Participants cross cold and muddy waters during the Strong Race competition near Tukums May 4, 2014. About 6500 people competed in this extreme running race, which includes cross-country running, elements of agility and power discipline. (Photo by Ints Kalnins/Reuters)

Participants dressed as Santa Claus take part in the Great Edinburgh Santa Run on December 11, 2011 in Edinburgh, Scotland. Around a thousand people took part in the annual fundraising event, with all money raised being donated to the charity “When You Wish Upon a Star”. (Photo by Jeff J. Mitchell/Getty Images)

Israelis participate in a “Zombie Walk” during the Jewish holiday of Purim on March 6, 2012 in Tel Aviv, Israel. The carnival-like Purim holiday is celebrated with parades and costume parties to commemorate the deliverance of the Jewish people from a plot to exterminate them in the ancient Persian empire 2,500 years ago, as described in the Book of Esther. (Photo by Uriel Sinai/Getty Images)

Participants take pictures of themselves as others run past the Tiananmen gate during the Beijing Marathon in Beijing, China, September 17, 2016. (Photo by Damir Sagolj/Reuters)

A participant in the traditional dance of Los Historiantes poses for a photo during festivities in honour of St. Michael the Archangel in San Miguel Tepezontes, El Salvador September 28, 2016. (Photo by Jose Cabezas/Reuters)

Meghan Puhr participates in a virtual realty presentation during an Intel news conference before CES International, Wednesday, January 4, 2017, in Las Vegas. (Photo by John Locher/AP Photo)

A participant wearing Kokoshnik, the Russian traditional headwear, walks out of the water during winter swimming festival in the town of Podolsk, south of Moscow, Russia January 5, 2017. (Photo by Maxim Shemetov/Reuters)

Participants enjoy the “Color Me Run” festival in Hanoi, Vietnam, 28 May 2016. The festival which was inspired by the Holi Festival from India, attracted thousands of teenagers this year. (Photo by Luong Thai Linh/EPA)