Who says playgrounds are just for children? For Soichiro Saito and his fellow mates, age is just a number when it comes to having fun in a playground.

Every Friday, 79-year-old Saito and a class of senior citizens swing around on a jungle gym, made especially for the elderly, at a Tokyo park.

Showing off their physical strength and dexterity, they walk balance beams and stretch their muscles on specially designed poles.

Saito is one of many elderly Japanese citizens participating in an increasingly popular elderly workout class.

Playground equipment designed for the graying population is funded by local governments all across Japan.

With fewer and fewer Japanese having children and 25 million people in a country of 123 million above the age of 65 years old, it made sense for local governments to disassemble old children's playgrounds and convert them into fitness parks for the retired.

The workout classes, also funded by local governments, teach the elderly how to use the equipment properly and safely.

Thanks to the help of those trainers, Saito manages to hang on to the exercise bars while moving his waist in circles to stretch his back and side muscles. He says the exercises are very effective. 

[Soichiro Saito, Retired]:
“If I'm at home, I tend to slouch or lie down, but if I come here I straighten my back, as everyone else is working out with so much energy.”

And Saito is not alone in taking comfort in numbers.

Many more senior citizens are participating.

The class provides opportunities for them to mingle with other senior citizens in the area, and many participants take the class to stay fit and away from hospitals or nursing homes.

[Ikuko Yamakoshi, Retired]:
"My legs were really heavy as lead, since I'm sick, but it's much lighter now after the workout. My mind is cleared up as well."

Saito and Yamakoshi's class is conducted by the Association of Physical Fitness Promotion and Guidance — an organization that conducts about 50 elderly workout classes across Japan – fully funded by the local government.

[Masato Saijo, Association of Physical Fitness Promotion and Guidance]:
"There aren't many children using playground equipment now and most equipment is damaged and needs to be removed. This problem came about when the population started graying in Japan, so it was natural for us to replace old equipment with workout equipment for the elderly."

With nearly 40,000 centenarians, Japan has the world's oldest population and continues to age fast.

Japan already boasts the longest life expectancy in the world, with experts citing healthy diet, high quality health care and a tradition of active pensioners as factors in the phenomenon.

If this continues, one day older people may outnumber children.