HIIT gets marketed as a shortcut, and in terms of time efficiency, it genuinely can be — but the intensity that makes it efficient is also what makes it a poor starting point for someone brand new to exercise.
The core idea: short bursts, real effort, real rest
Alternating short, hard efforts with brief recovery periods is what defines HIIT — the value comes specifically from the intensity of the work interval, not just from moving fast.
Best suited to members with a training base already
Someone with a few months of consistent training under them gets more benefit, and less injury risk, from HIIT than someone in their first week who hasn't yet built basic conditioning or movement competency.
As a group class format, it works well precisely because the format itself creates accountability — a timer and a group make the hard intervals easier to push through than solo training often does.