Running is the most democratic sport in the world and it has never been more popular. More than half-a-million runners finished a marathon in the US alone last year - compared to just over 100,000 20 years ago.<br /><br />Ultra-marathons in extreme conditions are undergoing huge growth across the globe. But is the age-old sport even good for you?<br /><br />As the billion dollar running industry races forward, Andy Richardson follows the growth and science of pounding the pavement over time, while preparing to run 42km for the first time - at the Antarctic Ice Marathon.
