Why Heat Slows You Down (And How to Work With It)

Does this Montana heat wave have you changing your exercise plans? 

The heat is no joke, and when the heat isn’t seeming to go away, it’s important that we are being safe about our exercise! Continue reading for more tips about staying safe while exercising in this heat.

Exercising in the heat puts extra stress on your cardiovascular system. How does your body regulate that extra heat?

In short, your body has decreased blood flow when exercising in the heat compared to a temperate climate. This causes your body to reach an anaerobic state, where the body is not using oxygen as quickly anymore. As a result, your body uses more muscle glycogen, causing your body to tire faster than when exercising in a temperate environment. 

You may feel as though you cannot work as hard in the extreme heat, and you may be wondering why. When your body heats up, it has to redirect blood flow toward your skin to cool you down, which means less oxygen-rich blood is getting to your working muscles. This lowers your VO2 max, or your body's ability to use oxygen efficiently during exercise. So even at the same effort level, you're getting less out of it. In the end heat does limit your performance so you might want to save your PR attempts and max-efforts for cooler conditions.

All of that heat your body generates during exercise has to go somewhere. The body works hard to maintain a safe, stable core temperature so it can keep functioning and it has a couple of built-in ways to do that:

1. Evaporation. The most effective method is sweating. Your body secretes sweat through the skin, covering a large surface area so it can evaporate into the air and carry heat away with it. A small amount of cooling also happens through breathing, but the skin does the heavy lifting here.

   
   

2. Circulatory System. As mentioned previously, the body’s rate of blood flow changes in different temperatures. In hot ambient temperatures, blood flow decreases to bring skin temperature closer to the ambient temperature. This system mostly delivers the heat to the skin to be processed as sweat.

Now that we know what happens inside of our bodies when exercising in intense heat, let’s think about how we can set ourselves up for success.

If we are exercising indoors with air conditioning, it’s easy to assume the heat isn’t a factor but it actually does still play a role even when you are not standing directly in it. When the heat is intense, your body is using a lot of the mechanisms we discussed earlier, sweating and a decrease in blood flow, throughout the day, not just during your workout. Even the walk from your car to the gym has your body on overdrive.

This means that your body is losing more water and salt, so you need more of both to feel and perform your best. To combat this, make sure that you are drinking enough water, not just while working out, but throughout the day, and include some electrolytes in there as well. Even during the heat, make sure you are consuming enough calories, even if you don’t feel like it. It is common to have a decreased appetite in the heat, but your body still needs the calories to carry you through your day.

Now what about exercising outside? There are many additional considerations to take into account when planning on exercising outside in intense heat. First, think about the forecast. The temperature, the sun and UV rays, the conditions you will be exercising in, and the duration you will be out. If you can, plan to avoid exercising in the late afternoon, when both the temperature and the UV are at their peak. You can also think about moving your workout to a shady place to decrease the impact of the sun. Additionally, consider reducing intensity and duration of your workout to reduce the stress on your body. 

Heat stroke can happen fast, in as little as 10-15 minutes in severe conditions. If you are in doubt about the safety of exercising out in the heat, stay safe and transition your workout to indoors, or reschedule it for a cooler day. 

Don’t forget our gym has great air conditioning and friendly faces, so definitely stop in on those super hot days (and any other time!) And don’t forget about our hikes, we have a couple more this summer and we plan to start earlier in the morning to beat the heat!

- Coach Morgan

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Resources:

Institute of Medicine (US) Committee on Military Nutrition Research; Marriott BM, editor. Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington (DC): National Academies Press (US); 1993. 3, Physiological Responses to Exercise in the Heat. Available from: https://www.ncbi.nlm.nih.gov/books/NBK236240/