NOTE: End date changed to 12/31/2022 per PI; original end date was 9/30/2021 (Ed., 5/3/21)

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, and Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures as those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities will be larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance metrics include time to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the Computerize Dynamic Posturography test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the HRP Standard Measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used to quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate is collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump-down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This study will contribute to gap closure by providing information regarding any functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help in determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

Our study’s findings reveal that partial gravity significantly impacts the execution of maneuvers that require greater reliance on balance control, such as tandem stance, seat egress and walk, and recovery from potential falls. Similar declines in maneuvers demanding high dynamic control of postural equilibrium are also evident in astronauts immediately after their return from space. Therefore, it can be inferred that the decreases in postural control that astronauts will experience upon landing on the Moon or Mars may surpass those observed in our study. Consequently, in-flight countermeasures targeting vestibular and proprioceptive systems will be crucial to sustain crewmembers’ balance function, enabling them to successfully execute critical mission tasks.

Three additional investigations were performed to further explore the effects of gravity levels and gravity transitions on vestibular function (see section D1 “Changes in approach and reasons for change”). The first was a literature review of potential benefits and human systems integration of parastronauts with bilateral vestibulopathy for spaceflight missions. Upon landing after long-duration spaceflight, astronauts often experience motion sickness and impaired performance of functional tasks. Parastronauts with bilateral vestibulopathy are immune to motion sickness; therefore, these individuals might be better prepared for landing after spaceflight. They have adapted strategies for maintaining balance and orientation without relying on vestibular inputs, potentially making them more stable and less prone to disorientation in microgravity or rotating environments. Their unique adaptations may allow them to perform many mobility tasks more effectively during critical mission phases, such as vehicle egress, when other crew members might be more affected by vestibular issues. While they may not perform all tasks, these parastronauts can excel in specific roles that leverage their unique abilities, contributing to the mission’s overall success in specialized capacities. We propose using lunar gravity achieved during parabolic flight and prolonged centrifugation as models to study how functional task performance might be less impaired in parastronauts with bilateral vestibulopathy compared to healthy individuals when landing on the Moon after extended exposure to microgravity (Ramsburg et al., 2025).

Data from a separate parabolic flight experiment were analyzed to assess how individuals perceive the amplitude of passive body translation in microgravity and hypogravity. Six blindfolded participants reported their perceived amplitudes of whole-body translations ranging from 25 to 250 cm along the three spatial axes under 0 g, 1 g, and 1.8 g conditions. Results showed that the perceived amplitudes of these translations were accurate in 1 g. However, subjects significantly underestimated distances in 0 g and overestimated them in 1.8 g. These results have been published in a peer-reviewed journal article (Clement et al., 2025a). These findings suggest that alterations in gravitational cues disrupt the vestibular system’s ability to provide accurate information on body movement, leading to altered motion perception. More specifically, in 1 g, the otolith organs detect both gravitational and inertial accelerations, allowing the brain to distinguish between gravity and self-motion. In 0 g, however, the otoliths respond solely to inertial acceleration, leading to errors in motion perception. Conversely, in hypergravity conditions–such as the 1.8 g pull-up phase of a parabolic flight–translation amplitude is overestimated. This suggests that the brain relies on an expected ratio between inertial and gravitational forces. When gravity increases, acceleration is perceived as stronger, resulting in an overestimation of motion. Since other factors, such as proprioceptive inputs and temporal cues are also impacted by altered gravity levels, external tools like visual and proprioceptive aids must be developed to help astronauts maintain spatial orientation during critical spaceflight operations.

A final separate analysis was performed to investigate how short-duration spaceflight affects private astronauts’ performance of mission-critical functional tasks that challenge balance and locomotor control systems shortly after they return to Earth. Ten astronauts were assessed while they performed three functional tests (sit-to-stand, tandem walk, and walk-and-turn) before spaceflight and a few hours after returning from missions lasting from 4 to 21 days (Mean ± SD; 10.4 ± 7.4 days). Their performance was compared to that of 36 astronauts who returned from long-duration missions lasting from 5 to 12 months (6.8 ± 1.7 months). For all tasks, there were no significant differences in preflight performance between short and long duration groups. Shortly after returning from spaceflight, the short-duration astronauts had difficulty standing, walking, and turning around obstacles, and they experienced terrestrial readaptation motion sickness. However, the performance of these functional tasks was less impacted after short-duration missions than long-duration missions. These results have been published in a peer-reviewed journal article (Clement et al., 2025b). The decrements in postural and locomotor control after short-duration ISS missions are comparable to those seen after Space Shuttle missions of similar length, suggesting that these effects are not dependent on the spacecraft type or the launch and re-entry characteristics. Although individual responses vary, the overall performance impairments are generally less severe after short-duration missions compared to long-duration missions. Longer missions involve more substantial physiological changes—such as greater losses in muscular strength and proprioception function — that can compound sensorimotor disruptions and further impact performance. As a result, shorter missions may require fewer or less-intensive countermeasures than long-duration flights, allowing for faster recovery, simplified rehabilitation, and more efficient use of resources during re-adaptation to Earth’s gravity.

