There is a saying that eating rice cake while lying down is easy. It suggests that something can be done easily. In Europe, it might change to the phrase ‘making money while lying down.’ If one lies on a water bed in a hospital for ten days, they can receive nearly 8 million won. This is a reward for participating in medical research essential for space exploration, experiencing the bodily changes humans would undergo in outer space here on Earth.

The European Space Agency (ESA) announced on the 13th (local time) that it will conduct a study involving lying on a water bed for 10 days to replicate the effects of space travel on the body. This experiment, named Vivaldi 3, will take place at the MEDES space hospital in Toulouse, France.

A applicant lies on a waterbed while eating at the Médecine Spatiale hospital in Toulouse, France. The waterbed simulates a microgravity environment in space./ESA
A applicant lies on a waterbed while eating at the Médecine Spatiale hospital in Toulouse, France. The waterbed simulates a microgravity environment in space./ESA

◇Experience zero gravity on a water bed

During the experiment, participants will lie in a container similar to a bathtub covered with waterproof material. The container is filled with water, making it akin to a water bed. The ESA explained, ‘Experiment participants float without getting wet, experiencing a sensation similar to what astronauts feel on the International Space Station (ISS), as if they are not physically supported at all.’

The eligibility criteria include male participants aged 20 to 40 years. They must be non-smokers in good health, with a height between 165 and 180 cm, and a BMI (Body Mass Index) between 20 and 26. In Korea, individuals exceeding a BMI of 25, which is considered obese, would be included, but the standards are different in the West. In the United States and Europe, a BMI of 30 is typically the threshold for obesity.

As the name suggests, Vivaldi 3 is the third and final field of the Vivaldi experiment aimed at understanding the effects of zero gravity on the human body. This experiment will be conducted with 10 volunteers. They will be hospitalized for 21 days.

During the first five days, basic medical checks will be conducted, followed by lying on the water bed for the next ten days. The final five days will be for recovery and assessing the body’s condition post-zero gravity. Participants can make phone calls during the experiment but cannot meet outsiders. While the experience may be lonely and tedious, the compensation of 5,000 euros (approximately 7.9 million won) is substantial.

The European Space Agency (ESA) conducts bicycle riding and centrifuge rotation tests by having 12 Namsung individuals lie in bed for two months to respond to changes in the body experienced in a microgravity environment./ESA

◇Astronauts changing like aliens in movies

The Vivaldi experiment was set up to investigate the effects of near-zero gravity on the human body on Earth. According to the ESA, astronauts' bodies change to resemble those of aliens featured in movies after spending extended periods in space.

When standing on Earth, gravity causes blood to flow downward, but in space, where gravity is significantly reduced, blood circulates evenly throughout the body. As a result, more blood accumulates in the head than on Earth, causing astronauts aboard the ISS to always appear to have swollen faces.

Simultaneously, calcium loss from bones averages 1% per month. Proteins also exit the muscles. Astronauts who were aboard the Russian space station ‘Mir’ experienced a 20% reduction in muscle protein after a year. This means that prolonged exposure to space can lead to astronauts' heads swelling while their limbs become slender, resembling characters in movies. The astronauts stationed on the space station exercise desperately for two hours a day, tying ropes to their bodies while running on treadmills to counteract these bodily changes.

In 2023, the ESA also conducted experiments involving cycling while lying down in a rotating device, similar to a centrifuge. In space, reduced gravity prevents blood from pooling in the legs, necessitating forced exercise to facilitate blood flow. During that experiment, participants cycled while spinning in a centrifuge to draw blood toward their legs, effectively doubling the gravity. This experiment recreated the conditions of exercising in zero gravity on Earth.

A woman with a bungee cord is seen running up a wall. While there are circuses that run motorcycles up cylindrical walls, it is impossible for a person. However, if gravity is weak like on the moon, a person can run horizontally on a vertical wall to exercise./University of Milan, Italy

◇Inspired by circus acrobatics

Scientists from the University of Milan discovered a method last year to simulate artificial gravity effects in space. Similar to motorcyclists racing along the inside walls of a cylinder in a circus, astronauts could run along the walls of a cylinder on the moon to achieve a gravity-like effect, as experienced on Earth. The research team, led by Professor Alberto Enrico Minetti at the University of Milan, stated in the international academic journal ‘Royal Society Open Science,’ ‘Individuals settling on the Moon in the future could mitigate health issues caused by weak gravity by merely completing several laps along the inner cylindrical walls each day.’

Professor Minetti’s research team drew inspiration from the circus act known as ‘the wall of death,’ where motorcyclists race along the inside walls of a cylinder. When a motorcycle speeds along the cylindrical wall, inertia forces it against the wall, generating centrifugal force directed outwards. This force causes friction between the wall and the motorcycle tires, preventing slipping.

Humans cannot run fast enough, like motorcyclists, to generate the necessary inertia to counteract Earth’s gravity. However, the research team postulated that in conditions of reduced gravity, humans could theoretically run along the walls like motorcyclists. The University of Milan team conducted experiments under conditions mimicking the weak gravity environment of the moon to demonstrate this possibility.

Scientists believe that experiments simulating zero gravity environments on Earth can benefit not only astronauts but also patients, the elderly, and individuals with musculoskeletal conditions who need to remain in bed. The bodily changes astronauts face in space are analogous to the weakening of muscles and bones experienced by the elderly or patients confined to bed on Earth. The ESA noted, ‘Results obtained in space will help develop better treatments for the elderly and patients with musculoskeletal disorders or osteoporosis.’

References

European Space Agency (2025), https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Extended_space_dive

Royal Society Open Science (2024), DOI: https://doi.org/10.1098/rsos.231906

European Space Agency (2023), https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Around_the_bed_in_60_days