If you want to build muscle, you need to strength train - but swimming is one form of cardio that can help inch you closer to your goals. "Muscle is built by repetitive motions, using the same muscles over and over again," Cindy Dallow, PhD, a sports dietitian and triathlon coach, told POPSUGAR. Plus, unlike the air you pass through when running or walking, water provides a bit of resistance, mounting an even greater challenge to your muscles. "This activity stimulates muscle protein synthesis, which is what increases strength, assuming adequate protein is consumed," she explained.
So, whether you're breast stroking or back stroking, as the laps add up, so will your muscle gains - at least in your upper body. "Swimming increases strength in some of the shoulder and back muscles," Dr. Dallow said. Perhaps more importantly, "it improves aerobic capacity and cardiorespiratory fitness." In one study, women who swam for 60 minutes three times a week for 12 weeks showed significant improvements in flexibility and cardiovascular endurance, in addition to losing body fat.
Still, to better tone your body, you should keep up with your strength-training routine. If the gains weren't motivation enough, it could help prevent injuries in the pool. "Many swimmers develop shoulder injuries, so having a strong upper body helps prevent that from happening, in addition to making them a strong swimmer," Dr. Dallow said.