Participants stretch their bodies as they pose for pictures before the Beijing International Marathon in Beijing, China, September 20, 2015. About 30,000 runners participated in the annual running event. (Photo by Kim Kyung-Hoon/Reuters)

A participant sets off on a penny-farthing bicycle at the start of the The Tweed Run in central London, Britain, May 14, 2016. The Tweed Run, a very British public bicycle ride through London's streets, with a prerequisite that participants are dressed in their best tweed cycling attire. (Photo by Hannah McKay/Reuters)

This picture taken on January 25, 2015 shows a participant taking part in an ice water challenge in Zhangjiajie, central China's Hunan province. Participants were required to stay in an ice pond, holding an ice block while eating ice-cream with an electric fan blowing at them. (Photo by AFP Photo/Stringer)

Four men dressed as zombies participate in a Zombie Walk procession in the streets of Paris October 12, 2013. (Photo by Benoit Tessier/Reuters)

A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)

A participant smiles at the annual Christopher Street Day parade on Kurfuerstendamm in Berlin, Germany, June 27, 2015. (Photo by Fabrizio Bensch/Reuters)

Participants pose for a photographers during the Miss Iraq Pageant in Baghdad, December 19, 2015. (Photo by Ahmed Saad/Reuters)

Participants take part in a New Year's Jump into the Sea in Portoroz , Slovenia, January 1, 2016. (Photo by Srdjan Zivulovic/Reuters)