Do You Sweat When You Swim? Here’s What Research Says

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It seems like a simple question with an obvious answer, doesn’t it? It shouldn’t be difficult to figure out that swimmers sweat. And really, it’s not.

But before you just hop in the pool for another challenging workout and forget about it, you want to consider a few crucial factors like hydration, electrolytes, and even nutrition.

Because this is one of those aspects of your swim training that’s easy to overlook— and it can end up costing you.

Do Swimmers Sweat?

Swimmers sweat when they swim. If body temperature increases during a hard swimming workout, your body sweats to cool down- even in water. Most of the time, swimmers don’t notice they are sweating because the water washes it away. Signs of sweating while swimming include: heavy breathing, thirst, and warmth.

It’s important to note that sweating can harm your swimming performance if you don’t manage it well. We’ll get to that later in the article- for now, let’s first discuss why you sweat, as it’s important to understand.

Why Do Swimmers Sweat? a Quick Deep-Dive into Human Physiology 

In biology, there is a term called homeostasis. It means that your body maintains a constant internal environment, despite internal and external changes.

Your core body temperature is a part of this internal environment. Our bodies aim to sustain a core body temperature of ± 37˚C / 98.6˚F. It does this through thermoregulation.

That means if body temperature decreases, your body will try to heat itself by shivering, vasoconstriction, and hormonal changes. You might have experienced this if you’ve ever swum in a freezing pool.

A similar thing happens when body temperature increases, but this time your body will try to cool itself down by sweating, vasodilatation, and other mechanisms. 

During exercise such as swimming, two things happen that lead to an increase in core body temperature. 

Firstly, according to primary care doctor Ava Williams, MD, only 20 percent of energy is used for muscle contraction- the remaining 80 percent? Well, that is converted to and lost as heat. 

Secondly, metabolic reactions such as cellular respiration also produce heat. There are two types: aerobic and anaerobic. 

Aerobic exercise is typically classified as light to moderate-intensity endurance exercise, while anaerobic exercise is characterized as high-intensity exercise lasting for short periods (90 seconds or less). Swimming is a combination of both aerobic and anaerobic training.

Cellular respiration takes place at all times- usually, this happens aerobically. This process creates ATP (energy) for our bodies, and heat is a byproduct.

Typically aerobic respiration releases about 50% of energy as heat, while anaerobic respiration releases 70% of energy as heat. 

However, during exercise, the tempo of this process increases significantly as your muscles require more energy.

A study published in the Journal of Nutrition and Metabolism noted that high-intensity exercise could increase ATP demand by 1000 times. This means that cellular respiration takes place at a higher rate to replenish this ATP along with other energy systems at work.

As a result, more heat is produced as a byproduct leading to a rise in core body temperature. 

That said, there are other factors that will also determine how much your body temperature rises during exercise, such as the environment around you (e.g., a hot day).

Because of this increase, your body has to cool itself down- and with several million sweat glands, sweating is the primary way your body achieves this.

When excess heat is present, the hypothalamus in the brain stimulates these sweat glands to release fluid.

As the sweat evaporates (or washes away), heat is removed, and your body cools down. 

In fact, according to the University of Michigan Health, it’s estimated that during intense exercise, the body loses up to 85% of its heat through sweating.

Uninvited Visitors: Dehydration and the Performance Crash

Now that you understand that you sweat while swimming- and why it happens, it’s important to discuss how sweating can affect your swimming performance.

Dehydration happens when your body loses more fluids than you take in. There are only a few causes for this— sweating is one of them.

Dehydration is detrimental to your swimming and can cause a performance crash. 

swimmer fatigued

Dehydration can affect both your physical and mental state. 

Physical symptoms include fatigue, headaches, cramps, nausea, and dizziness- all of which will rapidly turn your swimming workout into a nightmare.

Mental function will also weaken, affecting focus, motor control, and decision making, which are all valuable skills for swimmers. 

In other words, being dehydrated is like doing your meet warm-up in a busy pool, getting kicked by a breaststroker in the lane next to you, and jamming your finger in the lane line all at once

In their book, Sports Nutrition 2nd Edition, by Asker Jeukendrup and Michael Gleeson, the effects of dehydration on exercise performance are discussed. 

Studies cited by the authors note that dehydration diminishes exercise performance when an athlete is dehydrated at only 2 percent of their body weight. While dehydration of 5 percent body weight can decrease an athlete’s capacity for work by up to 30 percent. 

