Why Running in the Heat Feels Harder and What to Do to Stay Safe

Running in the heat can and will challenge the body and mind much more intensely because the body responds to the heat in a very specific way, slowing us down and making our effort seem that much greater. Therefore you should not be trying to run your normal pace until you are acclimated to the heat temperature zone.

When we run in the heat, our “rate of perceived exertion” feels higher than at normal temperatures.

What is Rate of Perceived Exertion (RPE)?

Our internal pace, the pace that we feel we can sustain while running at various levels, is what we perceive to be a given effort during our runs. For example, if you are a runner that generally runs a 5K distance at an 8:00min mile pace, and that feels “comfortable” for you, one would say that your RPE for that pace is at a level 6 on a scale of 1-10. However, add the element of heat into the mix, and running at that pace will now feel like an effort level of 7 or 8. Why is this? Our pace for performance becomes affected by the heat at a rate of 7-10% degradation once we reach a temperature of 75 degrees or higher.

Our metabolic response to running in the heat is as follows:

  • Body temperature increases, and therefore we perspire more to cool the body. The more we sweat, the more fluid we lose.
  • Oxygen uptake increases as blood volume decreases. Less blood flow is circulating through your heart and muscles; therefore your pulmonary system begins to work harder to initiate oxygen flow between the lungs and the muscles. This happens because the blood and oxygen circulates to the skin first in order for the body to sweat to cool your internal temperature down.
  • Glycogen depletion increases as the cardio-pulmonary system continues to work harder to maintain blood and oxygen flow throughout the body.
  • Lactate levels increase as the pulmonary system is working harder to increase oxygen levels.

The Next Step

First we must recognize that we can acclimate to running in the heat.

In general, it takes 5-10 runs in the heat for our bodies to then adapt and bring down that level of RPE.

How do we adapt? Common sense is the first key! We need to hydrate, and to accept the fact that we must slow down.

Here is an outline of helpful things to do when running in the heat:

  • Replace and keep your electrolytes balanced. It is important to follow a 1:1 ratio of water and electrolytes. I use a hydration belt with two bottles, one for water, and the other for my electrolyte drink. There are many options, but it is important to have something that has a fair amount of sodium, i.e. Gatorade is often used during races for that reason. If you don’t want the sugar, I find Nuun tablets are great, just add some salt! Nuun tablets can be prepared the night before, just drop into your water and dissolve. Also, simple salt packages from any Bodega!
  • Slow down! Do not go by your normal pace. This can be frustrating for many runners, but is important to go by “feel” or RPE. Leave the GPS home for those first 5 or so runs in the heat. Your body will adapt quickly and your pace will eventually increase.
  • Run/walk for distance runs in extreme heat. This will ensure that you check in with yourself regularly. Use the time you would stop for hydration as your walking interval.
  • Wear sunscreen and a hat. It’s very important that you protect yourself from the sun, as your skin’s temperature increases, blood oxygen will travel to the skin and begin depletion to the muscles.
  • Be smart. If you feel any signs of exhaustion, dizziness, confusion, or you stop sweating, STOP! If you feel any signs of heat exhaustion or heat stroke, seek medical help immediately.
  • Try to run before 10 or after 5. Running in the midday during the heat can only increase the risk of heat exhaustion and heat stroke.

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