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What if you jogged for about 20-30 mins and then switched over to doing a couple of sprints? Do you think this would be effective or not? I would like to maintain some distance, but at same time also build more leg muscle.

You do not need to run the distance to keep your endurance up. High intensity work will improve endurance better than low intensity work.

Read: http://www.alwyncosgrove.com/Endurance.html

I would suggest ONLY doing the "Sprint Repeats" workout at the end of the article and forget the 20-30 minutes of steady state work, at least for now.

Generally speaking, long duration moderate cardio burns more calories during exercise; HIIT burns more calories after exercise. Each has a place in a cardio training program.
Here is a bit of comparison from the research:

Long duration Moderate: burns a higher proportion of fat to calories during the moderate exercise; other benefits are increasing aerobic capacity and increasing cardio and respiratory endurance. It is the endurance training for your cardio vascular system.

HIIT: burns a higher proportion of fat to calories after cardio exersice (up to 6 hours); other benefits are- gives the largest increase in metabolism, increased cardio and respiratory output; it is the strength training for your cardio vascular system.

After 24 hours, the fat oxidation levels off to normal for both types of exercise. Both types of cardio exercise can lead to the loss of lean body mass; the way to avoid this is to keep your total fitness program balanced and to counter act the loss of lbm through resistance exercises.

Over time, HIIT will decrease fat mass more than straight moderate cardio will. That is over months and months, not weeks.

A balanced cardio training program addresses both goals: that of fat loss and that of strengthening your cardio vascular system.

I alternate the longer moderate with the HIIT. Because HIIT is so demanding, my old body can't tolerate it two days in a row. I save the low intensity stuff for the grocery store and the mall.

Keep working at the HIIT to build up your skill. You will progress and be pleasantly surprised.

I agree that - generally speaking - aerobic training isn't an either/or proposition.

I disagree with northernbelle on the following points:

1) "Both types of cardio exercise can lead to the loss of lean body mass"

True, but HITT will preserve much much much much more lbm.

2) "Over time, HIIT will decrease fat mass more than straight moderate cardio will. That is over months and months, not weeks."

It IS over weeks, and by the end of the month there will definetly be a noticable difference. This difference will become even more noticable over months.
http://www.exrx.net/FatLoss/HIITvsET.html

I do agree that "A balanced cardio training program addresses both goals: that of fat loss and that of strengthening your cardio vascular system."
But we are not talking about addressing both goals. We are talking about: "I would like to maintain some distance, but at same time also build more leg muscle."

For this purpose I believe doing hitt exclusively (+weights) would be more effective.

For this purpose I believe doing hitt exclusively (+weights) would be more effective

How does this sound to you guys?

HIIT twice a week (monday and thursdays)
Longer distance running once a week (Saturday. 5-7 miles)

That's in addition to playing pickup games of ultimate frisbee or football or whatever.

My goal is to lose some fat, while gaining some speed and endurance.