# Twelve taikonauts developed noisier motor timing in orbit even when the task minimized gravity, pointing to sleep loss, confinement and workload instead

> Twelve taikonauts became less consistent at keeping a steady finger-tapping rhythm while living aboard the China Space Station. Their fingers could still make each tap normally, yet the internal timing signal used to continue the rhythm grew less reliable during missions lasting...

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Published: 2026-08-21T07:50:02+00:00
Categories: Explainer, Space

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Twelve taikonauts became less consistent at keeping a steady finger-tapping rhythm while living aboard the China Space Station. Their fingers could still make each tap normally, yet the internal timing signal used to continue the rhythm grew less reliable during missions lasting three to six months.

A [study](https://www.nature.com/articles/s41526-024-00439-8) published in **npj Microgravity** traced the change mainly to greater variation in movement planning. The researchers described this variation as central noise, a measure of how much the brain's timing signal shifts from one movement to the next.

The findings suggest that sleep disruption, heavy workloads and other pressures of orbital life can influence basic motor control. "Our study provides evidence that nonspecific stressors can profoundly affect motor performance during spaceflight," the paper's abstract states. The experiment cannot identify one stressor as the cause, although its design reduced many direct effects of weightlessness.

## The 12-taikonaut timing test

The research involved **12 taikonauts**, the term commonly used for Chinese astronauts. They served on the first four crewed missions to the **China Space Station**. The group was unusually large for an in-flight human performance experiment, since access to trained space crews remains extremely limited.

Each participant completed the task during two sessions before launch, two or three sessions in orbit and two sessions after returning to Earth. An age-matched and gender-matched control group performed the same tests on the ground. The control group helped the researchers separate spaceflight-related changes from the practice people gain by repeating a task.

The [research team](https://pubmed.ncbi.nlm.nih.gov/39567559/) included Yu Tian and colleagues at the China Astronaut Research and Training Center, along with researchers connected with [Peking University](https://english.pku.edu.cn/). The paper was published on November 21, 2024.

During each trial, a taikonaut listened to a metronome and tapped a key 20 times in step with its beat. The sound then stopped and the participant continued tapping 30 more times from memory. Trials used intervals of 360, 460 and 610 milliseconds, allowing the team to examine several tapping speeds.

## Why finger tapping isolates brain control

Weightlessness changes many parts of human movement. Signals from the inner ear no longer describe the pull of gravity in the familiar way. Muscles carry less body weight, while information from joints and limbs can feel different. Astronauts must adjust how they judge position, force and motion.

A large arm movement could therefore become slower or less accurate for several reasons. Changes in balance, vision and limb position could all affect the result. A tiny finger movement places much lower demands on those systems, especially when the finger only needs to press a lightweight key.

The **synchronization-continuation task** also separates two forms of timing. During synchronization, the metronome supplies a fresh signal for every tap. During continuation, the participant must remember the pace and produce it without an outside guide.

The taikonauts stayed closely aligned with the metronome, with an average timing error of less than five milliseconds during synchronization. Their main difficulty appeared after the pacing sound ended. The gaps between self-timed taps became more variable in orbit, even though the average tapping interval remained close to the target.

## Central timing noise rose in orbit

The researchers used a mathematical tool called the **Wing-Kristofferson model** to study the uneven tapping. The model divides timing variation into two estimated sources. Central noise describes changes in the internal signal that plans when an action should occur. Motor noise describes variation introduced as the muscles carry out that action.

According to the [model analysis](https://pmc.ncbi.nlm.nih.gov/articles/PMC11579370/), the increase during spaceflight came mainly from **central timing noise**. The effect was strongest while the taikonauts tried to maintain a remembered rhythm without hearing the metronome.

Longer tapping intervals naturally produced more central variation, as earlier timing studies would predict. Spaceflight raised that variation further. Statistical comparisons found significantly higher central noise in orbit than before launch and after landing.

Central noise is a mathematical estimate rather than a direct recording of individual brain cells. Even so, it provides a way to separate uncertainty in action planning from small errors made by the moving finger. The pattern suggests that orbital life affected the internal control of timing more strongly than the physical tap.

## Motor execution remained stable

The estimate for **motor execution** showed no significant change across the preflight, in-flight and postflight phases. Target tapping speed also produced no clear effect on motor noise. The fingers appeared capable of carrying out each simple press with the same basic consistency.

