When I built my bike I added a small computer to measure heart rate and calories burned. I have discovered two things about my riding. The first being that my rides have gone from 10-20 miles to 40-50 miles per ride. The second is that I typically ride at a pace determined by my target heart rate. My goal is to spend over an hour at a heart rate of ~130, (being 70 years old). I simply adjust the assist level (I reprogrammed to 9 levels of assist) to keep my heart rate where I want it. Bottom line is that my heart rate is under control and thus calories burned goals are achieved. You