Simulating a weightlessness experiment, lie in bed with your head down and your feet high for 90 days. How long can you last?

If you have to lie down for 24 hours a day, and keep your head down and your feet up, how long can you last? Recently, the 90-day long-term head-down bed rest experiment of astronauts has attracted attention. As a classic physiological experiment simulating weightlessness, participants need to undergo many tests. So, how is this experiment carried out? What is its significance?

Studying long-term weightlessness

As we all know, outer space is a weightless environment. People who live in a gravity environment for a long time may face various physiological and psychological changes once they enter a weightless environment. Relevant data show that weightlessness can lead to bone loss, skeletal muscle atrophy, adverse effects on the vestibular and visual systems of the inner ear, and a series of problems such as decreased sports endurance and standing endurance.

In order to study the adverse effects of weightlessness on the human body and to ensure the health and work efficiency of astronauts, researchers have to spend a lot of energy observing the physiological changes in the human body after weightlessness in order to explore protective measures. The most common weightlessness research is to create weightlessness conditions on an airplane. Normally, an airplane will experience weightlessness when it is doing a parabolic flight, but this can only provide a few tens of seconds of weightlessness, and it is impossible to observe the changes in the human body under weightlessness for a long time. The immersion method of simulating weightlessness, which uses the natural buoyancy of water to offset part of the effect of gravity, can be observed for a long time, but it still cannot avoid the influence of gravity.

In addition to the above two methods, lying in bed with the head down is also a classic method of simulating weightlessness. When the head is down and the feet are up for a long time, the body fluids will move to the head and chest, and the leg muscles and bones will also be affected accordingly. These changes are similar to the changes in the body after weightlessness. Through this experiment, researchers can obtain data on the effects of long-term weightlessness on the human body.

The head-down bed experiment originated in the 1970s, when Soviet astronauts often felt their bodies sliding down while sleeping after returning to Earth after completing their space missions. In order to change this abnormal feeling, they decided to raise the foot of the bed to the level they felt. Researchers found that the physiological changes caused by -6° head-down bed position are closest to the physiological changes caused by weightlessness during space flight. Soon, head-down bed position became a standard experiment for the world's major space powers to study weightlessness.

Volunteers undergo long-term head-down bed rest experiment

Lying down for 90 days to set a new world record

At the beginning of my country's manned space program, it conducted a 7-21-day head-down bed rest experiment for short-term flights. After 2006, in order to further develop subsequent manned space flight, my country has implemented several large-scale experiments with longer periods.

In 2007, my country organized the first 60-day head-down bed rest experiment on the Earth Star No. 1 with the participation of overseas scientific research institutions. All 21 volunteers were male. This experiment systematically studied the changes in the immune function of Chinese volunteers for the first time. Although the experiment cannot completely replicate all the changes in the immune function of astronauts in the outer space environment, it still provides a scientific basis for the protection of weightlessness in future long-term space flights.

From June to July 2009, the China Astronaut Research and Training Center conducted a 30-day head-down bed rest experiment. Researchers also obtained a large amount of data and found that neuromuscular electrical stimulation can slow down the rate of disuse atrophy of lower limb muscles, but it cannot reverse it. After that, my country successively carried out 15-day head-down bed rest experiments for women and 45-day head-down bed rest experiments, and both achieved significant results.

In 2019, the China Astronaut Research and Training Center conducted a 90-day, 36-person head-down bed rest experiment, also known as the "Earth Star 2" experiment. This experiment not only broke the world record for duration and number of participants, but also involved 22 teams. Since the entire experiment is divided into three stages, namely a 15-day pre-bed rest adaptation test period, a 90-day bed rest period, and a 33-day test recovery period after getting up, the actual duration of the experiment is nearly 140 days.

Volunteers in the "Earth Star 2" experiment exercise on a treadmill in the supine position to test their cardiopulmonary function

Lying down experiment is not easy

In the "Earthsat-2" experiment, there were quite a lot of exercises and tests for the volunteers, including orthostatic endurance, cardiopulmonary function, muscle strength, muscle volume and bone density. In order to be more objective and realistic, the 36 volunteers were randomly divided into 5 experimental groups, and the experiment was carried out in batches in bed.

In the 15 days before the experiment, the subjects need to gradually adapt to the head-down bed posture. The subjects are familiar with a series of daily activities such as eating, drinking, showering, urinating and defecating in a -6° head-down posture. All volunteers need to maintain this posture throughout the experiment. For normal people, it is not a particularly easy thing to maintain this posture for a long time, not to mention completing daily activities.

The subjects' running and cycling exercise patterns are completely different from our daily exercise patterns. When lying in bed with their heads down, their posture is completely sideways, the treadmill becomes a vertical treadmill, and the bicycle pedals are rotated 90 degrees. During the experiment, the subjects can measure their daily heart rate, blood pressure, and body temperature and record the data. At the same time, the subjects were also asked to write a diary, and of course the writing was also completed in the head-down bed position.

In the "Earth Star 2" experiment, volunteers rode bicycles in a supine position to test their cardiopulmonary function

The subjects were also taught to control their breathing and standing posture during vertical running, and to control the movement of joints and muscle strength to ensure the effectiveness and safety of the exercise. This experiment paid special attention to psychological support. The researchers designed some games and activities to keep the subjects in a good mental state. To prevent accidents, the researchers also conducted timely and efficient psychological assessments for the subjects. During the experiment, the space hero Yang Liwei also came to the scene to communicate with the subjects. With the support of their idols, they must be very encouraged.

Through this experiment, researchers found that running for 30 minutes a day, four days a week, can help people maintain aerobic endurance after 90 days of head-down bed rest. In addition, it is recommended that other factors that affect bone loss, such as medication and nutritional interventions, should be considered in protective measures.

The era of China's space station has arrived. The astronauts' successful long-term stay in the space station is closely related to the efforts of countless scientific researchers on the ground, in addition to their own efforts. It is their continuous efforts to ensure that the protective measures used by astronauts in orbit are effective and efficient, and to protect the astronauts' long-term stay. (Author: Lin Yinzhi, review expert: Jiang Fan, deputy director of the Science and Technology Committee of China Aerospace Science and Technology Corporation)