Has Serena been forced to cover the court at all in any of her matches so far at the US Open? The big story is her invincible serve which is true....but my premise is that if any opponent can catch her on a bad service day or have the capacity to return serve, they stand a chance to execute a counterpunch type strategy....the extended rally, a dink and deep, or keep ball in play and force Serena to run around.....I question her fitness and more than that her "overhang". Eventually, that extra mass on top and bottom has to exact a coefficient of drag type penalty and wear her down....it's that simple. Most of the big "overhang" women (Kivitova, Keys, Townsend, Makarova, Kuznetsova, et al) are long gone....Halep, bless her heart, had the good sense to get rid of the top overhang and look how that step has advanced her performance.