Visual guidance of the human foot during a step

Vestibular input modulates stepping balance reactions early in the pre-step phase through to post-recovery

Compensatory stepping reactions to recover balance are frequently performed, however, the role of sensory feedback in regulating these responses is not fully understood. Specifically, it is unknown whether vestibular input influences compensatory stepping. Here, we aimed to assess whether step responses utilize vestibular input by combining medio-lateral galvanic vestibular stimulation (GVS) with step-inducing balance perturbations via unpredictable anterior-posterior platform translations. Step responses were assessed for any lateral differences due to the illusory sense of left (LGVS) or rightward (RGVS) postural motion in terms of pre-step weight-shifts, center of mass (COM) motion and step-placement as well as lateral stability when recovering balance. GVS evoked clear differences from the pre-step phase onwards, in an asymmetrical pattern depending on the GVS direction relative to the right step-leg side. RGVS induced a leftwards postural shift to create a larger stability margin to the right (p < 0.0007), opposing the illusory motion and reducing the fall towards the unsupported side during the step; however, RGVS caused no change in step-width. Conversely, LGVS evoked a leftward step placement (p < 0.0001) in the direction of the mis-sensed motion, but without any rightward shift in postural motion. This asymmetry is consistent with vestibular input predictively modulating pre-step lateral weight-shifts and foot-placement in accordance with step mechanics, specifically in controlling frontal plane stability when lifting the foot to step.

Regional activity and effective connectivity within the frontoparietal network during precision walking with visual cueing: an fNIRS study

Precision walking (PW) incorporates precise step adjustments into regular walking patterns to navigate challenging surroundings. However, the brain processes involved in PW control, which encompass cortical regions and interregional interactions, are not fully understood. This study aimed to investigate the changes in regional activity and effective connectivity within the frontoparietal network associated with PW. Functional near-infrared spectroscopy data were recorded from adult subjects during treadmill walking tasks, including normal walking (NOR) and PW with visual cues, wherein the intercue distance was either fixed (FIX) or randomly varied (VAR) across steps. The superior parietal lobule (SPL), dorsal premotor area (PMd), supplementary motor area (SMA), and dorsolateral prefrontal cortex (dlPFC) were specifically targeted. The results revealed higher activities in SMA and left PMd, as well as left-to-right SPL connectivity, in VAR than in FIX. Activities in SMA and right dlPFC, along with dlPFC-to-SPL connectivity, were higher in VAR than in NOR. Overall, these findings provide insights into the roles of different brain regions and connectivity patterns within the frontoparietal network in facilitating gait control during PW, providing a useful baseline for further investigations into brain networks involved in locomotion.

Seeing does not mean processing: where we look and the visual information we rely on change independently as we learn a novel walking task

People use vision to inform motor control strategies during walking. With practice performing a target stepping task, people shift their gaze farther ahead, transitioning from watching their feet contact the target to looking for future target locations. The shift in gaze focus suggests the role of vision in motor control changes from emphasizing feedback to feedforward control. The present study examines whether changing visual fixation location is accompanied by a similar change in reliance upon visual information. Twenty healthy young adults practiced stepping on moving targets projected on the surface of a treadmill. Periodically, participants' visual reliance was probed by hiding stepping targets which inform feedback or feedforward (targets < or > 1.5 steps ahead, respectively) motor control strategies. We calculated visual reliance as the increase in step error when targets were hidden. We hypothesized that with practice, participant reliance on feedback visual information would decrease and their reliance on feedforward visual information would increase. Contrary to our hypothesis, participants became significantly more reliant on feedback visual information with practice (p < 0.001) but their reliance on feedforward visual information did not change (p = 0.49). Participants' reliance on visual information increased despite looking significantly farther ahead with practice (p < 0.016). Together, these results suggest that participants fixated on feedback information less. However, changes in fixation pattern did not reduce their reliance upon feedback information as stepping performance still significantly decreased when feedback information was removed after training. These findings provide important context for how the role of vision in controlling walking changes with practice.

Visual feedback influences the consistency of the locomotor pattern in Asian elephants (Elephas maximus)

Elephants are atypical of most quadrupeds in that they maintain the same lateral sequence footfall pattern across all locomotor speeds. It has been speculated that the preservation of the footfall patterns is necessary to maintain a statically stable support polygon. This should be a particularly important constraint in large, relatively slow animals. This suggests that elephants must rely on available sensory feedback mechanisms to actively control their massive pillar-like limbs for proper foot placement and sequencing. How the nervous system of elephants integrates the available sensory information for a stable gait is unknown. Here we explored the role that visual feedback plays in the control of the locomotor pattern in Asian elephants. Four Asian elephants (Elephas maximus) walked with and without a blindfold as we measured their stride time intervals. Coefficient of variation was used to assess changes in the overall variability of the stride time intervals, while approximate entropy was used to measure the stride-to-stride consistency of the time intervals. We show that visual feedback plays a role in the stride-to-stride consistency of the locomotor pattern in Asian elephants. These results suggest that elephants use visual feedback to correct and maintain proper sequencing of the limbs during locomotion.

Increased Metabolic Demand During Outside Walking in Darkness With No Vision or With Visual Aid

INTRODUCTION

For tactical reasons, the foot-borne soldiers sometimes undertake nighttime operations. However, the metabolic demand during walking in complete darkness may be markedly increased. The purpose of this study was to investigate if metabolic demand and kinematics would change while walking on a gravel road and a slightly hilly trail in darkness with or without visual aid.

MATERIALS AND METHODS

Fourteen cadets (11 men and 3 women, age: 25 ± 7 years, height: 178 ± 8 cm, and weight: 78 ± 13 kg) walked at 4 km/h on a straight gravel road and on a slightly hilly forest trail (n = 9). Both trials were performed at nighttime under four different conditions, wearing a headlamp (Light), blindfold (Dark), monocular (Mono), or binocular (Bino) night vision goggles. During the 10-minute walks, oxygen uptake, heart rate, and kinematic data were assessed. Ratings of perceived exertion, discomfort, and mental stress were evaluated after each condition using a category ratio scale. Physiologic and kinematic variables were evaluated using repeated-measures analysis of variance, whereas ratings were evaluated using non-parametric Friedman analysis of variance.

RESULTS

Oxygen uptake was higher in all three conditions with no or limited vision (Dark, Mono, and Bino) than in the Light condition (P ≤ 0.02) when walking on both the gravel road (+5-8%) and the forest trail (+6-14%). Heart rate was higher during the Dark than during the Light condition when walking on the forest trail, whereas there was no difference between conditions on the gravel road. During both trials, gait frequency was higher during the Dark than during the Light, Mono, and Bino conditions. Ratings were generally low during all conditions.

CONCLUSIONS

Walking on a gravel road or a forest trail wearing a blindfold or visual aid increased the metabolic demand. Thus, it appears that the metabolic demand is higher during overground walking with night vision goggles than with full vision, which may influence the performance of nighttime operations.

