By Stephanie Apstein As the Beijing Games carry on through frigid temperatures and frosty conditions, athletes reveal the cold, hard truth about competing in a polar climate. BEIJING — Sometimes, when Summer Britcher is waiting at the top of the luge track, hands ready to grip the handles and explode at speeds north of 70 miles per hour, body tensed, mind focused on steering the ideal course, she pauses and allows herself to feel excited—and not just about the race. “I’m like, man, in 45 more seconds I’m gonna be warm,” she says. “As soon as I pull off, I can’t feel the cold, right? When you’r…