#bodymassunderestimation — Public Fediverse posts
Live and recent posts from across the Fediverse tagged #bodymassunderestimation, aggregated by home.social.
-
DATE: July 30, 2026 at 09:00AM
SOURCE: PSYPOST.ORG** Research quality varies widely from fantastic to small exploratory studies. Please check research methods when conclusions are very important to you. **
-------------------------------------------------TITLE: New space station study reveals a hidden side effect of long-term microgravity on the human brain
A study conducted aboard the China Space Station revealed that astronauts exhibited increased movement durations and altered motion profiles when reaching for a target with their arm, compared to a control group and their own baseline motion profiles on Earth (i.e., before flight). Analysis showed that the differences stemmed from reduced initial force and later compensation, indicating that the astronauts tended to underestimate the effective mass of their own limbs in microgravity. The paper was published in eLife.
Mass is a fundamental property of matter that describes both how strongly an object resists acceleration and how it participates in gravitational interactions. Unlike weight, mass does not depend on the local strength of gravity and is measured in kilograms. An astronaut with a mass of 80 kilograms on Earth still has a mass of 80 kilograms in orbit.
Weight, however, is the gravitational force acting on a mass and is commonly expressed as the product of mass and gravitational acceleration. Astronauts and objects appear weightless in orbit because they and their spacecraft are continuously falling around Earth together. This state is called microgravity because very small residual accelerations remain owing to factors such as atmospheric drag, vibrations, and movements within the spacecraft.
Although objects have almost no apparent weight in microgravity, they retain their mass. Consequently, pushing a massive object in space requires more force than pushing a less massive one, just as it does on Earth. Objects also retain momentum, so a heavy object moving through a spacecraft can be difficult and dangerous to stop despite appearing weightless. Gravity therefore determines how mass is experienced through weight and support forces, but it does not change the mass itself or its fundamental inertial properties.
Study author Zhaoran Zhang and his colleagues note that astronauts tend to show slowed general movements while aboard space stations. One reason for this is that fast movements in microgravity can destabilize body posture, make the arrest of accelerated objects harder, and increase the risk of collisions. However, slowed movements persist even when a person’s body is fully constrained and these risks are eliminated.
One hypothesis proposed to explain this is that the brain treats microgravity as a novel situation and adopts a strategy prioritizing safety and postural stability over speed. The second hypothesis is that the brain underestimates the mass of body segments (like the arms) in microgravity.
To test these hypotheses and compare them, the study authors conducted an experiment leveraging a unique biomechanical property of human arm movement called anisotropic inertia. Anisotropic inertia of the human arm means that the arm resists acceleration differently depending on the direction of movement because of its joint configuration, mass distribution, and biomechanical structure. Because of this, if humans underestimate the mass of their own arm in microgravity, it would show up as reduced peak speed or acceleration of the arm when they try to reach for something.
Participants in this study were 12 astronauts from the first four missions of the China Space Station (i.e., taikonauts) and 12 right-handed residents of Beijing serving as a control group. Ten of the astronauts were male and two were female. Their average age was 50 years. The control group participants were matched with them on age and gender.
The experimental task was conducted using a tablet. At the start of each trial, an orange circle appeared at the bottom of the screen, signaling participants to move their right index finger to this start circle. After a 0.5- to 1-second delay, a target appeared in one of three possible locations, 12 cm from the circle at different angles. Participants were instructed to reach the target quickly and accurately, pausing briefly before returning to the start. If more than 0.65 seconds elapsed before they reached the target, they would get a “too slow” message. In half of the trials, there was a 50 ms “beep” sound. Each session included 120 trials with 3 target directions. The position of the index finger was recorded continuously during the trial.
The astronauts completed multiple training sessions on the ground before their flight to the space station to familiarize themselves with the task. The control group was included to assess the confounding effects of repeated measurements and evaluate practice effects. All tests on the ground were conducted using identical devices and software for both the astronauts and the control group.
Results showed some differences in participants’ response speeds depending on the direction the target was in. However, comparisons between pre-flight and in-flight metrics revealed that astronauts actually had faster reaction times when initiating the reach for a target in space than they had on the ground before the flight. Furthermore, there were no significant differences in their reaction times between their stay at the China Space Station and after their flight, indicating that the faster reaction was likely the effect of practice rather than a microgravity influence. A similar pattern was found in the control group as well.
Although the astronauts’ reaction times were faster, further analysis showed that their overall movement durations were longer while in microgravity. They were particularly longer when reaching for targets at 90° and 135° angles—directions where the effective mass of the moving limb was higher due to anisotropic inertia. This effect was not observed in the control group, indicating that it was specific to spaceflight. The astronauts also showed altered hand movement profiles while in microgravity.
