Abstract
While walking, our locomotion is affected by and adapts to the environment based on vision- and body-based (vestibular and proprioception) cues. When transitioning to downhill walking, we modulate gait by braking to avoid uncontrolled acceleration, and when transitioning to uphill walking, we exert effort to avoid deceleration. In this study, we aimed to measure the influence of visual inputs on this behavior and on muscle activation. Specifically, we aimed to explore whether the gait speed modulations triggered by mere visual cues after transitioning to virtually inclined surface walking are accompanied by changes in muscle activation patterns typical to those triggered by veridical (gravitational) surface inclination transitions. We used an immersive virtual reality system equipped with a self-paced treadmill and projected visual scenes that allowed us to modulate physical–visual inclination congruence parametrically. Gait speed and leg muscle electromyography were measured in 12 healthy young adults. In addition, the magnitude of subjective visual verticality misperception (SVV) was measured by the rod and frame test. During virtual (non-veridical) inclination transitions, vision modulated gait speed by (i) slowing down to counteract the excepted gravitational “boost” in virtual downhill inclinations and (ii) speeding up to counteract the expected gravity resistance in virtual uphill inclinations. These gait speed modulations were reflected in muscle activation intensity changes and associated with SVV misperception. However, temporal patterns of muscle activation were not affected by virtual (visual) inclination transitions. Our results delineate the contribution of vision to locomotion and may lead to enhanced rehabilitation strategies for neurological disorders affecting movement.
Highlights
In order to maintain stability during bipedal locomotion, the musculoskeletal system continuously adapts to changing walking conditions via a complex motor process that relies on multisensory integration (Wall-Scheffler et al, 2011; Kimel-Naor et al, 2017; Cano Porras et al, 2020)
We aimed to explore whether the gait speed modulations triggered by mere visual cues after transitioning to virtually inclined surface walking are accompanied by changes in muscle activation patterns typical to those triggered by veridical surface inclination transitions
We aimed to explore whether the gait speed modulations triggered by mere visual cues after transitioning to virtualinclined surface walking are accompanied by changes in muscle activation patterns
Summary
In order to maintain stability during bipedal locomotion, the musculoskeletal system continuously adapts to changing walking conditions via a complex motor process that relies on multisensory integration (Wall-Scheffler et al, 2011; Kimel-Naor et al, 2017; Cano Porras et al, 2020). The braking effect prevents gravitational-driven uncontrolled speeding-up and allows the walker to descend in a steady gait speed, either faster or slower than walking on a leveled surface (Sun et al, 1996; McIntosh et al, 2006; Kimel-Naor et al, 2017; Cano Porras et al, 2020). We found that vision modulates gait speed, postural adjustment, and spatiotemporal gait parameters shortly after transition to a virtual inclination for approximately 20 s (Cano Porras et al, 2020) It remains unclear whether individuals which are more dependent on visual inputs than others would respond by greater modulations in gait speed following a virtual visual inclination. It is unclear whether patterns of muscle activation are affected by mere virtual inclinations
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