Question: What burns more calories: longer low-intensity aerobic workouts or short high intensity sessions?

Answer:

For years those cardio machines have been directing people to the "fat burning zone" by keeping their heart rate lower for longer periods of time. In this time, our nation has gotten fatter and has experienced more overuse injuries than ever!

The truth is, research shows that short, high intensity aerobic exercise burns more calories in less time than low-intensity programs. Here is a classic example: A 154 pound person who runs at a pace of 8 mph will burn 320 calories in 20 minutes (pretty intense!). That same person, walking at 3 mph for an hour will burn only 235 calories.*

For most women running 8 mph is pretty fast, but using interval training can get you there, too. Interval training is where you increase and decrease intensity at specific intervals during your workout. This could be as simple as running for 10 seconds and then walking for a minute, or running as hard as you can between every 10th telephone pole and then jogging the rest of the time.

It is important to understand, however, that high intensity training is not for everyone. Beginners need to first develop a cardio "base" and need to strengthen key muscle groups to avoid injury. It is also important not to perform high intensity sessions everyday. The body needs a recovery period after pushing it to its limit.

An example of a balanced week of training would be:
Monday: High intensity-20-30 minutes
Tuesday: easy cardio
Wednesday: more challenging cardio but still steady pace
Thursday: High intensity workout
Friday: rest
Saturday: steady pace longer workout

Of course it is always recommended that you see your doctor before starting a new exercise program if you've never exercised, are a smoker, are overweight, or have a chronic health condition.

*( from Elizabeth Quinn http://sportsmedicine.about.com/cs/conditioning/a/aa112701a.htm?p=1 )