Further analyses indicated that these differences stemmed from reduced initial force generation in the feedforward phase (when the hand is initially propelled toward the target) followed by compensatory, feedback-based corrections. This, along with the other findings, is highly consistent with the hypothesis that the brain underestimates the mass of the arm in microgravity.
“These findings provide support for the body mass underestimation hypothesis while being inconsistent with the strategic slowing hypothesis. Importantly, the sensory estimate of bodily property in microgravity is biased but immune from sensorimotor adaptation, calling for an extension of existing theories of motor learning,” the study authors concluded.
The study contributes to the scientific understanding of the specificities of motor behavior in microgravity. However, humans learn motor behaviors, and it is possible that movement patterns could further change as astronauts gain more long-term experience with microgravity. This does not mean their motion profiles would eventually become identical to those on Earth, but they could adapt as they find even more effective ways to operate in a weightless environment.
The paper, “Evidence that humans underestimate body mass in microgravity: kinematic signatures in reaching movements during spaceflight,” was authored by Zhaoran Zhang, Yu Tian, Chunhui Wang, Changhua Jiang, Bo Wang, Hongqiang Yu, Rui Zhao, and Kunlin Wei.
-------------------------------------------------
Private, vetted email list for mental health professionals: https://www.clinicians-exchange.org
Unofficial Psychology Today Xitter to toot feed at Psych Today Unofficial Bot @PTUnofficialBot
-------------------------------------------------
#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #SpaceStationResearch #MicrogravityEffects #BodyMassUnderestimation #ArmKinematics #SpaceflightMotorLearning #AnisotropicInertia #NASAChinaStation #SpaceMedicine #eLifeStudy #AstronautMovement
-
DATE: July 30, 2026 at 09:00AM
SOURCE: PSYPOST.ORG** Research quality varies widely from fantastic to small exploratory studies. Please check research methods when conclusions are very important to you. **
-------------------------------------------------TITLE: New space station study reveals a hidden side effect of long-term microgravity on the human brain
A study conducted aboard the China Space Station revealed that astronauts exhibited increased movement durations and altered motion profiles when reaching for a target with their arm, compared to a control group and their own baseline motion profiles on Earth (i.e., before flight). Analysis showed that the differences stemmed from reduced initial force and later compensation, indicating that the astronauts tended to underestimate the effective mass of their own limbs in microgravity. The paper was published in eLife.
Mass is a fundamental property of matter that describes both how strongly an object resists acceleration and how it participates in gravitational interactions. Unlike weight, mass does not depend on the local strength of gravity and is measured in kilograms. An astronaut with a mass of 80 kilograms on Earth still has a mass of 80 kilograms in orbit.
Weight, however, is the gravitational force acting on a mass and is commonly expressed as the product of mass and gravitational acceleration. Astronauts and objects appear weightless in orbit because they and their spacecraft are continuously falling around Earth together. This state is called microgravity because very small residual accelerations remain owing to factors such as atmospheric drag, vibrations, and movements within the spacecraft.
Although objects have almost no apparent weight in microgravity, they retain their mass. Consequently, pushing a massive object in space requires more force than pushing a less massive one, just as it does on Earth. Objects also retain momentum, so a heavy object moving through a spacecraft can be difficult and dangerous to stop despite appearing weightless. Gravity therefore determines how mass is experienced through weight and support forces, but it does not change the mass itself or its fundamental inertial properties.
Study author Zhaoran Zhang and his colleagues note that astronauts tend to show slowed general movements while aboard space stations. One reason for this is that fast movements in microgravity can destabilize body posture, make the arrest of accelerated objects harder, and increase the risk of collisions. However, slowed movements persist even when a person’s body is fully constrained and these risks are eliminated.
One hypothesis proposed to explain this is that the brain treats microgravity as a novel situation and adopts a strategy prioritizing safety and postural stability over speed. The second hypothesis is that the brain underestimates the mass of body segments (like the arms) in microgravity.
To test these hypotheses and compare them, the study authors conducted an experiment leveraging a unique biomechanical property of human arm movement called anisotropic inertia. Anisotropic inertia of the human arm means that the arm resists acceleration differently depending on the direction of movement because of its joint configuration, mass distribution, and biomechanical structure. Because of this, if humans underestimate the mass of their own arm in microgravity, it would show up as reduced peak speed or acceleration of the arm when they try to reach for something.
Participants in this study were 12 astronauts from the first four missions of the China Space Station (i.e., taikonauts) and 12 right-handed residents of Beijing serving as a control group. Ten of the astronauts were male and two were female. Their average age was 50 years. The control group participants were matched with them on age and gender.