Stable motor noise supports the researchers' decision to use a light finger-tapping task. A movement involving the whole arm, balance or precise hand guidance would be more exposed to the physical effects of microgravity. Finger tapping reduced those demands and gave the team a clearer view of internal timing.

The result also helps explain why performance with the metronome remained accurate. An outside beat supplied immediate guidance, so the taikonauts could correct each tap as the task continued. Self-paced tapping relied on memory and sustained concentration for periods lasting about 11 to 18 seconds, depending on the chosen rhythm and individual performance.

Spaceflight therefore appears to have affected actions that depend heavily on an internal plan. Tasks supported by frequent sound, sight or touch signals may remain steadier because astronauts receive repeated information about when and how to respond.

## Timing recovered after landing

Higher timing variation was already present when testing began about **four weeks after launch**. The researchers reported no clear improvement during the later in-flight sessions, suggesting that the effect continued after the crew had spent months adapting to weightlessness.

Performance eventually returned to its preflight level around four weeks after landing. The ground control group showed no matching rise and fall, which supports an association with the spaceflight environment rather than repeated exposure to the test.

Recovery after landing suggests that the central timing change was reversible in this group. The experiment did not establish whether every astronaut would recover at the same rate, especially after a longer mission or a journey beyond low Earth orbit.

The timing of the tests also leaves an important gap. Critical onboard duties prevented data collection during the first week of flight, when crews often face intense adaptation demands. The researchers suggested that the effect might have been larger during this early period, although measurements will be needed to test that possibility.

## How spaceflight stress affects attention

Life in orbit places pressure on mental resources. Crew members follow crowded schedules and carry out demanding technical work. Sleep can be disrupted, while confinement and limited privacy continue throughout the mission. Changes in daily light cycles can also interfere with the body's internal clock.

The researchers propose that such conditions increase cognitive strain and reduce the attention available for self-directed movement. The continuation phase required **attention and working memory** because each taikonaut had to hold the tempo in mind while producing a long series of taps.

Similar timing tasks have linked central noise with brain systems involved in attention and planning. People must remember an interval, decide when it has passed and send a movement command at the chosen moment. Small shifts at any stage can widen the gaps between taps.

The study design supports a broad stressor explanation, although it cannot measure the separate contribution of workload, fatigue or disrupted sleep. Direct measurements of these conditions alongside repeated motor tests could help future researchers identify which pressures have the strongest relationship with timing.

## Risks for lunar and Mars crews

Future **long-duration missions** will require crews to maintain careful control while operating equipment and responding to changing conditions. Many spacecraft tasks depend on a sequence of well-timed actions, especially when a person must work from memory or continue without constant guidance.

A simple tapping test does not reproduce the full demands of piloting, robotic operations or emergency repairs. It can still reveal a basic change in the way people organize movement over time. Larger timing variation could become more important when a complex task offers little room for delay or uneven action.

External cues may offer one practical form of support. Audio signals, visual prompts and carefully designed control feedback can help guide action when internal timing becomes less steady. Mission planners could also place the most demanding manual tasks at times when crew members are rested and workload is lower.

The researchers argue that **preflight training** should prepare crews to cope with the challenging working environment of space. Training could include sustained-attention exercises and practice under high workload, while onboard monitoring could reveal when an astronaut's timing begins to vary.

## Study limits and future tests

The participation of 12 space travelers gives the study more statistical strength than earlier orbital motor-timing experiments involving only two or three people. Even so, **small sample size** remains a central limit in astronaut research. Individual differences can carry substantial weight when every participant represents a large share of the group.

The model also infers central and motor noise from tapping patterns. Brain imaging and other direct neural measurements were outside the scope of the experiment. Future studies could combine timing tests with measures of sleep, workload and alertness to examine how changes in daily conditions track performance.

Researchers could also test astronauts during the first days after launch and at shorter intervals after landing. Such measurements would show how quickly the timing change begins, whether crews adapt during very long missions and how recovery progresses once normal gravity returns.

More complex tasks may reveal where the effect becomes operationally important. Experiments involving tool use, remote controls or coordinated hand movements could compare actions guided by continuous feedback with actions performed from memory. Results from lunar crews would add another gravity level, while eventual Mars missions would test human timing during far longer periods away from Earth. Broader mission context is available from [NASA's Human Research Program](https://www.nasa.gov/hrp/).