Each year, thousands of competitors pit themselves against the elements, extremes of geography and their own psyches to take part in the world's hardest physical challenges. From the cold of the highest peaks to the unforgiving heat of the desert, by water, bike or foot seemingly ordinary people are undertaking extraordinary feats. Are You Tough Enough? looks at over 70 of the most extreme marathons, triathlons, bike rides and other iconic endurance...