If you know anything about water sports, then you know swimming is a no-impact form of cardio that gives your body a break from the pounding of running without the risk of losing your fitness. But for most of us, “pool time” is a thing that usually happens in the summer for fun or, worst case scenario, when you’re working through an injury.
When a metatarsal stress fracture forced me to take a break from running earlier this fall, I had no other choice but to head to the pool to supplement my marathon training. I swam about two miles (or 3,200 meters) of freestyle each morning to cross-train, and it got me thinking: Even when you aren’t injured, can swimming help make you a better runner?
To find about the benefits of swimming for runners, we spoke to two experts with experience in both sports. Here, they discuss the pros of the pool exercise.
1. Improves Cardio Without Impact
Swimming is unique because it uses several different muscle groups—glutes and hips for kicking, core for rotating and flip-turning at the wall, shoulders and arms for pulling—and it actually works our hearts harder than other exercises, says Jay Dicharry, physical therapist and author of Running Rewired.
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“When you exercise horizontally, your blood return is higher, because the blood doesn’t have to compete with gravity to move throughout your body,” he says. “So you heart pumps harder to keep the blood cycling to the muscles. I’ve seen a lot of athletes hit a higher VO2 max in the pool than on land.”
Dicharry, who swam competitively and coached Master’s swimming in the past, explains that no matter your skill level in swimming, you can benefit from laps.
“You can actually get a better workout if you’re not very good at it,” he says. Here’s why: Newbies tend to make thrashing movements—which require a lot of effort—to get to the wall, while advanced swimmers with more economic strokes conserve energy by gliding and rotating efficiently. Still, seasoned swimmers can get an incredible workout by increasing the speed and length of their efforts, he explains.
One way to boost your cardio effort more in the pool is to incorporate high-intensity intervals, such as fast, 100-meter repeats with 10 seconds of rest between each. “I see a lot of swimmers get in the pool and loaf around,” he says. “But intervals are a great way to give your engine a boost while putting very little stress on your muscles and ligaments.”
In fact, if you’re relatively strong in both running and swimming, maintaining a long, hard effort in the pool will burn about as many calories in the same time as running on land. For instance, if a 120-pound woman swims an hour of freestyle at a steady clip of 1:30 per hundred yards, she will burn about 750 calories, according to this swimming calculator based on a University of Wisconsin study. If the same woman ran for an hour at 7:30 pace, she would burn 726 calories, according to our calorie burn calculator.
One challenge of swimming is that it’s hard to measure heart rate unless you have a waterproof, swimming-specific watch like the Apple Watch Series 4 or Fitbit Charge 3. Earl Walton, head coach of New York City-based triathlon club Tailwind Endurance, says he instructs his swimmers to check their heart rates the old-school way, holding two fingers to the pulse in their neck for 10 seconds and multiplying that number by six.
“Every time you rest on the wall, you get instant feedback on how hard your body is working,” Walton says.
That absence of data calculating your efforts can also be a blessing. “Runners tend to fixate on data, and swimming can be a nice counterbalance,” he says. “Swimming is more about how your body is feeling in the water.” That break from following numbers strictly can be refreshing both mentally and physically for us.
“When you replace a day of running with a low-impact exercise like swimming, your brain perceives it as a day off,” Dicharry says. “Even if you’re working just as hard.”
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2. Builds Stronger Muscles
Having a strong core—the complex muscle group that supports the spine—is key for distance running, as it maintains your posture and stabilizes your hips. It’s especially important during long races when we’re fatigued. When your form begins to falter in mile 20 of a marathon, you can count on your core to keep you upright and moving forward.
Swimming is a fantastic exercise for strengthening that core, Walton says. When you do freestyle, for example, your abs, obliques, and lower back muscles help you maintain a streamline position and rotate you from side to side, while your upper back muscles work with your shoulders to pull through the water, he explains.
“A strong core does way more than just making you look fit.” The coach notes that strengthening these muscles boosts thoracic mobility, which is key for maintaining good posture and reducing lower back pain.
Dicharry also points out that while many athletes focus on the upper body aspects of the exercise, your hip flexors and legs are just as important for driving your stroke. “People figure they’ll just pull and save their legs,” he says. “But kicking will make you so much more powerful in the water. Plus, you’re strengthening your quads, hamstrings, and glutes by activating them.”
3. Helps You Bust Out of an Exercise Rut
Walton suggests that runners utilize swimming during a transition period, whether they are in a training lull, taking some time off post-marathon, trying to survive the winter, or moving from marathon to triathlon seasons.
“Since it’s a non-impact sport, swimming helps you recover and hit refresh,” he said. “It also lets you tap into another gear that you might not be able to reach in other sports like running, due to injury or burnout.”
For injured runners especially, having an outlet to stay competitive is important not only for your fitness, but your mental health. When I first fractured my foot, I could only push off the pool wall with one foot, but I still threw myself into going a little farther and faster each swim session. Even if I couldn’t run, I found solace in the fact that my heart, body, and mind were healing and growing stronger every day in the pool.
And the best part? That strength carried over to dry land. Though my injury totally derailed my marathon training plan and forced me to substitute much of my running with cross-training sessions in the pool, the aerobic fitness I maintained through swimming not only allowed me to finish November’s New York City Marathon—my first 26.2 mile race—but to race it even faster than I thought.
“It’s funny,” Walton says, “I’ve watched many of my athletes have breakthroughs in the pool, and then they have a breakthrough in running soon after.”
4. Prevents Injury
Of all the low-impact cross-training exercises—including cycling, elliptical, and rowing—swimming causes the least biomechanical stress (i.e. high-impact pounding) on the body, which is why it’s an obvious favorite for runners preventing or rehabbing an injury, says Dicharry.
“For injury-prone runners who often get hurt when attempting higher mileage, swimming in the place of a run is a great way to get that extra cardio volume without getting hurt,” he says. But while swimming helps runners maintain fitness and allows their bones and ligaments to rest, it doesn’t cure injuries. For the best recovery, injured runners need to isolate the root cause of their injury and do specific strength exercises to help correct and heal it, Dicharry says.
Walton, who has raced several marathons as well as triathlons, notes that pool time has helped him stave off injuries and stay in shape when sidelined from running throughout his career. “Swimming is the secret sauce that holds me together,” he says.
Walton adds that if injured runners are craving an exercise that resembles running more than swimming, but can’t handle the impact of the elliptical, they can jog in the pool wearing a weighted belt. Aqua jogging—which mimics the movement of running in the water—is also a good option for people who have never swam before and don’t want to commit to learning the strokes, he says.
The Bottom Line
Swimming is a fantastic cross-training exercise because it gets your heart pumping, strengthens muscles you don’t normally use (ahem, upper body), builds aerobic endurance, and offers an outlet to be competitive outside of running. For injured runners, the non-weight bearing aspect of the sport is key, but even healthy folks can—and should—reap the benefits of pool time.
Hailey first got hooked on running news as an intern with Running Times, and now she reports on elite runners and cyclists, feel-good stories, and training pieces for Runner's World and Bicycling magazines.