Have you ever wondered, what is the maximum gravity humans can survive? As humankind reaches for the stars and envisages settling planets beyond our own, understanding the potential impacts of varied gravitational conditions becomes a crucial area of research. Recently, scientists delved into the physical constraints imposed by gravity on human functioning. The study, titled “Effects of Exoplanetary Gravity on Human Locomotion Ability” by Nikola Poljak, Dora Klindzic, and Mateo Kruljac, was published in The Physics Teacher’s September 2019 issue. The research considered ultimate limits, including the breaking point of the human skeleton and the maximum gravitational force that human muscles can overcome to lift the body.

## The Human Body’s Breaking Point

In their groundbreaking research, the scientists set out to understand the limitations of the human body under varying gravitational conditions. One area of focus was determining the gravitational threshold at which our skeleton would break under its own weight. Simultaneously, they studied muscle capacity, particularly when it comes to lifting the body from the ground in heightened gravitational conditions.

Their findings suggest that the human body exhibits remarkable resilience and adaptability. According to the research, even under a gravitational pull four times stronger than that of Earth (4G), humans could potentially maintain normal locomotion given adequate and rigorous training.

So, 4G is probably the maximum gravity humans can survive for long durations. However, the higher g loading probably leads to shorter lifetimes.

### Wait, what is the G?

“G” commonly stands for gravity, particularly when discussing the gravitational force on Earth.

In physics, “g” refers to the acceleration due to gravity, which is approximately 9.8 meters per second squared (m/s²) on the surface of the Earth at sea level. This means that, in a vacuum and close to the Earth’s surface, an object will increase its speed by about 9.8 m/s for each second that it’s falling, due to the pull of Earth’s gravity.

Sometimes, the term “G-force” is used to describe the force exerted by gravity or acceleration on a body. When people talk about “1G”, “2G”, “3G”, etc., they’re often referring to multiples of the Earth’s gravitational acceleration. So 1G is the normal force of gravity we feel on Earth, 2G is twice the force of Earth’s gravity, and so forth.

For example, astronauts and fighter pilots might experience several G’s of force during takeoff, which can feel like several times their weight pressing down on them.

## Energetic Expenditure of Walking Under High Gravity

Beyond bone and muscle strength, the scientists investigated the energetic requirements of walking in increased gravity. They developed an innovative model that represents the human leg as an inverted pendulum. This approach offered fresh insights into the energy expenditure involved in locomotion under heightened gravity.

Once again, their findings support the surprising robustness of the human body. According to the new model, humans could potentially adapt to walking even under gravity as high as 4G, although this would require significant physical training and conditioning.

## The Gravity Struggle: Earthly Concerns and Zero Gravity Issues

It’s important to remember that these findings pertain to healthy, trained individuals. For people with existing health conditions, the story may be different. Individuals suffering from knee problems, back pains, obesity, and other health issues may find Earth’s gravity of 1G challenging to manage. Increased gravitational force could exacerbate their discomfort and mobility issues.

Conversely, the absence of gravity brings its own set of problems. Extended periods in zero-gravity (actually microgravity) environments, such as those experienced by astronauts, can lead to muscle atrophy, weakened immunity, bone density loss, and a variety of other health issues.

## Towards an Interplanetary Future

The scientists’ research on the effects of exoplanetary gravity on human locomotion represents a significant step towards understanding the conditions under which humans could live and function on other planets. As we venture further into space, these insights will be invaluable in preparing humans for the challenges that lie ahead and ensuring our survival in new worlds.

Although many hurdles remain, and further research is needed, these early findings indicate that the human body is more capable of adapting to varying gravitational conditions than previously imagined.

## Sources

• Study: Effects of Exoplanetary Gravity on Human Locomotion Ability on pubs.aip.org