My understanding it is the duration of the flash that will freeze the subject, the 1/160th exposure helps the background be lighter, a shorter exposure might make the back ground very dark, great if you really want the subject to pop, not so great if you want to show them in context.
I'm sure someone will correct me now I have put my lack of knowledge out there!
Edit, put right the exposure speed, which I miss read from 1/60 to 1/160 which probably makes the rest of my post nonsense
A kid asked me this: "I've been shooting with my 6d;70-200;and 580exii. My problem is how do I capture them running,dunking, etc if i can only set my shutter to 1/160 using my flash???!!"
What do I tell him? Pls help, he thinks I am a cool photographer but I really do not know how this works. I would love to help him and learn. THX.