how long does my running stride have to be?

[REG]

I like to jog and I am working towards having great flexibility in my legs for my martial arts kicking. However I am confused as to how long one's running stride, during a middle-to-long distance run, has to be in order to maintain full flexibility in the legs. How do you do it while not overextending the stride and maintaining a good elongated stride during an endurance run? Are you supposed to exaggerate your running gait the whole time as if your doing full splits in the mid-air during each stride? This doesn't seem to make any sense to me. Please help to clarify this for me.