Other studies in the book note that sprint capacity can also decrease by 45 percent following dehydration of as little as 2.5 percent of body weight. 

Knowing that dehydration is detrimental to your swimming performance, we should discuss how to combat this. But before we can do that, we first need to know how much swimmers sweat. 

How Much Do You Sweat When You Swim?

This is an important question to ask because you’ll want to make sure that you are consuming enough fluids during workouts to replace what is lost from sweating while you swim- but more on this in a minute.

Various studies have been done on the topic, and all of them have roughly similar findings. 

The first study, published in the Journal of Science and Medicine in Sport, found that on average male swimmers had a sweat rate of 138 ml per kilometer of swimming and female swimmers a sweat rate of 107 ml per kilometer of swimming. 

swimming sweat rate chart

With that in mind, most elite swimming workouts range anywhere between 4-6 kilometers in distance. This means that, on average, during a single workout, you’ll be sweating 490-735 ml/ 17-25 ounces of fluid. 

Another study, published in the International Journal of Sports Nutrition and Exercise Metabolism, found that swimmers had a sweat rate of 210 ml to 410 ml per hour of swimming. The participants in the study were elite-level nationally ranked swimmers.

Most elite swimming workouts last about 2 hours, which would equate to 420-820ml/ 14-27 ounces of fluid sweated throughout the workout. 

In both of these studies that’s about a full water bottle of fluid that you’re losing! 

While these studies can give us a general idea of how much swimmers are sweating during workouts, they don’t tell you precisely how much you are sweating when you swim. Luckily, you can do a simple test yourself to determine this.

I highly recommend you do this since everyone is different, and your body type affects how much you sweat. Also, males and females have different sweat rates- typically men sweat more.

You require a scale, a measured water bottle, and somewhere to take notes for the test.

Start by doing 1-2 laps in the pool. Then get out, towel dry yourself, a weigh yourself on the scale. Note that down. Also, note how much fluid is in your bottle before starting the workout.

Once your swimming workout is done, towel dry and weigh yourself again. You’ll most likely notice you’ve lost weight. 

Again, measure how much fluid is left in your bottle and determine how much you drank during the workout. Note both of these measurements. 

Once you have these measurements, you can find out how much you sweated during practice using these equations:

  • Weight at start of workout – weight at end of workout = bodyweight lost (1).
  • Bodyweight lost (1) in Ibs x 455 = ml fluid lost (2) / bodyweight lost in Kg x 1000 = ml fluid lost (2). 
  • Ml fluid in bottle at start of workout – ml fluid in bottle at end of workout = ml fluid drank (3).
  • Ml fluid lost (2) + ml fluid drank (3) = sweat lost in ml (4).

I should mention that the test described above comes from the book: “Eat Right, Swim Faster: Nutrition for Maximum Performance.” If you are serious about your swimming and would like to learn more about how to optimize your nutrition for top swimming performance, I highly recommend you grab yourself a copy.

That said, keep in mind that other factors like water temperature and training intensity will also affect how much you sweat. 

For example, if the water is hot or it’s warm outside, you’ll sweat more when swimming. Humid indoor pools can also contribute significantly to extra sweating.

On the contrary, if the water is cold or a chilly breeze is blowing outside, you’ll sweat less when swimming.

This phenomenon is clear in a study published in the Journal of Science and Sports. The study found that swimmers participating in a 5km race at three different temperatures had the highest dehydration percentage and sweat rate in 32˚C water and the lowest in 23˚C water.

A similar thing goes for workout intensity. If the swimming workout was hard, you’ll sweat more. If it was easy or moderate-intensity, you’ll sweat less.

This means that if you want the most accurate results from the test, you should do it a few times under different circumstances. Thereafter you can calculate how much you sweat on average. 

How Swimmers Can Combat the Performance Crash

We’ve seen that sweating can cause dehydration and subsequently that dehydration can lead to a severe reduction in your ability to perform in the pool. 

So what can we do to combat this? Luckily, the answer is quite simple. 

Sweat is mostly water and a small amount of electrolytes. Therefore all you need to do is hydrate well and replace lost electrolytes. 

Hydration Tactics for Optimal Swimming Performance 

To avoid dehydration, you have to stay hydrated throughout the entire day. But it’s especially important to pay attention to your hydration before, during, and even after swimming and other workouts.

A general guideline is that athletes should drink water equivalent to half their body weight in ounces every day. 

E.g., If you weigh 160 pounds, you’ll need to drink 80 ounces of water per day.

