Tried the VTZF 4U today. At first, when using it to warm up, the shots are terrible. Mostly three quarter of the court. But after one game, when I ask my friend to hit with me, my shot is back to the court effortlessly. I can feel my smash power but it seems to be weaker. In another words, when I smash with Ti-10 it has more direct kill compare to VTZF. Besides that, I tried a few continuous smash, my arm is a little sore. Does it mean the racket doesn't suit me? Or I need more time to adapt to it? I was using AT700 first gen but then it broke and my friend borrowed his Ti-10 to me for a few months. Can I train my arms to adapt to the racket?