Gist
Yes. HIIT is one of the most effective time-efficient methods for improving cardiorespiratory fitness and VO2 max in adults.
Yes. HIIT can support fat loss and may reduce body fat in some programmes, but it is not uniquely superior to other exercise when calorie balance is matched.
Yes. HIIT can support weight loss and is time-efficient for improving fitness, but lasting weight loss still depends on maintaining an overall calorie deficit.