Vision Affects Gait Speed but not Patterns of Muscle Activation During Inclined Walking—A Virtual Reality Study

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.

Vision affects gait speed but not patterns of muscle activation during inclined walking – a virtual reality study

While walking, our locomotion is affected by and adapts to the environment based on vision-based and body-based (vestibular and proprioception) cues, all contributing to an “Internal Model of Gravity”. During surface inclination transitions, we modulate gait to counteract gravitational forces by braking during downhill walking to avoid uncontrolled acceleration or by exerting effort to avoid deceleration while walking uphill. In this study, we investigated the role of vision in gait modulation during surface inclination transitions by using an immersive large-scale Virtual Reality (VR) system equipped with a self-paced treadmill and projected visual scenes that allowed us to modulate physical-visual inclinations congruence parametrically. Gait speed and leg muscle electromyography (EMG) were measured in 12 healthy young adults. In addition, the magnitude of subjective visual misperception of verticality was measured by the rod and frame test. During virtual (non-veridical) inclination transitions, vision modulated gait speed after transitions by (i) slowing down to counteract the excepted gravitational ‘boost’ in virtual downhill inclinations and by (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 subjective visual verticality misperception. However, temporal patterns of muscle activation, which are significantly affected by real gravitational inclination transitions, were not affected by virtual (visual) inclination transitions. Our results delineate the contribution of vision to functional locomotion on uneven surfaces and may lead to enhanced rehabilitation strategies for neurological disorders affecting movement.Significance statementA crucial component of successful locomotion is maintaining balance and speed while walking on uneven surfaces. In order to reach successful locomotion, an individual must utilize multisensory integration of visual, gravitational, and proprioception cues. The contribution of vision to this process is still unclear, thus we used a fully immersive virtual reality treadmill setup allowing us to manipulate visual (virtual) and gravitational (real) surface inclinations independently during locomotion of healthy adults. While vision modulated gait speed for a short period after inclination transitions and this was predictive of individual’s visual dependency, muscle activation patterns were only affected by gravitational surface inclinations, not by vision. Understanding the vision’s contribution to successful locomotion may lead to improved rehabilitation for movement disorders.

Effects of downhill walking in pulmonary rehabilitation for patients with COPD: a randomised controlled trial

The development of contractile muscle fatigue (CMF) affects training responses in patients with chronic obstructive pulmonary disease (COPD). Downhill walking induces CMF with lower dyspnoea and fatigue than level walking. This study compared the effect of pulmonary rehabilitation (PR) comprising downhill walking training (DT) to PR comprising level walking (conventional training (CT)) in patients with COPD.In this randomised controlled trial, 35 patients (62±8 years; forced expiratory volume in 1 s (FEV1) 50±17% predicted) were randomised to DT or CT. Exercise tolerance (6-minute walk test distance (6MWD); primary outcome), muscle function, symptoms, quality-of-life and physical activity levels were assessed before and after PR. Absolute training changes and the proportion of patients exceeding the 30 m 6MWD minimally important difference (MID) were compared between groups. Quadriceps muscle biopsies were collected after PR in a subset of patients to examine physiological responses to long-term eccentric training.No between-group differences were observed in absolute 6MWD improvement (mean 6MWD change 77±46 m DT versus 56±47 m CT; p=0.45), however 94% of patients in DT exceeded the 6MWD MID compared to 65% in CT (p=0.03). Patients in DT tended to have larger improvements than CT in other outcomes. Muscle biopsy analyses did not differ between groups.PR incorporating downhill walking confers similar magnitudes of effects to PR with conventional walking across clinical outcomes in patients with COPD, however, offers a more reliable stimulus to maximise the achievement of clinically relevant gains in functional exercise tolerance in people with COPD.