I've actually been doing this for a long time while skipping rope...I used to do martial arts,we used to skip rope as a warm up.Then you'd be skipping rope all winter 'cause its the easiest way to keep in shape during the winter(with all the rain,no fun running outside).We used to do the running in place with the high knee raises as an exercise too.So somewhere I put 1 and 1 together and started doing this while skipping rope(this is at a fairly high pace)for 3 or 4 minutes at a time as a way of interval training I would skip rope and mix it up with that exercise.If you can do that for half an,hour you can can run 7miles easy