Looks good! Your animations are always so smooth. A little advice though from when I was learning about walk/run cycles, make the head bob up and down a little bit, like when they're being supported by a bent knee their head is lower than if they're being supported by a straight leg. Makes the whole thing look more natural
I really like this run cycle, if I had to make one critique, (mind you I cannot use Flash so super kudos) Is that there is no up/down motion during the running. Otherwise, the pose and actual anatomy of the run cycle is quite excellent and sooo much better than I could ever hope to do.