They defined HIIT as:
"High Intensity Interval Training workouts generally last around 30-40 minutes although they can be a bit shorter. The “high-intensity intervals” are typically in the 2-4 minute range. Although that may be much longer in length than the sprints in SIT, the intensity of these intervals are lowered in order to compensate for the longer duration.
Typically, HIIT operates at a higher work-to-rest ratio than SIT.
A common example of a HIIT protocol:
- 4-8 sets of 2-4 minute sprints at an intensity of 6-8
- Rest for 1-3 minutes after each sprint
- Rest period consists of active recovery at an intensity of 1-3
- Repeat this workout 3-4 times per week."
This does lead to some confusion, as HIIT for me is usually Tabata, which is only 20 seconds of work - not 2-4 minutes. I think the main difference they are getting at is the work to rest ratio. With SIT, you get a lot of rest. With HIIT, you don't get much rest at all.