Metabolic Demands and Kinematics During Level Walking in Darkness With No Vision or With Visual Aid

INTRODUCTION

Uniformed services commonly perform foot-borne operations at night, while using visual aid in terms of night vision goggles (NVG). During slow-level walking, complete lack of visual input alters kinematics and markedly increases the metabolic demand, whereas the effect on kinematics and energy expenditure of restricting the peripheral visual field by wearing NVG is still unknown. The purpose was to evaluate whether metabolic demands and kinematics during level walking are affected by complete darkness with and without visual aid.

MATERIALS AND METHODS

Eleven healthy men walked on a treadmill (inclination: +2.3°, velocity: 4 km/h) with full vision in a lighted laboratory (Light), and in complete darkness wearing either a blindfold (Dark), or restricting the visual field to about 40° by wearing monocular (Mono) or binocular (Bino) NVG. Oxygen uptake ($\dot{\text{V}}$O2) was measured to evaluate metabolic demands. Inertial measurement units were used to estimate kinematics, and the outcome was validated by using a motion capture system. Ratings of perceived exertion, discomfort, and mental stress were evaluated after each condition using a Borg ratio scale. Physiologic and kinematic variables were evaluated using repeated measures analysis of variance (ANOVA), whereas ratings were evaluated using non-parametric Friedman ANOVA.

RESULTS

$\dot{\text{V}}$ O2 was 20% higher in the Dark (1.2 ± 0.2 L/min) than the Light (1.0 ± 0.2 L/min) condition. Nominally, $\dot{\text{V}}$O2 in the Mono (1.1 ± 0.2 L/min) and Bino (1.1 ± 0.2 L/min) conditions fell in between those in the Light and Dark conditions but was not statistically different from either the Light or the Dark condition. Step length was shorter in the Dark (-9%, 1.22 ± 0.16 m) and Mono (-6%, 1.27 ± 0.09 m) conditions than in the Light condition (1.35 ± 0.11 m), whereas the Bino (1.28 ± 0.08 m) condition was not statistically different from either the Light or the Dark condition. The three conditions with no or limited vision were perceived more physically demanding, more uncomfortable, and more mentally stressful than the Light condition, and the Dark condition was perceived more mentally stressful than both NVG conditions.

CONCLUSIONS

The study confirms that complete lack of visual cues markedly reduces the mechanical efficiency during level walking, even under obstacle-free and highly predictable conditions. That $\dot{\text{V}}$O2 and step length values for the NVG conditions fell in between those of the Light and Dark conditions suggest that both foveal and peripheral vision may play important roles in optimizing the mechanical efficiency during level walking.

The perceived control model of falling: developing a unified framework to understand and assess maladaptive fear of falling

BACKGROUND

fear of falling is common in older adults and can have a profound influence on a variety of behaviours that increase fall risk. However, fear of falling can also have potentially positive outcomes for certain individuals. Without progressing our understanding of mechanisms underlying these contrasting outcomes, it is difficult to clinically manage fear of falling.

METHODS

this paper first summarises recent findings on the topic of fear of falling, balance and fall risk-including work highlighting the protective effects of fear. Specific focus is placed on describing how fear of falling influences perceptual, cognitive and motor process in ways that might either increase or reduce fall risk. Finally, it reports the development and validation of a new clinical tool that can be used to assess the maladaptive components of fear of falling.

RESULTS

we present a new conceptual framework-the Perceived Control Model of Falling-that describes specific mechanisms through which fear of falling can influence fall risk. The key conceptual advance is the identification of perceived control over situations that threaten one's balance as the crucial factor mediating the relationship between fear and increased fall risk. The new 4-item scale that we develop-the Updated Perceived Control over Falling Scale (UP-COF)-is a valid and reliable tool to clinically assess perceived control.

CONCLUSION

this new conceptualisation and tool (UP-COF) allows clinicians to identify individuals for whom fear of falling is likely to increase fall risk, and target specific underlying maladaptive processes such as low perceived control.

Assessment of functional mobility and gait during a timed up and go test in adults with total blindness

BACKGROUND

The loss of vision leads to behavioral and motor adaptations that do not necessarily translate to good functioning with regards to daily tasks.

AIM

To investigate differences in functional mobility in adults with total blindness, and analyze differences in spatiotemporal gait variables with and without the use of a cane, and wearing shoes or barefoot.

METHODS

We used an inertial measurement unit to assess the spatiotemporal parameters of the gait and functional mobility in seven subjects with total blindness and four sighted participants during the timed up and go test (TUG) test performed under conditions: barefoot/shod; and with/without a cane (blind subjects).

RESULTS

Significant differences between groups were found in total TUG test time and in the sub-phases when the blind subjects executed the TUG barefoot and without a cane (p < .01). Other differences were found in trunk movement during sit-to-stand, and stand-to-sit where blind subjects when without cane and barefoot, they had a greater range of motion than sighted subjects (p < .01). Also, BMI has a moderate to strong influence in the execution of the TUG in blind subjects (p < .05) CONCLUSION: This study showed that, when using a gait-assistance device and wearing shoes, blind subjects have similar functional mobility and gait as sighted subjects, suggesting that an external haptic reference can compensate for the lack of vision. Knowledge of these differences can provide a better understanding of the adaptive behavior in this population, thereby assisting in minimizing the occurrence of trauma and falls.

The visual control of locomotion when stepping onto moving surfaces: A comparison of younger and older adults

Stepping between static and moving surfaces presents a locomotor challenge associated with increased injury frequency and severity in older adults. The current study evaluates younger and older adults' behaviours when overcoming challenges sampling moving walkway and escalator environments. Twelve younger adults (18-40 years, Male = 8) and 15 older adults (60-81 years, Male = 5) were examined using an integration of optoelectronic motion capture and mobile eye-tracking. Participants were investigated approaching and stepping onto a flat conveyor belt (static or moving; with or without surface (demarcation) lines). Specifically, the four conditions were: (i) static surface without demarcation lines; (ii) static surface with demarcation lines; (iii) moving surface without demarcation lines; and (iv) moving surface with demarcation lines. A two (age group) x two (surface-condition) x two (demarcation-condition) linear mixed-model revealed no main or interaction effects (p > .05) for perturbation magnitude, indicating participants maintained successful locomotion. However, different adaptive behaviours were identified between conditions with moving and accuracy demands (e.g., moving surfaces increased step length, demarcations reduced step length). Between subject effects identified differences between age groups. Older adults utilised different behaviours, such as earlier gaze transfer from the final approach walkway step location. Overall, the current study suggests that adaptive behaviours emerge relative to the environment's specific demands and the individual's action capabilities.

Accuracy-speed-stability trade-offs in a targeted stepping task are similar in young and older adults

Introduction

Stepping accuracy, speed, and stability are lower in older compared to young adults. Lower stepping performance in older adults may be due to larger accuracy-speed-stability trade-offs because of reduced ability to simultaneously fulfill these task-level goals. Our goal was to evaluate whether trade-offs are larger in older compared to young adults in a targeted stepping task. Since sensorimotor function declines with age, our secondary goal was to evaluate whether poorer sensorimotor function was associated with larger trade-offs.

