"Rule number one, do not wear cotton!" Schlachter says. "It does nothing but weigh you down and hold mud and water." Stick to synthetic wicking fabrics instead. That includes underwear: spring for a pair like EMS's Men's Techwick Boxer Briefs ($20) or Women's Techwick Seamless Hipster Bikini ($16), which will draw away moisture.
Call, who's been known to race shirtless, says that he wears "regular running shorts" made of nylon or poly blends. "Any running shorts will do, but preferably without external pockets as they will fill up with water and mud," he says. For vision correction, Call wears contacts instead of glasses, which get dirty too fast in the mud-and-water-filled obstacles