Low impact
There's no ground impact when you swim, and so you protect the joints from stress and strain. In fact, the Arthritis Foundation strongly recommends swimming and water activities for this reason, so much so that they sponsor water classes all over the country. Water aerobics classes are also desirable for this reason, because even if you do jump and hit the bottom of the pool, you do so with less force because you're buoyant in the water. Not only that, but if you wear or hold a flotation device during a water aerobics class, the impact is even less.
Can be continued for a lifetime
Because there's no impact with swimming, it can be continued for a lifetime. If you check the United States Masters Swimming (http://www.usms.org/) Web site for age categories of their swim competitions, you will find a 100- to 104-year-old age group! And the master of fitness, Jack La Lanne, who died in 2011, still swam one hour every day at age 93!
Builds cardiorespiratory fitness
Swimming improves endurance. In one study of sedentary middle-aged men and women who did swim training for 12 weeks, maximal oxygen consumption improved 10% and stroke volume (the amount of blood pumped with each beat which indicates heart strength) improved as much as 18%.
Builds muscle mass
In a study of men who completed an eight-week swimming program, there was a 23.8% increase in the triceps muscle (the back of the arm). My take on muscle mass and swimming is that if you have been doing no resistance exercise at all and you start to swim, you will certainly get more toned and you may even gain mass like the men in this study. But even without the gain in mass, it's well worth the strength and tone that you will almost certainly gain.
An alternative when injured
When athletes are injured, particularly in the lower extremities, they are frequently told to swim to maintain their fitness level. Swimming helps them stay in shape, and it's even part of the rehabilitation. That's because the resistance of the water makes the muscles work hard without the strain or impact that is experienced on land.
It's a break from the summer heat
There's nothing like it during the hot days of summer, whether it's at the beach or in the pool. It's relaxing, the movements are smooth and rhythmic, and it's a great workout.
It's a family affair
Swimming and other water activities are something the entire family can share. With rising levels of obesity in children as well as adults in the United States, family physical activities and good role-modeling may be one way to stem the epidemic of inactivity and obesity facing our nation.
Burns calories
Swimming burns lots of calories, anywhere from 500-650 per hour depending on how efficiently you swim (you burn more flopping around than swimming cleanly!) and how buoyant you are (the more body fat you have, the more you float and the fewer calories it takes to swim). Very early and original research on swimming and calorie expenditure showed that swimming, regardless of the stroke, burned about 89% of the calories burned during running and 97% of the calories burned during cycling for the same time period. Stated another way, swimming burns about 11% fewer calories than running but only 3% fewer calories than biking. One important caveat about this data is that calorie expenditure is dependent on the intensity of exercise, and so it's entirely possible to burn more calories swimming than running in the same period of time as long as you swim hard enough, and particularly so if compared to running at light intensity.
medicinenet.com