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The Science (and strategy) Behind Sweating

Posted by: on May, 19 2016

Found on Competitor.com and written by Jen Weir, CSCS, CPT

This article first appeared on Women’s Running.

Sweating is a natural process critical for helping our hard-working bodies deal with the hot temperatures. As the mercury rises, so does your risk of dehydration and complications from the heat. Don’t let the summer swelter put a damper on your training efforts—it’s time to get serious about your hydration.hydrating

Why Do We Sweat?

It doesn’t matter if you’re running in a snow storm or under the scorching summer sun—your working muscles create a slight bump in body temperature. As your body begins to warm up, part of the brain sends a signal to the sweat glands to get busy.

Your sweat glands start pumping out fluids to moisten the skin, which are quickly evaporated. This evaporation of sweat removes heat from your skin’s surface and helps to cool you off. When the humidity is high, the evaporation process is suppressed, increasing your risk of overheating. The hotter you get, the more sweat you produce as your body painstakingly tries to keep your body at a safe and stable temperature.

The Stresses of Running In The Heat

Blood is actually a pretty big deal when you’re running. It is what keeps us going, granted the heart and lungs do all the heavy lifting. During a run, your blood shuttles oxygen and nutrients to your working muscles and exchanges them for metabolic waste to be carried away. When you add a hot day to the equation, things get interesting. Your blood is already working overtime toting everything around, but now it’s also tasked with keeping your body at a safe temperature.

Increased body heat forces the redirection of some of that oxygen-rich blood away from your muscles and to your skin. As the blood reaches the surface of your body, it’s cooled by the air before returning to your heart, thereby helping you maintain a stable body temperature but causing your heart rate to increase an effort to fuel muscle and allow you to maintain your running intensity. This is one of the factors that make it more difficult to perform well in the heat. Despite the fact that your body is already shunting blood to the surface in an effort to cool you off, it’s not enough to keep you at a safe core temperature. Enter sweat.

The Physiological Effects Of Sweating

While sweating is an absolute necessity for preventing overheating, excessive fluid loss through sweating can annihilate your performance and have severe consequences for your health. Studies have shown a mere 2 percent drop in body weight from sweat loss can hinder your performance. This is definitely an issue for long distance runners who have shown fluid losses as high as 6 to 10 percent!

Your body comprises about 60 percent water, with one-third of that found in extracellular fluids, which includes the fluids surrounding your cells and your blood plasma. Some of the fluids you lose through sweat come from this extracellular source, which means the more you sweat, the lower your blood volume drops. This limits the amount of blood available to fuel your muscles and keep you cool. With a dwindling energy supply and increasing body temperature, your performance is compromised.

Hydration, Your Saving Grace


You can definitely minimize these effects with adequate and timely hydration. Before you even step foot out the door, do your best to ensure a solid hydration base. Katie Wichman, registered dietician and fellow runner, recommends downing two to three cups of water two hours beforehand, followed by one cup of water about 10 minutes before your run.

Add Salt

If you’re feeling adventurous, give in to those salt cravings before your next run. Research performed by David Morris, an assistant professor of kinesiology at the University of Texas of the Permian Basin, shows sodium ingestion prior to exercise increases water consumption and retention during the hydration period.  Eating or drinking something high in sodium an hour or two before your run will increase your thirst and compel your body to retain more water—both of which will improve your hydration status, thereby allowing you to run faster and farther than if you abstained from the sodium.


You’ve heard to trust and listen to your body, but in the case of hydration, this isn’t an exclusive way to hydrate. The human body is pretty inefficient at gauging its level of hydration—when you feel thirsty, you’re already on your way to dehydration. Wichman proposes drinking 4 to 8 ounces, about 4 to 8 gulps, every 15 to 20 minutes to avoid this point. On extra hot or humid days, this should increase to 5 to 10.5 ounces every 15 minutes. If you can stomach them, sports drinks are a great addition to your hydration plan to help counter the effects of electrolyte loss that often occurs with high-sweat rates.


Despite your best efforts of staying hydrated during your run, chances are you’ll still finish with some level of dehydration. When the sweat’s running faster than you can slurp out of your water bottle, it’s just not feasible to drink as much as you need to keep up with fluid loss. After your run, aim to take in 20 to 24 ounces of water or sports drink for every pound of body weight lost. To determine sweat loss, simply weigh yourself, naked, before and after your run. If you do this a couple of times, you’ll get a general idea of how much you need to drink after your runs in the heat.