NOTE: End date changed to 12/31/2022 per PI; original end date was 9/30/2021 (Ed., 5/3/21)

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, and Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures as those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities will be larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance metrics include time to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the Computerize Dynamic Posturography test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the HRP Standard Measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used to quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate is collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump-down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This study will contribute to gap closure by providing information regarding any functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help in determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

In addition, there were significantly more falls recorded at lower gravity levels. However, reduced gravity did not affect the time required to settle after jumping down. These results have been published in a peer-reviewed journal article (Clement et al., 2024). Additional analyses of head-trunk coordination showed alterations in magnitude-squared coherence (MSQ) in pitch and velocity root mean square deviation (RMSD) in roll, suggesting increased coordination (or “locking”) between the head and trunk at low levels of partial gravity.

We also analyzed data from a separate parabolic flight experiment in which 6 participants reported the perceived amplitude of whole-body translations ranging from 30 to 250 cm along the three spatial axes under 0 g, 1 g, and 1.8 g conditions. Results showed that the perceived amplitudes of these translations were accurate in 1 g. However, subjects significantly underestimated distances in 0 g and overestimated them in 1.8 g. These findings suggest that, in microgravity, the lack of gravitational cues disrupts the vestibular system’s ability to provide accurate information on body movement, leading to altered motion perception.

NOTE: End date changed to 12/31/2022 per PI; original end date was 9/30/2021 (Ed., 5/3/21)

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, and Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures as those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities will be larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance metrics include time to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the Computerize Dynamic Posturography test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the HRP Standard Measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used to quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate is collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump-down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This study will contribute to gap closure by providing information regarding any functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help in determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

Gravity level had a significant effect on performance, with the greatest changes from 1 g tending to be at the 0.25 g level. Lower gravity levels were associated with (1) increased times to complete the seat egress and walk task and the recovery from fall task; (2) decreased change in heart rate during the recovery from fall task; (3) decreased rail balance times; and (4) increased cone of stability distance in the anterior-posterior direction. These preliminary results were presented at the 2024 NASA Human Research Program Investigators' Workshop and are reported in a manuscript that has been submitted to Nature Microgravity. A follow-up analysis of head motion, namely angular velocity around the yaw plane, confirmed the slower turn rates during the seat egress and walk task. In addition, lower gravity levels were associated with larger magnitudes of upward head pitch while exiting the turn compared to entering the turn, suggesting that subjects might have adjusted their gaze as a strategy for maintaining balance or overall functional performance in partial gravity.

These data suggest that there is a negative dose-response relationship between gravity level and functional task performance. The largest changes in performance were expected at the lowest gravity level (0.25 g) because subjects would no longer be able to use the gravitational reference for the perception of upright. Understanding the extent of performance deficits informs the risks and design of countermeasures for exploration spaceflight missions.

NOTE: End date changed to 12/31/2022 per PI; original end date was 9/30/2021 (Ed., 5/3/21)

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, and Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures as those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities will be larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance metrics include time to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the Computerize Dynamic Posturography test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the HRP Standard Measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used to quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate is collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump-down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This study will contribute to gap closure by providing information regarding any functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help in determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

The protocol and informed consent have been approved by the NASA Institutional Review Board (eIRB) and the French Ethical Committee. The physical layout and the mechanical and electrical requirements of the experiment have been approved by NOVESPACE (the operator of the aircraft) and are documented in an Experimental Safety Data Package. This document served as the basis for a Test Readiness Review (TRR) conducted at NASA Johnson Space Center in the Biomedical Research and Environmental Sciences Division. All hardware and racks have been built and inspected per requirements.

The equipment is being shipped to Bordeaux and the study team is planning to arrive at NOVESPACE during the week before the flights for the installation of equipment in the aircraft. Pilot testing and safety reviews will be completed on the aircraft prior to the parabolic flights.

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures than those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities get larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance during this test include times to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the computerized dynamic posturography (CDP) test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the Human Research Program (HRP) standard measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate is collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10 s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This task will contribute to gap closure by providing information regarding any changes in functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

The NASA Human Health Countermeasures (HHC) Element has required that 12 subjects are tested per experiments, for 10 parabolas at each g-level. We have updated our study proposal and budget to accommodate these requirements. These changes were approved by the HHC Element Scientist.

We have submitted the protocol and informed consent to the NASA Institutional Review Board (eIRB). The submission is in review. The aim is to have all studies approved by the NASA eIRB no later than August 2022. We have also started looking at and finalizing the physical layout, as well as the mechanical and electrical requirements of the experiment, and we have submitted a draft of our Experimental Safety Data Package to NOVESPACE.

We will analyze the execution of four critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, Tandem Stance) during the partial gravity and normal gravity phases of parabolic flight by using the same equipment and procedures than those previously used on astronauts returning from International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities get larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

The four specific aims include:

Specific Aim 1: Seat Egress and Walk. The purpose of this test is to measure the ability to rise from a seated position and walk while avoiding obstacles to test mobility. This test is identical to the Sit-to-Stand and Walk-&-Turn test used for Standard Measures after spaceflight and bed rest. In this test, subjects are requested to rise from a seated position as quickly as possible without using their hands and walk as quickly and safely as possible straight ahead towards a cone (4 m distance), walk around the cone, then return and sit back down in the chair. On the way to and back from the cone, subjects step over a 30-cm obstacle. Two trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. Performance during this test include times to complete the trial, turn rate during the turn, obstacle contact, and head-torso coordination.

