Skeleton involves a person riding a small sled down a frozen track while lying face down. The sport is a more intense form of luge because skeleton competitors leap onto the sled and slide downhill head first. Skeleton athletes can reach up to 80 mph on straightaways, causing forces up to 5g, so the helmet is a critical component for attitude as well as safety.

A mass pillow fight in Trafalgar Square in central London on April 5, 2014 on International Pillow Fight Day. (Photo by Jane Scanlan)

The competition, which is run by the Royal Observatory Greenwich in association with BBC Sky at Night Magazine, is now in its sixth year and has received over 2,500 entries. Photo: Centre of the Heart Nebula by Ivan Eder (Hungary). Situated 7500 light years away in the “W”-shaped constellation of Cassiopeia, the Heart Nebula is a vast region of glowing gas, energized by a cluster of young stars at its centre. The image depicts the central region, where dust clouds are being eroded and moulded into rugged shapes by the searing cosmic radiation. (Photo by Ivan Eder)

ESA astronaut Samantha Cristoforetti on the International Space Station 3 February 2015 during her Futura mission. Samantha is living and working on the Station as part of the Expedition 42 crew. Picture released on February 10, 2015. (Photo by ESA/NASA)

In this photo taken Saturday, February 14, 2015, Benjamin Miller, 20, from Georgia, in the US, is gored by a bull during the “Carnaval del Toro” in Ciudad Rodrigo, Spain. An American youth is recovering in the intensive-care unit of a hospital in western Salamanca after being savagely gored during a bullfighting festival celebrating Carnival, officials said Sunday. Surgeon Enrique Crespo said he was called to operate on 20-year-old Benjamin Miller from Georgia, who had been gored and tossed by a large fighting bull on Saturday, the first day of nearby Ciudad Rodrigo's “Carnaval del Toro”. (Photo by Jose Vicente/AP Photo)

Polar bear twins make their first public appearance with their mother “Freedom” at Ouwehands Zoo Rhenen, in Rhenen, The Netherlands, 19 February 2015. The twins, who were born in November 2014, have not been named because their gender has not yet been determined. (Photo by Bart Maat/EPA)

A eunuch dances during a rally to mark the congregation of thousands of eunuchs from different parts of India, in Jammu, India, Friday, March 13, 2015. The term eunuchs is used in India to describe transvestites, transsexuals and others who identify themselves as neither male nor female but as a member of a third gender. They traditionally survive by begging, dancing at weddings or blessing newborn babies and are frequently subjected to discrimination. (Photo by Channi Anand/AP Photo)

A group of students sit on top of a bus at Kemusu street in Boyolali, Central Java of Indonesia, March 20, 2015 in this picture taken by Antara Foto. (Photo by Yusuf Nugroho/Reuters/Antara Foto)