The Gravity Loading Countermeasure Skinsuit (or “Skinsuit”) is an intravehicular activity suit for astronauts that has been developed to simulate the effects of Earth gravity. The Skinsuit produces a static load from the shoulders to the feet with elastic material in the form of a skin-tight wearable suit ,. This wearable system is intended to supplement exercise during future missions to the moon and Mars (where current exercise equipment may be too large and bulky for the small spacecraft) and to further attenuate microgravity-induced physiological effects in current ISS mission scenarios.
The Skinsuit targets multiple physiological systems, aiming to mitigate spaceflight-induced musculoskeletal adaptations, such as spinal elongation. Additionally, the Skinsuit may provide benefits to the sensorimotor system, which have not been tested in previous studies. The sensorimotor effects of microgravity are difficult to simulate on Earth, even in bed rest analogs or body-weight suspension, due to the constant force of gravity on the body and body-load receptors. The goal of this project is to use the microgravity afforded by a parabolic flight to explore a research question: Can the Skinsuit restore sensorimotor functions that are typically altered in microgravity?
Microgravity unloading affects body-load receptors, such as mechanoreceptors in the skin and muscles. In combination with adaptations in the vestibular system, sensorimotor adaptations may affect posture, locomotion, balance, and proprioception upon return to Earth . Our hypothesis is that Skinsuit loading (including axial body load and foot pressure) will cause an increase in postural muscle activity in reduced gravity environments, partially restoring the muscle activity levels typically seen in 1G. If proven correct, this hypothesis will indicate if the Skinsuit has the potential to provide muscle atrophy attenuation or prevent the degradation of typical 1G motor control strategies. By maintaining typical 1G motor control strategies in parallel to microgravity adaptations, we aim to move toward dual adaptation to different gravity levels, allowing astronauts to more rapidly adjust to 1G upon return to Earth.
Several Skinsuit versions have been developed over the past decade with various design modifications (Figure 2). Previous Skinsuit experiments, including ground experiments, parabolic flights, and ISS flights, have primarily studied operational feasibility, loading magnitude, and spinal elongation attenuation. The investigation of sensorimotor effects and microgravity EMG patterns associated with the Skinsuit is novel.
The experimental protocol for the flight was developed over the course of the Fall 2020 semester, and experiment measurables will include electromyography (EMG) and foot pressure. During the flight, the participant will perform arm movements with and without the Skinsuit for comparison to typical 1-G muscle activation patterns and postural control strategies. In parallel to developing an experimental protocol to answer questions about physiology, we have also designed and fabricated the next-generation Skinsuit  (Figure 1).
This work aims to characterize the function and physiological effects of the Skinsuit and may elucidate short-term changes in human sensorimotor function in microgravity. Overall, the proposed work would support the goal of the Skinsuit project in enabling humans to adapt to multiple levels of gravity, bringing us one step closer to long-term space habitation.
The content of the following blog posts will encompass study rationale, experimental design, flight logistics considerations, and prototype development.
The mechanical properties of the Skinsuit fabric will depend on yarn and fabric structure (knit structure, density, thickness, etc.). Different mechanical properties are required in the axial and circumferential directions to apply appropriate loading levels to the body. The following requirements will be refined as Skinsuit developments progress.
The material will provide forces between 100 N/m and 2000 N/m in the axial direction with strains less than 150%
The material will have a <10% change in expected force in the axial direction over 100 cycles to 2000 N/m.
The material will provide forces between 50 N/m and 500 N/m in the circumferential direction with strains less than 150%
The material will have a <10% change in expected force in the circumferential direction over 100 cycles to 500 N/m.
The material will have low stiffness in the circumferential direction to accommodate donning/doffing and small changes in circumference.
The material will be:
Breathable / Moisture-wicking (i.e. appropriate for exercising)
Opaque (There were some problems in previous suits with see-through fabric.)
Antimicrobial (Can be implemented in later prototypes. Laundry is not available on the ISS.)
