Riding a fixed gear has been a part of my conditioning (I'm not serious enough to call it training) regimen for the last few years. I head for the countryside on a 45-year old track bike equipped with low gearing (about 72 inches), a front brake, and Look pedals. Of course, on these days I stick to flatter terrain. But I find it's a good recovery workout, it helps my suppleness and flexibility, and it's good for my pedaling form.