Modern tennis also uses an open stance: rather than face the side of the court to hit a forehand shot, players stay facing forward. That allows for the faster shots that the game now demands, says Rafael Bahamonde, professor of kinesiology at Indiana University. The older, closed stance meant that players hit forehand shots from the shoulder. But the open stance pulls in the elbow and wrist, as well. “The shoulder is a bigger joint, and can withstand bigger forces,” he says. “When you start using your wrist to flip the racket, you’re using a joint that isn’t as strong.” Shoulder injuries used to be more prevalent in tennis players, Bahamonde says, but the changing shots led to more wrist and elbow problems.