Previously Used Materials
I have performed an initial literature review of the sensorimotor effects of spaceflight, which will be expanded upon in later work. Balance, posture, and movement rely on inputs from several physiological sensors (Figure 4). In microgravity, the sensor stimuli are significantly altered. The otolith organs are particularly affected by the loss of their primary stimulus: gravity. Additionally, pressure is no longer applied to the soles of the feet and axial mechanical loading is not applied to the body. The body likely adapts to these changes by altering the gain and sensitivity of some sensors. The integration centers may rely more on visual inputs in microgravity to compensate . Upon return to Earth, physiological adaptations during spaceflight can result in ataxia, disorientation, and posture and locomotion impairment .
A large majority of the research in spaceflight neuroscience focuses on the vestibular system (inner ear), as this is most relevant for space sickness and rapid adaptations to gravity changes (~3 days, but potentially weeks to months for full adaptation). In this case, “sensorimotor effects” refer to the sensory inputs from vestibular organs and how they can affect movement. In the scope of the Skinsuit project, we are interested in position- and loading-related sensorimotor effects. The effect of vestibular adaptations is likely of greater magnitude and thus, appears to dominate the literature in space neuroscience and our understanding of sensorimotor changes in microgravity. Wearable devices cannot reintroduce the gravito-inertial forces to affect the vestibular system, but they can provide foot pressure and skin pressure, perhaps restoring stimuli for mechanoreceptors, proprioception processes, and certain motor control strategies.
Unloading in microgravity affects body load receptors  and causes changes in proprioception . In combination with adaptations in the vestibular system, these sensorimotor adaptations may affect posture, locomotion, balance upon return to Earth . English et al. detail the use of exercise countermeasures to re-introduce body loading and maintain some of the typical afferent feedback required for locomotion and other movements . In addition to exercise, studies suggest that foot pressure or plantar stimulation in microgravity may enhance neuromuscular activation and prevent neuromuscular degradation ,. For example, studies show that muscle activation patterns change in microgravity relative to preflight measurements . Layne et al. used an arm raising movement which is known to involve whole-body coordination, with muscle activation in the lower limbs and postural muscles in addition to the arms. This effect is decreased in microgravity. By re-introducing foot pressure in microgravity using special pneumatic shoes, muscle activation in the lower limbs was enhanced during arm raises compared to a control condition with no foot pressure . These studies were largely performed by Layne in the 1990s (often in collaboration with Kozlovskaya from the Russian Institute for Biomedical Problems). While these papers seem to be commonly cited for changes in motor control strategies, I have yet to find any recent publications with similar experiments. Additionally, there is likely much more that needs to be understood following Layne’s work. Layne et al.’s results stated there was “enhanced” neuromuscular activity. This described the higher levels of activity with foot pressure and the earlier onset of muscle activity. However, the control in this study was microgravity without foot pressure. Results were not compared to 1-G data.
Kozlovskaya et al. suggest that the Penguin Suit, another countermeasure suit and the precursor to the Skinsuit, may produce sensorimotor effects, specifically the restoration of mechanoreceptors in the skin and muscles . However, this comment is not supported with any quantitative evidence or references to the literature.
Another note from the literature mentions that there is currently no adequate analog for sensorimotor adaptations. While this statement was made primarily in regards to the vestibular system, it seems accurate for mechanical load sensors as well . Even in bed rest analogs or body-weight suspension, there is a constant force of gravity on the body and body-load receptors.
The system block diagram for the Zero-G flight is included in Figure 5. This primarily includes two sensor systems connected to a laptop: the Novel Pressure Sensor System and the Delsys Electromyography (EMG) System.
The concept of operations is included below. In the experimental protocol for each parabolic cycle, a single participant will be asked to perform rapid unilateral arm raises, which are known to prompt postural muscle activation in 1-G. The experiment will include three conditions: suited condition #1 (wearing the Skinsuit), suited condition #2 (wearing the Skinsuit with the stirrups disconnected), and an unsuited condition (nonspecific clothing).
Experiment Protocol, Suited Condition #1
Save Data, Restart Recording
Experiment Protocol, Suited Condition #1
Save Data, Restart Recording
Experiment Protocol, Suited Condition #2
Doff Skinsuit, Ensure that all sensors are still secure, Save Data, Restart Recording
Experiment Protocol, Unsuited Condition
After rigorous material testing, a 100% PrimeflexTM warp knit fabric has been selected for the Skinsuit. PrimeflexTM is composed of two types of polyester PET (polyethylene terephthalate) and PTT (polytrimethylene terephthalate), which provide bi-component stretch with high recovery forces. Different fabric structures (knitting, weaving, yarn density, etc.) can be used with the Primeflex material and will influence the mechanical properties.
