Astronaute

Résumé

vignette|Bruce McCandless II est le premier astronaute américain à réaliser une sortie extravéhiculaire libre. Un astronaute est le membre de l'équipage d'un véhicule spatial. Les termes cosmonaute, taïkonaute ou spationaute sont couramment utilisés pour désigner les astronautes russes ou soviétiques, chinois ou français. Les cosmonautes sont choisis initialement parmi les pilotes militaires. Les critères de recrutement ont évolué par la suite et, si une bonne condition physique est toujours nécessaire, l'accent est désormais mis sur l'équilibre psychologique, la compétence technique ou scientifique selon le poste occupé et la capacité à s'exprimer dans les langues des principales nations spatiales (anglais, russe). Voyager dans l'espace reste encore un privilège rare puisque, en 2021, après soixante ans d'activité spatiale, seules un peu plus de ont séjourné dans l'espace, en moyenne à deux reprises, dont une cinquantaine de femmes. Le premier homme cosmonaute est Youri Gagarine en

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https://fr.wikipedia.org/wiki/Astronaute

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Head position during various locomotor executions after prolonged microgravity exposure

Grégoire Courtine

Head orientation in the sagittal plane was assessed before and the second and sixth days after a prolonged microgravity exposure (6 months) in 7 astronauts, which were instructed to execute various locomotor movements (stair ascent, jump down and level walk). Crewmembers systematically flexed down the head when they executed the locomotion the second day post-flight compared to the pre-flight walk. Cephalic orientation was normally positioned when movements was performed the sixth day after Earth re-entry. This head flexion may reflect a strategy used by cosmonauts to increase the vestibular sensibility, and then improve the control of the dynamic equilibrium during locomotor movements. The high rate of re-adaptation indicated that cosmonauts rapidly recovered their normal walking capacities despite the prolonged microgravity exposure

2002

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Recovery of locomotor function was investigated in seven cosmonauts exposed to microgravity for 6 months. Crew members executed a locomotor task with visual cues (eyes open, EO) and without them (eyes closed, EC). The locomotor task consisted of ascending a two-step staircase, jumping down from a 30-cm high platform, and finally walking 4 m in the straight-ahead direction. Subjects were tested before the flight (D-30), and on the second day (R+2) and the sixth day (R+6) after the flight. Cosmonauts succeeded in all locomotor sub-tasks as early as R+2. In particular, microgravity exposure did not prevent cosmonauts from producing a straight walking trajectory even when blindfolded (deviation at R+2 with EO 2.0±0.7°, and with EC 4.7±1.9°). However, lateral movements of trunk were found to be increased at R+2 (16%), suggesting post-flight gait instability. Modifications of the timing of forward trunk movements were also detected at R+2. Unexpectedly, coordination patterns between head and trunk movements remained unchanged. The maximum amplitude of head pitches was 5° or less. Yet, the cosmonauts held their heads at lower positions at R+2 in comparison with their pre-flight postures, and they lowered their heads even further during blindfolded locomotion. In general, comparable spatial and temporal modifications of head and trunk movements at R+2 were observed during the stair and gait cycles. Mean values of locomotor descriptors measured at R+6 did not deviate from the pre-flight baseline. When performing jumps after the return from their flight, cosmonauts decreased the amplitude and speed of head rotation by approximately 50% in comparison with the pre-flight values. In addition, the timing of head pitches was uncertain after weightlessness. All the above changes endured at R+6. Previous studies reported that prolonged exposure to microgravity adversely affects the motor performance in the initial hours upon re-entry to Earth. However, gait analysis revealed that cosmonauts recovered near-optimal locomotor abilities as early as the second day post-flight. Results suggest a notable capability of the central nervous system to rapidly accommodate to changing physical environment and body properties. The role of head stabilization at a lower position is conjectured to be an adaptive response to microgravity-induced motor disorders

2004

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2004