Is HIIT the fastest method to increase cardio?

Google and many others seem think it is, but I thought I’d get a second opinion. No pun intended…
Would you guys agree?
Specifically, the aim is increasing my gas tank for grappling, so basically successive, intense five minute rounds for around half an hour or so.
The ‘best’ way is not surprisingly more grappling, but its currently not a practical option.

I’ve got a sled, grassy hill, sledge hammer and tractor tyre and imagination at my disposal.

I’m thinking of teeing off with something like a vanilla thirty second on / off for say five minutes and going from there.

HIIT isn’t something I’m really familiar with and could be barking up the wrong tree entirely, so if you guys have a better idea, I’m all ears.

Cheers

What’s your current conditioning base? As far as improving predominantly anaerobic efforts, yes, HIIT is likely to be superior to LISS. That said, I think you’re getting a fair bit of HIIT during your grappling sessions and may benefit from bringing up your cardio base via aerobic training. So back to the original question, where is your cardio now and what are you doing for it?

So back to the original question, where is your cardio now and what are you doing for it?

Beside around two hours LISS rucking once per week and one or two sessions of actual BJJ, nothing else cardio specific.
I’m also in week three of my second round of the Low ISF 3 day. So I’m basically fairly ‘active’ at least five nights per week.
52, 173cm, 78 kg and not to banged up, just in case you’re wondering.

I think if you added the conditioning that’s in the Low Fatigue template for right. now and ran that for the next ~4-6 weeks and see how you do. Between the rucking and BJJ, I would cautiously add conditioning- both LISS and HIIT.

Thanks mate, cheers.