Astronaut Joe Acaba foreground assisted crewmates before they began a spacewalk.

Astronaut Joe Acaba (foreground) assisted crewmates Randy Bresnik (top right) and Mark Vande Hei (rear) before they began a spacewalk on Oct. 10. Bresnik and Vande Hei were performing the In-Suit Light Exercise protocol where the astronauts perform light exercise and pre-breathe pure oxygen before beginning a spacewalk. The technique helps purge nitrogen bubbles from their bodies to prevent them from experiencing “the bends” at the lower pressure inside the space suit.