BACKGROUND AND OBJECTIVES: The parameters of vestibulo-ocular reflex (VOR) are believed to indicate the quantitative value of vestibular function and the differences in them are related to the susceptibility of motion sickness. The purpose of this study was to investigate the effects of repetitive multiaxial 3-dimensional rotation training on VOR parameters. MATERIALS AND METHODS: Fifteen healthy volunteers were randomly assigned to 3 different groups according to the mode of exercise training. Aerotrim exercise was done as a method of repetitive multiaxial 3-dimensional rotation training. The changes in VOR parameters after 9 weeks of exercise training in Aerotrim training group were compared with that of other groups. RESULTS: While the values of VOR gain in Aerotrim training group after 9 weeks of exercise training were significantly lower than baseline values at rotation frequencies of 0.01, 0.04, 0.08, 0.16, and 0.32 Hz, values of VOR gain in other groups showed no difference between before and after exercise training. In all groups, there were no significant differences in VOR phase and symmetry values between before and after exercise training. CONCLUSION: This study showed that VOR parameters changed after 9 weeks of repetitive multiaxial 3-dimensional rotation training, and vestibular habituation might eventually occur. Since vestibular habituation is known to contribute to mitigating the frequency and the degree of motion sickness, we suggest that repetitive multiaxial 3-dimensional rotation training can be used as the countermeasure for student pilots or astronauts, who are often exposed to unusual motion and positional status in actual 3-dimensional space.
Astronauts ; Humans ; Motion Sickness ; Reflex, Vestibulo-Ocular

AIMTo verify the hypothesis that repeated body position change training can improve human head-down tilt (HDT) tolerance.

METHODSSix young healthy subjects were trained with repeated position change for 9 times and 11 days according to protocol of alternative head-down and head-up tilts, each time of training lasted for about 35 min. Their HDT tolerance (- 30 degrees/30 min) were determined before and after training.

RESULTS(1) Compared with the data before training, subjects' symptom scores during HDT test after training decreased significantly (6.00 +/- 3.79 vs 1.00 +/- 0.63, P < 0.05), magnitude of the decreased heart rate increased significantly (-0.6 +/- 2.5 vs -4.4 +/- 3.6, P < 0.01). (2) Before training, blood flow volume of internal jugular vein (IJV) during HDT decreased significantly and that of internal carotid artery (ICA) increased significantly at the beginning period of HDT compared with pre-HDT (P < 0.01), while blood flow volume of the common carotid artery (CCA) presented increasing trend. After training, there was no significant difference in blood flow volume of IJV between during HDT and pre-HDT, that of ICA and CCA presented decreasing trend in the final period of HDT compared with Pre-HDT.

CONCLUSIONRepeated body position change training can improve human head-down tilt tolerance. And its main causation is that headward shift of blood volume is restrained to some extend during HDT after training.

Adaptation, Physiological ; physiology ; Adolescent ; Astronauts ; Cardiovascular Physiological Phenomena ; Head-Down Tilt ; Humans ; Male ; Posture ; physiology ; Weightlessness Simulation ; Young Adult

The hand strength of astronauts, when they are outside the space capsule, is highly influenced by the residual pressure (the pressure difference between inside pressure and outside one of the suit) of extravehicular activity spacesuit glove and the pressure exerted by braided fabric. The hand strength decreases significantly on extravehicular activity, severely reducing the operation efficiency. To measure mechanical influence caused by spacesuit glove on muscle-tendon and joints, the present paper analyzes the movement anatomy and biomechanical characteristics of gripping, and then proposes a grip model. With phalangeal joint simplified as hinges, seven muscles as a finger grip energy unit, the Hill muscle model was used to compute the effects. We also used ANSYS in this study to establish a 3-D finite element model of an index finger which included both bones and muscles with glove, and then we verified the model. This model was applied to calculate the muscle stress in various situations of bare hands or hands wearing gloves in three different sizes. The results showed that in order to achieve normal grip strength with the influence caused by superfluous press, the finger's muscle stress should be increased to 5.4 times of that in normal situation, with most of the finger grip strength used to overcome the influence of superfluous pressure. When the gap between the finger surface and the glove is smaller, the mechanical influence which superfluous press made will decrease. The results would provide a theoretical basis for the design of the EVA Glove.
Astronauts ; Fingers ; physiology ; Finite Element Analysis ; Gloves, Protective ; adverse effects ; Hand Strength ; physiology ; Humans ; Mechanical Phenomena ; Pressure ; Space Suits ; adverse effects