Interval training doesn't just mean maximal all-out, puking efforts. It really means training your body to work at different power and heart-rate zones to develop your overall fitness.

For example, the most effective intervals are probably "sweet spot" zone training intervals which are somewhat below lactate threshold (and won't cause you to puke or to suffer to an extreme degree).

If someone is really interested in developing a complete training program, you really need to first learn how to establish your training zones and then how to set up an interval program based on these zones. If you just go out and do a few all-out efforts on occassion, you won't receive the maximal benefit (and you probably won't enjoy it very much).

A good place to start to learn some of this would be to spend $17 and study this book. http://www.amazon.com/Training-Racin...8295531&sr=8-1 Even if you never buy a powermeter and only use a cheap heartrate monitor, this book will teach you how to set up a very effective (and enjoyable) training regimen.