In June, mercury levels rise across the U.S., prompting many to visit their local pool, lake or beach for a refreshing dip in cool water. But swimming is more than just a popular summer pastime; it’s also one of the best exercises for overall health. The unique water environment creates physiological changes in the body that set swimming apart from land-based activities and make it a rigorous workout accessible to people of all ages and abilities.
“The beauty of water is that it produces buoyancy,” says Bruce Becker, a clinical professor in the Department of Rehabilitation Medicine at the University of Washington.
Becker has studied the rehabilitative potential of swimming for 40 years, and he witnessed the water’s healing effects after a child diagnosis of polio. He says his physician used aquatic therapy to keep his limbs strong and agile as he recovered from the virus.
“It allowed me to have essentially fully functional joints throughout my life,” Becker says.
Why Swimming is Healthy
Water’s buoyancy makes swimming a low-impact activity that’s easier on the joints than many land-based exercises, so people with arthritis or injuries can minimize pain while also getting a quality workout.
“Folks that are even substantially over ideal body weight can exercise quite vigorously without damaging their joints and incurring pain,” Becker says.
While supporting painful joints, water (which is more than 800 times denser than air) also provides resistance that quickly builds muscle strength throughout the body.
Swimming especially impacts the heart, says Becker. “The physiology of aquatic immersion changes a whole bunch of things within the circulatory system,” he says.
One of those things is the volume of blood that moves through the heart. The compressive force of water squeezes the body’s veins and drives blood from the extremities to the core. Consequently, the heart pumps more blood to the lungs and arteries, which dilate to accommodate the increased volume.
“Overall, the output of blood throughout the body increases by about 30 percent, which is really pretty significant in terms of increasing blood flow to muscles and other organs,” says Becker.
The heart isn’t the only organ working overtime in the water — the lungs pull extra weight, too. The aquatic environment “presents a real challenge to the muscles of respiration,” says Becker.
Because of increased blood in the lungs and higher pressure on the chest wall, he says, breathing muscles work about 60 percent harder during chest-deep immersion than they do on land. For that reason, experts recommend hydrotherapy for people with diseases that affect respiratory function such as chronic obstructive pulmonary disorder, muscular dystrophy and even COVID-19. Becker says cross-training with aquatic exercise can also help land-based athletes increase their respiratory endurance.
Avoid the Heat
Another unique feature of water is its capacity to store and conduct heat. Water draws heat away from the body more efficiently than air, so swimming in an 80-degree pool feels better than running in 80-degree air. Exercise-induced heat exhaustion is a common problem for athletes and can lead to heat stroke and death, but Becker says people exercising in cold water or comfortably heated pools face little danger of overheating.
“You're more likely to risk hypothermia rather than hyperthermia,” he says.
Swimming also benefits the spine. In a paper involving 331 patients, researchers concluded that swimming helps reduce lower back pain. Buoyancy provides cushion for the vertebrae, and the body’s horizontal position eliminates spinal pressure that upright activities often trigger, such as running and cycling. If you’re swimming laps, backstroke and freestyle are easier on the spine than butterfly and breaststroke, which require the back to arch.
Like other forms of aerobic exercise, swimming has been shown to lower blood pressure, elevate mood, improve sleep and extend lifespan. It’s a full-body workout that recruits muscles from the legs, arms, core and everywhere in between. If you want to try swimming for exercise, Becker recommends seeking out a local YMCA or community pool, which should offer a wide variety of affordable aquatic programs. With a bathing suit and access to water, nearly everyone can dip their toes into H2O to not only cool off this summer but also improve their overall fitness and health.