The experimental task was conducted using a tablet. At the start of each trial, an orange circle appeared at the bottom of the screen, signaling participants to move their right index finger to this start circle. After a 0.5- to 1-second delay, a target appeared in one of three possible locations, 12 cm from the circle at different angles. Participants were instructed to reach the target quickly and accurately, pausing briefly before returning to the start. If more than 0.65 seconds elapsed before they reached the target, they would get a “too slow” message. In half of the trials, there was a 50 ms “beep” sound. Each session included 120 trials with 3 target directions. The position of the index finger was recorded continuously during the trial.
The astronauts completed multiple training sessions on the ground before their flight to the space station to familiarize themselves with the task. The control group was included to assess the confounding effects of repeated measurements and evaluate practice effects. All tests on the ground were conducted using identical devices and software for both the astronauts and the control group.
Results showed some differences in participants’ response speeds depending on the direction the target was in. However, comparisons between pre-flight and in-flight metrics revealed that astronauts actually had faster reaction times when initiating the reach for a target in space than they had on the ground before the flight. Furthermore, there were no significant differences in their reaction times between their stay at the China Space Station and after their flight, indicating that the faster reaction was likely the effect of practice rather than a microgravity influence. A similar pattern was found in the control group as well.
Although the astronauts’ reaction times were faster, further analysis showed that their overall movement durations were longer while in microgravity. They were particularly longer when reaching for targets at 90° and 135° angles—directions where the effective mass of the moving limb was higher due to anisotropic inertia. This effect was not observed in the control group, indicating that it was specific to spaceflight. The astronauts also showed altered hand movement profiles while in microgravity.
Further analyses indicated that these differences stemmed from reduced initial force generation in the feedforward phase (when the hand is initially propelled toward the target) followed by compensatory, feedback-based corrections. This, along with the other findings, is highly consistent with the hypothesis that the brain underestimates the mass of the arm in microgravity.
“These findings provide support for the body mass underestimation hypothesis while being inconsistent with the strategic slowing hypothesis. Importantly, the sensory estimate of bodily property in microgravity is biased but immune from sensorimotor adaptation, calling for an extension of existing theories of motor learning,” the study authors concluded.
The study contributes to the scientific understanding of the specificities of motor behavior in microgravity. However, humans learn motor behaviors, and it is possible that movement patterns could further change as astronauts gain more long-term experience with microgravity. This does not mean their motion profiles would eventually become identical to those on Earth, but they could adapt as they find even more effective ways to operate in a weightless environment.
The paper, “Evidence that humans underestimate body mass in microgravity: kinematic signatures in reaching movements during spaceflight,” was authored by Zhaoran Zhang, Yu Tian, Chunhui Wang, Changhua Jiang, Bo Wang, Hongqiang Yu, Rui Zhao, and Kunlin Wei.
-------------------------------------------------
Private, vetted email list for mental health professionals: https://www.clinicians-exchange.org
Unofficial Psychology Today Xitter to toot feed at Psych Today Unofficial Bot @PTUnofficialBot
-------------------------------------------------
#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #SpaceStationResearch #MicrogravityEffects #BodyMassUnderestimation #ArmKinematics #SpaceflightMotorLearning #AnisotropicInertia #NASAChinaStation #SpaceMedicine #eLifeStudy #AstronautMovement
-
DATE: July 30, 2026 at 09:00AM
SOURCE: PSYPOST.ORG** Research quality varies widely from fantastic to small exploratory studies. Please check research methods when conclusions are very important to you. **
-------------------------------------------------TITLE: New space station study reveals a hidden side effect of long-term microgravity on the human brain
A study conducted aboard the China Space Station revealed that astronauts exhibited increased movement durations and altered motion profiles when reaching for a target with their arm, compared to a control group and their own baseline motion profiles on Earth (i.e., before flight). Analysis showed that the differences stemmed from reduced initial force and later compensation, indicating that the astronauts tended to underestimate the effective mass of their own limbs in microgravity. The paper was published in eLife.
Mass is a fundamental property of matter that describes both how strongly an object resists acceleration and how it participates in gravitational interactions. Unlike weight, mass does not depend on the local strength of gravity and is measured in kilograms. An astronaut with a mass of 80 kilograms on Earth still has a mass of 80 kilograms in orbit.
Weight, however, is the gravitational force acting on a mass and is commonly expressed as the product of mass and gravitational acceleration. Astronauts and objects appear weightless in orbit because they and their spacecraft are continuously falling around Earth together. This state is called microgravity because very small residual accelerations remain owing to factors such as atmospheric drag, vibrations, and movements within the spacecraft.
Although objects have almost no apparent weight in microgravity, they retain their mass. Consequently, pushing a massive object in space requires more force than pushing a less massive one, just as it does on Earth. Objects also retain momentum, so a heavy object moving through a spacecraft can be difficult and dangerous to stop despite appearing weightless. Gravity therefore determines how mass is experienced through weight and support forces, but it does not change the mass itself or its fundamental inertial properties.
