Interval training involves alternating "work" periods (sometimes also referred to as "sprint" intervals) of higher intensity exercise with low intensity "recovery" periods. Each pair of a work interval and also a recovery interval is often called a round, as well as your total workout is based on a warmup, a desired quantity of rounds, followed by a cool-down.
Intense Interval training (HIIT) is a very demanding style of workout, and the phrase "high intensity" often scares many trainees, so don't be afraid to start out too simple and easy , slowly increase the a higher level difficulty. When I was reading Turbulence Training, Craig Ballantyne a great explanation for interval intensity. If over a scale of 0 - 10, 0 is just not moving at all and 10 is running on your life.. then the ideal work interval is around an 8. A essential thing to remember though is that even 'running for your life' will be different speeds for different people.
Remember that if you have not trained in quite a while... or have never tried HIIT before, then a good work interval of 8 could possibly be too much for you. For you, a good work interval can be quite a fast walk pace. It really depends on you and you should definitely not be afraid to start out too simple and easy , progress to increased difficulty. You can make it harder at the next workout, but if you go to hard prior to being ready you could set yourself back with injuries or maybe get discouraged.
An example Beginniner's Workout
3-5 minutes easy walking
Walk at the leisurely pace. Just receive the blood moving and acquire loosened up. Spend the very last minute walking a small bit faster to get you ready for the first interval.
Half a minute of fast Walking
Remember the 0-10 intensity scale? If you're just getting started with some walking intervals than have a 6. This needs to be a fast/brisk walk. Imagine you are late for a big interview and extremely need to hurry. If you cannot maintain this for 30 seconds, shoot for 20.
90 seconds of slow walking
Immediately drop your speed to what you may need to catch your breath, but keep moving. A complete standstill is too taxing on the heart. As you recover you can bring the pace up again somewhat. If you need more than 90 seconds at first than go ahead and take it. Aim for 6 rounds of the and then follow it with another 3-5 minutes of easy walking being a cool down.
Do this 3 x per week, being sure to take a day off in between each workout. Once you get a handle on the 30:90 intervals, add an extra round in. When you're able to do 8 rounds of 30:90, then first give attention to cutting down the amount of recovery time. Go to 30 seconds of fast walking followed by 75 seconds of slow recovery. Again drop down to 6 rounds. When you're able to handle 8 rounds again, cut another 15 seconds off of your recovery time and drop returning to 6 rounds. By doing this you aren't following a strict schedule that claims you should be at this level doing X quantity of reps by day X, however are steadily progressing at your own rate. Make sure to log everything down in the journal so that you can view your progress.
When you are back to 8 rounds of 30:60 second intervals, then try upping the job intervals by Just a few seconds while keeping the recovery period fixed at One minute. Drop to 6 total rounds and come back to 8, you can add 15 more seconds of training until your rounds are One minute of brisk walking (likely to be almost a jog at this point) and 60 seconds of slow recovery. Right now, I promise that you will be transformed for a couch potato and ready (and hopefully energetic willing and able) to begin pursuing more intense varieties of training.