Specific Aim 2: Tandem Stance. The Tandem Stance test is a standard test of static postural stability. This test is similar to the computerized dynamic posturography (CDP) test performed on astronauts as part of their Medical Requirements and on bed rest subjects as part of the Human Research Program (HRP) standard measures (Postural Equilibrium Control). In this test, at the sound of a tone subjects are instructed to stand upright in a heel-to-toe fashion with their arms crossed on their chest. This test is performed with the eyes open and with the eyes closed. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The maximum time (prior to taking a step) as well as the medial-lateral peak-to-peak sway angle (p-p sway) is used quantify postural stability.

Specific Aim 3: Recovery from Fall and Stand. The purpose of this test is to measure the ability to maintain postural control after standing up from a prone position. Impairment in the ability to rise from a prone position is one of the strongest independent risk factors associated with serious fall-related injuries. In this test, subjects rest in a prone position, then stand up as quickly as possible and maintain a quiet standing position. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units. The anterior-posterior and medial-lateral peak-to-peak sway angle (p-p sway) is used to compute the equilibrium score, where 12.5 is the maximum theoretical p-p sway. This test also induces an orthostatic challenge. Therefore, heart rate and blood pressure are collected continuously throughout this test. This cardiovascular data is used to detect potential signs of orthostatic intolerance during this active head-up tilt test.

Specific Aim 4: Jump Down. In the Jump Down test, at the sound of a tone subjects perform a two-footed hop from a height of 30 cm onto a force plate that measures the ground reaction forces on landing. After landing, subjects are instructed to remain still on the force plate, in the standing position, with arms at their sides for 10 s. After 10 s, subjects will also perform a maximal voluntary lean in one direction to quantify changes in the limits of stability at different g-levels. Two jump down trials will be performed per parabola. A video camera records each trial and body motion (head and torso) is recorded from triaxial inertial measurement units.

Study Participants. Twelve subjects (6 male, 6 female) will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. In addition, each subject will perform all the functional task tests in 1 g on the ground prior to the flight and in 1 g during the flight between parabolas when the aircraft flies straight and level.

Risk Characterization, Quantification\Evidence. This task will contribute to gap closure by providing information regarding any changes in functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement will also help determining the gravity threshold for these functional tasks. These functional task tests are selected to simulate critical mission tasks that crewmembers may be required to perform when they land on another planet with partial gravity.

Countermeasure\Prototype Hardware or Software. This task will contribute to gap closure by determining the gravity threshold for these functional tasks.

The Human Health & Countermeasures (HHC) Element Scientist required that 12 subjects are tested per experiments, for 10 parabolas at each g-level. We have updated our study proposal and budget to accommodate these requirements. These changes will need to be approved by the HHC Element Scientist.

We have also started looking at and finalizing the physical layout and electrical requirements and we will start our Johnson Space Center Institutional Review Board (JSC IRB) submission soon. The aim is to have all studies approved by NASA IRB no later than August 2021.

The results published in the following paper helped us design our experiment protocol for the NASA supported experiment (Functional Task Tests in Partial Gravity during Parabolic Flight):

Meskers AJH, Houben MMJ, Pennings HJM, Clément G, Groen E. Underestimation of self-tilt increases in reduced gravity conditions. J Vestib Res. 2021 Apr 16. Online ahead of print. https://pubmed.ncbi.nlm.nih.gov/33867364

We propose to analyze the execution of 4 critical mission tasks (Seat Egress and Walk, Recovery from Fall and Stand, Jump Down, Tandem Walk) during the partial gravity and hypergravity phases of parabolic flight by using the same equipment and procedures than those previously used on astronauts returning from the International Space Station (ISS) missions and ground-based subjects during axial body unloading. Our hypothesis is that the limits of stability for these activities get larger when the gravity level is reduced. The largest decreases in performance are expected at the lowest gravity level (0.25 g) because subjects will no longer be able to use the gravitational reference for their perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions.

Twelve subjects will be tested during 3 flights of 30 parabolas, including 10 parabolas at 0.25 g, 10 parabolas at 0.5 g, and 10 parabolas at 0.75 g. Performance metrics will include (a) the time for the subject to complete the test (Seat Egress and Walk, Recovery from Fall and Stand); (b) the time elapsed between the start of motion and the stabilization of upright posture (Recovery from Fall and Stand, Jump Down); (c) the mean sway speed during quiet standing (Recovery from Fall and Stand, Jump Down); (d) changes in heart rate and blood pressure (Recovery from Fall and Stand); (e) the percentage of correct steps and torso acceleration (Tandem Walk); and (f) the severity of motion sickness symptoms.

The deliverables will include (a) a dose-response relationship between these performance metrics versus gravity levels between 0 and 1; and (b) a better understanding of the gravity-threshold effects on human vestibular and sensorimotor sensitivity and function.