Methods

Twenty-five young (median 22 years old) and 25 older (median 70 years old) adults stepped into projected targets in conditions with various levels of accuracy, speed, and stability requirements. We determined trade-offs as the change in performance, i.e., foot placement error, step duration, and mediolateral center of pressure path length, between each of these conditions and a control condition. To assess age-related differences in the magnitude of trade-offs, we compared the change in performance between age groups. Associations between trade-offs and measures of sensorimotor function were tested using correlations.

Results

We found an accuracy-speed and an accuracy-stability trade-off in both young and older adults, but trade-offs were not different between young and older adults. Inter-subject differences in sensorimotor function could not explain inter-subject differences in trade-offs.

Conclusion

Age-related differences in the ability to combine task-level goals do not explain why older adults stepped less accurate and less stable than young adults. However, lower stability combined with an age-independent accuracy-stability trade-off could explain lower accuracy in older adults.

Older adults and stroke survivors are steadier when gazing down

BACKGROUND

Advanced age and brain damage have been reported to increase the propensity to gaze down while walking, a behavior that is thought to enhance stability through anticipatory stepping control. Recently, downward gazing (DWG) has been shown to enhance postural steadiness in healthy adults, suggesting that it can also support stability through a feedback control mechanism. These results have been speculated to be the consequence of the altered visual flow when gazing down. The main objective of this cross-sectional, exploratory study was to investigate whether DWG also enhances postural control in older adults and stroke survivors, and whether such effect is altered with aging and brain damage.

METHODS

Posturography of older adults and stroke survivors, performing a total of 500 trials, was tested under varying gaze conditions and compared with a cohort of healthy young adults (375 trials). To test the involvement of the visual system we performed spectral analysis and compared the changes in the relative power between gaze conditions.

RESULTS

Reduction in postural sway was observed when participants gazed down 1 and 3 meters ahead whereas DWG towards the toes decreased steadiness. These effects were unmodulated by age but were modulated by stroke. The relative power in the spectral band associated with visual feedback was significantly reduced when visual input was unavailable (eyes-closed condition) but was unaffected by the different DWG conditions.

CONCLUSIONS

Like young adults, older adults and stroke survivors better control their postural sway when gazing down a few steps ahead, but extreme DWG can impair this ability, especially in people with stroke.

Between a Walk and a Hard Place: How Stepping Patterns Change While Navigating Environmental Obstacles

Maintaining a consistent relationship between each footfall and the body's motion is a key mechanism to maintain balance while walking. However, environmental features, for example, puddles/obstacles, impose additional constraints on foot placement. This study investigated how healthy young individuals alter foot placements to simultaneously manage body-centric and environmental constraints during an obstacle-crossing task. Consistent step length promotes balance for all steps, whereas accurate foot placement around the obstacle is essential to avoid a trip. While crossing an obstacle, any error in positioning one foot relative to the obstacle can be compensated by selecting the placement of the subsequent step. However, compensation will necessarily alter step length from its average value. The interstep covariance index computed from two consecutive foot placements was used to quantify this tradeoff between body-centric and environmental constraints for six consecutive steps while approaching, crossing, and resuming unobstructed gait after crossing the obstacle. The index declined only when either one or both feet were adjacent to the obstacle. The decline was driven in part by a tendency toward higher step length variability. Thus, changes in the stepping patterns to address the environmental constraint occurred at the cost of the body-centric constraint. However, the step length never ceased to be controlled; the interstep covariance index was positive for all steps. Overall, participants adapted foot placement control to account for the larger threat to balance. The environmental constraint was prioritized only when a potential trip posed greater threat to balance compared with the threat posed by variable step length.

Probing the deployment of peripheral visual attention during obstacle-crossing planning

Gaze is directed to one location at a time, making peripheral visual input important for planning how to negotiate different terrain during walking. Whether and how the brain attends to this input is unclear. We developed a novel paradigm to probe the deployment of sustained covert visual attention by testing orientation discrimination of a Gabor patch at stepping and non-stepping locations during obstacle-crossing planning. Compared to remaining stationary, obstacle-crossing planning decreased visual performance (percent correct) and sensitivity (d') at only the first of two stepping locations. Given the timing of the first and second steps before obstacle crossing relative to the Gabor patch presentation, the results suggest the brain uses peripheral vision to plan one step at a time during obstacle crossing, in contrast to how it uses central vision to plan two or more steps in advance. We propose that this protocol, along with multiple possible variations, presents a novel behavioral approach to identify the role of covert visual attention during obstacle-crossing planning and other goal-directed walking tasks.

Backward Walking Styles and Impact on Spatiotemporal Gait Characteristics

Forward walking (FW) is a common balance assessment tool. However, its sensitivity is limited by the ceiling effect. Reverse gait, such as backward walking (BW), has been reported to have more advantages than FW for balance assessment. Three factors related to postural instability (i.e., increased speeds, restricted arm swing, and reduced visual feedback) during BW were investigated to determine BW conditions that have the potential to predict falls. Three-dimensional analyses were used to analyze seven walking conditions. FW and BW at self-selected and fast speeds were analyzed to identify the effects of speed. Walking with normal arm swings, crossed arms, and abducted arms during BW was tested to determine the effects of arm position. BW with closed and open eyes was compared to investigate the effects of visual feedback. BW had a significantly shorter step length than FW at high speeds. When the arms were abducted, the stance phase (%) was significantly lower compared to when arms were crossed during BW. Moreover, BW with closed eyes revealed significantly higher mediolateral center of mass (COM) displacements than with open eyes. We observed that BW with fast speeds, a crossed arm position, and closed eyes has the potential to help assess fall risk because it requires higher balance ability through spatiotemporal and COM adjustment.

Locomotion control during curb descent: Bilateral ground reaction variables covary consistently during the double support phase regardless of future foot placement constraints

During community ambulation, anticipatory adaptations in gait are key for navigating built, populated and natural environments. It has been argued that some instability in gait can be functionally beneficial in situations demanding high maneuverability, and while the mechanisms utilized to maintain locomotor balance are well understood, relatively less is known about how the control of gait stability changes to facilitate upcoming maneuvers in challenging environments. The double support phase may be important in this regard; since both feet can push off the ground simultaneously, there is greater control authority over the body's movement during this phase. Our goal was to identify how this control authority is exploited to prepare for upcoming maneuvers in challenging environments. We used synergy indices to quantify the degree of coordination between the ground reaction forces and moments under the two feet for stabilizing the resultant force and moment on the body during the double support phase of curb descent. In contrast to our expectations, we observed that the kinetic synergy indices during curb descent were minimally influenced by expected foot targeting maneuvers for the subsequent step. Only the resultant moment in the frontal plane showed reduced stability when targeting was required, but the synergy index was still high, indicating that the resultant moment was stable. Furthermore, the synergy indices indicated that the main function of the ground reaction variables is to maintain stability of whole-body rotations during double support, and this prerogative was minimally influenced by the subsequent foot targeting tasks, likely because the cost of losing balance while descending a curb would be higher than the cost of mis-stepping on a visual target. Our work demonstrates the salience of stabilizing body rotations during curb negotiation and improves our understanding of locomotor control in challenging environments.

