Cycle riding can be tough- takes a lot of training before you can call yourself a cyclist. You find that out on the first hill you come to when the legs give out and the lungs feel as though they are going to burst.

But you can overcome some of this problem by being fit in the first place. Spinning classes and a good cardio vascular workout at the gym can help by giving you some initial fitness- or even a lot. What it can't give you though is that "Bike fitnes" required to do a 20 mile ride up hills at speed.

That you will find after about 2 years of hard riding. And it will be hard till you get that bike fitness.