# Two astronauts spent 17 days in orbit, and spinal changes were still evolving three months later with the direction tied to damage present before launch

> Seventeen days in orbit were followed by measurable changes in the lower backs of two astronauts and several changes were still developing three months after landing. MRI scans showed shifts in spinal disc signals and changes in the muscles that stabilize the...

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Byline: ARGO.net Editorial Team
Published: 2026-08-22T04:00:02+00:00
Categories: Explainer, Space

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Seventeen days in orbit were followed by measurable changes in the lower backs of two astronauts and several changes were still developing three months after landing. MRI scans showed shifts in spinal disc signals and changes in the muscles that stabilize the lumbar spine.

The findings come from a [peer-reviewed study](https://pmc.ncbi.nlm.nih.gov/articles/PMC11930261/) published in the **Journal of Pain Research**. The researchers examined two members of the first private astronaut mission to the International Space Station, using special MRI methods to track water-related signals inside spinal discs and changes in nearby muscles.

The case series is small, so its results remain preliminary. Even so, it offers a close look at how a brief commercial flight may affect people who already have silent signs of spinal wear. Such questions will grow more important as private missions carry older passengers and as national space agencies prepare crews for longer journeys.

## The Ax-1 astronauts and MRI timeline

The two participants flew aboard **Axiom Mission 1**, also known as Ax-1. The mission carried four private astronauts to the International Space Station in April 2022. NASA reported that the crew completed [17 days in space](https://www.nasa.gov/news-release/nasa-updates-coverage-for-axiom-mission-1-departure-from-space-station/) before beginning the trip home.

Researchers studied two male crew members, ages 53 and 64. Both were healthy, with no history of chronic pain or spinal surgery. Their initial scans still revealed common age-related changes, including disc bulges and degeneration of small spinal joints, although the men had no symptoms from those findings before flight.

Each astronaut received an MRI about two weeks before launch. A second scan was taken about two weeks after the mission, followed by another assessment three months later. The schedule allowed the team to compare the spine before flight, during early recovery on Earth and after a longer period under normal gravity.

The Ax-1 mission completed more than 25 experiments aboard the station. Crew members also followed demanding schedules that included about two hours of daily exercise, usually with equipment such as a treadmill or stationary bicycle. NASA later confirmed the safe [Ax-1 splashdown](https://www.nasa.gov/blogs/spacestation/2022/04/25/axiom-mission-1-crew-safely-splashes-down-near-florida/) off Florida on April 25, 2022.

## Microgravity changes how spinal discs hold water

On Earth, body weight regularly presses on the spine. The pressure rises while a person stands and moves, then falls during sleep. Spinal discs lose a small amount of water during the day and draw it back overnight, creating a natural daily cycle.

In **microgravity**, the usual downward load largely disappears. The spine can lengthen, while the soft discs between the vertebrae have more room to absorb water. Their gel-like centers swell and push outward against strong rings of fibrous tissue.

Each disc has a central region called the nucleus pulposus. Water-attracting molecules inside this center help the disc resist pressure and cushion movement. An outer ring, called the annulus fibrosus, limits how far the center can expand. Thin endplates above and below the disc control the movement of water and nutrients between the disc and surrounding tissues.

Extra swelling can stretch the outer ring and may contribute to pain during flight. Loading returns rapidly after landing, placing weight on tissues that have spent days or months in a very different mechanical environment. A [systematic review](https://pmc.ncbi.nlm.nih.gov/articles/PMC11630706/) published in 2024 found that lower back pain is common during and after spaceflight, while weakening lumbar muscles may slow the return of spinal stability.

Astronauts also face an elevated risk of **disc herniation** after returning to gravity. A herniation occurs when disc material pushes through a weakened section of the outer ring. The new case series explored whether the condition of a disc before launch could influence how it reacts to weightlessness.

## Disc signals rose after 17 days in orbit

The researchers used **DIXON water-only MRI** to isolate signals associated with water inside the discs. They also used **T1rho MRI**, an imaging method that is sensitive to molecules called proteoglycans. Proteoglycans help discs attract and retain water.

Axial DIXON images showed a strong postflight signal increase in most lumbar discs. Across the measured levels, the first astronaut had an average increase of about 64 percent. The second astronaut had an increase of about 20 percent.

T1rho scans pointed in the same general direction soon after flight. Signal intensity rose by about 15 percent across the first astronaut's discs and by around 10 percent in the second astronaut. Higher signal strength can indicate changes in hydration and disc chemistry, although MRI signal intensity is an indirect measure rather than a sample of the tissue itself.

The longer-term DIXON results differed between the astronauts. Signals in the first astronaut's discs generally declined by the three-month assessment. Several discs in the second astronaut continued to show rising hydration-related signals, with only the lowest lumbar disc showing a slight loss.

