The European Space Agency writes to say
◾The applicant must have the normal range of motion and functionality in all joints.
Historically, IMHO, astronauts came from a flight/test-pilot background. Physical fitness may have been mandatory for orbital flight, and for the lunar programme. It may even be necessary for any missions that involve actually landing on a body exhibiting significant gravitational attraction.
NASA and other Space Agencies have similar physical mobility requirements from their astronauts.
Wikipedia writes to say
What began as the selection of military fighter and test pilots in the 1960s, with a considerable focus on physical capability, has evolved into a selection that now selects for aptitude in engineering, sciences, life sciences, and mathematics
Say instead the astronaut is headed to the ISS where she/he is expected to be in free-fall most of the time. A person with a reduced range of motion (I'm specifically of the mind of restricted movement of the lower-limb) might actually be better suited for free-fall - as long as other physical, social, mental health parameters are met. About the only time I imagine full-range of motion in the lower-limb/s might be necessary would be at launch/landing.
I've never been an astronaut, or even close to medicine let alone space-medicine so I may be wrong. Feel free to poke me in the rib if my premise is flawed!
- Do astronauts aboard the International Space Station (ISS) actually use their legs? (Goes without saying they're in Earth orbit since they are aboard the ISS)
- Is the physical fitness requirement that an astronaut prove full-range of mobility in all limbs relevant to astronauts headed to the ISS, or low-gravity bodies such as Phobos/asteroids?