NASA astronaut Karen Nyberg, Expedition 36 flight engineer, equipped with a bungee harness, exercises on the Combined Operational Load Bearing External Resistance Treadmill (COLBERT) in the Tranquility node of the International Space Station. Its use is one of the ways astronauts and cosmonauts maintain muscle mass and bone density in a zero-gravity environment.
Astronaut Andrew Feustel reenters the Space Station after completing an 8-hour, 7-minute spacewalk at 10:12 a.m. EDT as NASA space shuttle Endeavour makes its last visit to the International Space Station on May 22, 2011 in space. After 20 years, 25 missions and more than 115 million miles in space, Endeavour is on its final flight to the International Space Station before being retired. (Photo by NASA via Getty Images)