When we picture space travel, we often imagine highly trained astronauts moving gracefully inside a spacecraft. This requires the physical ability to endure launch inside a rocket and to move effectively in zero gravity. Space agencies have long maintained strict fitness standards for astronauts, which can limit who is eligible to fly.
A New Perspective on Astronaut Fitness
Yet, a notable shift is underway that is prompting new questions about what it takes to live and work beyond Earth. An interview published by Live Science introduces us to astronaut John McFall. After losing his right leg above the knee in a motorcycle accident at age nineteen, he went on to become a surgeon and Paralympic sprinter. Now, his involvement with the European Space Agency is prompting researchers to revisit questions about human spaceflight and disability.
McFall takes a very down-to-earth view when asked how his training has been important personally to him. "To me personally, it doesn't make a difference," he shares. "In terms of 'what an achievement for me,' I don't tend to think of it like that."
Surprising Physiological Perks of Weightlessness
Living in microgravity forces the human body to adapt in highly unusual ways, often causing a series of uncomfortable medical challenges for traditional astronauts. In the Live Science interview, McFall explains that in zero gravity, body fluids shift from the lower body toward the torso and head. As a result, increased pressure in the head can make it harder for astronauts to see clearly because of pressure around the optic discs. One possible effect of having an amputated limb is that less fluid may shift upward than in a person with two legs.
When looking closely at these unique physical dynamics, McFall highlights the scientific curiosity surrounding how his body will perform in weightlessness. "It's a good question because we don't actually know. We can hypothesise, but until we actually get into space and conduct some science that's specifically relevant to my disability, we won't know. But there are some theoretical benefits," he explains.
Apart from fluid transfers, being in zero gravity for an extended period of time is generally very hard on human bones. Without the resistance of walking on Earth, the human body begins to break down bone mass and weaken. This leads to increased amounts of calcium that are filtered by the body through the urine and, therefore, greatly increases the likelihood of forming kidney stones when floating around in space. It is possible for astronauts whose bodies have lower levels of calcium in their lower leg bones but still have complete metabolic capabilities in processing calcium to be much less at risk of kidney issues than other astronauts. Researchers are exploring potential benefits and challenges of weightlessness for individuals with disabilities, particularly regarding fluid shifts and bone density.
Redefining Daily Movement and Prosthetic Needs Inside a Spacecraft
Navigating the interior of a space station requires an entirely different set of physical movements compared to walking down a city street. The regular routines of maintaining equipment, organising cargo, and staying anchored while working with your hands are all completely transformed when you are floating. The main question is whether a person needs two lower limbs to stabilise themselves while performing delicate tasks in microgravity. While a prosthesis is necessary on Earth for stability and mobility, its role inside a space station remains an open question that can only be answered during a mission.
McFall raises these exact operational questions when considering day-to-day life aboard a spacecraft. "Again, we don't know," he points out. "The question is, do you really need both your lower limbs to help you stabilise and support yourself whilst your hands are doing tasks?" He further notes, "But in space, we don't know whether it's going to be an advantage or be required for these intravehicular activities. Where I would definitely need to use one is on a long-duration mission where I need to exercise a lot. I use a prosthesis to exercise on Earth, and I would use a prosthesis to exercise in orbit."
Though floating around might not require a traditional mechanical leg at all times, certain critical phases of a space mission leave absolutely no room for compromise. A specialised modular prosthesis may be needed during launch so an astronaut can exit the vehicle on foot in an emergency.
Additionally, staying fit throughout a long space journey demands extreme exercise routines to avoid muscle atrophy, which will necessitate a special prosthetic apparatus that is perfectly fitted to work on board exercise equipment. Through the development of specialised mobility aids for space, researchers may also identify design improvements that could benefit prosthetics on Earth.
