Nicolas Vandenelsken, a 30-year-old Frenchman, is running 100 marathons in as many days to raise awareness of the carbon footprint left by major sporting events. The "eco-adventurer" as he calls himself has already crossed ten regions since he left on 3 September.
"I do to my body what we do to the planet," explained Nicolas Vandenelsken, as he reached Paris on his 84th marathon.
Vandenelsken, who had doctors check his fitness before setting out, said that "with my mental strength and with my training, I am able to get through this".
But he added: "I wouldn't advise anybody to run 100 marathons in 100 days, because I expect to feel the impact of this in my joints in five or 10 years' time."
100 marathons in 100 days
His itinerary of 42.2-kilometre marathons is to resemble a heart when seen on a map of France.
100 cities are staged in 11 regions and 49 French departments. Along the way, Vandenelsken - who is an activist in two organisations dedicated to climate awareness in sport such as Uni-Vert Sport - has met children, non-profit organisations and farmers to alert them to the climate crisis.
On 25 November, he had a meeting in Paris with French Sports Minister Amelie Oudéa-Castera, saying he told her, "Sport is an incredible lever to reach a maximum number of people."
Nicolas Vandenelsken used to work in the sports events sector before leaving everything: "I didn't see any point in working for events that serve to promote brands and encourage over-consumption," explains the eco-adventurer.
But he said his concern went well beyond one major event.
"My aim is to get a law voted," he added.
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