# Ten private astronauts returned from flights lasting four to 21 days with measurable trouble standing, walking and turning around obstacles

> Ten astronauts who spent between 4 and 21 days in space showed movement problems within hours of returning to Earth. Balance suffered, turns became slower and heel-to-toe walking grew less accurate, raising concerns about how crews would move during the first critical...

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Published: 2026-08-21T09:55:02+00:00
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Ten astronauts who spent between 4 and 21 days in space showed movement problems within hours of returning to Earth. Balance suffered, turns became slower and heel-to-toe walking grew less accurate, raising concerns about how crews would move during the first critical period after landing.

The findings come from a [2025 study](https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2025.1677377/full) in **Frontiers in Physiology** by Gilles Clément and colleagues. Researchers tested astronauts before flight and about 3.6 hours after landing, then compared their results with those of 36 astronauts returning from missions lasting several months.

The short-flight group recovered enough control to perform better than the long-flight group on every movement test after landing. Even so, the results show that **short-duration spaceflight** can interfere with skills needed to leave a spacecraft, avoid obstacles and move safely during an emergency.

## A few days in orbit can disrupt movement

Human balance depends on signals from the eyes, inner ears, muscles and joints. The brain blends those signals to estimate which way the body is moving and where the ground lies. In orbit, the usual pull of gravity fades, so the brain begins using a different mix of information.

When an astronaut returns to Earth, gravity suddenly becomes a strong guide again. The brain must adjust its control of posture and movement, while the legs must support full body weight. During the early hours of that process, an astronaut may feel unsteady or sick and may need extra time to stand.

Researchers call this process readaptation. The study focused on **sensorimotor control**, which describes how the brain receives sensory information and uses it to guide movement. Short missions produced smaller changes than long missions, yet several balance and walking measures still declined after flight.

## Three tests reveal the postflight changes

The researchers selected tasks that resemble basic movements a crew member might need after landing. Participants completed a **sit-to-stand test**, a heel-to-toe balance walk and a short obstacle course that required a 180-degree turn.

During the sit-to-stand task, each astronaut rose from a chair without using their hands and tried to remain still for 10 seconds. A motion sensor attached to the trunk measured how long it took the person to reach a stable standing posture.

The **walk-and-turn test** required participants to approach a cone four meters away, step over a 30-centimeter obstacle, circle the cone and return to the chair. Researchers measured the total completion time and the speed of the turn. Nine short-flight astronauts and 25 long-flight astronauts completed this test because it was added later in the project.

Cameras recorded each trial, while body-worn sensors captured trunk movement. The paper said, "The novelty of our study is the demonstration of a significant decline in walking and obstacle-avoidance performance within 3 - 4 h of landing."

## Walking without clear visual cues becomes harder

For the **tandem walk**, astronauts took 10 steps while placing each foot directly in front of the other. They crossed their arms over their chests and completed trials with their eyes open and closed. A pressure-sensitive walkway or trained video reviewers counted the correct steps.

Before flight, the short-duration group completed nearly every eyes-open step correctly. After landing, the median fell to about 70 percent. The long-duration group dropped from a perfect preflight median to about 38 percent after landing.

Closing the eyes made the task more demanding because visual information could no longer help the brain correct each step. After the short flights, the median correct score was about 33 percent. Astronauts returning from long missions recorded a median of roughly 4 percent.

The eyes-closed results point to the importance of the **vestibular system**, the balance organs inside the inner ear. They sense head motion and the direction of gravity. Once vision is removed, the brain relies more heavily on those inner-ear signals and on information from muscles and joints.

## Long missions cause deeper performance losses

Mission length was linked with the size of the decline. Short-flight astronauts took a median of 2.62 seconds to stabilize after standing, compared with 2.02 seconds before flight. The change in this group fell short of the study's threshold for statistical significance.

Astronauts returning from long missions needed a median of 4.24 seconds after landing, more than twice their preflight time of 1.89 seconds. Four people in the long-duration group could not complete some or all of the tasks because of motion sickness, difficulty standing or limits imposed by recovery operations.

The obstacle course produced another clear separation. The short-flight group completed it in a median of 13.51 seconds after landing. The long-flight group needed 25.02 seconds. Their median speed around the cone also fell to about 46 degrees per second, while the short-flight group turned at about 85 degrees per second.

Long stays in microgravity can bring greater losses in muscle and bone, along with stronger changes in movement control. ISS astronauts exercise regularly to limit physical decline, yet the findings suggest that current programs may leave gaps in immediate post-landing performance. Publication details and the study abstract are also available through its [PubMed record](https://pubmed.ncbi.nlm.nih.gov/41089561/).

## Why gravity feels unfamiliar after landing

The inner ear contains small organs that normally detect straight-line motion and the pull of gravity. In orbit, gravity no longer provides the steady downward signal experienced on Earth. The brain adapts by changing how much weight it gives to information from the inner ear.

