"Which method burns the most calories and slims legs quickly?

A. Speed walking for 40 minutes.

B. Alternating jogging and speed walking for 3-minutes intervals.

C. Jogging on it's own.

Thank you very much for your advice, I'm a great fan of yours." --jadubb

In general, the more intensity you can add to something, the better results you will get. With that in mind, it depends on what you mean by a jog. Walking a mile in 12 minutes will burn more calories than a 9-minute mile jog. But once you get faster than a 9-minute mile, you will burn more calories running or jogging. Walking and running also use different muscle groups, so alternating is really the best strategy for overall training.

Jeff Galloway, an accomplished runner and trainer, has turned thousands of "normal" runners into marathoners by incorporating something like one of the strategies you outlined. He has them run a mile, then walk a minute to change muscle groups and lessen fatigue. Interval training, where you alternate peak intensity with an easier recovery pace, is one of the best calorie-burning and metabolism-boosting strategies out there. I like to do intervals a couple times per week.

Here is a workout I do on the treadmill that you might want to try. I warm up for about 10 minutes with some light intensity walking and jogging. Then I put the incline to 3% and walk for 2 minutes. Then I elevate it to the 6% grade for 2 minutes, the 9% grade for 2 minutes, the 12% grade 2 minutes and then up to the 15% grade for 2 minutes (if the treadmill I'm using will go that high). Then I go down and climb that hill again. After two climbs, I cool down. Try to get in two high-intensity interval workouts per week, alternating with steady-state workouts -- and remember to have fun!