Sensorimotor Reorganizations of Arm Kinematics and Postural Strategy for Functional Whole-Body Reaching Movements in Microgravity

Abstract

Understanding the impact of weightlessness on human behavior during the forthcoming long-term space missions is of critical importance, especially when considering the efficiency of goal-directed movements in these unusual environments. Several studies provided a large set of evidence that gravity is taken into account during the planning stage of arm reaching movements to optimally anticipate its consequence upon the moving limbs. However, less is known about sensorimotor changes required to face weightless environments when individuals have to perform fast and accurate goal-directed actions with whole-body displacement. We thus aimed at characterizing kinematic features of whole-body reaching movements in microgravity, involving high spatiotemporal constraints of execution, to question whether and how humans are able to maintain the performance of a functional behavior in the standards of normogravity execution. Seven participants were asked to reach as fast and as accurately as possible visual targets while standing during microgravity episodes in parabolic flight. Small and large targets were presented either close or far from the participants (requiring, in the latter case, additional whole-body displacement). Results reported that participants successfully performed the reaching task with general temporal features of movement (e.g., movement speed) close to land observations. However, our analyses also demonstrated substantial kinematic changes related to the temporal structure of focal movement and the postural strategy to successfully perform -constrained- whole-body reaching movements in microgravity. These immediate reorganizations are likely achieved by rapidly taking into account the absence of gravity in motor preparation and execution (presumably from cues about body limbs unweighting). Specifically, when compared to normogravity, the arm deceleration phase substantially increased. Furthermore, greater whole-body forward displacements due to smaller trunk flexions occurred when reaching far targets in microgravity. Remarkably, these changes of focal kinematics and postural strategy appear close to those previously reported when participants performed the same task underwater with neutral buoyancy applied to body limbs. Overall, these novel findings reveal that humans are able to maintain the performance of functional goal-directed whole-body actions in weightlessness by successfully managing spatiotemporal constraints of execution in this unusual environment.

Double-Step Paradigm in Microgravity: Preservation of Sensorimotor Flexibility in Altered Gravitational Force Field

“…The experiment was conducted onboard the A-310 ZERO-G aircraft chartered by the French national space research center (CNES) and Novespace during the CNES #128 parabolic flight campaign including 3 days of flight. Parabolic maneuvers were similar to those that we described in previous studies (Bringoux et al, 2012;Saradjian et al, 2013;Macaluso et al, 2017). Participants stood upright in front of two LEDs-defined circular targets (target area diameter: 4 cm) with their feet fastened to the cabin floor by means of footstraps ( Figure 1A).…”

“…The present study aimed to challenge the sensorimotor flexibility of fast and accurate goal-directed pointing movements performed in microgravity which have been observed in previous studies (e.g., Papaxanthis et al, 2005;Macaluso et al, 2017;White et al, 2018) by presenting unpredictable jumps in target location following movement onset. Our results revealed that the overall performance and kinematics of motor corrections in response to target jumps were unaffected during the 0g phases of parabolic flight as compared to 1g baseline.…”

“…This was presumably achieved by rapidly updating internal models from the new dynamic properties of the environment as suggested in previous studies (Papaxanthis et al, 2005;White et al, 2018), although gravity-independent factors, such as intersegmental dynamics may also be at work in updating the representation of limb dynamics (Flanders and Herrmann, 1992). The fact that movements performed in microgravity also exhibit kinematic features that mostly remained in the normogravity standards (e.g., Macaluso et al, 2017) supports an optimal reorganization of movement planning in a feedforward manner based on initial state estimates of the sensorimotor system. If the feedback controller ruling online motor corrections is linked to thefast adapted-feedforward controller, we should also observe early accurate corrective responses to vertical target jumps in microgravity, preserving normogravity-like kinematics during initial microgravity exposure.…”

“…We replicated the analyses performed by Macaluso et al (2017) who used a similar experimental setup in normo-and microgravity. Index finger and shoulder position data were filtered using a digital second-order dual-pass Butterworth filter (cutoff frequency 10 Hz).…”

“…The present study aims to challenge these two hypotheses by assessing human capabilities to produce online motor corrections consecutive to an unpredictable change of target location in microgravity. We recently reported that individuals with no experience in microgravity were able to execute accurate wholebody reaching at the earliest time of microgravity exposure during parabolic flights (Macaluso et al, 2017). This was presumably achieved by rapidly updating internal models from the new dynamic properties of the environment as suggested in previous studies (Papaxanthis et al, 2005;White et al, 2018), although gravity-independent factors, such as intersegmental dynamics may also be at work in updating the representation of limb dynamics (Flanders and Herrmann, 1992).…”