What Swimming ACTUALLY Does To Your Body

Have you ever wondered what really happens to your body when you dive into the pool? Why do your muscles feel like they’re on fire after a sprint? What’s up with that post-swim glow? And could swimming actually make you live longer?

In our new video, we’re breaking down the science of swimming—from energy systems to why your heart and lungs love it just as much as you do. So grab your goggles, and let’s dive in!

Benefits of Swimming

Before we get into the crazy science behind what happens to your body while swimming, I want to highlight an amazing study published by Harvard Medical School.

In this study, they observed over 40,000 men aged 20 to 90, swimmers had the lowest mortality rate, with only 2% passing away during a 13-year period. Compare that to 8% for runners, 9% for walkers, and 11% for those who were inactive. Pretty amazing, right?

This study was conducted for 13 years and looked at deaths among over 40,000 men ages 20 to 90. Only 2% of the swimmers passed away during that time. Compare that to 8% of runners, 9% of walkers, and 11% of those who were inactive.Pretty amazing, right?

If you’re into numbers, here’s another impressive stat for you. According to The American Heart Association, 30 minutes of swimming a day can reduce coronary heart disease in women by 30 to 40%. That’s because swimming raises HDL levels, also known as “good” cholesterol, so for every 1% increase in HDL, the risk of dying from heart disease drops by 3.5%. 

Energy Systems 101

Now let’s dive into some energy systems 101. We’re not going to go TOO deep, but understanding energy systems is key to knowing how each type of workout impacts your body in different ways.

First, we have ATP (adenosine triphosphate), the energy “currency” of your body. There are three main ways the body spends ATP.

The first one is the Phosphagen System. This is used during short bursts of high-intensity work, lasting 5-15 seconds. For swimmers, think of sprinting a 25-yard freestyle at full throttle or a start off the blocks. During those short bursts, the body taps into stored ATP for quick energy without needing oxygen. The phosphagen system doesn’t last long, as muscles have limited ATP stores

Then comes the Glycogen System. When a swimmer continues beyond the phosphagen system’s capacity, the body shifts to the glycolytic system, so the body starts using glycogen – stored glucose in the muscles and liver – to generate more ATP without oxygen. As glucose breaks down, lactic acid is produced, which eventually leads to fatigue. This system powers efforts lasting up to 2 minutes, such as a 100-meter freestyle or butterfly swim.

And then finally the Aerobic System. This one is used for anything lasting longer than 2 minutes. It pretty much relies on oxygen to convert carbohydrates, fats, and proteins into ATP, since the body has used all of its storage by that point. The aerobic system is highly efficient and supports endurance efforts and this is where most of your swimming time is spent.

In most swim workouts, energy systems overlap. Short bursts of high-intensity effort (like sprint sets) start with the phosphagen system, transition into glycolysis for longer sprints, and rely on the aerobic system for sustained work during distance training or recovery between high-intensity sets. Training in all these systems is essential for swimmers to develop speed, endurance, and recovery efficiency.

Body Responses During Swimming

Now that you have a rough idea of what the 3 energy systems are, let’s dive into what you ACTUALLY FEEL AND EXPERIENCE during your swim. Let’s take a closer look at how some of the key parts of our bodies are impacted.

The Blood and Heart

According to the American Heart Association, swimming is an aerobic activity that enlarges your heart and increases blood flow throughout your body. Since swimming engages almost every muscle in the body, your heart has to pump more oxygenated blood to keep everything running smoothly.

Stronger and more efficient heart muscles pump more and more blood with every beat which means more oxygen and nutrients are delivered to your tissues, enhancing your overall stamina. A stronger heart can also make your blood vessels expand, which lowers blood pressure. 

And did you know that the horizontal position you maintain while swimming helps improve blood circulation? Yes, gravity doesn’t work against your heart as much when you’re in the water, making it easier for your heart to pump blood. By maintaining good blood flow, you’re helping to keep your arteries and veins healthy.

The Skin

Have you ever noticed how your skin changes color after a hard swim? That redness comes from your blood vessels dilating and bringing heat to the surface. It’s your body’s way of cooling down and showing you’re putting in the effort, so it’s a GOOD sign!

