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Why Does Swimming Make You Tired? Post-Swim Drowsiness Explained

If you are a runner, there’s a good chance that you can run for quite a number of miles without stopping, which generally should lead you to believe that you are in “good shape“ and able to handle other types of exercise fairly well.

But, if you’ve ever jumped in the pool and done even a few laps, you might find yourself panting or seemingly out of breath and tired, leaving you to ask: Why does swimming make you tired?

Perhaps you have ambitions of training for a triathlon and would like to balance out your running training with swimming, or you would like to keep your workout routine varied to prevent boredom and reduce the risk of overuse injuries.

In this article, we will discuss why swimming can make you tired, looking at the most common causes of feeling tired after swimming and aiming to answer the question: “Why does swimming make you tired?”

We will cover: 

  • Why Am I So Tired After Swimming?
  • Why Does Swimming Make You Tired?

Let’s dive in! 

A tired swimmer on the edge of the pool.

Why Am I So Tired After Swimming?

As a UESCA-certified Triathlon Coach and Running Coach, my athletes often ask me questions like “Why am I so tired after swimming?” or “Why does the pool make me tired when I can run and bike long distances without feeling so tired?”

First and foremost, if you are wondering, “Is it normal to feel tired after swimming?” the answer is yes, many athletes, even endurance athletes who are “in shape, “ often feel tired after swimming.

That said, what do we mean by swimming making you tired: sleepy, tired, or physically tired in terms of out of breath or feeling out of shape?

Ultimately, either can occur, but the causes of feeling tired after swimming will vary depending on whether you mean muscularly or cardiovascularly fatigued after swimming versus exhausted or sleepy after swimming.

While it is common to feel tired after swimming because of the unique aerobic and muscular demands of the sport along with certain characteristics of swimming in a pool, extreme fatigue after swimming or feeling exhausted by swimming can be indicative of more serious underlying issues with your nutrition, health status, sleep habits, etc. 

If you examine our list of common causes for swimming making you tired and don’t feel like any of these reasons should amount to the degree of exhaustion you experience after swimming, you should definitely speak with your doctor, work with a nutritionist, or consider getting lab work done to investigate other causes of feeling tired from swimming.

A swimmer adjusting her goggles.

Why Does Swimming Make You Tired?

So, why does swimming make you so tired? Why does the pool make you tired?

Here are some of the reasons why swimming is tiring or factors that can contribute to feeling tired after swimming:

#1: Swimming Is Physically Demanding

At its core, swimming is a physically demanding sport.

Swimming provides a full-body workout that not only challenges your cardiovascular system (which can make you feel breathless while swimming and increase your heart rate), but also works most of the major muscles in your body.

Because swimming is a full-body workout and elevates your heart rate, you burn a lot of calories while you are swimming, and it can be physically exhausting.

This is particularly true if you are unaccustomed to aerobic exercise and/or don’t use the muscles worked by swimming frequently or at the same intensity or duration that you do when you feel tired after swimming workouts.

As with any form of intense physical exercise, you have to give your body time to adapt and “get in shape“ to handle swimming workouts without feeling completely fatigued after swimming.

A swimmer swimming in the pool.

#2: Swimming Workouts Can Be Intense

Depending on how you are structuring your swimming workouts or pool training sessions, you are likely challenging both your aerobic and anaerobic energy systems when you swim.

This can drain your glycogen reserves and leave you feeling depleted after pool workouts.

Even if you are a distance runner or endurance athlete, many people feel more tired after swimming vs running or cycling because of the structure and intensity of pool workouts for triathletes, runners, or endurance athletes.

Because pool laps can be so monotonous, a lot of swimmers, triathletes, or other athletes don’t just get in the pool and swim easy laps at a steady pace in the way that you might go for a jog or moderate bike ride.

Instead, many swimming workouts involve swimming intervals with fast laps followed by rest (like 10 x 50m swim sprints).

This is akin to heading to the track and doing a bunch of sprints, or 400 or 800-meter repeats if you don’t run very often.

These types of swimming workouts are metabolically demanding and also challenging for your cardiovascular and muscular systems because you have to produce a tremendous amount of power to swim fast, and most swimming strokes use a lot of muscles.

All of this, in turn, means that your heart rate, caloric expenditure, and exhaustion from swimming will all be more significant than if you were doing a leisurely swim at a steady pace.

A swimmer swimming in the pool.

#3: Water Provides Resistance 

Swimming is tiring for your muscle fibers because they have to fight against the resistance provided by water. 

Water resistance is much greater than air resistance, so it can be more challenging to swim than walk or run your muscles, depending on the strokes that you do, your body weight, how fast you are swimming vs running, etc.

Furthermore, many of the muscles worked by swimming are used in different ways while you swim than they may be while performing other types of exercise.

For instance, swimming involves a lot of trunk rotation for your abs and lower back muscles.

Most of the walking, running, and everyday movements we do take place in the forward and backward direction (sagittal plane) without a lot of transverse plane rotation.

Moreover, depending on your body composition, you may have to work harder to maintain buoyancy and keep your body in a prone or supine position as you swim along the top surface of the water so that you don’t sink.

If you don’t have a lot of body fat and you have a lot of muscle mass, you will have to constantly be moving your limbs to stay afloat.

These various factors of the muscular demand of swimming mean that even if you do a lot of core workouts, strength training, and other types of exercise, swimming often uses your muscles in different ways, which can cause full-body fatigue.

A swimmer swimming in the pool.

#4: Swimming In Cold Water Is Energy-Demanding

The human body always wants to maintain temperature homeostasis within a small, finite temperature range.

If you are swimming in a cold pool or doing open water swimming in cold water, just being in the cold water for the duration of your swimming workout can be exhausting for the body.

Your body might be trying to stave off succumbing to hypothermia by shivering, particularly once your swimming workout is over.

Shivering burns calories and is exhausting for the body.

Plus, if you swim in a cold pool or cold water for a long workout, it can take quite a bit of time for your body temperature to return to normal.

A person diving into a pool.

During this process, your hypothalamus may send various signals to the body to help you conserve energy so that excess calories can instead warm you up and restore normal core body temperature.

This may make you feel sleepy or compelled to be inactive as almost a survival mechanism until homeostatic core body temperature is restored.

Furthermore, swimming in cold water can cause vasoconstriction of your blood vessels, particularly those smaller blood vessels like the capillaries servicing the skeletal muscles.

This can impede oxygen and nutrient delivery, which means that your muscles won’t be getting all of the resources and energy they need as easily while swimming in cold water and even after swimming in cold water until the vasoconstriction resolves.

Essentially, you might feel really tired until your body temperature normalizes after swimming in cold water.

A swimmer swimming in the pool.

#5: Fueling Errors

Another cause of swimming feeling tiring is poor pre-workout nutrition and not fueling or drinking during longer swim workouts.

Many people are afraid to eat before swimming so that they do not get stomach cramps, or your pool may only be open in the early morning hours for swimming laps.

If you do not have enough glycogen or you are hungry or become dehydrated while swimming, your muscles won’t have the calories or ready access to glucose, and your blood plasma volume will drop.

All of this can make you feel tired while swimming and can compromise recovery after swimming workouts.

You can learn more about the muscles worked by swimming different swimming strokes here.

A swimmer getting ready to jump in the pool.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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