Welcome to WebMD Live's Sports and Fitness Auditorium. Well, let's begin with a little background information. Probably the shoulder and elbow tend to be the most common, due to overuse, because it's a very repetitive sport. Probably the lower back and the knees would be next in line.
Equipment is one factor to look at.
Physical conditioning and preparation, and proper instruction, and good technique. Well, let's begin with equipment. From an upper extremity standpoint, the first thing to look at is the racquet itself. Racquet material can vary tremendously, from graphite to the more high tech material of carbon and titanium. As you move from graphite to carbon and titanium, the racquet stiffness increases.