A neuromuscular model of human locomotion combines spinal reflex circuits with voluntary movements

Existing models of human walking use low-level reflexes or neural oscillators to generate movement. While appropriate to generate the stable, rhythmic movement patterns of steady-state walking, these models lack the ability to change their movement patterns or spontaneously generate new movements in the specific, goal-directed way characteristic of voluntary movements. Here we present a neuromuscular model of human locomotion that bridges this gap and combines the ability to execute goal directed movements with the generation of stable, rhythmic movement patterns that are required for robust locomotion. The model represents goals for voluntary movements of the swing leg on the task level of swing leg joint kinematics. Smooth movements plans towards the goal configuration are generated on the task level and transformed into descending motor commands that execute the planned movements, using internal models. The movement goals and plans are updated in real time based on sensory feedback and task constraints. On the spinal level, the descending commands during the swing phase are integrated with a generic stretch reflex for each muscle. Stance leg control solely relies on dedicated spinal reflex pathways. Spinal reflexes stimulate Hill-type muscles that actuate a biomechanical model with eight internal joints and six free-body degrees of freedom. The model is able to generate voluntary, goal-directed reaching movements with the swing leg and combine multiple movements in a rhythmic sequence. During walking, the swing leg is moved in a goal-directed manner to a target that is updated in real-time based on sensory feedback to maintain upright balance, while the stance leg is stabilized by low-level reflexes and a behavioral organization switching between swing and stance control for each leg. With this combination of reflex-based stance leg and voluntary, goal-directed control of the swing leg, the model controller generates rhythmic, stable walking patterns in which the swing leg movement can be flexibly updated in real-time to step over or around obstacles.

Backward Walking Training Impacts Positive Effect on Improving Walking Capacity after Stroke: A Meta-Analysis

Objective: The meta-analysis aimed to investigate the potential effect of backward walking training (BWT) on walking function improvement among stroke patients. Data sources: Eligible studies were systematically searched in PubMed, Embase, Web of Science, and Cochrane Library. Methods: Heterogeneity among enrolled studies was assessed. Weighted mean difference (WMD) with its 95% confidence interval (CI) was used to pool the outcomes. Results: Seven articles were included. BWT significantly improved motor functions of stroke patients including 10-meter walk test (WMD (95% CI) = 0.11 (0.01, 0.21) meters/second; p = 0.03); cadence (WMD (95% CI) = 4.00 (0.99, 7.02) step/minute; p < 0.01); Berg balance scale (WMD (95% CI) = 4.38 (2.60, 6.15); p < 0.01); paretic step length (WMD (95% CI) = 5.32 (1.97, 8.67) cm; p < 0.01); and stride length (WMD (95% CI) = 6.61 (0.70, 12.51) cm; p = 0.03) as compared with control group. Conclusion: Our study revealed that BWT had a positive influence on walking function improvement among patients after stroke.

Effects of vision on energy expenditure and kinematics during level walking

Purpose

We have previously observed substantially higher oxygen uptake in soldiers walking on terrain at night than when performing the same walk in bright daylight. The aims of the present study were to investigate the influence of vision on mechanical efficiency during slow, horizontal, constant-speed walking, and to determine whether any vision influence is modified by load carriage.

Methods

Each subject (n = 15) walked (3.3 km/h) for 10 min on a treadmill in four different conditions: (1) full vision, no carried load, (2) no vision, no carried load, (3) full vision with a 25.5-kg rucksack, (4) no vision with a 25.5-kg rucksack.

Results

Oxygen uptake was 0.94 ± 0.12 l/min in condition (1), 1.15 ± 0.20 l/min in (2), 1.15 ± 0.12 l/min in (3) and 1.35 ± 0.19 l/min in (4). Thus, lack of vision increased oxygen uptake by about 19%. Analyses of movement pattern, by use of optical markers attached to the limbs and torso, revealed considerably shorter step length (12 and 10%) in the no vision (2 and 4) than full vision conditions (1 and 3). No vision conditions (2 and 4) increased step width by 6 and 6%, and increased vertical foot clearance by 20 and 16% compared to full vision conditions (1 and 3).

Conclusion

The results suggest that vision has a marked influence on mechanical efficiency even during entrained, repetitive movements performed on an obstacle-free horizontal surface under highly predictable conditions.

Comparison of forward versus backward walking on spatiotemporal and kinematic parameters on sand: A preliminary study

The purpose of this study was to investigate the spatiotemporal and kinematic parameters of backward walking (BW) and forward walking (FW) on sand. Randomly selected subjects (n = 28) were categorized into a sand group (SG, n = 14) and an overground group (OG, n = 14). SG was directed to perform both FW and BW on sand, while OG performed the same on the overground. Spatiotemporal and kinematic parameters were measured using the LegSys + device. The comparative findings of both the groups showed that the spatiotemporal parameters of SG varied significantly from those of OG in both FW and BW conditions (p < 0.05). The kinematic parameters varied significantly between the two groups only in the FW condition (p < 0.05). When compared within each group, spatiotemporal and kinematic parameters in the BW condition were significantly different from those in the FW condition. However, the percentages of stance, swing, and double support were not significantly different between FW and BW conditions (p > 0.05). This study suggests that sand walking is associated with a different gait pattern than overground walking, as evident from the analysis of the results of spatiotemporal and kinematic parameters in both FW and BW conditions. Therefore, sand walking can be used as a new approach to gait and balance training in clinical practice.

The Role of Muscle Spindle Feedback in the Guidance of Hindlimb Movement by the Ipsilateral Forelimb during Locomotion in Mice

Safe and efficient locomotion relies on placing the foot on a reliable surface at the end of each leg swing movement. Visual information has been shown to be important for determining the location of foot placement in humans during walking when precision is required. Yet in quadrupedal animals where the hindlimbs are outside of the visual field, such as in mice, the mechanisms by which precise foot placement is achieved remain unclear. Here we show that the placement of the hindlimb paw is determined by the position of the forelimb paw during normal locomotion and in the presence of perturbations. When a perturbation elicits a stumbling corrective reaction, we found that the forelimb paw shifts posteriorly relative to body at the end of stance, and this spatial shift is echoed in hindlimb paw placement at the end of the swing movement. Using a mutant mouse line in which muscle spindle feedback is selectively removed, we show that this posterior shift of paw placement is dependent on muscle spindle feedback in the hindlimb but not in the forelimb. These findings uncover a neuronal mechanism that is independent of vision to ensure safe locomotion during perturbation. This mechanism adds to our general knowledge of how the nervous system controls targeted limb movements and could inform the development of autonomous walking machines.

