Quick: What comes to mind when you picture the morning water aerobics class at your local health club? Do you conjure up images of swim caps, nose plugs and the grasping of foam noodles?

How about svelte athletes who’ve traded the pavement for the pool? Experts say their numbers are increasing.

Runners and tennis players in particular are discovering the benefits of working out in water, which provides the resistance needed to strengthen muscles and burn calories, without the strenuous effects of pounding on pavement or tearing up the court.

In fact, the trend began after athletes turned to underwater exercising to rehabilitate after injuries. Water buttresses the body, taking some of the burden off of you. For example, if you are exercising in water up to your neck, you support only about a tenth of your actual weight.

Joints, therefore, are spared the excessive jarring sometimes associated with land-based activities, lowering the risk of re-injury. Water pressure also helps minimize swelling.

Finnish researchers have found that aquatic training aids neuromuscular conditioning. Other scientists have showed shallow-water exercise leads to metabolic and cardiovascular health benefits in women. Both findings were published in the journal Medicine and Science in Sports and Exercise.

Whether you’re in training or mending an injury, you just might get a better workout in water. You may burn more calories in the pool than you would by doing the same exercise on land because of water’s natural resistance.