The Gravity Loading Countermeasure Skinsuit

One of the hallmarks of long-duration spaceflight is physiological deconditioning seen in the absence of gravity. Negative changes in bone, muscle, and other physiological systems occur rapidly in space, and have the potential to severely limit the human space exploration program. One countermeasure concept that may aid in helping prevent deconditioning is the Gravity Loading Countermeasure Skinsuit, which uses elastic materials to provide bodyweight loading similar to that seen in the presence of gravity. Preliminary work performed in our lab produced prototype garments that were characterized for comfort and wearability, but had design deficiencies that prevented them from providing full bodyweight loading to the subjects. In order to create an effective countermeasure garment we first developed a model of suit-body interactions through computational simulations to inform suit design. The model was developed using OpenSim, a musculoskeletal modeling program developed at Stanford University. The model was developed using a previously validated musculoskeletal model, with the suit model implemented using OpenSim’s inherent classes of bodies and actuators. After the model was developed and verified, a simple motion simulation was performed to test how changing the material properties and static loading levels of the suit changed the loads it provides to the body. The results of the simulation showed that suit material stiffness in the range of commercially available elastic materials could provide loading in microgravity similarly to bodyweight motions on earth, and that different levels of material stiffness are necessary for the different joints. It also showed that the suit could still provide high dynamic loads to the joints during movement even if the suit did not provide full bodyweight loading during the static upright pose. Using the lessons learned from the modeling efforts and previous suit prototypes, we then designed, built and characterized prototype suits. Previous suit prototypes utilized spandex as the sole loading material, which had many deficiencies. To improve the suit loading we investigated new loading materials, and chose two for use in new prototypes: narrow elastics and resistive exercise bands. These were shown to have much higher loading capacity than the old spandex, with increased durability for long-term use. These new loading materials were integrated into a soft loading exoskeleton comprised of nylon webbing. This exoskeleton was worn over a spandex bodysuit that provided an interface between the subject and the loading exoskeleton. During suit testing, the suits provided 76-84% bodyweight loading to the subjects, which was significantly higher than the previous suit prototypes. However, there was over-loading at the shoulder due to insufficient suit anchorting, and the load at the feet was concentrated on the heel, which both led to comfort issues. The suits were then evaluated to test their potential for efficacy in ameliorating musculoskeletal deconditioning in earth-based analogs of unloading. During a 4 hour bed-rest study, no effect of the suit on spinal elongation was observed, most likely due to the short length of the test and a high level of noise in the height measurements takes. Subjects also participated in an exercise study on the Enhanced Zero-gravity Locomotion Simulator (eZLS) vertical treadmill at NASA Glenn Research Center. Subjects walked and ran in simulated microgravity in both suited and unsuited conditions. The suit increased the subjects’ physiological workload based on heart rate and subjective data. Subjects were able to walk and run normally in the suit. Motion capture and ground reaction force data was input into the OpenSim model, and showed that the suit increased force on both the muscles and bones during running, which shows that the suit may be effective in ameliorating physiological deconditioning if used as a countermeasure during long-duration spaceflight.