Icy road ahead-rapid adjustments of gaze-gait interactions during perturbed naturalistic walking

Most humans can walk effortlessly across uniform terrain even when they do not pay much attention to it. However, most natural terrain is far from uniform, and we need visual information to maintain stable gait. Recent advances in mobile eye-tracking technology have made it possible to study, in natural environments, how terrain affects gaze and thus the sampling of visual information. However, natural environments provide only limited experimental control, and some conditions cannot safely be tested. Typical laboratory setups, in contrast, are far from natural settings for walking. We used a setup consisting of a dual-belt treadmill, 240∘ projection screen, floor projection, three-dimensional optical motion tracking, and mobile eye tracking to investigate eye, head, and body movements during perturbed and unperturbed walking in a controlled yet naturalistic environment. In two experiments (N = 22 each), we simulated terrain difficulty by repeatedly inducing slipping through accelerating either of the two belts rapidly and unpredictably (Experiment 1) or sometimes following visual cues (Experiment 2). We quantified the distinct roles of eye and head movements for adjusting gaze on different time scales. While motor perturbations mainly influenced head movements, eye movements were primarily affected by the presence of visual cues. This was true both immediately following slips and—to a lesser extent—over the course of entire 5-min blocks. We find adapted gaze parameters already after the first perturbation in each block, with little transfer between blocks. In conclusion, gaze–gait interactions in experimentally perturbed yet naturalistic walking are adaptive, flexible, and effector specific.

The Strength of the Corticospinal Tract Not the Reticulospinal Tract Determines Upper-Limb Impairment Level and Capacity for Skill-Acquisition in the Sub-Acute Post-Stroke Period

Background. Upper-limb impairment in patients with chronic stroke appears to be partly attributable to an upregulated reticulospinal tract (RST). Here, we assessed whether the impact of corticospinal (CST) and RST connectivity on motor impairment and skill-acquisition differs in sub-acute stroke, using transcranial magnetic stimulation (TMS)–based proxy measures. Methods. Thirty-eight stroke survivors were randomized to either reach training 3-6 weeks post-stroke (plus usual care) or usual care only. At 3, 6 and 12 weeks post-stroke, we measured ipsilesional and contralesional cortical connectivity (surrogates for CST and RST connectivity, respectively) to weak pre-activated triceps and deltoid muscles with single pulse TMS, accuracy of planar reaching movements, muscle strength (Motricity Index) and synergies (Fugl-Meyer upper-limb score). Results. Strength and presence of synergies were associated with ipsilesional (CST) connectivity to the paretic upper-limb at 3 and 12 weeks. Training led to planar reaching skill beyond that expected from spontaneous recovery and occurred for both weak and strong ipsilesional tract integrity. Reaching ability, presence of synergies, skill-acquisition and strength were not affected by either the presence or absence of contralesional (RST) connectivity. Conclusion. The degree of ipsilesional CST connectivity is the main determinant of proximal dexterity, upper-limb strength and synergy expression in sub-acute stroke. In contrast, there is no evidence for enhanced contralesional RST connectivity contributing to any of these components of impairment. In the sub-acute post-stroke period, the balance of activity between CST and RST may matter more for the paretic phenotype than RST upregulation per se.

Conscious Movement Processing, Fall-Related Anxiety, and the Visuomotor Control of Locomotion in Older Adults

Objectives

Older adults anxious about falling will often consciously process walking movements in an attempt to avoid falling. They also fixate their gaze on the present step rather than looking ahead to plan future actions. The present work examined whether conscious movement strategies result in such restricted visual planning.

Methods

A total of 18 community-dwelling older adults (age^mean = 71.22; SD = 5.75) walked along a path and stepped into two raised targets. Repeated-measures analyses of variance were used to compare gaze behavior and movement kinematics when participants walked: (a) at baseline (ground level); (b) under conditions designed to induce fall-related anxiety (walkway elevated 0.6 m); and (c) in the absence of anxiety (ground level), but with explicit instructions to consciously process movements.

Results

Participants reported increased conscious movement processing when walking both on the elevated walkway (fall-related anxiety condition) and at ground level when instructed to consciously process gait. During both conditions, participants altered their gaze behavior, visually prioritizing the immediate walkway 1–2 steps ahead (areas needed for the on-line visual control of individual steps) at the expense of previewing distal areas of the walking path required to plan future steps. These alterations were accompanied by significantly slower gait and increased stance durations prior to target steps.

Conclusions

Consciously processing movement (in the relative absence of anxiety) resulted in gaze behavior comparable to that observed during conditions of fall-related anxiety. As anxious participants also self-reported directing greater attention toward movement, this suggests that fall-related anxiety may disrupt the visual control of gait through increased conscious movement processing.

Gazing down increases standing and walking postural steadiness

When walking on an uneven surface or complex terrain, humans tend to gaze downward. This behaviour is usually interpreted as an attempt to acquire useful information to guide locomotion. Visual information, however, is not used exclusively for guiding locomotion; it is also useful for postural control. Both locomotive and postural control have been shown to be sensitive to the visual flow arising from the respective motion of the individual and the three-dimensional environment. This flow changes when a person gazes downward and may present information that is more appropriate for postural control. To investigate whether downward gazing can be used for postural control, rather than exclusively for guiding locomotion, we quantified the dynamics of standing and walking posture in healthy adults, under several visual conditions. Through these experiments we were able to demonstrate that gazing downward, just a few steps ahead, resulted in a steadier standing and walking posture. These experiments indicate that gazing downward may serve more than one purpose and provide sufficient evidence of the possible interplay between the visual information used for guiding locomotion and that used for postural control. These findings contribute to our understanding of the control mechanism/s underlying gait and posture and have possible clinical implications.

Validity and Reliability of The 3-Meter Backward Walk Test in Individuals with Stroke

OBJECTIVES

The 3-m backward walk test (3MBWT) is used to evaluate neuromuscular control, proprioception, protective reflexes, fall risk and balance. The aim of our study was to reveal the test-retest reliability and validity of the 3MBWT in stroke patients.

MATERIALS AND METHODS

This study included a total of 41 stroke patients [age 59 (35-78) years]. 3MBWT, Berg Balance Scale (BBS), Timed Up and Go test (TUG) were applied to the patients. The second evaluation (retest) was carried out by the same physiotherapist two days following the first evaluation (test) in order to measure test-retest reliability.

RESULTS

Cronbach's alpha coefficient was found to be 0.974 (excellent). For intra-rater agreement, the ICC values in the individual test were 0.985. The SEM value was 1.11 sec, the MDC value was found to be 1.57 sec. A moderate correlation was revealed between the 3 m-backward walking speed and BBS (r: -0.691, p: 0.001) and TUG (r: 0.849, p: 0.001).

CONCLUSIONS

The 3MBWT was observed to be valid and reliable in stroke individuals. It is an effecive and reliable tool for measuring dynamic balance and falls in stroke.

