Couple of minor corrections, first HIIT is not for the marginally fit, it is a high demand workout. Regardless of how fit you are HIIT will in fact increase your level of fitness. The various charts and electronic monitors use algorithms based on averages so are at best marginally accurate. Your rate of perceived exertion (RPE) is your best determinate as to how hard you are working. A heart rate monitor provides only a guesstimate of your calorie consumption, that can only be accurately measured in a laboratory setting. HIIT causes what is called excess post-exercise oxygen consumption (EPOC) which a heart monitor can not measure. A recent study indicates that you will use up to 40% more calories running than you will walking so it is I believe safe to assume there is a differential between calories used at steady state as opposed to interval training.
None of this answers your question but I believe getting any form of accurate value is tenuous at best.
Thanks mplane37. that is really useful information.
Fitness Minutes: (79,213)
1/26/12 5:12 A
It is true that HIIT makes you burn more calories after the workout because your body needs to adopt to respond to the new, higher demands caused by the HIIT. The problem is it is hard to calculate accurately how many calories are burned after the exercise, even with a heart rate monitor, even though your heart rate remains higher than the resting HR after an HIIT session. This is because the heart rate monitors are often calibrated for the range between 90 and 150bpm AND actively cardio exercising. For the very same reason, HR monitors cannot tell you the calories burned during strength training, even when your HR falls between these two extremes.
It must also be pointed out that, the HIIT is for people who are not yet fully fit. For a very fit person, HIIT will not do much except shorten the workout for the same calories burned, and will not burn any calories after the exercise, because the body of the fit person is already good enough to respond to intense exercise.
So the returns are diminishing as we get fit with this kind of exercise. Still, I strongly suggest it because it burns more fat while getting fit and it is far less boring and thus more engaging, which makes it likely that we stick with the exercise.
One last point: If the average HR of a HIIT session remains the same as that of steady exercise, the HR monitor will report the same calories burned in both exercises. The point in HIIT is to put demands on the body to force it to improve, not merely increase the HR moderately for a while and reduce it way down next. For example, I remember that after getting used to working out at an average 140bpm for an hour, when my average went to 150bpm for 40 minutes, it placed such a high demand on my cardiovascular system that my heart rate did not go down to resting HR for the next 10 hours or so, and I ended up sleeping only a few hours that night. If I don't place that kind of demand, none of these happens.
What I've been reading tho is HIIT makes your body more calories post workout than a slow jog/walk would. Which is why I started doing HIIT. If what I've been reading isn't true :) I'd rather be fast walking to be honest. lol
FWIW in the meantime, when I used my HRM to compare HIIT with sprint/walk intervals vs a steady state slow jog at my normal pace, it reported the same burn for the same time. Whether 20 minutes of HIIT or 20 minutes at a steady state, I would burn about the same.
Fitness Minutes: (112,042)
46,222 1/25/12 10:17 P
Because of the varying intensity, normal cardio trackers make it difficult to track this type of workout accurately, therefore as the previous poster mentioned, this would be an ideal situation to use a heart rate monitor.