In 1993, water aerobics were only for senior citizens or patients who needed rehabilitation therapy. Nowadays, it encompasses a variety of trendy underwater sports, all of which are healthy.

"The body has 90 percent support when underwater. That means the joints only have to offer 10 percent support," says Theodor Stemper, a sports scientist at the Bergischen University in Wuppertal.

The buoyancy adds comfort and alleviates pressure on the joints. "That lets a person participate in a lot of aqua-training, even if they're overweight or have never done it before," says Stemper. Aqua-fitness is also great for pregnant women or people suffering from joint injuries.

Aids like the "noodle" or an aqua-jogging belt add to the benefits of buoyancy.

"An aqua-jogging belt with a high back is ideal for beginners, since it helps balance the body better," advises product manager Karsten Hermanns.

Apart from buoyancy, water pressure can prove beneficial. For every extra meter of water depth, the pressure rises by 0.1 bar, a measure of pressure.

"That creates a comfortable massaging effect, especially for the legs and rump. It also promotes the circulation of blood through the skin, muscles and connective tissue. Also, the flow of blood from the legs back to the heart is assisted through support of the venous valves. It also promotes the metabolism," Stemper says.

All these effects can be achieved in aqua-relaxing and aqua- balancing, which involves minimal physical exertion. The floating effect helps promote relaxation.

All other forms of aqua-fitness require some form of activity. And all have positive effects on health.

"Aqua-jogging, aqua-running or aqua-aerobics all help train heart and circulatory endurance. Aqua-boxing or hydropower builds up the musculature and the musculoskeletal system," adds Peter Freyer, a sports instructor at the North Rhine Westfalian swimming association in Duisburg.

Training in water always has a bigger impact than training in air, as water is 1,000 times denser. "That means I'm working against significantly greater resistance. A lot more is being demanded of the body," Freyer says.

That's even more so when the speed is upped or resistance increased. That can be achieved with gloves, paddles or shoes with larger soles.

(Agencies via China Daily January 16, 2008)