Prior to any experiments, the subject will be sized for a custom Skinsuit. Detailed body measurements will be obtained manually with a soft tape measure or using a 3D body scanner. A suit will be custom fabricated based on these measurements.
During the experimental procedure, the subject will be asked to perform simple body movements (e.g. arm flexion or extension) while wearing several wearable sensing systems. This will include 1) surface electromyography sensors adhered to the skin and 2) pressure sensors on the skin and in the soles of the subject's shoes. Video may also be recorded while the subject is performing the task, to record progress. The subject will also be prompted with qualitative survey questions before and after each trial, asking about their perception and disorientation during the experiment.
The experimental protocol will include an unsuited condition (i.e. non-specific clothing or tight-fitting athletic wear). There may be 1 to 2 suited conditions in which the subject will wear the Skinsuit (with or without Skinsuit stirrups disconnected). Trials may occur during multiple environmental conditions including 1-G, microgravity, and partial gravity. In any combination of the above conditions and environments, the subject may also be blindfolded or allowed full vision. The same activity (i.e. simple body movements while data is recorded from body-worn sensors and, if needed, video) will be performed in each condition/environment.
The participant will be asked to wear tight-fitting athletic wear under the Skinsuit to ensure modesty when donning and doffing the suit during the Zero-G flight.
For the flight tests: The flight will consist of about 20 cycles of flight profile. A flight profile will consist of a period of hypergravity and a period of microgravity (or partial gravity). During the phase of microgravity (or partial gravity), which will last approximately 20 seconds, the subject will perform the previously mentioned activity (i.e. simple body movements while data is recorded from body-worn sensors and, if needed, video) during suited and unsuited conditions.
During pre-flight tests in the Human Systems Laboratory at MIT, the subject will again perform simple body movements while data is recorded from body-worn sensors.
In order to collect data from human subjects, institutional review board (IRB) approval must be obtained. At MIT, this is also referred to as the Committee on the Use of Humans as Experimental Subjects (COUHES).
An application was submitted and approved which described the relevant personnel, funding sources, experimental protocol, potential risks to the participants, possible benefits, and other relevant information about the study. In addition, a consent form was drafted for submission with the COUHES application. This document provides information to the experiment participants, and they are required to sign the consent form before participating in the experiment.
I visited our fabricator (Liz at Costume Works, Somerville, MA) on-site to try on the Skinsuit for the first time. The suit was almost complete, except for missing stirrups and ankle stays. There was some donning difficulty but this was not unexpected.
Suggested Modifications: To address donning difficulties, Liz will add donning assist loops, strategically placed at the hips. We also added a thumb loop at the base of the zipper on the back and reinforced areas along the SARs where we heard ripping during the fitting session. The stirrups and ankle stays were also added during this set of modifications, and an MIT patch was added to the yoke.
A few more iterations of modifications were performed this week.
Skinsuit Fitting Session #2: Following Thanksgiving, I tried on the suit after our initial suit modifications and the addition of the ankle stays and the stirrups. The ankle stays restricted the ankle circumference. It was not wide enough to get around my feet, and I was unable to don the suit.
Skinsuit Modifications #2: Liz extended the open section of fabric on the back of the ankle to make it wide enough for me to don. In the future, we will add this new measurement (circumference around widest part of ankle w/ ball of foot) to our list of measurements. She also added loops to the tops of the stirrup straps in an attempt to allow the wearer to independently tighten the stirrups
Skinsuit Fitting Session #3: The suit was donned successfully; however, significant assistance was required. The zipper-pull is a bit thin and difficult to use. Additionally, the mobility restrictions of the suit make it difficult to pull the stirrups over the feet and tighten the stirrups. Upon trying to tighten the stirrups, it also became apparent that the stirrups are very difficult to tighten. Compared to the previous MKV suit, it seems like the straps on our new suit are much thicker and cannot easily slide through the buckle. It's difficult to access the full loading potential of the suit, because we can't tighten the stirrups adequately.
Skinsuit Fitting Session #4: The stirrup buckles were replaced with plastic strap adjusters to allow stirrups to be tightened much more easily. The zipper pull was also replaced with a more durable ribbon material.