Research

Artificial Gravity as a Countermeasure for Human Spaceflight Deconditioning

There have been proposals over the years for centrifuge modules on the ISS to study artificial gravity. Image credit: Mark Holderman/NASA.

Astronauts experience a strong physiological deconditioning during space missions, primarily due to the weightless conditions. Some of these adverse consequences include bone loss, muscle atrophy, sensory-motor/vestibular deconditioning, visual impairment, and overall cardiovascular adaptation, which may lead to orthostatic intolerance when astronauts are exposed again to a gravitational environment. Physiological deconditioning will be even more challenging in future long-duration space missions, for example to Mars, in which astronauts will be exposed to weightlessness for six to eight months before landing without external help to support egress. In order to mitigate these negative effects, several countermeasures are currently in place, particularly very intensive exercise protocols. However, despite these countermeasures, physiological deconditioning still persist to a certain degree, highlighting the need for new approaches to maintain the astronauts’ physiological state within acceptable limits.

Artificial gravity (generated by centrifugation) has long been suggested as a comprehensive countermeasure that is capable of challenging multiple physiological systems at the same time, therefore maintaining overall health during extended weightlessness. However, human centrifuges hasn’t been tested in space, and there are still many questions about its implementation (including centrifuge configuration, exposure time, gravity level, gravity gradient, and use/intensity of exercise, etc). We want to investigate these research questions using a combination of human experiments on ground-based centrifuges and modeling techniques of physiological systems to complement the experimental results.

Augmenting Exercise Protocols With Interactive Virtual Reality Environments

Adherence to exercise has long been a bane of the modern human experience, despite its litany of extolled virtues. A variety of strategies have developed over the decades to encourage us to stick with our fitness goals, but as technology improves the fidelity of the virtual world to the real one, many once-implausible strategies are becoming plausible.

Team dynamics, an engaging environment, and a personalized program are just a few of the strategies which can be combined and employed using a virtual reality system. Imagine: instead of looking at the inside of a ship’s hull for six months, you could don a helmet and join any number of other participants (real or virtual) across any distance or time while you work out.

This study will examine the efficacy and viability of such a technology using already-established exercise protocols from the International Space Station and previous NASA studies. This research will be done in collaboration with former astronaut Dr. Gregory Chamitoff’s ASTRO Center and the Human Clinical Research Facility.

Bimanual Coordination

Despite humanity’s decades-long relationship with spaceflight, we still do not know the range of gravity levels (or gravity doses) that sustain normal physiological function. This is a concern because astronauts are required to utilize bimanual coordination, a domain of sensorimotor function and physiology, for numerous operational tasks. Critical tasks involving bimanual coordination, such as landing a spacecraft or piloting a rover, may be required during micro/partial gravity or during rapid G-transitions. Previous investigations have provided evidence of decrements in sensorimotor performance in hypo-gravity and hyper-gravity environments. However, these experiments focused primarily on unimanual control, and there is a lack of research on bimanual coordination performance in altered gravity.

We will use various analogs (i.e., head down tilt (HDT)/head up tilt (HUT), short-radius centrifuge, and parabolic flight) to simulate altered gravity. Subjects will be asked to complete two different bimanual coordination tasks at various G-levels (0 to 1.8 G). The first task will require subjects to coordinate forces produced by their left and right triceps while the second task will involve coordinating elbow flexor-extensor movements. We will then compare performance on these tasks between each gravity level that we test. Additionally, we are interested in looking for any evidence of bimanual coordination adaptation after repeated exposure to altered gravity.

Experiments conducted using the centrifuge and parabolic flight also allow us to study bimanual coordination performance during G-transitions. We will use data from these experiments to determine the relationship between gravity dose and bimanual coordination performance and estimate the range of gravity levels that elicits an “Earth-like” performance. During the parabolic flight experiments, we will also investigate the potential impact of an anti motion sickness drug (Promethazine) on bimanual coordination. Work on this project is being done in collaboration with Dr. Bonnie J. Dunbar’s Aerospace Human Systems Laboratory and Dr. Deanna Kennedy’s Neuromuscular Coordination Lab.

Biomechanics and Musculoskeletal Analysis

The musculoskeletal system might experience importent detriments in extreme environments. We use modeling approaches and computational tools to investigate human biomechanics and musculoskeletal performance in challenging environments, such as human-spacesuit interactions and musculoskeletal performance to novel exercise devices.

Human Spacesuit Interaction – Extravehicular Activity (EVA) is a highly demanding activity during space missions. The current NASA spacesuit, the Extravehicular Mobility Unit (EMU), might be thought of as the ‘world’s smallest spacecraf’ and is quite an engineering achievement. However, the EMU has also led to discomfort and musculoskeletal injuries, mainly due to the lack of mobility in the pressurized suit that makes moving and operating within the suit challenging. We are developing a new musculoskeletal modeling framework in OpenSim to analyze human-spacesuit interaction and musculoskeletal performance during EVA.

