Gravitationally Challenged Meaning

Example : 1996, Diane Ketcham, "Long Island Journal," New York Times, 3 March (retrieved 29 Aug. 2010):  [T]he chunky Mr. Ackerman took to the stage. First he told fat jokes. . . . "I'm not fat. I'm gravitationally challenged."2002, Tania Kindersley, "A job for nanny," spectator.co.uk, 6 July (retrieved 29 Aug. 2010):  In America fat is the new f-word—instead, it's nutritionally endowed, or person of mass, or gravitationally challenged.2003, Leonard Klady, "MCM Review: Johnny English ," Movie City News, 18 July (retrieved 29 Aug. 2010):  Consider that the person asking is Mr. Bean, the diminutive, awkward, gravitationally challenged, accident-prone incarnation served up by Rowan Atkinson.