What should you be doing during a HIIT rest interval?

' If you're sprinting down a street, on a track or treadmill, then casually walk for the rest interval, though more fit people may find that a slow jog works.

If you're using hills, than walk slowly on flatter areas.  If you're pedaling, pedal very slowly with light tension.  As long as the rest interval restores your heart rate and breathing to normal; as long as you rest just long enough to begin feeling that you can go all-out again for next blast. '