This excerise has a rare combination of core stability and dynamics.
The one leg stand with the barbell this is difficult on its own, tilt the trunk over very slowly with the free leg always inline with the trunk and the hips level, keep the tors pointing downward. With this exercise it is okay to bent the support leg a little.
The swing-forward-lunge. This exercise is best when you slowly tilt forward. Once your body feels it is falling over the tripping reflex kicks in, rushing your free leg forward. Concentrate on pushing your hips forward, the leg will follow.
The lunge is best when it's snappy, it will create that impact we are looking for in running. The high platform will keep your hamstrings save.