I am new to cycling (riding just over a year and addicted! ) and trying to improve the efficiency of my training. I ride 100-150 miles a week and go to 2-3 spinning classes each week. I constantly find myself working at a very high heart rate. (Example: last weekends ride of 102 miles in 5 hours and 3 minutes at an average HR of 157. In spinning classes I usually average 163-165 for the hour). I just don't feel like I am riding hard enough if I am not pushing myself to average 20+ MPH (which results in my high HR). I see the pros riding 25-27 miles an hour at rediculously low HR's. How do they get there? What am I missing?