There are mechanisms involved when the body burns fat, not muscle, which are well known about. We tend to feel that much of the problems people have with it are in the execution. What this basically means is that the amount of motivation a person possesses may waiver after some time. An additional point that's a cause for concern is why this has happened. While we know there are many differences among people, and we cannot possibly guess what they all are, we can mention one possibility. Something that many people may do is pick an approach that simply isn't best for them. Yet when they fail in their efforts they might not attempt to find an alternative method. Finding what works best for you and is the best fit is important to your success.
Interval training is one approach to exercise that those who are serious about losing fat can do. A variety of exercises can be used to do this. Just to give some examples of the most popular ones, you could use a stationary or real bike, a jump rope or a treadmill. Fat loss can and will be achieved when doing cardio exercises like long distance running. But long distance approaches won't be best for you if you want to be most effective. We are trying to draw a distinction on the 'most effective' method of losing fat.