The exercise is also a social occasion at which grannies can chat, joke and gossip over coffee or tea during a break or after training.
"I was formerly a shy person but now I feel like a totally different character," said Lee Jeong-Suk, 68, who also holds a black belt and took up the martial art to overcome depression after her husband's death.
Taekwondo, an Olympic event since 2000, is practiced by some 60 million people in 182 countries across the world, according to the WTF.
The federation in 2004 launched reforms to bolster its status as a global sport as the IOC reviews all 28 Olympic events. Some may be dropped in future.
The federation says its reforms focus on making taekwondo more commercially successful and more interesting.
The grannies fit the bill, attracting increasing public recognition.
"Once out in a park after appearing on a TV show, we were all surprised to see kids scrambling to get our autographs," said Yoon.
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