John McFall running on the Altered G Treadmill

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. This marked a significant milestone in ESA’s Fly! initiative, which aims to enable a professional astronaut with a physical disability to join as a fully integrated crew member on a long-duration mission to the International Space Station (ISS). 

With John’s selection, ESA entered the Feasibility Study phase of the Fly! initiative to address challenges associated with John’s specific type of disability (lower limb amputation). 

On Earth, activities like sitting, standing, and walking place stress on the bones in the lower back, hips, and legs, helping to maintain their density and strength as we age. In space, the lack of gravity removes these stresses, causing astronauts' load-bearing bones to weaken much faster than they would on Earth. To counter this, astronauts use a specialised treadmill to simulate weight-bearing exercise in microgravity. 

Amputees use prosthetic blades with specific stiffness for support during running. The Altered G (AlterG) Treadmill, often used for rehabilitation on Earth, mimics weightless conditions and was used in the Fly! Feasibility Study to identify the ideal blade stiffness for running on the ISS treadmill. Future parabolic flight tests will refine the stiffness and range of movement of the prosthetic knee to optimise running in microgravity.