Interval training is very effective and efficient. It's best for people who are at a decent level of fitness. I would also suggest that you take a class or work with a personal trainer to get started, so you get an optimal routine. I like tabata intervals. It's a good idea to know your training heart rate and check when you are getting started to make sure you are in a training zone and not way too high or too low. When you are doing a maximum interval you shouldn't feel like your heart is racing, dizzy or you can't catch your breath - you are overdoing it.
