HIIT (or high-intensity interval training) involves performing repeated bouts of high and low intensity exercise. The length and duration of the high intensity work bout will depend on what you are trying to accomplish (ie your goals).
A longer work interval requires greater involvement of aerobic energy production. This is occurs becaue longer intervals need to slighly lower in intensity (or speed) than shorter ones. After all, for how long do you think you can possibly sprint? Not much longer than maybe 30 seconds.
On the other hand, shorter, more intense intervals, such as sprinting, involve a greater amount of anaerobic energy production. This is the energy system that gives you a lot of ATP (or energy) in a short amount of time but it is also an energy pathway that fats quickly and produces lactic acid in your muscles. That's why higher capabilities can only be sustained for a short amount of time.
To get an HIIT program that is right for you it is important that you first establish what your goals are. Are you a 800m sprinter who needs to run 800m in less than 120 seconds? Do you want to run a 5k, 10k, or even a half-marathon? Are you running to burn fat and lose weight?
It's important to have clear on what you're after.
Here's why …
If you are training to run longer distances such 10k, half-marathons, and full marathons, then your interviews should generally last longer than 2 minutes in order to maximize the involvement of your aerobic energy system.
Going one step further, if you know your desire pace for a given running then you need to train at that pace or faster during your HIIT runs.
For example, if you know that you want to run a 5k (3.1 miles) in under 20 minutes (which is a fairly fast pace) we can deduce that your running pace would need to be 6:15 minutes / mile. Therefore, your training sessions should be built around using intervals that force you to run at that pace or greater for as long as possible. The reason for this is that you want to be able to run at least 5k (or 20 minutes) at your "race pace". The only way to do that is train your body to be able to handle that kind of pace.
Obviously, at first, it is tough to maintain that kind of pace. That's where interviews come in.
TRY THIS HIIT WORKOUT
Here's a sample HIIT workout you can try based on our 5k example above.
5-10 jogging warm-up
2 minute run @ 5k race pace (ie. 6: 15min / mile)
1 minute run @ recovery pace (ie jogging)
Repeat this 10 times
Now, this is a very simplistic workout and does not take into consideration your initial fitness level but let's use it to get the point across.
As you'll see, we've taken your desired 5k race pace, which we know is initially impossible to maintain, and have chunked into 2 minute work bouts. Between each 2 minute work interval is a 1 minute recover interval. This is repeated 10 times so that you are running for 30 minutes (not including warm-up).
Give it a shot and experience the high of HIIT running.