Valery Bystritskii, 10, gets a fellow student into a lock at Bunny's Gym in July 2015 in Winchester, Tennessee. (Photo by Mike Saliba/Barcroft USA)

An officer of the Afghan border police throws an assault rifle to a policeman participating in a military exercise on the outskirts of Herat, Afghanistan, Monday, September 7, 2015. Twelve female and seventy male border police personnel participated in the military exercise near the border with Iran in Herat province. (Photo by Hoshang Hashimi/AP Photo)

A U.S. army soldier exercises in front of a M270A1 multiple launch rocket system as they prepare for a live-fire training exercise of the 6-37th Field Artillery Regiment at a training area near the demilitarized zone separating the two Koreas, in Cheorwon, South Korea, March 9, 2016. (Photo by Kim Hong-Ji/Reuters)

A man exercises in the early morning on a hilltop overlooking Kabul, Afghanistan March 3, 2016. (Photo by Mohammad Ismail/Reuters)

79 year old Constance Ngubane spars in the ring as she takes part in a “Boxing Gogos” (Grannies) training session hosted by the A Team Gym in Cosmo City in Johannesburg on September 19, 2017. The grandmothers, many of whom are over 70 have been training with coach Claude Maphosa and claim that they no longer suffer from the ailments they had before, and are stronger than ever. The grannies travel from all over Cosmo City for the twice weekly sessions. Coach Maphosa is in the process of planning events in other areas for grannies who have been inspired by the story, to join in. (Photo by Gulshan Khan/AFP Photo)

In this January 11, 2018 photo, a skater jumps a ramp during the inauguration of a new recreational space for skateboarders, created in an abandoned gym at the Educational complex Ciudad Libertad, a former military barracks that the late Fidel Castro turned into a school complex after the revolution in Havana, Cuba. Foreign skateboard enthusiasts supply their Cuban counterparts with boards and other equipment. (Photo by Ramon Espinosa/AP Photo)

A woman, covered in mud, dances during the traditional “Bloco da Lama” or “Mud Block” carnival party, in Paraty, Brazil, Saturday, February 14, 2015. Revelers in the seaside colonial town threw themselves into deposits of black, mineral-rich slime, emerging covered head-to-toe in the sludge. Bikinis and trunks disappeared beneath the mud, which highlights both gym-pumped pectorals and beer-fed guts. (Photo by Leo Correa/AP Photo)

Muay Thai boxer Nong Rose Baan Charoensuk, who is transgender, trains at a gym in Buriram province, Thailand, July 3, 2017. Born Somros Polchareon, Rose said she identified as a woman at an early age and began wearing makeup and a sports bra in the ring.(Photo by Athit Perawongmetha/Reuters)