Today we are not looking at the fat burning benefits of sprinting, but rather comparing the mechanics between sprinting and long distance running. It is not only a question of stride frequency and power output.
Running and Rolling
Generally a good running technique is characterized by a fluent movement where no body part is pulling the breaks. By consciously thinking about specific technique corrections, such as lifting the knees higher, most people would unintentionally force the body to an unnatural movement and each step would most likely land in front of the body's center point of gravity.
The natural forward motion can be maintained by staying relaxed and allowing only the directly engaged muscles to do the work. You can see most professional track and field athletes letting their legs circle way beyond the finish line as they try to avoid breaking their speed pattern abruptly.
Sprint Like a Horse
Races up to 400m are categorized as sprints and they all start from starting blocks. What sets these disciplines apart from longer races is also the running style. Instead of effortless forward rolling, the emphasis leans more towards the violent foot strike and the bounding like stride-cycle. The motion of the feet can be compared to digging sand with your hands. Maybe an even more accurate comparison would be a race horse. The hoofs of a race horse do not move in a bicycle type of circle. (This is also a reason why most track and field coaches would advise not to ride too much bicycles as it could interfere with the pattern of your stride-cycle.) The harder the feet hit the ground in a sprint, the faster you go.
The most obvious difference between sprinting and regular running is how high the knees are lifted in front of the body. But to encourage a young athlete to 'lift-the-knees' will in most cases lead to the young athlete dropping their hip. Instead, I suggest to encourage the runner to lift the recovering heel faster, higher and straight up. I find that this cue allows you to easily switch from regular running to sprinting.
Part II of this article can be found here