He can win the US Open but the abdominal strain muscle is Always concerning! How's can Rafa let loose and rip into a serve. Here's my two cents worth. The 4 serves , the kick, the spin, the slice and the flat serve, all which Rafa can hit very good but not enough for him to win free points with a jaded stomach. The serves that are the hardest is the flat ( lowest margin probability) and the kick because it has to hit and move away from the body. These are the serves that win the free points. However, the kick serve required the most strain on the abdominal and lower oblique muscle. If Rafa can't win free points on his serves, he will have to grind 90 percent of his points to win a match which takes a toll on the body as well as the mind .The unknown is how stable is Rafa's stomach muscles..