I gave in and grabbed a heart rate monitor today.
Then I was doing some research and found a Calories Burned calculator. http://www.braydenwm.com/calburn.htm
The calculator gathers typical info like age and weight, and also has an input section for heart rate and VO2. My HRM didn't collect my VO2 max, so I'm going to assume that the "Calories Burned" feature on my HRM could be more accurate.
I had my first HIIT workout with my HRM, 1:3 sprints and jogs, that is 30 seconds sprinting and 1 minute 30 seconds jogging, for 40 minutes. I averaged about 175 on the sprints and 155 on the jogs- I have a max HR of about 200, I only topped about 183 during this particular exercise. So I input this information accordingly to the above calculator, and used a VO2 max of 45, which is the said average for a sedentary male. It came out as about 160 kcals for 10 minutes of sprints and about 390 kcals for 30 minutes of jogging.
I don't entirely trust FDs calories burned from exercise statistics. I've never used these formulas to calculate calories burned. Anybody have a confirmation, second opinion, recommendation...?