It sounds like you're really wanting to do more of a time lapse type thing. Traditionally, the person moving "normally" must stand still. Then you play back the whole thing back at a faster rate. That is the easiest way to do it. You'll notice in the videos like that the person often looks a little jumpy.
There are other ways to do it, like using After Effects (or something similar) to merge the two videos, but it's an involved process to do it well. Another method is to shoot stills of the person and put those into the video via software, similar the processed used for Bullet Time.