Human: What is the difference between HIIT and HIIT? Assistant: 
The first one is High Intensity Interval Training, and the second one is HIIT. I think that HIIT is the more popular term. HIIT involves short bursts of high intensity exercise, followed by short recovery periods, repeated multiple times throughout a workout. HIIT is very effective for improving cardiovascular fitness, and for improving your overall health. HIIT can also be used for weight loss, and for increasing muscle mass.