Or more to the point, what is a fixed gear bike--I assume it only has one gear. So, you have to pedal harder, right? Excuse my ignorance, I'm just trying to get some basic info.

I have two road bikes and like them very much: for training purposes, is it useful to get a fixed gear bike?? What are the benefits? What will take some getting used to? Do they cost more or less than a usual road bike?

Any answers would be helpful. Thanks!