Hi:
You could always invest in a heart rate monitor... You program it according to your weight, sex, age and as you exercise it calculates: total time exercised; time you were in your zone, i.e. within your calculated heartrate, your peak heartrate, i.e., the "highest" and the total calories burned. I have a Polar M32 heart rate monitor,it costs about 100.00, but is well worth the investment. My heart rate is programed at: 112 - 150; 112 being my lowest and 150 my max heart rate... it will beep when I go below 112, or above 150... You will get into your anerobic zone if you go over your peak heart rate, which is what you want to do sometimes. But you wouldn't have to guess about how many calories you burn, and you can keep a record of how many calories you burn, daily, weekly, etc. I hope this helps... Dee;-)