Vision does not impact walking performance in Argentine ants

Many walking insects use vision for long-distance navigation, but the influence of vision on rapid walking performance that requires close-range obstacle detection and directing the limbs towards stable footholds remains largely untested. We compared Argentine ant (Linepithema humile) workers in light versus darkness while traversing flat and uneven terrain. In darkness, ants reduced flat-ground walking speeds by only 5%. Similarly, the approach speed and time to cross a step obstacle were not significantly affected by lack of lighting. To determine whether tactile sensing might compensate for vision loss, we tracked antennal motion and observed shifts in spatiotemporal activity as a result of terrain structure but not illumination. Together, these findings suggest that vision does not impact walking performance in Argentine ant workers. Our results help contextualize eye variation across ants, including subterranean, nocturnal and eyeless species that walk in complete darkness. More broadly, our findings highlight the importance of integrating vision, proprioception and tactile sensing for robust locomotion in unstructured environments.

Foot-placement accuracy during planned and reactive target stepping during walking in stroke survivors and healthy adults

BACKGROUND

The high prevalence of falls due to trips and slips following stroke may signify difficulty adjusting foot-placement in response to the environment. However, little is known about under what circumstances foot-placement adjustment becomes difficult for stroke survivors (SS), making the design of targeted rehabilitation interventions to improve independent community mobility difficult.

RESEARCH QUESTION

To investigate the effect of planned and reactive target-stepping on foot-placement accuracy in stroke survivors and young and older healthy adults?

METHODS

Young (N = 11, 30 ± 6 years) and older (N = 10, 64 ± 8 years) healthy adults and SS (N = 11, 67 ± 9 years) walked, at preferred pace, on a force instrumented treadmill. Each participant walked to illuminated targets, visible two steps in advance (planned) or appearing at contralateral midstance (reactive). Foot-placement error (magnitude and bias) and number of missed targets were compared.

RESULTS

All participants missed more reactive than planned targets (p = 0.05), and SS missed more targets than young (p < 0.001) and older (p = 0.001) adults. But no interaction showing SS missed more reactive targets than other groups was found. For all groups: reactive adaptations to steps in the antero-posterior plane resulted in lower error than planned adaptations (p = 0.027). Lengthening steps where undershot more than shortening (p < 0.001) by all groups. Reactive medio-lateral adaptations over all induced larger error (p = 0.029) than planned and changed the direction of bias (p = 0.018).

SIGNIFICANCE

SS experience difficulty making all adjustments, they showed increased error in all conditions but less pronounced difference between planned and reactive stepping. SS may use a reactive control strategy for all adjustments, in contrast to healthy young adults who may plan foot-placement in advance. The likelihood of stroke survivors misplacing a step is large, with 9.8% targets missed; possibly leading to falls. Further investigation is needed to understand foot-placement control strategies used by SS and the role of planning in gait adaptability.

Effects of calf muscle conditioning upon ankle proprioception

Ankle proprioception is crucial for balance and relies upon accurate input from calf muscle spindles. Spindle input, in turn, depends upon the physiological and mechanical properties of surrounding muscle tissue. Altering these properties could affect ankle proprioception, with potential consequences for balance. Here we determine the effects of prior muscle cooling, stretch and contraction upon performance of a contralateral ankle joint matching task. Participants stood passively leaning against a board oriented 22° rearward from vertical. Their right ankle was rotated to a randomised position between ± 6° plantar/dorsiflexion. The task was to align the left ankle to the same position, without vision. In the first experiment, immediately prior to each testing session, participants either produced a strong calf muscle contraction in a fully plantarflexed (tiptoe) posture or underwent 15° dorsiflexion stretch. Contraction had no effect on task performance, whereas stretch produced a significant bias in ankle placement of 0.89 ± 0.6°, indicating that participants perceived their foot to be more plantarflexed compared to a control condition. In the second experiment, the right lower leg was cooled in iced water (≤ 5°C) for 10 minutes. Cooling increased joint matching error by ~0.4°, through a combination of increased bias and variability. These results confirm that conditioning the triceps surae muscles can alter perception of ankle joint position. Since body movement during quiet stance is in the order of 1°, the magnitude of these changes are relevant for balance.

Comparisons of Spatiotemporal and Ground Reaction Force Components of Gait Between Individuals with Congenital Vision Loss and Sighted Individuals

Introduction:

The understanding of abnormalities in biomechanical parameters of gait in individuals with vision loss (i.e., blindness or low vision) has clinical importance. The aims of this study were to compare the spatiotemporal and ground reaction force variables of sighted individuals with those with vision loss.

Methods:

Ten sighted males and 10 young males with congenital vision loss were recruited. A Vicon motion analysis system with four cameras and two Kistler force plates was used to quantify spatiotemporal and ground reaction force components of both groups during walking without shoes. Sighted individuals walked in eyes-open and eyes-closed conditions.

Results:

Results showed that the stride and step length, walking speed, the vertical and posterior–anterior reaction forces in heel contact and push-off phase, and the impulse of the control group during walking with the open- and closed-eyes conditions were significantly smaller than those in persons with vision loss ( p < .05).

Discussion:

Vision loss is associated with decreased step and stride length, slower walking, and smaller propulsive reaction force. These kinematic and kinetics alterations suggest an adaptation to a new neuromuscular response for dynamic postural control as a result of lack of vision. These alterations in the long term may result in rigidity and muscle weakness.

Implications for practitioners:

A rehabilitation program to enhance mobility and strength is suggested for individuals with vision loss.

Children With Developmental Coordination Disorder Exhibit Greater Stepping Error Despite Similar Gaze Patterns and State Anxiety Levels to Their Typically Developing Peers

This study examined stepping accuracy, gaze behavior, and state-anxiety in children with (N = 21, age M = 10.81, SD = 1.89) and without (N = 18, age M = 11.39, SD = 2.06) developmental coordination disorder (DCD) during an adaptive locomotion task. Participants walked at a self-selected pace along a pathway, placing their foot into a raised rectangular floor-based target box followed by either no obstacles, one obstacle, or two obstacles. Stepping kinematics and accuracy were determined using three-dimensional motion capture, whilst gaze was determined using mobile eye-tracking equipment. The children with DCD displayed greater foot placement error and variability when placing their foot within the target box and were more likely to make contact with its edges than their typically developing (TD) peers. The DCD group also displayed greater variability in the length and width of their steps in the approach to the target box. No differences were observed between groups in any of the gaze variables measured, in mediolateral velocity of the center of mass during the swing phase into the target box, or in the levels of self-reported state-anxiety experienced prior to facing each task. We therefore provide the first quantifiable evidence that deficits to foot placement accuracy and precision may be partially responsible for the increased incidence of trips and falls in DCD, and that these deficits are likely to occur independently from gaze behavior and state-anxiety.

