[quote=@Dazsos]
I don't see any use arguing your point beyond saying... no, you're wrong... running does require both feet frequently be lifted off the ground. [i]Try it for yourself.[/i]  
[/quote]

As a cross-country runner, I can attest that it actually doesn't.  It's perfectly possible to run with one foot always on the ground... just not very fast.  You're half right, in that [i]quick[/i] running does require airtime.  Here's an example of proper sprinting form for reference:

https://www.youtube.com/watch?v=PH-3cHxXAK0