After landing, those signals may feel unusually strong or confusing. Earlier research cited by the authors found that astronauts can overestimate their body tilt after spaceflight. Animal studies have also found increased sensitivity in nerves carrying balance information during readaptation to Earth gravity.

Such changes may explain slower turns and unstable walking. Moving around a cone requires the brain to track body rotation, update its sense of direction and guide the feet around an obstacle. Each part of the movement depends on several sensory signals arriving in the proper order.

Crews also reported **terrestrial readaptation motion sickness**. Average ratings were higher and more varied among long-duration astronauts, although the statistical comparison between groups remained uncertain. The full open-access paper is preserved in [PubMed Central](https://pmc.ncbi.nlm.nih.gov/articles/PMC12515966/).

## Emergency exits could become more difficult

Postflight balance problems have direct operational consequences. A crew may need to leave a capsule quickly after landing, especially if smoke, fire, water entry or another hazard develops. Standing from a low seat and stepping over spacecraft hardware can demand many of the same abilities measured in the study.

**Emergency egress** may also occur before recovery teams reach the vehicle. Private astronauts often have less flight experience than career crews and their missions can last only several days. The new results indicate that a brief stay in orbit still creates a period of reduced movement control.

Landing conditions could add further demands. A capsule may settle at an angle or move with ocean waves. Crew members might need to release restraints and follow a narrow path while wearing a pressure suit. Motion sickness could reduce attention and make coordinated movement more difficult.

The study did not test an actual emergency exit. Its tasks served as practical measures of abilities involved in one, including rising, controlled walking and obstacle avoidance. More realistic simulations could help researchers estimate how much time crews need and which movements create the greatest risk.

## Lessons for private flights and Moon missions

Commercial missions are carrying more private astronauts into orbit, making short-flight recovery an important safety issue. The 10-person group included participants from Axiom, Fram2 and Soyuz taxi missions. Eight were first-time space travelers, while two had already completed long ISS missions.

Future lunar crews will face another gravity transition. After traveling through weightlessness, **Artemis astronauts** will need to stand and work in lunar gravity, which is about one-sixth as strong as Earth's. They may have to leave a lander and begin surface operations before their balance systems fully adjust.

A Mars crew would encounter a similar challenge after a much longer journey. Mars gravity is about 38 percent of Earth's and astronauts would need to handle unfamiliar terrain after months of reduced loading on the body. The study tested Earth landings, so applying its results to the Moon or Mars requires care.

NASA's wider effort to collect standard sensorimotor measurements can help mission planners compare flights of different lengths. Information about related NASA-supported work appears in the agency's [research task record](https://taskbook.nasaprs.com/tbp/tbpdf.cfm?id=17653).

## Balance training may support faster recovery

Exercise programs in orbit usually focus on protecting muscles, bones and heart health. The researchers suggest that **balance training** could also help astronauts prepare for the first hours after a gravity change. Training could challenge foot placement and body control while limiting visual information.

Recovery teams may also use early rehabilitation after landing. Guided standing and walking exercises could help the brain reconnect inner-ear signals with information from the legs. Any program would need to account for motion sickness and the large differences seen between individuals.

Other possible tools include wearable devices that provide extra sensory cues. A vibration against the skin, for example, could warn a crew member that the body is leaning. Researchers have studied sensory aids as a way to support posture when the natural balance system provides confusing information.

Medication may reduce nausea, although some motion-sickness drugs can cause sleepiness. Future work could examine drug timing and delivery while pairing treatment with movement training. The goal would be stable performance during the short period when landing operations place heavy demands on the crew.

## Small groups leave important questions open

The short-duration group contained only 10 people and the obstacle test included nine. Results from a sample of that size can reveal strong patterns, while estimates of individual risk remain limited. Larger studies could show how age, mission experience and physical condition influence recovery.

Training also differed between the short-flight participants and professional astronauts assigned to long ISS missions. Two members of the short-flight group had extensive previous experience, which may have helped them prepare for postflight symptoms. Exercise routines during the missions varied as well.

The researchers assigned the worst recorded score to several long-duration astronauts who were physically unable to finish a task. The method helped represent serious impairment in the analysis, although it also added an estimate where a direct measurement was unavailable. No short-flight participant required this treatment.

Testing occurred several hours after landing because recovery locations and operations limited access to the crews. Changes may have been stronger immediately after touchdown, or some people may have begun adapting before the tests. Measurements at several points during the first day would reveal how quickly each skill returns.

Despite those limits, the comparison places short and long missions under the same set of functional tests. The findings show that a few days in orbit can influence movement during a narrow but demanding period, when astronauts must once again trust their feet, their inner ears and the pull of gravity. Broader mission context is available from [NASA's Human Research Program](https://www.nasa.gov/hrp/).