title: Recovery of the locomotor function after prolonged microgravity exposure. I. Head-trunk movement and locomotor equilibrium during various tasks.
abstract: 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 degrees, and with EC 4.7+/-1.9 degrees ). 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 degrees 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.
authors.affiliation: ERM 207 INSERM Motricité & Plasticité, UFR STAPS, Université de Bourgogne, 21078, Dijon, France. gcourtin@ucla.edu
authors.forename: Grégoire
authors.initials: G
authors.lastname: Courtine
authors.forename: Thierry
authors.initials: T
authors.lastname: Pozzo
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001696:Biomechanical Phenomena; D003463:Cues; D005684:Gait / Q000502:physiology; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D009334:Neck Muscles / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D020127:Recovery of Function / Q000502:physiology*; D012683:Sensory Deprivation / Q000502:physiology; D013026:Space Flight; D014893:Weightlessness / Q000009:adverse effects*