T Nation

HIIT and Energy Source


I've been doing some HIIT type work at the end of my Muay Thai classes as a means for extra fat loss and some work capacity improvment.

I read an article recently that stated that the major source of energy for HIIT is carbohydrates. What if, however, one wasn't consuming a large amount of carbs and had a diminished supply of glycogen (due to low carb consumption)?

The energy would then likely come from either muscle or fat then, yeah? If one supplmented with BCAA's before said HIIT, this would encourage the use of stored fat for HIIT energy, would it not?

I ask because I'd like to continue to use HIIT in my repertoire of fat loss tools, but I don't want to cause much detriment. I do other things as well, but would like to do a 15ish minute HIIT (currently stair runs with body-weight squats in between up-downs) around 5x/week.

Any thoughts/suggestions on this?



Your body uses primarily carbohydrates during HIIT stuff due to the intensity of the exercise. Using Fats is much too slow, so even if you are carb depleted, you are still going to use carbohydrates if the intensity level is high enough.

If you were to perform HIIT at a high intensity level with no carb consumption and depleted glycogen, as you're suggesting, the result is going to be fatigue, not burning fat instead of carbohydrates.

However, it sounds to me like what you're doing for HIIT does not have a high enough intensity level to begin with. If you are running stairs, then doing squats, then running more stairs, etc. continuously for 15 minutes, you are going to be burning primarily fat anyways, because if you are doing an exercise constantly for 15 minutes, it is not intense enough to be using carbohydrates as the energy source.


Ah, I see... So if I were doing something like K-Bell circuits or BW circuits or something of the like where at some point I NEEDED rest, something like a 3:1 or 4:1 work:rest ratio, that would be more along the lines of "HIIT"?


So would it be accurate to say that HIIT is a tool best used for conditioning vice fat loss? If one is already in the desired body fat bracket, I imagine that carbohydrate consumption would be a little higher, so the use of HIIT seems to be a viable option.

Otherwise, would it be advisable to ingest carbohydrates sometime soon prior to the HIIT session if a "very low carb" dieter desires to do HIIT? Again, the question comes if this will be a primarily a conditioning effort, or will there be some highly-desireable fat loss occuring?


Yea that would be more along the lines. The intensity has to be high enough that rest is required.

For example, a 100 yard sprint at near max speed, would be HIIT. Running a mile is not


1- Using HIIT type stuff for conditioning depends on what kind of conditioning you're after. If it's an intermittent sport like say football, then HIIT type stuff should be the primary if not the only method for conditioning. Something like combat sports or basketball would need a blend of HIIT stuff and longer duration as well

2- If you're going to do HIIT type conditioning seriously, then some carbohydrates are needed in the diet, or else performance is going to be inhibited. It's my opinion that it isn't really necessary that the carbs come before the workout, just that they are included in the diet as a whole.

You can still eat "low carb", but you're going to require some carbs if this type of training is taken seriously. Just include some carbs here or there. This is mostly to ensure that glycogen levels can be restored from session to session.

3- You will definitely see gains in conditioning from this kind of training, and if diet is in order you will see fat loss as well. HIIT type conditioning has been proven to be effective for fat loss just as well or better than longer duration conditioning



What are your thought on my current diet protocol?

I train for soccer 2-3 times a week, and in the gym twice a week.I eat high protein, low carb and high fats for meals that are not before/after training, and eat high protein, high carb and low fat for meals directly before/after training. I am wondering if eating high carb 2-3 hours before training(usually rice) would be enough time to digest the carbs and have my glycogen levels ready to go for training??? I also have a small chocolate bar/cookies about 20 minutes before training.




It should be, like I said above, It's my opinion that it really doesn't make a big difference when you get your carbs, it's just important that you are consistently eating them.

I'm not a believer in things like tracking calories/macros or eating a million times a day. I basically follow Jim Wendler's template for eating:

3-4 meals a day, and at each meal:
large serving of meat or eggs
vegetables or fruit
possibly some carbs


Simple yet effective, love Wendler's stuff. 531 for athletes has been the best weights programme I have ever used and that diet advice is solid.

I agree though the main thing is to get some carbs in to perform optimally when using HIIT. In my experience recovery is severely reduced when on too low carbs with HIIT. OP, just make sure you get them from good sources and don't eat carbs in excess. See how your body responds and adjust accordingly to your goals based on fat loss and performance.