Kinematic features of whole-body reaching movements underwater: Neutral buoyancy effects

Abstract

Astronauts' training is conventionally performed in a pool to reproduce weightlessness by exploiting buoyancy which is supposed to reduce the impact of gravity on the body. However, this training method has not been scientifically validated yet, and requires first to study the effects of underwater exposure on motor behavior. We examined the influence of neutral buoyancy on kinematic features of whole-body reaching underwater and compared them with those produced on land. Eight professional divers were asked to perform arm reaching movements toward visual targets while standing. Targets were presented either close or far from the subjects (requiring in the latter case an additional whole-body displacement). Reaching movements were performed on land or underwater in two different contexts of buoyancy. The divers either wore a diving suit only with neutral buoyancy applied to their center of mass or were additionally equipped with a submersible simulated space suit with neutral buoyancy applied to their body limbs. Results showed that underwater exposure impacted basic movement features, especially movement speed which was reduced. However, movement kinematics also differed according to the way buoyancy was exerted on the whole-body. When neutral buoyancy was applied to the center of mass only, some focal and postural components of whole-body reaching remained close to land observations, notably when considering the relative deceleration duration of arm elevation and concomitant forward trunk bending when reaching the far target. On the contrary, when neutral buoyancy was exerted on body segments, movement kinematics were close to those reported in weightlessness, as reflected by the arm deceleration phase and the whole-body forward displacement when reaching the far target. These results suggest that astronauts could benefit from the application of neutral buoyancy across the whole-body segments to optimize underwater training and acquire specific motor skills which will be used in space.

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

“…Overall, individual trends for both focal and postural observations are clear and systematic (as illustrated in the Supplementary Figure 1 ). Remarkably, the stabilized motor features observed in microgravity in the present study appear close to those previously reported when participants performed the same task underwater with neutral buoyancy applied to body limbs (Macaluso et al, 2016 ). The following section discusses the behavioral analogies observed in both environments.…”

“…They had no prior experience of microgravity exposure. As the present study is part of a scientific program studying human motor behavior in different force fields, participants were previously tested in normogravity and underwater for the same task as reported in Macaluso et al ( 2016 ). None of the participants suffered from neuromuscular or sensory impairments, as confirmed by a medical examination prior to the experiment.…”

“…Data presented below describe behavioral features of reaching movements in the sagittal plane and some of them are detailed in Macaluso et al ( 2016 ). First, we analyzed the fingertip trajectory, success rate (index fingertip within a given target area), index final deviation from target center, reaction time (RT), movement duration (MD), and mean tangential velocity (Vmean endpoint ).…”

Coherent Multimodal Sensory Information Allows Switching between Gravitoinertial Contexts

“…However, different this novel dynamic is, we posit the switching is also made possible because low level multisensory signals are coherently affected which allows adaptation. We speculate the same phenomenon occurs during parabolic flights, when participants are exposed to a series of gravitational environments or underwater, when neutral buoyancy is exerted on body segments as opposed to body center of mass (Macaluso et al, 2016). …”

“…Adaptation of motor responses has been reported following changes in gravity during parabolic flights (Hermsdörfer et al, 1999; Augurelle et al, 2003; Mierau et al, 2008; Crevecoeur et al, 2009a), in gravitoinertial environments (Dizio and Lackner, 1995; Nowak et al, 2004; Göbel et al, 2006) and underwater (Macaluso et al, 2016). However, exposures were either constant or occurred in a reproducible manner and could eventually be predicted.…”