Exercise using the HULK Device – Astronauts experience physiological deconditioning in space due to the extended exposure to microgravity including, but not limited to, muscle atrophy, loss of strength, and bone loss. Current countermeasures on the International Space Station include resistance training as well as aerobic exercises, and the use of the Advance Resistive Exercise Device (ARED) has been effective in reducing spaceflight musculoskeletal deconditioning. However, the ARED is a bulky device and compact devices that minimize mass and volume are necessary for use within the new space exploration vehicles. In collaboration with NASA Ames, we are investigating exercise performance on the Hybrid Ultimate Lifting Kit (HULK), a new lighter and more compact exercise device under development.

Cardiovascular Physiology after Deconditioning

Led by Dr. Adrien Robin and Dr. Ana Diaz-Artiles and supported by a postdoctoral grand from the Translational Research Institute for Space Health (TRISH), this project examines how graded gravitational stress (from head-down to head-up tilt) shapes cardiovascular and ocular function in healthy adults. In a crossover design, participants (men and women) complete two deconditioning protocols: (1) 48 hours of head-down bed rest and (2) a drug-induced hypovolemia (using diuretic). During each session we systematically vary body angle and continuously measure hemodynamics, fluid transfert, and vascular/ocular indices. Our goal is to define sex-specific dose–response curves to gravity and identify mechanisms of deconditioning. Findings will inform astronaut health risk models and enable individualized countermeasures such as optimized exercise, fluid loading, and compression garments. The work also translates to Earth, supporting better management of syncope, safer perioperative positioning (e.g. Trendelenburg position), and more effective rehabilitation strategies for older or bedridden patients.

Closed-Loop Compression Garment

Maintaining adequate blood flow and pressure is essential to ensure that vital organs, particularly the brain, receive sufficient oxygen and nutrients. Under normal conditions, the cardiovascular system can regulate sudden changes in blood pressure and blood flow. However, rapid fluid shifts toward the lower body, known as orthostatic intolerance (OI), can sometimes overwhelm the body’s regulatory mechanisms. This can lead to hypotension and symptoms such as dizziness or fainting, and in severe cases can progress to temporary loss of consciousness. To counteract these effects, compression garments are commonly employed in both medical and operational environments. Examples of this can be seen in pilots through the use of G-suits during high-G maneuvers and astronauts who wear specialized garments to help their cardiovascular systems readjust after returning from space.

Despite their utility, current compression systems have notable drawbacks. They often fail to adapt to individual physiological differences, meaning compression may be applied at the wrong time or at an ineffective level. Many current garments are also bulky and cumbersome, manually operated, and only offer a single static pressure setting, limiting their effectiveness. Recent advances in soft robotics and smart materials, such as shape memory alloys, have improved actuation capabilities, but these systems remain user-controlled and lack full autonomy, which is essential for an individual performing complex tasks such as landing a space vehicle. This research effort focuses on the development of a next generation compression garment that automatically adjusts in real time using biometric feedback, offering a personalized and adaptive countermeasure for OI in demanding environments.

Exercise in Altered Gravity Enviroments

Artificial Gravity Combined with Exercise

In order to investigate physiological responses of centrifugation combined with exercise, we conducted a human experiment on 12 subjects using the MIT short-radius centrifuge. The centrifuge was constrained to a radius of 1.4 meters (the upper radial limit for a centrifuge to fit within an International Space Station (ISS) module without extensive structural alterations), and a cycle ergometer was added for exercise during centrifugation. We tested different levels of artificial gravity (0g, 1g, and 1.4g at the feet in the centripetal direction) and exercise intensity (25W warm-up, 50W moderate, and 100W vigorous) while collecting a variety of data including cardiovascular parameters, foot forces, and subjective comfort and motion sickness data.

Subjects successfully completed the exercise protocol and they tolerated the centrifugation well and motion sickness was minimal. Foot forces measurements indicate that there is a significant effect of both artificial gravity (AG) level and workload intensity on peak forces generated during ergometer exercise. The cardiovascular responses were more prominent (measured as larger deviations from their baseline values) at higher levels of artificial gravity and exercise intensity. In particular, cardiac output, stroke volume, and pulse pressure significantly increased with both AG level and workload intensity, suggesting that the combination of artificial gravity and exercise may be beneficial against cardiovascular deconditioning in space. Mathematical models were fit to these variables across the condition tested. These results suggest that centrifugation combined with exercise may be effective in improving musculoskeletal and cardiovascular functions during long-duration spaceflight. This work was partially supported by Fulbright Commission, the NSBRI (PI: Larry Young), and the MIT/Skoltech Seed grant.

