Unicharm Corp. has developed the first adult diapers in the world to help elderly people with walking difficulties move about more easily.

The product, to go on sale in Japan on Feb. 4, responds to the needs of a healthy life expectancy market spurred by the nation's rapidly graying population, according to Unicharm officials.

In the Japanese market, adult diapers have outsold baby diapers since 2011. The domestic adult diaper market has been growing at an annual rate of 5 percent and is expected to expand.

Aging causes abdominal muscles to weaken, shifting the body's natural center of gravity forward, thus making it more difficult to walk. But this particular diaper stabilizes the pelvis through a special sheet that increases pressure around the stomach and improves the ability to stretch armpit muscles.

The diapers' effectiveness was confirmed based on the improved ease with which wearers raised their legs and the lengthening of their steps, according to Unicharm, which has developed the product in collaboration with Hyogo University of Health Sciences.

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"It appears that the diaper makes the wearers straighter," said Kotaro Kawaguchi, a professor of orthopedic and sports physical therapy at the university's School of Rehabilitation.

"Being able to move on their own improves their quality of life," Kawaguchi said.

Unicharm's newest product is priced at 1,600 yen ($15) for packs of 18 medium-sized diapers for a waist size of 60 to 85 centimeters and those of 16 large-size diapers for a waist size of 75-100 cm.

A variety of adult diapers cater to domestic consumers, with mainstream ones having thin pads. A selling point for Kao Corp.'s adult diapers is that they are soft, using its technology developed for baby diapers.

Daio Paper Corp. sells products featuring the prevention of leaking from around the legs.