With HIIT, users alternate between intervals of high- intensity and low-intensity exercise. (Example: 60 seconds high, 45 seconds low.) HIIT offers many benefits. My favorite? Efficiency. You can both tone and burn an optimal amount of calories in the least amount of time. Next on the benefits list: naturally raising your energy levels—by boosting endorphins and improving oxygen circulation. I prefer doing HIIT workouts in the early afternoon (often a HIIT-designated Peloton ride instructed by Alex Toussaint) to propel me into the second half of the day.
Source: Ben Meer