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.