Next year, ultra-marathon runner and former Liberal MP Pat Farmer, 48, will attempt to run 21,000 kilometres, from the North Pole to the South, without a day off. He will average 85 kilometres a day, less when he's running on ice, for about 11 months. In the cold, he will drink olive oil to stop himself wasting away. Even so, he will waste, running down even the fat on the soles of his feet.

"You do get to a point where you feel the bones kind of grinding together," he says.

Long distance running can take a toll on the body. Credit:iStock

Popular wisdom says that while running might give you great lungs, it also takes a toll on the body and the more you do it, the higher the toll. Running ultra-marathons - any event over 42.2 kilometres, with no upper limit - must surely, therefore, be madness.

Examples of these gruelling events include the Trans America Footrace, 5100 kilometres over 70 consecutive days; the North Face 100, 100 rugged kilometres run over 24 hours in the Blue Mountains; and the Marathon des Sables, 250 kilometres over seven days through the Sahara Desert. And there's no shortage of people signing up. There has been a five-fold increase in ultra-marathon participation in Australia over the past five years.