Friday, June 19, 2015

Why am I running so much slower in the heat?

I was running my tempo runs around an 8:30 minute pace in the winter and early spring.  Now that it is in the 90’s, I am struggling to keep my tempo runs under a 9:30 pace.  I have gained a few pounds, but I am stronger than I was back then as well.  Why am I running slower in the heat?  I recently ran across a few articles on that discusses what happens to your body when you run in the heat and how to make it more manageable.

Why is it so much harder to run in the heat?

The body has the ability to cool itself down through sweating.  Contrary to popular belief, it is actually the evaporation of sweat that cools you down, not sweating itself.  If you live in a humid area, your body has problems cooling itself because while you are still sweating, it will be more difficult for the sweat to evaporate.  In order for your body to sweat and cool you down, it must increase the blood flow to the surface of the skin.  This is why your skin turns red when you are working really hard.  With all of the blood moving to the surface to cool you down, it reduces the amount of blood that goes to your heart and other muscles that are working on overdrive.  This is one of the reasons why it is so much harder to run in the heat. (1)

Your body wants to be efficient, pumping as much blood with each heartbeat as possible.  When your blood is being pumped to the skin and away from your heart, it leaves less blood to be pumped with each beat of your heart.  This means that your heart rate needs to increase to make up for the lack of blood.  So when it seems like it’s a harder workout, it actually is.  Your heart rate will most likely be higher than it was in cooler weather.  (1)

Your muscles perform best when they can pull oxygen from your blood.  When your muscles are not getting as much oxygen, they fatigue faster as you go from an aerobic workout to an anaerobic workout (because your muscles aren’t getting enough oxygen).  You will not only fatigue more quickly, but you will have lactate buildup more quickly as well.  (1)

Your VO2 max will decrease as well, which is the maximum amount of oxygen your body will be able to take in and convert to energy.  Basically the heat will make you less efficient, making your workout a lot harder than when it is cool out. (1)

So what can you do to make it easier to run in the heat? 

Try Pre-Cooling: Research has shown that athletes perform better if they cool their bodies before heading out for a run in the heat.  Take a cold shower or keep the AC in the car on maximum when you are on the way to your run. (2)

Stay Hydrated: You lose a lot of fluids from sweat in the heat, so it is important to replenish that loss to keep your blood volume as normal as possible.  This will also allow your oxygen levels to remain higher.   I like to pre-hydrate starting a few hours before my runs. (2)

Run Early or Late: It just make sense to run in the morning or evening if possible to avoid the higher temperatures.  Your workouts will be better and you will feel more comfortable. (2)

Slow Down:  Run based on perceived level of exertion (or how hard your workout feels) instead of your pace or heart rate.  Just because you are running much slower doesn’t mean that you aren’t getting a good workout in.  Heat illness is actually caused by the muscles producing heat, causing you to overheat, not the temperature being too hot, so slowing down may help to reduce the chances of heat illness. (2)

Take Baby Steps:  It takes about 10 days for your body to fully acclimate to the heat.  If you haven’t been running in the heat, start out slow that first hot day and slowly increase your mileage or intensity each run until your body has acclimated to the heat.  After your body is used to the heat, you can train at a more normal level. (2)

Listen To Your Body:  Don’t try to push through feelings of fatigue, discomfort, light headedness, nausea, or if you stop sweating.  These are all signs of heat illness.  If you have these symptoms, stop immediately and find a cool spot to rest until your body can recover.  It’s better to take a break than end up in the hospital. (2) put out some great articles about how your body reacts to running in the heat and tips to make it more manageable.  Be safe and make sure you stay hydrated.  There are tons of great hydration options from hand-held bottles to belts, to backpacks.  Here are a few reviews of hydration items I have tried:

Data Reference:

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