You should then adjust this amount based on factors like the weather outside (is it hot or humid?) and how hard and long you are training on a particular day since you might need to drink more water on these days.

Hydration timing before workouts is also essential. Here are some timing guidelines:

  • Drink 16 ounces/ 400-500 ml of water 2-3 hours before your swimming workout. 
  • Drink 8 ounces/ 200-250 ml of water 30 minutes before your swimming workout.
  • Drink 4-6 ounces/ 100-200 ml of fluid every 10-20 minutes while swimming.
  • Drink 8 ounces/ 200-250 ml of water within 30 minutes after swimming.

If you completed the test discussed earlier where we calculated how much fluid you are losing from sweat during workouts, you can also calculate your sweat rate to determine how much fluid you should drink during workouts. 

Here’s the formula to do that:

Sweat lost in ml (4) ÷ length of workout = sweat rate in ml/ hour.

When you know your sweat rate, you can calculate how much fluid you need to drink during workouts by multiplying your sweat rate by the duration of your workout in hours. 

How Swimmers Can Know They Are Well Hydrated: Two Simple Tests

A simple and accurate test you can do to tell if you are hydrated well enough is to look at the color of your urine. Ideally, your urine color should be somewhere between colorless and a light yellow. 

If it’s a darker yellow or amber color, it means your urine is more concentrated and indicates that you aren’t consuming enough fluids. 

Another test you can do is to use a hydration calculator. This is a less accurate measurement, but the tool can help you to know if you are getting enough fluids every day or not.

hydration calculator for swimmers

A Word About Sports Drinks

Water is the preferred hydration method for athletes in most cases, but if your workouts last longer than an hour, including a sports drink is a good idea.

Sports drinks provide your body with easily absorbable carbohydrates and electrolytes. Carbohydrates are needed for energy, while electrolytes play many vital roles and are lost when you sweat. 

Gatorade and Powerade are good options for sports drinks. Just avoid the low-calorie types as they won’t provide you with enough energy.

If you can’t find those drinks make sure that your drink contains the following per every 8 ounces/ 250ml: 14 grams carbohydrates, 28mg potassium, and 100mg sodium.

Eating to Fuel the Sweat

Your diet can also contribute additional fluids and electrolytes which will help keep you hydrated and maintain the electrolyte balance in your body.

Fruits and vegetables are foods that are both high in water and electrolytes. They also have many other essential minerals and vitamins necessary for your health as a swimmer and in general. 

The National Health Service recommends eating at least five portions of fruit and vegetables every day. One portion is equivalent to 80 grams.

Some fruits and vegetables high in electrolytes include:

  • Spinach.
  • Kale.
  • Avocados.
  • Broccoli.
  • Potatoes.
  • Almonds.
  • Beans.

How to Know If You Are Sweating While Swimming

male swimmer swimming freestyle

Since the pool water instantly washes away any sweat released while swimming, it’s hard to actively tell if you are sweating. 

However, there are a few methods you can use to know if you are sweating while swimming.

The first method is to look for signs indicating you are sweating when you swim- three signs to look out for include heavy breathing, thirst, and feeling warm. 

Heavy breathing is an obvious indication that you are sweating in the water. Like sweating, heavy breathing is another technique the body uses to cool down. As you inhale, the air is warmed, then exhaled again, resulting in heat loss. 

A study published in the Journal of Applied Physiology notes that heavy breathing is used to increase evaporative heat loss. The study also notes that sweating accompanies heavy breathing in larger mammal species- such as Humans. 

This means, if you are breathing heavily, you’re probably sweating as well, as both are mechanisms used to cool down and accompany each other. 

The second obvious sign to look out for is thirst. 

However, I should mention that thirst is a sign of dehydration caused by sweating- and as discussed, this isn’t something swimmers want as it can negatively affect performance. 

If you feel thirsty during swimming workouts, you need to fix your hydration. Refer to the hydration guidelines discussed earlier in this article.

The last sign of sweating to look out for is feeling warm. 

Feeling warm is an obvious sign of sweating, but one that might not always be as evident while swimming since the pool water cools your skin. 

However, if the pool water is warm or you are doing a particularly tough set, you’ll likely notice that you feel warm on certain parts of your body- and this is a clear indication that you’re probably sweating as well.

This feeling of warmth is most likely to be noticed on your face since it’s outside the water when you are resting. 

However, I’ve found that you can also feel it in other areas that spend more time outside of the water, like your upper chest and shoulders. Areas of your body underwater generally stay cooled better.