Image quality limited the three-month comparison. The axial DIXON scans from that visit could not support a full numerical analysis and usable T1rho data were also unavailable. The researchers therefore had more complete measurements for the period before flight and shortly after landing than for the final follow-up.

## Baseline degeneration may affect recovery

The second astronaut began the mission with more advanced **baseline degeneration** in the lumbar discs. His discs also showed a longer-lasting rise in hydration-related signals after the flight. The researchers suggest that pre-existing wear may help explain why two people with similar exposure produced different MRI patterns.

A healthy outer ring resists swelling as the disc draws in water. Degeneration can weaken that ring and alter the endplates that control the flow of dissolved material. Under microgravity, a weakened disc may expand more easily because body weight no longer supplies the usual opposing pressure.

Degenerated discs may also contain small cracks and changes in their internal chemistry. Nerve fibers can grow deeper into damaged tissue, which may increase sensitivity when pressure or hydration changes. The combination could help explain why some astronauts experience severe back pain while others report mild or temporary symptoms.

The relationship remains a hypothesis based on two participants. Age, individual anatomy, exercise history, the timing of scans and ordinary daily changes in disc hydration could also affect the results. The team could not schedule every MRI at the same time of day, even though spinal discs naturally gain water overnight and lose some while a person is upright.

Larger studies could test whether degeneration seen before launch predicts swelling, pain, or slower recovery. If the link holds, preflight MRI screening may help doctors explain individual risks to professional astronauts and private passengers.

## Back muscle changes persisted for three months

Spinal discs form only part of the lower back's support system. Deep **paraspinal muscles** run beside the vertebrae and control small movements. Among them, the multifidus helps keep each section of the lumbar spine steady during walking, lifting and changes in posture.

The researchers measured muscle cross-sectional area, which provides an estimate of muscle size. They also examined fatty infiltration, a sign that some working muscle tissue has been replaced or mixed with fat.

The first astronaut showed a small early decrease in the multifidus and erector spinae muscles at the lowest lumbar levels. Muscle size later returned close to its starting level, although fatty infiltration increased across many of the measured locations. The second astronaut showed a clearer reduction in muscle area, along with increased fat in the multifidus.

Earlier research involving longer missions found that weakening of the multifidus was linked with a flatter lumbar curve and reduced movement between spinal segments. The [six-astronaut study](https://pmc.ncbi.nlm.nih.gov/articles/PMC6339989/) suggested that muscle loss can reduce spinal control when crews return to Earth's gravity.

Recovery also varied by muscle and spinal level in the Ax-1 participants. As the study abstract stated, "These changes had not stabilized by the final follow-up at 3 months." Continued changes after landing could mean that **muscle atrophy** and changes in muscle quality follow different recovery schedules.

## Why a two-astronaut study leaves major questions

Two participants cannot represent the wide range of people who may travel to space. The study functions as a detailed case series, allowing researchers to observe each person closely while offering limited power to separate a real biological pattern from normal individual variation.

The astronauts were also older than many career crew members and already had silent degenerative findings. Their results could be especially relevant to commercial travelers, since private passengers may enter space with a wider range of ages and health histories.

Several technical limits narrowed the analysis. Some three-month MRI sequences were missing or lacked the quality needed for measurement. The team relied on MRI and did not use dynamic X-rays or CT scans, which could have provided information about spinal movement and bone structure.

Follow-up ended after three months, while some measurements were still changing. A longer study could reveal whether disc signals eventually return to their starting levels and whether muscle fat declines with training. Researchers also need pain scores and movement tests alongside imaging, because a visible tissue change does not always produce symptoms.

Future projects could scan larger groups at fixed times of day, then follow them for six months or longer. Including astronauts with different degrees of disc degeneration would help scientists test whether preflight spinal condition consistently predicts the response to microgravity.

## What the findings mean for future crews

Moon and Mars crews will spend far longer in reduced gravity than the Ax-1 astronauts. Their spines will also face repeated changes in loading, first during launch, then in weightlessness and later on the surface of another world. A return to Earth would add another major shift.

Exercise equipment aboard the International Space Station helps protect muscles and bones, yet small stabilizing muscles may need more focused work. Training programs could place greater attention on the multifidus and other deep lumbar muscles before launch. In-flight resistance exercises may then help preserve strength, followed by **targeted rehabilitation** after landing.

Preflight imaging could support individual planning if larger studies confirm the link between disc condition and postflight changes. A traveler with advanced degeneration might need a different exercise program, closer medical monitoring, or a fuller discussion of the risk of pain and herniation.

Commercial missions make such planning increasingly relevant. Private astronauts may spend only days in orbit, yet the Ax-1 results suggest that a **17-day spaceflight** can be followed by tissue changes lasting for months. The effect varied sharply between the two people studied, making personal health history a central question for future research.

Protecting the spine will require better measurements before flight and continued monitoring after return. The small Ax-1 study provides an early view of the process, while larger missions and longer follow-up periods will show which changes are temporary and which require active treatment.