Since we’re talking about skin, another important factor to consider is the chlorine in the water. While it helps keep the water clean, chlorine strips away the natural oils that protect your skin, and can have a drying and irritating effect, leaving it feeling dry, tight, and sometimes itchy after swimming. To minimize chlorine’s impact, it’s a good idea to shower after swimming and applying a good post-swim moisturizer.

The Muscles

Depending on which stroke you’re swimming, you’re going to engage different muscles. Freestyle, for example, primarily works the deltoids, triceps, and lats, along with the core muscles to stabilize the body. Backstroke, on the other hand, focuses on the lats, hamstrings, quads, and glutes. Breaststroke engages the pecs, biceps, inner thighs, and calves, while Butterfly uses mainly the shoulders, chest, abs, and legs.

One thing is for sure, it doesn’t matter which stroke you’re swimming, your body will go through a process called muscle fiber recruitment and microtearing, which are a normal part of building strength.

Basically, swimming activates different types of muscle fibers, including both slow-twitch (Type I) and fast-twitch (Type II) fibers. Slow-twitch fibers are endurance-based, providing the stamina for longer swims, while fast-twitch fibers power explosive movements like sprints or turns.

As you swim, particularly during intense training sessions, your muscles experience tiny tears, or microtears. This is a natural process in muscle building and it stimulates the body’s repair process, which leads to muscle growth.

After swimming, your body begins to repair the damaged muscle fibers which is why you might feel sore after a tough workout. This process usually takes from 24 to 48 hours and involves fusing muscle fibers together, which increases the size and strength of the muscles. This is why rest and recovery are CRUCIAL, because that’s when muscle growth occurs, not during the swim itself.

The repetitiveness of swimming also helps increase metabolic rates, meaning that the body burns more calories even at rest, further aiding in the maintenance of a healthy weight and muscle tone.

Lungs

One of the most important organs when it comes to swimming is your lungs. Studies have shown that competitive swimmers exhibit higher total lung capacity (TLC) and forced vital capacity (FVC) than runners or athletes in non-aquatic sports. This happens because unlike other sports where you can breathe freely, swimming forces you to time your breaths, which increases your lung capacity and efficiency.

When you hold your breath during swimming, your body experiences mild hypoxia, a fancy term for “low oxygen levels”. This triggers adaptations that help your lungs and body become more efficient at utilizing oxygen, increasing red blood cell production, enhancing oxygen transport to muscles and expelling carbon dioxide. 

Over time, it makes your body quicker and more efficient at regulating your breathing, aside from also improving your VO2 max—your body’s ability to utilize oxygen efficiently.

In sum, the more efficient your lungs, the better your overall performance.

Brain

Let’s not forget the brain! One of the most immediate effects of swimming is its ability to stimulate the release of endorphins, the “feel-good” hormones, so it can be amazing for mental health and even effective in combating feelings of depression and anxiety. The  unique low-gravity environment of water provides a meditative experience unlike any other sport and some people often describe experiencing a “swimmer’s high”.

Your brain gets a boost from the increased blood flow and oxygen, leaving you feeling more awake, alert, and focused after a swim.

The rhythmic nature of swimming—breathing in sync with your strokes and the repetitive motion of moving through the water—can have a meditative effect. That, combined with the water’s effect of muffling external noises, helps to reduce stress levels and induces a state of relaxation. Additionally, the soothing properties of water and the consistent breathing pattern required in swimming can mimic the effects of certain relaxation techniques used in therapy.

When you swim, you’re depleting the body’s energy reserves in a healthy way, which helps regulate your body’s internal clock and reduces insomnia by leading to a more restful night’s sleep. 

Studies show that swimmers maintain better mental health throughout their lives, with master swimmers showing significantly higher mental wellness markers compared to the general population, even into their 60s and beyond.

Conclusion

So, what ACTUALLY happens to your body when you swim? From improving your cardiovascular health to building stronger muscles, increasing lung capacity, and boosting mental clarity—swimming is an all-around fantastic way to keep your body and mind healthy.

We’d love to know—how do you feel after swimming? Let us know in the comments!

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