1. What Exactly Is HIIT?
All HIIT is interval training, but not all interval training is HIIT. HIIT requires maximum effort, whereas any old interval training just calls for periods of heightened heart rate. Additionally, interval training can involve both short or long periods of high intensity, while HIIT is always short intervals. Think of it this way: if you're going at max effort, you should only be able to do it for a short amount of time. 

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