What regular swimming does for body and mind

I recently went for a swim for the first time in over a year. Standing over the sparkling, blue pool at my local gym, I tried to recall many of the stressful events from the past 16 months: moving to a new city -- Baltimore -- during a pandemic, starting a new internal medicine residency training program, and taking care of both Covid and non-Covid patients in the hospital had all taken their toll.

My first thought as I dove under the surface of the water was that I felt a little more buoyant than usual, likely due to the added pounds brought on by quarantine. But as I continued to glide through the water, my initial concern about weight gain was replaced by a feeling of catharsis, as though the water were cleansing me of the stress that had accumulated during the coronavirus pandemic. Stroke after stroke, I could feel my mood lifting, my mind clearing and my body loosening.

Thirty minutes later, I got out of the pool feeling confident and level-headed, ready to begin the first of four night shifts in the intensive care unit. I usually dread the first of these night shifts, but somehow the task seemed more manageable than usual. “Whatever happens tonight happens,” I told myself encouragingly. “No matter what, there will always be tomorrow.”

My improved mood was in no doubt related to my recent dip in the pool. Like all types of physical activity, swimming can improve your mood by stimulating the production of endorphins -- natural opioids produced in the brain -- as well as other neurotransmitters such as dopamine and serotonin.

But the benefits of taking a swim go far beyond a momentary lift in spirits -- especially right now.

Changing your mind

As we all emerge from isolation, experts say attending to our mental health needs to be a top priority.

“Americans have faced unprecedented hardship in the past months, but by focusing daily on caring for our own emotional well-being and supporting the well-being of those we love, we can successfully mitigate the mental health effects of the COVID-19 pandemic,” said former US Surgeon General Dr. Jerome Adams in a news release earlier this year.

“Although this is a difficult time in our nation's history, I remain steadfast in encouraging Americans to use healthy mechanisms to cope,” he added.

The prevalence of depressive symptoms in the United States increased more than threefold as Covid-19 spread, according to a recent study in the journal JAMA. Some high-risk groups, including health care workers and those under the age of 30, were at an even greater risk of developing anxiety or depression due to the pandemic, according to a different study published in the Journal of Psychiatric Research.

Regular exercise -- including swimming, running, yoga, weight training and even tai chi -- remains one of the most powerful tools we have to improve our mood and overall mental health. A 2016 meta-analysis that combined data from 23 randomly controlled trials showed that exercise was comparable to both antidepressants and psychotherapy in the treatment of depression.

While part of this is due to the production of endorphins, exercise also results in important structural changes in the brain, particularly in a primitive brain structure called the hippocampus. Along with another brain structure called the amygdala, the hippocampus is heavily involved in memory formation and the regulation of emotions.

Over time, regular aerobic exercise -- such as running and swimming -- reduces inflammation and promotes nerve growth in the hippocampus, with positive effects on both mood and memory, studies have shown. Conversely, atrophy, or shrinkage, of the hippocampus has been linked to the development of mood disorders such as depression and bipolar disorder.

Defying evolution

Our mental health is not the only thing that has been affected by the Covid pandemic: Our bodies have taken a toll as well. The average American gained approximately 7 pounds during the pandemic, according to another study published in JAMA.

“The effects of COVID on long-term health are worrying,” said Daniel Lieberman, professor in the department of human evolutionary biology at Harvard University, in an e-mail. Lieberman is also the author of “Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding.”

“To what extent these added pounds come from diet, (lack of) exercise or stress is difficult to unravel, but well documented declines in physical activity are clearly one cause,” Lieberman added.

As with all forms of aerobic exercise, swimming is also a great way to strengthen muscles and burn fat. But swimming comes with one additional benefit: Human swimmers typically spend about seven times as much energy to move a given distance compared to running.

This is because humans did not necessarily evolve to be expert swimmers, according to Lieberman. The fastest human swimmers can only attain speeds of about 4.5 miles per hour -- the speed at which most people switch from a fast walk to a slow run.

While this aspect of swimming may be frustrating for new swimmers, when it comes to losing weight, it may not be a bad thing.

“You have only to watch a seal or a beaver swim to realize that compared to mammals adapted for swimming, even the best human swimmers perform poorly,” Lieberman added. “The good news is that this inefficiency makes swimming a very effective exercise for burning calories.”

There are many other aspects of swimming that make it a uniquely beneficial form of exercise. For example, when we swim, we are completely horizontal, which increases blood return from the venous system to the heart.

This distinctive aspect of swimming comes with additional cardiac benefits as well. For example, maximum heart rates are about 10-15 beats slower during swimming compared to running, increasing the amount of time when the heart can relax and fill with blood, known as “diastolic function.” As a result, the heart's stroke volume -- or the amount of blood pumped by the heart during each beat -- increases by 30% to 60% during swimming, according to a 2013 study in the International Journal of Cardiology.

Swimming is also different from other forms of aerobic exercise because it relies on controlled breathing. Over time, this can lead to an increase in total lung capacity and improved overall lung functioning.

But if you have limited access to a pool or large body of water, or feel like you can't swim for very long, don't worry: What is most important is that you stay active this summer and choose an activity that you enjoy doing, according to Lieberman.

“If you struggle to exercise, remember that even a little exercise provides enormous benefits for both physical and mental health. You don't have to run a marathon or swim the English Channel,” Lieberman said. “And if you don't like to exercise, find a way to make it enjoyable. For most people, that means making it social. Exercising with friends will help you find the motivation to show up and keep going.”