Comparing the effects of space flight and water immersion on sensorimotor performance

Several studies documented the detrimental effects of microgravity during spaceflight on human motor control e.g. during aiming tasks. In addition to parabolic flight, water immersion has been used for simulating microgravity effects on earth. Until now, however, the validity of partial or full water immersion setups as test environments to explore effects on sensorimotor performance has not been tested. In the present paper, the results of three empirical studies were compared using the identical aiming task paradigm during forearm water immersion (N = 19), full body water immersion (N = 22), and during spaceflight (N = 3 astronauts). In line with prior research, slower aiming motion profiles were found during spaceflight (2 weeks in space) compared to the terrestrial experiments. Astronauts required substantially more time to approach target areas for the desired level of target matching precision in space. Average motion speed and speed variance decreased significantly. Intriguingly, the same overall effect pattern was evident in both partial and full water immersion, although the effect sizes tended to be smaller. Altogether, results indicate that water immersion is a valid form of weightlessness simulation. However, effects solely present during spaceflight (such as vestibular dysfunction) additionally contribute to performance losses.