STEVE INSKEEP, Host:
The game they're playing is a game a skill, but the technology matters too. The game we're seeing this week is in many ways different than it used to be, because the equipment has changed.
DAVID GREENE, Host:
Decades ago, tennis legends used heavy wooden rackets. Then they switched to lightweight graphite.
(SOUNDBITE OF A TENNIS VOLLEY)
GREENE: That changed the game and now the game is changing again.
ROMAN PROKES: It's the strings really, more so than the rackets.
INSKEEP: Roman Prokes makes a living stringing tennis rackets for stars like Pete Sampras and Andy Roddick. He says some players are switching from strings made of animal intestines. Many now deliver their power serves with strings of stiff polyester.
(SOUNDBITE OF STRINGING A RACKET)
PROKES: With the polyester strings, it kind of grabs the ball, you almost hold it on the strings, and it generates tremendous spin.
GREENE: Its backers claim polyester puts more spin on the ball. And tennis researcher John Yandell is among those who tried to find out why.
JOHN YANDELL: No one ever saw another human being hit a tennis ball. That event lasts about four milliseconds, which is about 20 times too fast for your eye to register.
GREENE: Yandell used high-speed video cameras to track what happens in those milliseconds. He took a look at Rafael Nadal and his polyester strings.
(SOUNDBITE OF A TENNIS VOLLEY AND GROANS)
GREENE: Tennis writer Joshua Speckman says the ball becomes more lively, because the strings are more lively in those milliseconds.
JOSHUA SPECKMAN: They're moving basically twice as much. They're sliding out of position and snapping back right where they came from before the ball leaves the strings
INSKEEP: The only problem is those stiff strings also tend to give players a sore arm. And not all tennis players have switched over to polyester.
GREENE: Earlier, we mentioned the Williams sisters, among the players at the U.S. Open. They still deliver their powerful serves with traditional strings, apparently finding that natural fiber is still more stylish than polyester.
INSKEEP: Also at the U.S. Open today, Rafael Nadal will take his polyester strings onto the court. He is the defending U.S. Open champion, and faces a match against Andrey Golubev. The top men's seed is Novak Djokovic and he is playing today.
GREENE: And you're listening to MORNING EDITION from NPR News. Transcript provided by NPR, Copyright NPR.