Sentence:  In athletics, triple jumper Ashia Hansen advises a thong for training because, while knickers <WSD>ride</WSD> up, ‘thongs have nowhere left to go': but in Beijing Britain's best are likely, she says, to forgo knickers altogether, preferring to go commando for their country under their GB kit. 
Meaning of the word marked with <WSD> tags:  Of clothing: to gradually move (up) and crease; to ruckle. (from 19th c.)