[user104658]

Can't really say if it's sexist without knowing their attitudes towards male sports stars. Males are occasionally jokingly asked to flex their biceps / show off a six-pack in these sorts of interviews sooo... no, not really sexist. Is it slightly inappropriate for them to be trivialised into something purely aesthetic when they obviously put a lot of effort into being good at their sport, and not "looking good for the cameras"...? Yes, maybe slightly inappropriate, both for the flexing men and the twirling girls.

HOWEVER, the words "mountain", "mole" and "hill" spring to mind. And to play devil's advocate... there's clearly a reason that the female tennis stars wear tight dresses instead of the shorts / t-shirt combo that most of the male tennis stars rock up in, and it isn't because it improves their sporting ability. Otherwise the men would be wearing slinky little dresses, too.