## 4 Discussion
Past research has shown that a fear of reinjury can increase the likelihood of reinjury [28]. This is seen in athletes [28], who train their bodies as rigorously, if not more so, than astronauts and non-athletes [29; 30]. There is also the psychological impact if an injury is to occur to an astronaut during a planetary EVA; rehabilitation of an injury is impacted by the psychological state of the person injured [28; 31], and becoming injured on a different planet entirely may have a severe effect on the astronaut's psychological state. These findings may not be a problem for low gravity, such as lunar gravity, which is roughly 1/6 Earth's gravity, as we have seen during the Apollo missions back in the '60s and '70s [13; 14; 15]. However, one of the upcoming missions is to have a planetary EVA on the surface of Mars, and Martian gravity is roughly 3/8 th that of Earth's gravity. This increase in gravity may impact astronauts' ability to perform tasks since it is a very lengthy voyage to the surface of Mars; it is estimated that the trip to Mars will take 400-600 days [32]. On a 180-day mission on board the International Space Station, despite in-flight exercise, an astronaut can lose 45% capacity for physical work, a 35% loss to produce force, a 20% loss in velocity, and a 15% loss in muscle volume [33]. The astronauts going to Mars will not have access to the exercise equipment aboard the International Space Station. We do not yet know what the full extent will be to the human body after such a lengthy journey in space because there has never been a mission in space for that extended period. The lengthy journey and increased gravity can become a significant factor, coinciding with the xEMU spacesuit instability, for astronauts' ability to mobilize and perform the necessary tasks needed on the surface of Mars. Standing balance for astronauts is important, and our study has scratched the surface of how the xEMU spacesuits affect astronauts' standing balance. Testing with a fully-fledged xEMU spacesuit will be the next step in understanding how spacesuits affect balance ability, but it was not carried out here, in that will require tremendous resources and personnel. The cost of an actual xEMU suit is in the order of several millions of dollars. Via discussions with spacesuit experts at NASA JSC with first-hand experience developing a mock xEMU spacesuit, developing a mock xEMU spacesuit is a multi-year project; this was not the scope of our work. To develop a mock xEMU spacesuit at the CBRE that behaves and mimics an actual xEMU spacesuit would require a tremendous amount of effort, time, and resources. Therefore, a weighted vest that raises the CoG was considered the best option, in that it allowed for the widest range of eligible participants, cost-efficient, customizable weightout, and minimized injury/safety concerns. However, the xEMU Vest simulates a superior shift in CoG but does not simulate the full weight, the motion of, or the pressurization of the actual xEMU spacesuit. The HUT may be the best possible method to test an xEMU spacesuit without the limitations of the xEMU Vest. The HUT limits the range of motion for the head, shoulders, and arms slightly and also alters the wearer's resting posture (as seen in Figure 2B). The HUT significantly affects the wearer's ability to maintain their balance in terms of body sway (TOTEX), speed of body sway (MVELO), and rate of body sway (MFREQ) with a superiorly raised and away from the body CoG shift. This shift mimics what is seen in the xEMU spacesuits; however, the xEMU spacesuits shift the CoG is higher and further away from the body than the HUT, so parameters that were significantly affected (TOTEX, MVELO, and MFREQ) may see even greater increases, i.e., more instability. Our baseline investigation and metrics presented here can be built upon by future studies tied to the xEMU spacesuit's impact on astronaut balance. Conceptualization, R.A.R.M. and L.A.T. ; methodology, R.A.R.M. and L.A.T. ; formal analysis, R.A.R.M. ; investigation, R.A.R.M.