Should one do fasted HIIT or not?

[xxispawn01xx]

Something I often read about is how glycogen is stored in your muscles etc. My question is what is the scientific literature’s consensus on fasted HIIT training (vs LISS/endurance)? From what I understand it’s unlikely in a <30 min session that you would deplete your glycogen stores, so if you get hungry/your stomach gurgles, is this just a response you should learn to ignore?

How about longer studies that actually track HIIT vs fasted HIIT, did particpants gain back weight? Were there any affects on sleep/stress due to the intensity of fasting+HIIT?

[Jordan_Feigenbaum]

XX,

Thanks for the thoughtful question. A few answers in line:

what is the scientific literature’s consensus on fasted HIIT training (vs LISS/endurance)

I’m not sure that I’ve seen much data on fasting LISS vs fasted HIIT as far as outcomes are compared. That said, when comparing fasting LISS to fed LISS, there aren’t any differences long term in outcomes like improvement in cardiorespiratory endurance, weight loss, etc.

Similarly, when comparing fasting HIIT to fed HIIT, there aren’t any differences either.

From what I understand it’s unlikely in a <30 min session that you would deplete your glycogen stores, so if you get hungry/your stomach gurgles, is this just a response you should learn to ignore?

Eh, it really depends on the individual and the task. I don’t think you can reliably say that you’ll deplete glycogen stores in < 30 minutes. I also don’t think that depletion of glycogen stores are reliably correlated with “stomach gurgles” and/or that you should use stomach rumblings to manage nutrition or exercise.

How about longer studies that actually track HIIT vs fasted HIIT, did particpants gain back weight?

There aren’t differences in weight loss or prevention of weight regain with fasted vs fed conditioning.

Were there any affects on sleep/stress due to the intensity of fasting+HIIT?

Not that I’m aware of.

To be clear, I don’t make a big deal about fasting vs fed cardio, as the outcomes are roughly the same. The times I prescribe fasted conditioning are for applications where people will be fasted or hungry during the competition.

[xxispawn01xx]

@Jordan_Feigenbaum

XX,

Thanks for the thoughtful question. A few answers in line:

I’m not sure that I’ve seen much data on fasting LISS vs fasted HIIT as far as outcomes are compared. That said, when comparing fasting LISS to fed LISS, there aren’t any differences long term in outcomes like improvement in cardiorespiratory endurance, weight loss, etc.

Similarly, when comparing fasting HIIT to fed HIIT, there aren’t any differences either.

Eh, it really depends on the individual and the task. I don’t think you can reliably say that you’ll deplete glycogen stores in < 30 minutes. I also don’t think that depletion of glycogen stores are reliably correlated with “stomach gurgles” and/or that you should use stomach rumblings to manage nutrition or exercise.

There aren’t differences in weight loss or prevention of weight regain with fasted vs fed conditioning.

Not that I’m aware of.

To be clear, I don’t make a big deal about fasting vs fed cardio, as the outcomes are roughly the same. The times I prescribe fasted conditioning are for applications where people will be fasted or hungry during the competition.

Good stuff, thank you!