Video: Improving Running Performance by Improving Running Mechanics

From video description:
Since runners take 1,000 strides per mile, any small problem in stride mechanics will be amplified 26,200 times during the marathon. A 4" bounce, for instance, results in running 3.3 vertical miles during the race. In this video, we measure their bounce, stride angle, overstride angle, toe lift angle, and crossover angles and compare them to African runners who are more efficient.

For more about the running efficiency read:
Improving Running Performance and Running Mechanics