If you want to test this for yourself, here is a challenging set you can try that will make you notice this feeling of warmth:

5x400s with fins and paddles on 05:45 descending to max 1-4 and holding the same time as number 4 for number 5.

I should note that you might not feel warm if the pool is very cold, but for average temperature pools, you’ll quickly notice it if you did the set correctly. The sensation can be described as a feeling of heat radiating from your skin.

Another more advanced way to know if you are sweating when you swim is to do the sweat rate test, discussed earlier in this article, where you weigh yourself before and after practice.

Sweating After Swimming: Explained

If you didn’t do a proper cool down after swimming or the workout was particularly straining, you might notice that you still feel hot after swimming. 

According to Dr. Ava Williams, the increase in body temperature from a hard workout can persist for 15-20 minutes after exercise before your body temperature returns to normal. 

This happens because your body is still working on its thermoregulating mechanisms, and it takes time to cool back down. 

Dr. Williams continues to note that even after exercise, your body will continue to pump more blood and you will sweat because of the heat coming from your muscles.

That said, a proper cool down will avoid this and help get rid of any lactate and tight muscles developed during the workout. 

I recommend always doing at least an 800 easy cooldown. Try to do half of it backstroke if you can. This should take you roughly 10-15 minutes- enough time for your body to cool down.

Open Water Swimming and Sweating: Questions and Tactics

open water swimmer

Open water swimming is more endurance-focused and therefore usually longer than pool events, allowing for less time to hydrate- if any at all.

While many open-water swimmers also train in pools, there may be times that you need to do an open-water swim as part of your training.

Do Wetsuits Affect Sweating When You Swim?

Swimming wetsuits are designed to warm you using insulative materials like neoprene. Usually, swimmers wear wetsuits in cold temperatures, so sweating won’t be as excessive, but in moderate or warmer temperatures, wetsuits can significantly increase sweating when you swim.

It’s recommended to use wetsuits in water temperatures of 10-25˚C/ 50-78˚F. Any warmer and the swimmer can overheat. 

That said, there are different wetsuit thicknesses. If you swim in the upper-temperature ranges, you’ll want a thinner wetsuit, and if you swim in colder water, you’ll need a thicker wetsuit. 

If you want to know which wetsuit thickness would be ideal for your water temperature, refer to this guide.

Hydration Strategies for Open Water Swimming

The same hydration advice given earlier applies to open water swimming. However, during open water swims, you can’t just stop at the side of the pool to rehydrate. 

Open water events are also often much longer than swimming events, allowing for more time to become dehydrated.

Here are some simple strategies to stay hydrated during open water races and training:

  • Start your race or workout well hydrated: drink 16 ounces of water 2 hours before and another 8-16 ounces 30 minutes before.
  • Consider purchasing a swim-buoy with storage for a water bottle for longer training sessions.
  • In longer races, make use of feeding stations to rehydrate.
  • If you are doing long training swims, it’s a good idea to have someone on a kayak with you that can carry hydration- and other nutrition supplies.

Wait, but What About the Pool- Is It Full of Sweat?

Now that you’ve realized that swimmers can sweat a lot throughout a workout, you might be worried that the pool is full of sweat. 

However, this is not the case and is not something to worry about.

The amount swimmers sweat is very minimal compared to all the water in the pool. Pools also have chemicals like chlorine to deal with this and regulate bodily fluids and other bacteria, algae, and contaminants. 

Does Swimming in Salt Water or Chlorine Dehydrate You?

Swimming in salt water or chlorine in itself won’t dehydrate you. This is because your body doesn’t absorb any water, chlorine, or salts when swimming. These substances simply stick to the surface of your skin and may cause a smell. That said, swimming is a physical activity and can dehydrate you if you don’t drink enough fluid.

While swimming in chlorine won’t dehydrate you, it may cause dry skin and damaged hair if you do not get rid of it after swimming. Therefore it’s a good idea to wash your hair with a swimmer’s shampoo, and your body with a swimmer’s body wash or shower gel after training. 

Is It Okay to Swim After Sweating?

Swimming after sweating is an excellent way to cool down your body, especially after a challenging dryland workout or weight session. That said, for many competitive swimmers, this will only be a temporary relief. When the main set starts, your body temperature will rise again as the workout intensity increases.

author image

I am Benjamin, a competitive swimmer with many years of experience in the sport of swimming. I am very passionate about competitive swimming and love sharing everything I have learned about the sport. I specialize in swimming butterfly and my favorite event is the 100m butterfly with the 50m and 200m fly closely following.