Someone linked me a site and wanted to know if the claims made were legit. I only clicked to see the heading - How To Boost Your Metabolism Using Interval Training - before I closed it down and told him what I thought about HIIT.
Quick summary -
1. There is no doubt that HIIT is superior to steady state cardio when it comes to improving metabolic conditioning when looking at effect/time invested.
2. Extremely overrated for fat burning. EPOC is minimal and certainly not as significant andf radical as some gurus/nutjobs/pranksters make it out to be. Choosing HIIT before lower intensity, steady state cardio solely for caloric burn is dumb as hell. Here's an example for you:
Let's use a fairly typical 10 min HIIT session as an example, in this case 15 s all out sprints followed by brisk walking for 45 s. 185 lbs male.
Sprints 2.5 min total = counting 25 kcal/min = 62,5
EPOC = 62,5 x 0,15* = 9,5
EPOC is approx 15%
Total for sprints = 62,5 + 9,5 = 72 kcal
Brisk walking 7.5 min total = counting 5 kcal/min = 38 kcal
Total calorie expenditure for a 10 min HIIT session = 110 kcal
...or the equivalent to 22 min brisk walking.
3. That last poit is very important. Even though you burn more calories in less than half the amount of time compared to, for example, brisk walking, HIIT is very draining on the central nervous system. In stark contrast to lower intensity cardio, which you can do for a much longer time, with much greater frequency. For someone interested in fat loss and strength maintenance, and not metabolic conditioning primarily, including HIIT too frequently is playing with fire.
So in conclusion, HIIT is great if conditioning is high on your list. And no, you can't have fat loss, optimal strength maintenance and conditioning all high on your list. Something has to give. Since most people, at least the clients I deal with, are interested in fat loss, HIIT is vastly overrated and the frequency to which it has to be integrated in order to create a substantial caloric deficit will cause most people to crash, and their lifts to plummet. Which is why I rarely recommend HIIT for someone that just wants to get lean, while keeping their strength up in the gym. If you aren't concerned with getting your resting heart rate low, and just want to look good naked, think twice before jumping on the HIIT bandwagon.
