Where I live it's fairly hilly, though until recently I lived in a town where it wasn't. As time has gone by, the hills here have gotten much easier to climb. On my daily commute (~3 miles each way), I can now sprint up even the biggest hills, whereas at first it was a major workout just pedaling to stay upright. It seems obvious that I'm becoming more fit and in tune with my environment. I'm wondering what this means in terms of calorie burning? As I get in better shape, does it take the same number of calories for me to climb the same hill, or is my increased fitness actually causing greater efficiency and therefore a reduction in the number of calories required to climb?