How do you log HIIT run?

You can make your own exercises and log it as a HIIT run and put in the time and calories burned.

I have several runs that I log this way because they don't fit into the MFP exercise box.

^^^^^ Ditto. I do HIIT on the treadmill, so when I'm done it shows the average mph for whole session. I figure its probably a little on the low end, but close enough. You see more of its benefits later on though anyway. It's never going to be true to the calorie count, even with an HRM.

I usually log it as a regular run at whatever my total average pace was over the whole distance. Sometimes I just log it as HIIT or Tabata if it was Tabata. I use the numbers off my HRM though so I can call it a green giraffe if I want to.

^^^This. Or sometimes I just log it as a flat 200 cals. Generally I'm not tracking my exercise cals to eat them back so I don't worry about it too much

I log it as "holy crap"

You can make your own exercises and log it as a HIIT run and put in the time and calories burned.

I have several runs that I log this way because they don't fit into the MFP exercise box.

this!