NEW YORK (AP) - First lady Michelle Obama says she hopes to still be playing tennis when she’s 90.

Obama visited the U.S. Open for the first time Friday to promote her campaign against childhood obesity and praise the U.S. Tennis Association’s initiative to build kid-sized courts.

Obama played doubles against Serena Williams, clocked 55 mph on her serve and even did some hula-hooping after speaking to a group of local children about the importance of exercise.

Obama was joined by former and current players Billie Jean King, John McEnroe, James Blake and Katrina Adams at Flushing Meadows before two men’s quarterfinal matches.

Obama says she didn’t get into tennis until after law school because there were few courts where she grew up in Chicago.

(Copyright 2011 by The Associated Press. All Rights Reserved.)