Tandem Walk in Simulated Martian Gravity and Visual Environment

Astronauts returning from long-duration spaceflights experience visual-vestibular conflicts that causes motion sickness, perceptions that the environment is moving when it is not, problems with walking, and other functional tasks. To evaluate whether astronauts will have similar decrements associated with visual-vestibular conflicts after they land on Mars following exposure to weightlessness, participants were held by a device that offloads their weight; first entirely (0 G) for 10 minutes, and then partially (0.38 G) or not at all (1 G) for 15 minutes. Tandem (heel-to-toe) walk was used to assess the subjects walking performance. Ten subjects performed 2 trials of 10 steps on a medium-density foam surface. Four conditions were investigated: (a) 1 G in virtual reality (VR); (b) 1 G in VR with a superimposed disorienting optokinetic simulation (VR+DOS); (c) 0.38 G in VR; and (d) 0.38 G in VR+DOS. Tandem walk performance decreased in VR+DOS compared to VR in both 1 G and simulated 0.38 G. Tandem walking performance in VR+DOS was better in 0.38 G compared to 1 G. Tandem walking performance in VR+DOS in 1 G was not significantly different from tandem walking performance after spaceflight or bed rest. The increased tandem walking performance in 0.38 G compared to 1 G was presumably due to an increased cone of stability, allowing larger amplitude of body sway without resulting in a fall. Tandem walking on a compliant foam surface in VR+DOS is a potential analog for simulating postflight dynamic balance deficits in astronauts.