Which sounds more appealing: doing only one thing over and over for an hour with the promise of a nice reward, or doing several small things for HALF an hour with the promise of the same or even better reward?
Six of one, a half-dozen of the other? Perhaps not. This is a comparison between two types of cardio exercise: endurance training, also called “steady-state cardio”---where you do the same thing for an extended period of time with little to no variation in speed or intensity---and high-intensity interval training, also called high-intensity intermittent training, or HIIT.
In contrast to steady-state cardio, HIIT involves pursuing a short burst of intense activity---sprinting for example---followed by a short “recovery” period of moderate activity. Then, as soon as the recovery is over, you burst back into the sprint. Here is a sample HIIT workout.
The strategy is to return to the intense activity before you have even started to truly recover from the previous sprint. HIIT has been shown (here in rats, and here in humans) to more effectively recruit activity in the mitochondria, which, as we all remember from biology class, are the power-plants of the cell. This activity lends itself to the oxidation, or chemical degradation, of fat cells.
But science aside (who needs it really? LOL jkjk), one attractive element of HIIT is that it is performed in a finite number of smaller time periods (as opposed to steady-state cardio, which can feel like aimlessly running on a hamster-wheel for an indefinite amount of time), making it more potentially engaging, more varied, and more psychologically rewarding because it involves pushing oneself to greater lengths.
This can result in a greater feeling of accomplishment, heightening the desire to do it again.
Not only that, but HIIT doesn’t even need to be performed on a cardio machine. It can be done with any exercise that increases your heart-rate to the point at which you are genuinely pushing yourself. How do you know you’re pushing yourself? Heavy breathing, sweating, and muscle burn, not in small muscles like biceps but big ones like legs or back. The main prerequisite is that you’re able to do the exercise with good form.
Here's a (fairly advanced) example of a non-cardio HIIT workout.
When should HIIT be used, and by whom? As described in a solid article debunking “HIIT myths” on LiveStrong, people who are athletically deconditioned (meaning not used to regular exercise) should not necessarily use HIIT as a “crash course” return to fitness.
No no no. Start out with steady state cardio until you can maintain it at the same speed continuously for 30 minutes. Get good at normal squats and lunges before doing the jumping versions. Know what I mean? Then give HIIT a shot.
Additionally, it is not required, or even necessarily beneficial, to use HIIT all the time. Steady-state training has its place; improving cardiorespiratory health, which is the primary function of steady-state cardio, has numerous benefits including fat loss and improving other areas of athletic performance such as resistance training.
Nor is HIIT a magic fat-burning bullet, and “the more HIIT the better.” As with any other form of exercise, if you don’t gradually increase the difficulty (or level of “overload”) over time, the results will diminish or level off. If you did nothing but HIIT all the time, you’d likely hit a wall: your workload will be too great to progress because you reached for it too soon, when it might’ve been a better idea to gradually increase up to that level.
The reason for this something called your VO₂Max, which is the upper limit on how much oxygen your body is capable of consuming during a specific activity. This limit can only be increased incrementally, through a gradual increase in the strength and size of the heart muscle, like any other muscle.
Guess what is pretty good at increasing your VO₂Max? Steady-state cardio. And guess what’s even better? HIIT and steady-state together.
Think of HIIT as a tool in your toolbox, just like resistance training, cardio, or pullups: very effective at what it does, but if you used it all the time, it would lose both its fascination and its effectiveness. And so would you.
For more information on VO₂Max, what it is and how to increase it, I suggest the following sites: