f(x)'s Krystal was a guest on 'Strong Heart' recently along with her other 'Kiss & Cry' members. On this day, she revealed the secret behind her '11 abs'. On the July 26th broadcast of 'Strong Heart', she said,

"There was a time during 'NU ABO' in which I was the only member who had a revealing outfit. I never worried about my abs before, so I was a little unsure about wearing revealing clothing. I was surprised when an article came up titled '11 abs' with captured images from our performance."

Krystal continued, "During my young trainee days, I went to jazz dance class and did a lot of sit ups so I have more muscle than fat." To dispel any feelings of envy, Krystal joked around and pointed to the enlarged screencap, saying, "I had eaten bread, so there was bread in my stomach." Source: TV Daily via Nate