When I put together my post about the Weather Channel Apps Run Score, I said I was going to investigate the notion they talked about in the science behind what they consider good running temperature conditions.

I’m quoting here: “Higher temperatures make your body use up more energy to cool you down. You’ll also lose fluids more rapidly. Lower temperatures can convert your body’s fuel source from less fat consumption to more carb consumption.”

I know that we burn carbs/glycogen stores as we run with more intensity and that there is also a Fat Burning Zone, which mostly for me meant a lighted area on a treadmill or other cardio machine at the gym, lol.

I didn’t much think about carbs vs fats as fuel, since so much of a runners life is carbs, carbs, carbs.

After reading the above quote in the GoRun index section of the Weather Channel App though, I wanted to research the idea that there is more carb burning vs fat burning depending on the temperature.

Wait, I’m Confused…

So I suck at Math, Chemistry…basically Sciency Things.

I can understand concepts behind the body and when it applies to runners especially (because I’m interested in it), BUT throw in numbers/formula’s/Medical Journally kind of data and I just want to go EAT some carbs, not try to absorb jargon.

I will send my husband (an engineer) a text if I need to adjust a recipe by a certain ratio or fraction so he can do the math for me!! And if he doesn’t answer, I text my son David…another engineer.

My research led me to some studies in Journals…so bear with me as I try to share, lol. I read an article at the Runners World website that helped break it down.

Runners World- Do You Burn More Calories Running in the Heat

The body chooses burning carbs…which is what your glycogen stores are made from…as the first resort for burning fuel during intense exercise.

This is why we carb load before a long race such as the marathon, and take carbs with us during the run. Fat is burned at a rate of 50% or more as the fuel source during rest or low intensity exercises…that is exercise that uses less than 65% of your aerobic capacity.

If you have ever been on a cardio machine at the gym like a treadmill or elliptical, a lot of them have a monitor that will show whether you are in the fat burning zone or cardio zone or whatever.

That 50% or more rate at a less than 65% aerobic capacity is where that zone parameter is coming from.

Even during higher intensity exercise, fat will be burned and the body will switch to that when the stores are low. But the body really wants to use carbs, which is why we can hit the wall so to speak if our glycogen stores are depleted.

Glycogen storage is increased by consuming carbs.. So both fat and carbs are used in exercise, but the body uses its fuel in different ratios.

Based on the study I mentioned earlier, (published in the Journal of Applied Physiology, Nutrition and Metabolism) those ratios are altered depending on the outside temperature.

This study showed that a higher proportion of carbs is burned in hot weather. Based on this notion, Runners World magazine recommends you plan to consume a bit more carbs in hot weather training vs. in cooler temps.

The Weather App

I think the information in the Weather App comes from how quickly our body uses up the carbs in the heat.

During hot weather, our glycogen is depleted faster (as is our hydration), so they will then turn to the fat in our bodies as fuel.

During a run that may be a bit longer, but isn’t really intense such as a run/walk or a very slow jog, the fat stores can fuel that without hitting the wall, so to speak.

Since the carb storage doesn’t go down as fast in the cooler temps, you are using those carb stores for a longer period of time.

So make sure to be aware of your bodies needs in hot weather, and take in a bit more carbs during bouts of intense exercise in the heat.