I'm curious to see if anyone has a theory about this. Now that he can clock them in the 130's that really bodes well for his future. Do you think there are any training techniques that he used to get it that fast. It seems like he has added 20 + miles per hour in the last year. When I saw him play at the U.S.Open I couldn't believe my eyes.
My wife and I were at the US Open in '06 and watched Young's first round match verses Djokovic. In the first set, Young was hitting in the 120s and low 130s on his first serve consistantly, and was placing them well. He won the first set. Then, about midway through the second set, all the wheels came tumbling off. He couldn't buy a first serve, and was hitting everything out. We came away thinking that he needed to get much tougher mentally and physically before he was ready for the top 100.
My point is that DY has been capable of hitting big serves in the 120-130 MPH range for a couple years now. He has excellent technique that maximizes the knee bend and shoulder rotation, allowing him to get huge racquet speed for a relatively short guy. In my opinion, the big improvement he's made over the past year is getting fitter overall and more confident from his results in challengers. As we all watched at the US Open and Pilot Pen this year, he is now able to sustain top 100 level play for more than a set or two, and can now beat players in that range. It's not just his service consistancy that's improved, but his overall strength mentally and physically that allows him to play at a higher caliber for longer periods.