Up until last week I was not able to fart while spinning, but mustered up the courage to try in the middle of a 50 mile ride. Worked fine to my amazement. However, it wasn't on a fixed gear, it was on my road bike. I'll have to give it a shoot on the fixed gear soon.

It's pretty satisfying to be able to do though, I used to hate doing it because it through off my pedal stroke, but now it's no problem.