What it means
During the hard intervals, effort is vigorous: by the CDC talk test, you can only say a few words before pausing for breath. Recovery periods let your heart rate come down before the next push. Sessions can be done on a bike, rower, track, hills or with bodyweight moves.
Reviews of HIIT studies report improvements in cardio fitness, blood pressure and blood sugar markers. Its biggest practical draw is efficiency: a HIIT session can take less time than steady cardio. Studies have not shown a clear advantage over moderate continuous exercise for weight loss.
Under the US activity guidelines, vigorous minutes count roughly double, so 75 minutes of vigorous activity a week meets the same goal as 150 minutes of moderate activity.
Start slowly if you are new to exercise, and ask your clinician first if you have heart disease or are early in a GLP-1 dose increase, when low energy and dizziness are more common.
Why it matters
HIIT can fit fitness gains into a busy week, but it should match your energy on GLP-1 treatment.