text: Their are alot of theories to this.  The best answer that I have is it all depends on your pulse, and the duration that you have your pulse elevated.  If you ride a bike, and your pulse never breaks 100, you will not burn alot.  You will burn much more the higher your pulse gets.  Their are formulas for calculating the total calories burned...I don't know them off hand, but it takes into account your weight, your age, your pulse, and duration of the activity.