The south of France is among thousands of places around the world that now stage ultramarathons: extreme running events covering anything above 26.2 miles to more than 100. They often take place on challenging terrain and require considerable physical and mental resilience. And they've become big business.

To find out more, Business Daily went to the Nice Côte d'Azur 100-mile race to speak to runners and organisers about the popularity of these sorts of events, and how they make money.

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Presented and produced by John Laurenson

(Picture: Woman and man running in a forest in the dark. Credit: Getty Images)