How About Running on Mars ? Influence of Sensory Coherence on the Running Pattern and on Spatial Perception in Simulated Reduced Gravity

Sammanfattning: Motor control, including locomotion, strongly depends on the gravitational field. Recent developments like lower-body positive pressure treadmills (LBPPTs) have enabled Earth- based studies on the effects of reduced body weight (BW) on walking and running. Yet, the observed adaptations to simulated hypogravity are not optimal. The present project aims at improving them by adding visual information mimicking a martian environment during running sessions on a LBPPT. Twenty-nine participants performed three sessions of four successive five-minute runs at preferred speed, alternating Earth- or Mars-like gravity (100 or 38% BW). They were displayed visual scenes using a virtual reality headset in order to assess the effects of the presence or absence of visual flow and vertical head oscillations during running. The gait was analysed using vertical ground reaction force, foot and sacrum accelerations. Evaluation of the visual vertical and of the sensitivity to the illusion of self-motion helped investigate the adaptations in the perception of gravity and motion. It was found that body weight reduction induces biomechanical adaptations independently of the visual context. Impact peak force and stance time decrease, the latter increasing flight time. Strong inter-individual differences in braking and push-off times appear at 38% BW, unobserved in previous studies at 60 and 80% BW. Additionally, the weight given to visual cues in the perceptual integration of gravity diminishes in hypogravity, in favour of increased reliance on the body long axis as a reference for verticality, all the more when visual scenes and locomotor activity are coherent. In that case, self-motion perception decreases without being influenced by hypogravity. Thus, locomotor and perceptual adaptations are impacted differently depending on a given sensory context. Motor control and spatial perception can then be updated independently relative to the gravitational and visual environment.