If you are trying to lose weight or change your body, you won't get there by doing a 30 minute moderate intensity workout 3-6 days per week. At best, you will burn 300-400 calories doing moderate exercise for 30 minutes (depending on your size, age, gender, etc). Having said that, 30 minutes of intense exercise, particularly "High Intensity Interval Training" otherwise known as "HIIT", is a different story. You don't necessarily burn a ton more calories during a HIIT workout, or intense workout. What's happening is that you are putting your metabolism to work for you for hours post workout. Here's why... Muscle burns fat, even at rest. The more you strength train, the more muscle you delvelop, resulting in more fat loss. This can be discouraging when you're watching the scales, but pay attention to how your clothes fit and you won't be disappointed.
The benefits of HIIT are that when doing intervals, your heart rate stays up for hours post workout. When your heart rate is up, you're burning calories. This type of exercise is becoming popular for those of us that have busy lives (myself included). Also, it's just plain FUN! It's hard to get bored when your workout is constantly changing.
I have blogged about HIIT before. I'm a believer. It's what I teach my clients. Let's face it....we are all busy. And knowing that you can get a valuable and effective workout in, in 30 minutes or less.....well....I mean seriously....it sells itself! And like I said, it is anything but dull!
That's all I have for today. I encourage you to study up on the benefits of HIIT and give it a try. You won't be sorry!