Study author Zhaoran Zhang and his colleagues note that astronauts tend to show slowed general movements while aboard space stations. One reason for this is that fast movements in microgravity can destabilize body posture, make the arrest of accelerated objects harder, and increase the risk of collisions. However, slowed movements persist even when a person’s body is fully constrained and these risks are eliminated.
One hypothesis proposed to explain this is that the brain treats microgravity as a novel situation and adopts a strategy prioritizing safety and postural stability over speed. The second hypothesis is that the brain underestimates the mass of body segments (like the arms) in microgravity.
To test these hypotheses and compare them, the study authors conducted an experiment leveraging a unique biomechanical property of human arm movement called anisotropic inertia. Anisotropic inertia of the human arm means that the arm resists acceleration differently depending on the direction of movement because of its joint configuration, mass distribution, and biomechanical structure. Because of this, if humans underestimate the mass of their own arm in microgravity, it would show up as reduced peak speed or acceleration of the arm when they try to reach for something.
Participants in this study were 12 astronauts from the first four missions of the China Space Station (i.e., taikonauts) and 12 right-handed residents of Beijing serving as a control group. Ten of the astronauts were male and two were female. Their average age was 50 years. The control group participants were matched with them on age and gender.
The experimental task was conducted using a tablet. At the start of each trial, an orange circle appeared at the bottom of the screen, signaling participants to move their right index finger to this start circle. After a 0.5- to 1-second delay, a target appeared in one of three possible locations, 12 cm from the circle at different angles. Participants were instructed to reach the target quickly and accurately, pausing briefly before returning to the start. If more than 0.65 seconds elapsed before they reached the target, they would get a “too slow” message. In half of the trials, there was a 50 ms “beep” sound. Each session included 120 trials with 3 target directions. The position of the index finger was recorded continuously during the trial.
The astronauts completed multiple training sessions on the ground before their flight to the space station to familiarize themselves with the task. The control group was included to assess the confounding effects of repeated measurements and evaluate practice effects. All tests on the ground were conducted using identical devices and software for both the astronauts and the control group.
Results showed some differences in participants’ response speeds depending on the direction the target was in. However, comparisons between pre-flight and in-flight metrics revealed that astronauts actually had faster reaction times when initiating the reach for a target in space than they had on the ground before the flight. Furthermore, there were no significant differences in their reaction times between their stay at the China Space Station and after their flight, indicating that the faster reaction was likely the effect of practice rather than a microgravity influence. A similar pattern was found in the control group as well.
Although the astronauts’ reaction times were faster, further analysis showed that their overall movement durations were longer while in microgravity. They were particularly longer when reaching for targets at 90° and 135° angles—directions where the effective mass of the moving limb was higher due to anisotropic inertia. This effect was not observed in the control group, indicating that it was specific to spaceflight. The astronauts also showed altered hand movement profiles while in microgravity.
Further analyses indicated that these differences stemmed from reduced initial force generation in the feedforward phase (when the hand is initially propelled toward the target) followed by compensatory, feedback-based corrections. This, along with the other findings, is highly consistent with the hypothesis that the brain underestimates the mass of the arm in microgravity.
“These findings provide support for the body mass underestimation hypothesis while being inconsistent with the strategic slowing hypothesis. Importantly, the sensory estimate of bodily property in microgravity is biased but immune from sensorimotor adaptation, calling for an extension of existing theories of motor learning,” the study authors concluded.
The study contributes to the scientific understanding of the specificities of motor behavior in microgravity. However, humans learn motor behaviors, and it is possible that movement patterns could further change as astronauts gain more long-term experience with microgravity. This does not mean their motion profiles would eventually become identical to those on Earth, but they could adapt as they find even more effective ways to operate in a weightless environment.
The paper, “Evidence that humans underestimate body mass in microgravity: kinematic signatures in reaching movements during spaceflight,” was authored by Zhaoran Zhang, Yu Tian, Chunhui Wang, Changhua Jiang, Bo Wang, Hongqiang Yu, Rui Zhao, and Kunlin Wei.
-------------------------------------------------
Private, vetted email list for mental health professionals: https://www.clinicians-exchange.org
Unofficial Psychology Today Xitter to toot feed at Psych Today Unofficial Bot @PTUnofficialBot
-------------------------------------------------
#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #SpaceStationResearch #MicrogravityEffects #BodyMassUnderestimation #ArmKinematics #SpaceflightMotorLearning #AnisotropicInertia #NASAChinaStation #SpaceMedicine #eLifeStudy #AstronautMovement