Hello everybody. I'm 21, about 6 feet tall, normally built. I have access to a gym and I play tennis once or twice a week. My problem is that although my groundies are pretty explosive my serve is just wort my grandpa's, especially in terms of speed. My coach says it's not a problem of motion and i think he's right since every coach I've had agrees. He says that it looks like I'm lifting and swinging a 20 lbs racquet. He also says it's strange cause my groundies are fast. I use a head lm prestige midsize but trying with a lighter racquet does not help much. I Don't think it's a raquet problem. I'm asking you if there's a muscular group to develop or any other kind of exercise that can help me develop swing speed specifically on my serve.