You might have heard about the 'afterburn' of exercise, a period of time after you've finished working out where your body continues to burn energy. From a physiological perspective this is known as "Excess post-exercise oxygen consumption" (EPOC) and is essentially a process where your body will use oxygen to restore the body back to it's 'normal' state.
Often EPOC or Afterburn is used as an example as to why to do one form or exercise or another, and to be quite honest personally I have used this as an explanation as to why high intensity interval training (HIIT) is the 'best' thing to do during training sessions. In fact, the information I received a few months back to confirm my assumptions suggested that the afterburn effect can continue up to 72hrs later if you pitch the workout at the right level! Sounds amazing, right?
But is this entirely true?
As ever with fitness and nutrition based thangs... the devil is in the detail.....
There's no denying that EPOC does create an afterburn effect. In fact, I can go further and say that there's no denying that the afterburn effect is much larger after a HIIT session than it is when compared with long slow steady state intensity training (LISS), but as a percentage, NOT as an actual amount of calories burned.
A 2006 study (noted below in case you fancy having a read!) showed that during endurance training (LISS) the EPOC created a 7% increase in calories burned. HIIT training though almost doubled this to around 13%! Fantastic! We've hit the goldmine! That's all the evidence we need to do HIIT isn't it?
People can do LISS style training for a long period of time as with it being a lower intensity it means you can go for longer. So let's stay someone trains at this level for an hour and they weigh 80kg, they'll burn roughly 640 calories in that time. The 7% EPOC afterburn equals a further 45 calories for a total of 685 calories burnt.
HIIT is more difficult of course and you'll be smoked within 20-25 minutes of working out (assuming you're working at the right intensity of course!!). In 20 minutes that same 80kg person will burn around 300 calories in that time, and with the extra 13% EPOC related afterburn you're adding in 40 calories. So a total of 340 calories.
So as a like for like comparison the difference is significant. The reality is that there is no amount of EPOC afterburn that is going to make up the deficit between working out for longer and a HIIT Session!
This of course isn't me trying to say that LISS is better than HIIT or the other way round, both types of training are important and useful to different people.
What I am saying is that the hype surrounding EPOC afterburn and particularly that with which you get it during a HIIT session has been massively overplayed, generalised and isn't entirely relevant. What matters most, in terms of weight loss, is the energy you expend during the session!
Every individual is different and will have different needs. People have lifestyle requirements that means a HIIT session is the best way of creating a calorie deficit, others due to a variety of factors including age, weight, fitness levels or medical history may require a different approach. What's important is that you take the best option for you!
Here's that study I mentioned earlier
LaForgia J et. al. Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. J Sports Sci. 2006 Dec;24(12):1247-64.