Individuals with unilateral transtibial amputation exhibit reduced accuracy and precision during a targeted stepping task

Accurate foot placement is important for dynamic balance during activities of daily living. Disruption of sensory information and prosthetic componentry characteristics may result in increased locomotor task difficulty for individuals with lower limb amputation. This study investigated the accuracy and precision of prosthetic and intact foot placement during a targeted stepping task in individuals with unilateral transtibial amputation (IUTAs; N = 8, 47 ± 13 yrs), compared to the preferred foot of control participant's (N = 8, 33 ± 15 yrs). Participants walked along a 10-metre walkway, placing their foot into a rectangular floor-based target with dimensions normalised to a percentage of participant's foot length and width; 'standard' = 150% x 150%, 'wide' = 150% x 200%, 'long' = 200% x 150%. Foot placement accuracy (relative distance between foot and target centre), precision (between-trial variability), and foot-reach kinematics were determined for each limb and target, using three-dimensional motion capture. A significant foot-by-target interaction revealed less mediolateral foot placement accuracy for IUTAs in the wide target, which was significantly less accurate for the intact (28 ± 12 mm) compared to prosthetic foot (16 ± 14 mm). Intact peak foot velocity (4.6 ± 0.8 m.s^-1) was greater than the prosthetic foot (4.5 ± 0.8 m.s^-1) for all targets. Controls were more accurate and precise than IUTAs, regardless of target size. Less accurate and precise intact foot placement in IUTAs, coupled with a faster moving intact limb, is likely due to several factors including reduced proprioceptive feedback and active control during prosthetic limb single stance. This could affect activities of daily living where foot placement is critical, such as negotiating cluttered travel paths or obstacles whilst maintaining balance.

Gaze-behaviors of runners in a natural, urban running environment

Gaze-tracking techniques have advanced our understanding of visual attention and decision making during walking and athletic events, but little is known about how vision influences behavior during running over common, natural obstacles. This study tested hypotheses about whether runners regularly collect visual information and pre-plan obstacle clearance (feedforward control), make improvisational adjustments (online control), or some combination of both. In this study, the gaze profiles of 5 male and 5 female runners, fitted with a telemetric gaze-tracking device, were used to identify the frequency of fixations on an obstacle during a run. Overall, participants fixated on the obstacle 2.4 times during the run, with the last fixation occurring on average between 40% and 80% of the run, suggesting runners potentially shifted from a feedforward planning strategy to an online control strategy during the late portions of the running trial. A negative association was observed between runner velocity and average number of fixations. Consistent with previous studies on visual strategies used during walking, our results indicate that visual attentiveness is part of an important feedforward strategy for runners allowing them to safely approach an obstacle. Thus, visual obstacle attention is a key factor in the navigation of complex, natural landscapes while running.

How accuracy of foot-placement is affected by the size of the base of support and crutch support in stroke survivors and healthy adults

BACKGROUND

The high prevalence of falls due to trips and slips following stroke may signify difficulty controlling balance and adjusting foot-placement in response to the environment. We know very little about how controlling foot-placement is affected by balance requirements and the effects of stroke. Therefore, in this study the research question is how foot-placement control is affected by balance support from crutches and reducing or enlarging the base of support. By understanding how foot-placement control and balance deficits following stroke interact, rehabilitation efforts can be more effectively targeted towards the cause of poor mobility.

METHODS

Young (N=13, 30±6 years) and older (N=10, 64±8 years) healthy adults and stroke survivors (N=11, 67±9 years) walked to targets on an instrumented treadmill with or without crutch support for balance. Targets were randomized to either reduce or increase the base of support in the antero-posterior (AP) or medio-lateral (ML) direction. Mean and absolute foot-placement error were measured using motion analysis. These outcomes were compared using repeated measures ANCOVA with walking speed as a covariate.

RESULTS

Overall, stroke survivors missed more targets (9.1±2.3%, p=0.001) than young (1.0±2.5%) and older (0.2±2.1%) healthy adults (p=0.001). However, there were no significant differences between groups in foot-placement error. Crutch support reduced both AP and ML foot-placement error (p=<0.001, AP 5.2±0.5cm unsupported, 4.1±0.4cm supported, ML 2.3±0.2cm unsupported, 1.9±0.2cm supported) for all participants. Interaction effects indicate crutch support reduced foot-placement error more when narrowing (unsupported 2.8±0.2cm, supported 1.8±0.2cm) than widening (unsupported 2.6±0.4cm, supported 2.4±0.4cm) steps (p<0.001), SIGNIFICANCE: Stroke survivors have greater difficulty accurately adjusting steps in response to the environment. Crutch support reduces foot-placement error for all steps, but particularly when narrowing foot-placement. These results provide support for the implication of walking aids, which support balance to improve ability to adjust footplacement in response to the environment.

Visual deprivation is met with active changes in ground reaction forces to minimize worsening balance and stability during walking

Previous studies suggest that visual information is essential for balance and stability of locomotion. We investigated whether visual deprivation is met with active reactions tending to minimize worsening balance and stability during walking in humans. We evaluated effects of vision on kinetic characteristics of walking on a treadmill-ground reaction forces (GRFs) and shifts in the center of mass (COM). Young adults (n = 10) walked on a treadmill at a comfortable speed. We measured three orthogonal components of GRFs and COM shifts during no-vision (NV) and full-vision (FV) conditions. We also computed the dynamic balance index (D_N)-the perpendicular distance from the projection of center of mass (pCOM) to the inter-foot line (IFL) normalized to half of the foot length. Locally weighted regression smoothing with alpha-adjusted serial T tests was used to compare GRFs and D_N between two conditions during the entire stance phase. Results showed significant differences in GRFs between FV and NV conditions in vertical and ML directions. Variability of peak forces of all three components of GRF increased in NV condition. We also observed significant increase in D_N for NV condition in eight out of ten subjects. The pCOM was kept within BOS during walking, in both conditions, suggesting that body stability was actively controlled by adjusting three components of GRFs during NV walking to minimize stability loss and preserve balance.

The development of visually guided stepping

Adults use vision during stepping and walking to fine-tune foot placement. However, the developmental profile of visually guided stepping is unclear. We asked (1) whether children use online vision to fine-tune precise steps and (2) whether precision stepping develops as part of broader visuomotor development, alongside other fundamental motor skills like reaching. With 6-(N = 11), 7-(N = 11), 8-(N = 11)-year-olds and adults (N = 15), we manipulated visual input during steps and reaches. Using motion capture, we measured step and reach error, and postural stability. We expected (1) both steps and reaches would be visually guided (2) with similar developmental profiles (3) foot placement biases that promote stability, and (4) correlations between postural stability and step error. Children used vision to fine-tune both steps and reaches. At all ages, foot placement was biased (albeit not in the predicted directions). Contrary to our predictions, step error was not correlated with postural stability. By 8 years, children's step and reach error were adult-like. Despite similar visual control mechanisms, stepping and reaching had different developmental profiles: step error reduced with age whilst reach error was lower and stable with age. We argue that the development of both visually guided and non-visually guided action is limb-specific.

