There is almost nothing that feels better than going for a swim on a hot summer day. Beyond being a fun way to cool down, swimming is a great way to get in shape. Swimming is also an excellent exercise for injury rehabilitation or for people with certain conditions like arthritis.

The fitness benefits of swimming are well established. Since swimming is a whole-body exercise it uses all of your major muscle groups, building strength, endurance and aerobic fitness. Highly trained swimmers have VO2max values, considered the best measure of aerobic fitness, that are similar to runners and cyclists.

Depending on the stroke and speed, swimming ranges between 5 to 10 METs. (METs are units used to measure the intensity of activity; one MET is equivalent to sitting at rest) For example, doing the backstroke at a moderate speed is about 5 METs while swimming laps freestyle with vigorous effort is about 10 METs.

This range is similar to walking at 4 mph up to jogging at a 9 minute per mile pace. What if you are just spending time in the pool or lake rather than swimming laps? Swimming leisurely is about 6 METs, still a decent workout.

Swimming is a great way to burn calories, too. Even at a moderate pace, swimming laps for 30 minutes can burn over 200 calories. The exact energy expenditure depends on the stroke (butterfly is highest, backstroke is lowest) and the speed, but for most people swimming will burn as many calories as spending the same amount of time exercising on land.

There are two big reasons for this. First, water is denser than air, so you need to expend more energy to move your body through the water. Second, swimming is a whole-body exercise which requires more muscle activity compared to walking or jogging which mostly involve the legs.

You may be surprised to learn that novice swimmers expend more energy per lap than elite swimmers. For example, one study showed that competitive swimmers expend only 280 calories to swim a mile, while less experienced swimmers burn about 440 calories to cover the same distance. The reason for this is that experienced swimmers are more efficient, so they expend less energy.

Aquatic exercise is popular for both therapeutic and fitness purposes, especially for people who don’t tolerate exercise on land well. When you are submerged up to your waist, 50% of your weight is supported; when you are up to your chest, about 75% is supported. This reduces the impact of exercise in the water, perfect for people who have arthritis, osteoporosis, severe obesity, or who are recovering from injuries.

Exercise in the water doesn’t have to mean swimming laps. Water aerobics, aqua walking or jogging, and resistance training using foam “weights” or webbed gloves offer safe ways to increase strength and endurance for almost everyone. Most fitness facilities that have a pool offer group aquatic exercise classes and you can find instructions online for exercises that you can do in a pool, lake, or even at the beach.

The hot summer weather makes swimming and other water activities appealing. But even if you don’t use the time for exercise, spending time playing in the pool or lake can still burn as many calories as going for a walk and is a great way to have fun and cool down!