Simulated Hypogravity Combined with Exercise

We are conducting studies using tilt platforms combined with cycle ergometer exercise to experimentally determine the impact of simulated hypogravity (including both microgravity and Lunar/Mars conditions) on various physiological parameters. We measure a number of cardiovascular and pulmonary system parameters using a variety of non-invasive equipment, including intraocular pressure with contact tonometers, whilst subjects carry out varying intensity exercise protocols across a range of conditions.

Lower Body Negative Pressure in Parabolic Flight

This experiment aims to better understand how the human body responds to graded Lower Body Negative Pressure (LBNP) under true microgravity conditions, provided by parabolic flight. LBNP is a promising countermeasure for the fluid shifts that occur in space, but most studies to date have been conducted on Earth using analogs such as supine or head-down tilt positions. While these approaches remove vertical hydrostatic gradients, they cannot fully replicate the absence of gravitational forces along the front-to-back human axis, which may influence venous return, tissue pressures, and overall cardiovascular regulation.

To address this limitation, our team will investigate cardiovascular, autonomic, and ocular responses to different levels of LBNP during short-duration microgravity phases in parabolic flight. By generating dose-response curves across multiple physiological systems, we aim to directly compare responses in true microgravity with those obtained under 1g analog conditions. The study will also assess sex-based differences in physiological adaptation, contributing to a more inclusive understanding of individual variability in countermeasure effectiveness and fluid regulation during spaceflight.

This project will deliver the most comprehensive and systematic dataset on LBNP responses ever collected in true microgravity. The results will inform the optimization of LBNP as a spaceflight health countermeasure, with direct applications for reducing risks such as Spaceflight-Associated Neuro-ocular Syndrome (SANS) and venous thromboembolism (VTE). Ultimately, the findings will help define the gravitational thresholds needed to maintain cardiovascular and ocular health duringlong-duration missions to the Moon and Mars.

Modeling Cardiovascular Physiology in Space

The cardiovascular (CV) system is one of the major physiological systems affected during spaceflight. Altered-gravity environments cause a change in the hydrostatic pressure distribution on the body, leading to a cephalad fluid shift where blood volume in the lower extremities reduces by up to 1L and increases in the trunk and head (also known as “puffy face/chicken leg” syndrome). This leads to hypovolemia, changes in hematocrit concentration, and aerobic deconditioning. It may also be a cause of spaceflight associated neuro-ocular syndrome (SANS).

We use a computational model of the CV system to reach beyond the limitations of existing data and study the effects of changing gravity levels. This model has been validated over a number of experimental studies and is continuously being extended to include the ability to model new conditions and physiological phenomena; including exercise, pulmonary function, long duration hemodynamic changes, and metabolic cost.

The CV model is being expanded to include cerebral autoregulation, which ensures a constant blood flow to the brain despite fluctuations in systemic blood pressure. Based on cerebral artery blood velocity findings from LBNP studies, we developed a cerebral autoregulation feedback mechanism that functions within the current CV model to analyze the dynamic blood flow behavior within the brain. This research effort creates a unique opportunity to explore cerebral perfusion in conditions where human experimentation is not feasible due to subject safety.

We are also integrating the ability to mimic trauma conditions and their associated CV effects for both astronauts and pilots. We are characterizing individual differences in a wide range of subject types – varying in body type, anthropometrics, sex, baseline CV characteristics, athletic ability, and hydration – to predict physiological responses to simulated acute blood loss in different gravity scenarios. A respiratory system model is also being developed to analyze the responses of hypoxic effects based on these individual differences.

Multisensory Virtual Reality

Future long duration exploration missions will require astronauts to spend prolonged periods in isolated and confined environments. Combined with sensory deprivation, loss of social connection, and a demanding workload, these factors can adversely affect an astronaut’s mood and stress levels. This places astronauts at an increased risk of developing adverse behavioral health conditions, which can cause performance decrements and jeopardize mission success. Current countermeasures used on the ISS will become increasingly difficult to use as missions venture further from Earth and begin to encounter significant communication delays. Virtual reality (VR) technology is a promising countermeasure, and continual advancements in VR technology have made it more robust and portable.

Our lab is currently investigating the potential of VR technologies to enhance behavioral health and performance. Natural environments provide many psychological, physiologic, and cognitive benefits, and incorporating many sensory modalities could improve realism and enhance benefits of the virtual nature experience. We have developed nature-inspired VR environments with multiple sensory inputs: audio, visual, olfactory (smell), and haptics (wind and thermal stimuli). Uniquely, the scents, wind, and temperature vary based on the user’s location within the virtual environment. For example, the scent of wet ground by a pond or cooler temperatures in the shade. We are using questionnaires along with the NASA Cognition battery to measure the impact of our multisensory VR countermeasure on behavioral health and performance in both a laboratory and operational setting (i.e., Naval ship). This countermeasure could also provide benefits to other populations who do not have free access to nature such as assisted living residents, post-op recovery patients, and individuals with seasonal affective disorder (SAD).