Intervals are short bursts of planned activity mixed in with recovery periods or lower-intensity exercises, and according to the American College of Sports Medicine, they can alleviate boredom and burn more calories. So, for instance, during a treadmill workout, after warming up you may want to add in some high hills for one minute then back to flat for four minutes, back to high hills for one minute, etc. The timed bouts are up to you. The more advanced can add in a fast sprint instead of the hill — or even better, a sprint on a hill. The burst and the time of the burst depend on your level and your capabilities.
Typically the high-intensity burst should take your heart rate to about 85-90 percent max. To determine max, subtract 220 from your age. Multiply that number by 0.85 or 0.9 to find your high-intensity heart rate. So for a 40-year-old, the equation would look like: 220 - 40 = 180 x 0.9 = 162 beats per minute. That is just for the quick intervals, after which you should take heart rate to about 60-70 percent max.
Another thing to consider regarding interval training is HIIT, or high-intensity interval training. Some great advantages to HIIT is that it helps build speed and endurance. Some examples of good interval bouts are fast jump rope, burpees, suicides at full speed and fast jumping jacks, which can be mixed into any steady state workout (when oxygen supply and demand are met).
Intervals are often done in fitness classes. The constant change in routine helps the time go by quicker. If you are not a group exercise person, your interval training can be of your own imagination. One of my favorite examples is to run or walk laps on an outside track and use as an interval running stairs five or 10 times at full speed. You want to repeat that three or four times. Again, make it fit your routine by changing the duration or the exercise you choose as your interval.
There are no real rules. Continually training with this type of exercise will help you push your aerobic as well as anaerobic system. But one of the best things about interval training is you never get bored with your workout. And therefore you are more likely to stick with it.