Jang Ha-jin made it to S.M. Entertainment's coveted training programme a decade ago after winning a talent contest. She stuck to a seven-day regimen for nearly three years, before giving it all up to return to a more sedate life.

Now studying a degree in engineering, Jang remembers being trapped in an energy-sapping timetable that included lessons in Chinese, since many K-pop bands were trying to make inroads into China.

"The most difficult part in fact was when I saw myself and felt like I didn't grow up," said Jang, 23, remembering her stressful teenage years.