A single man with a microphone stands among hundreds of jittery competitors with the Start sign looming overhead. They form a tight circle around him and fall silent awaiting final instruction. Click here to see the Full Slideshow for 10 Fitness Challenges that could KILL you "Tough Mudder is not a race, but a challenge. You will put teamwork and camaraderie before your course time," the speakers boom. "You will help your fellow mudders complete the course. " A collective "Hoo-rah" comes from the anxious crowd. "You will overcome all fears." Tough Mudder is a 10-12 mile obstacle race and
