HIIT combines ‘intervals’ of low-intensity exercise with intervals of very high-intensity exercise (95–100% effort). So, for example, you might run at just about full speed for ten seconds to one minute, and then jog or walk for 30 seconds all the way up to four minutes (more on ideal interval times and exercises later). At the core of HIIT is that activity has to be at a maximum or near-maximum level of effort for a short time, followed by activity that is of long enough duration and low enough intensity that it allows enough recuperation for the next very intense ‘work’ interval. So it’s basically the opposite of cardio. Instead of a steady pace throughout, HIIT has you working at full tilt in short bursts, each followed by very relaxed ‘active rest’ periods. The key consideration (because most people get this part wrong) is getting your rest times right and not being tempted to start the next interval too soon—you need to get that breathing rate and heart rate down so you’re able to put enough work into the next interval!
The most important attributes of HIIT are that you spend far less time exercising and yet the result is substantially greater fat loss and probably better maintenance of muscle tissue as compared to cardio. So for the price of a few short bouts of extremely demanding activity, you’ll spend less time exercising, yet get superior results!