Outside. I used to do the 1 minute efforts inside but I think I was actually coming up short relative to what I could actually put out (based on a few recent short power PRs outside). The best way do the 1 minute all out is to find a reasonably steep but not too steep hill (somewhere in the 5-7% range) and roll into it at around 10-15mph.
I have the lights on my Elemnt set to the power zones, so I’ll roll into the hill, find a gear and let the tension on the chain build, and as soon as I see Red on the Element (meaning I’m in zone 6), I hit the lap button and send it.