I suspect there is a nearly proportional relationship between calories burned and heart rate. If you have a resting heart rate of 55, and rest all day long, a 170 lb person will burn 1800 cal/24 hr, or 75 cal per hour. if you double your HR to 110 for an hour, in and ideal case, you will burn 150 cal/hr., or 75 cal/hr over what you would burn at rest. On long rides I try to eat about 40-50 cal /hr and do not gain weight doing this, so I can't be to far off.