Testing prosthesis fit in simulated microgravity

John McFall, a former Paralympic athlete and orthopaedic surgeon, was selected as the first member of the European Space Agency's Astronaut Reserve with a physical disability in 2022. His selection marked a historic step in ESA’s Fly! initiative, which explores whether a professional astronaut with a physical disability could join a long-duration mission to the International Space Station as a fully integrated crew member. 

The Feasibility Study phase of Fly! examines the challenges related to John’s lower limb amputation and aims to develop solutions for spaceflight adaptation, fitness, and prosthetic technology in microgravity. As part of this study, John took part in a fluid shift investigation at :envihab, a specialised research facility at the German Aerospace Agency’s (DLR) Institute of Aerospace Medicine.  

In microgravity, body fluids shift headward, causing astronauts to experience a 5-10% reduction in lower leg volume within the first few hours in space — a change that persists throughout the mission. The study investigated similar volume shifts in an amputated limb and their potential impact on prosthesis fit and comfort during spaceflight.  

To simulate the effects of microgravity, John first underwent tilt-table testing, transitioning from a 70° head-up position to a -20° head-down position, while 3D modelling cameras measured any volume changes in his stump. John performed moderate-intensity cycling in a -6° head-down position to assess how fluid shifts during exercise might influence the fit of his prosthesis.  

Exercise in space is critical as it helps counteract the physiological changes caused by microgravity. Fluid redistribution and muscle atrophy can affect prosthetic fit and comfort. The test aimed to determine whether adjustments—such as extra socks or a modified socket— would be necessary for future missions. The results showed that no adjustments were required. 

Fly! represents ESA’s commitment to increasing diversity in human spaceflight, expanding its astronaut talent pool, and pushing the boundaries of accessibility in space exploration. John’s expertise and direct involvement provide invaluable insights as ESA works towards making space missions accessible for all.