SEOUL - South Korean star Kim Jong-kook, who is a fitness fanatic, has started a YouTube channel, aptly called Gym Jong Kook.

Within a day of posting his first video on June 17 (Thursday), he already had 250,000 subscribers and has since more than tripled that number.

The popular singer-actor, who is best known for being in the cast of variety show Running Man, has so far only uploaded one four-minute video on the channel, but it has already amassed 5.1 million views by Sunday (June 20).

In it, the jovial muscleman is seen grunting as he works out in the gym - sometimes topless but always with a mask on - and showing off an impressive set of biceps.

"Rather than evaluate me based on the body you see, I hope that you will evaluate me based on my sincerity and consistency when it comes to exercise," said the 45-year-old.

He also revealed his pet peeves at the gym: "I can't stand looking at someone working out weirdly. I go insane when someone takes a long break. Break time is unnecessary."

"I'm very nosy when it comes to exercising," he added. "The fitness community says not to be nosy. You know, like getting in the way of people when they work out. That's what a lot of gym guys do."

When asked if it is true that those who work out with him tend to disappear the day after, he laughed and said: "There are people who don't call me back."

He revealed that others who trained with him did pick it up and named singer-actor Rain and singer-host Sung Si-kyung as those who stuck with it.

"I don't force people to work out if they don't want to. When I work out with someone who likes and wants to work out well, it feels completely different and gives me joy. Then I feel good and I eat good food with them after working out."

Future videos may see him surprising people who have said they would like to train with him, as well as sharing his meal plans.

He also showed a short snippet of how he bulked up from a scrawny teenager in 1995, which was when he made his singing debut, to his current physique and said he would be talking about his experiences and workout exercises.

He added: "As I'm not an expert, I'll try to share my passion for exercise rather than teaching."