to need to start replacing the glucose to keep your muscles firing with an easily digestible carb. 

In addition to the electrolytes, aim for 60-90 grams of carbohydrates per hour to avoid cramping and early fatigue.



Don’t just rely on thirst as an indicator. When you get dehydrated and fatigued, the body can play tricks on you. Know your hydration plan before you go out on a run. Many people underestimate both the effect of the heat and their own body’s needs. Make sure you have enough water, electrolytes and carbs to train effectively and, more importantly, get back home safely.



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