I recently purchased a Garmin 305 forerunner, a wrist device GPS. I inputted my personal info, age, weight, sex and it keeps track of my calories burned. I have found that when I walk, approximately 3-3.5 mph, it states I burn an average of about 85 calories per mile. However when I run, typically 7-7.5 mph, the calorie burn per mile jumps to about 130. This is pretty significant and I wondered if it was accurate. I would think a covered mile would burn the same amount of calories, regardless of how long it took so what am I missing here?