The flexible action system: Click-based echolocation may replace certain visual functionality for adaptive walking

People use sensory, in particular visual, information to guide actions such as walking around obstacles, grasping or reaching. However, it is presently unclear how malleable the sensorimotor system is. The present study investigated this by measuring how click-based echolocation may be used to avoid obstacles while walking. We tested 7 blind echolocation experts, 14 sighted, and 10 blind echolocation beginners. For comparison, we also tested 10 sighted participants, who used vision. To maximize the relevance of our research for people with vision impairments, we also included a condition where the long cane was used and considered obstacles at different elevations. Motion capture and sound data were acquired simultaneously. We found that echolocation experts walked just as fast as sighted participants using vision, and faster than either sighted or blind echolocation beginners. Walking paths of echolocation experts indicated early and smooth adjustments, similar to those shown by sighted people using vision and different from later and more abrupt adjustments of beginners. Further, for all participants, the use of echolocation significantly decreased collision frequency with obstacles at head, but not ground level. Further analyses showed that participants who made clicks with higher spectral frequency content walked faster, and that for experts higher clicking rates were associated with faster walking. The results highlight that people can use novel sensory information (here, echolocation) to guide actions, demonstrating the action system’s ability to adapt to changes in sensory input. They also highlight that regular use of echolocation enhances sensory-motor coordination for walking in blind people.

Vision loss has negative consequences for people’s mobility. The current report demonstrates that echolocation might replace certain visual functionality for adaptive walking. Importantly, the report also highlights that echolocation and long cane are complementary mobility techniques. The findings have direct relevance for professionals involved in mobility instruction and for people who are blind.

Control strategies for rapid, visually guided adjustments of the foot during continuous walking

When walking over stable, complex terrain, visual information about an upcoming foothold is primarily utilized during the preceding step to organize a nearly ballistic forward movement of the body. However, it is often necessary to respond to changes in the position of an intended foothold that occur around step initiation. Although humans are capable of rapidly adjusting foot trajectory mid-swing in response to a perturbation of target position, such movements may disrupt the efficiency and stability of the gait cycle. In the present study, we consider whether walkers sometimes adopt alternative strategies for responding to perturbations that interfere less with ongoing forward locomotion. Subjects walked along a path of irregularly spaced stepping targets projected onto the ground, while their movements were recorded by a full-body motion-capture system. On a subset of trials, the location of one target was perturbed in either a medial-lateral or anterior-posterior direction. We found that subjects were best able to respond to perturbations that occurred during the latter half of the preceding step and that responses to perturbations that occurred during a step were less successful than previously reported in studies using a single-step paradigm. We also found that, when possible, subjects adjusted the ballistic movement of their center of mass in response to perturbations. We conclude that, during continuous walking, strategies for responding to perturbations that rely on reach-like movements of the foot may be less effective than previously assumed. For perturbations that are detected around step initiation, walkers prefer to adapt by tailoring the global, pendular mechanics of the body.

Backward walking effects on activation pattern of leg muscles in young females with patellofemoral pain syndrome

Background/Aims:

Little is known regarding the activation of knee and hip muscles during backward walking in patellofemoral pain syndrome. This study examineD the effects of backward walking and forward walking on the activation of knee extensors, hip abductors, and adductors in patients with patellofemoral pain syndrome.

Methods:

A total of 20 females with patellofemoral pain syndrome and 20 age-matched typically healthy female controls participated in this study. Surface electromyography from vastus medialis obliquus, vastus lateralis, gluteus medius, and adductor longus muscles were collected during forward walking and backward walking.

Findings:

The patellofemoral pain syndrome group had a significantly higher normalised root mean square of the vastus medialis obliquus, vastus lateralis and gluteus medius muscles (P=0.001), without significant difference in adductor longus muscle activity during backward walking versus forward walking (P=0.098). During forward walking, the patellofemoral pain syndrome group showed significantly higher activation of adductor longus muscle (P=0.001) and significantly lower activation of the gluteus medius muscle (P=0.002) compared to the healthy group. During backward walking there was a significant increase in the vastus medialis obliquus and adductor longus muscle activity of the patellofemoral pain syndrome group compared to the control group (P=0.003, 0.001) respectively.

Conclusions:

Clinicians should consider backward walking training to increase the muscle strength of knee extensors and hip abductors when developing rehabilitation programmes for patients with patellofemoral pain syndrome.

The effects of robot-assisted gait training using virtual reality and auditory stimulation on balance and gait abilities in persons with stroke

BACKGROUND

Robot-assisted gait training provide a big therapeutic advantage in functional mobility for postural control.

OBJECTIVES

The purpose of this study was investigate the effects of robot-assisted gait training using virtual reality and auditory stimulation on balance and gait abilities in stroke patients.

METHODS

All subjects were randomly divided into three groups where twelve subjects were in the Virtual reality robot-assisted gait training group (VRGT), twelve subjects in the auditory stimulation robot-assisted gait training group (ARGT), and sixteen subjects in the control group. Subjects received virtual reality and auditory stimulation while undergoing robot-assisted gait training for 45 minutes, three times a week for 6 weeks, and all subjects had undergone general physical therapy for 30 minutes, five times a week for 6 weeks. All subjects were assessed with the Medical Research Council (MRC), Berg balance scale (BBS), timed up and go test (TUG), 10-meter walk test (10MWT), Fugl-Myer Assessment (FMA) and Modified Barthel Index (MBI) pre- and post-intervention.

RESULTS

Results showed that BBS, TUG, and 10MWT scores significantly improved post-intervention (p < 0.05), and the control group also had significantly improved in all areas post-treatment (p < 0.05). In addition, it has been confirmed that VRGT had significantly improved in MRC and FMA scores compared with the auditory stimulation. Also, it has significantly improved in MRC, BBS, TUG, 10MWT and FMA compared with control group (p < 0.05).

CONCLUSIONS

The results of this study showed improve balance and gait abilities after VRGT compared with general physical therapy and were found to be effective in enhancing the functional activity of persons with stroke.

What affects gait performance during walking while texting? A comparison of motor, visual and cognitive factors

Texting on a cell phone disrupts walkers' gait performance. The performance decrement has been attributed to increased motor demand, decreased visual information and increased cognitive load. However, relative contributions of motor, visual and cognitive factors are poorly understood. Here we quantitatively estimated the relative contributions of these factors by comparing multiple walking conditions. Thirty-two adults walked for 20 m, with or without a dual task on the phone. The dual task was either a cognitively demanding digit ordering task or a casual tapping task. Gait performance was assessed using gait speed, stride length, stride time and stride time variability. Results showed that texting negatively impacted gait performance. Importantly, we found that cognitive factor contributed the most, visual factor the least, and motor factor in between. Our findings resolve the inconsistency in the literature and unambiguously show that motor, visual and cognitive factors caused by simultaneous phone use all contribute to gait alterations. Practitioner Summary: Walking performance is typically worsened when a concurrent phone use task such as texting is performed. We found that visual, motor and cognitive factors contributed to this performance decrement with increasing importance. Besides resolving inconsistency among previous reports, we also raised theoretical and practical concerns for phone use during walking.

Gaze and the Control of Foot Placement When Walking in Natural Terrain

Human locomotion through natural environments requires precise coordination between the biomechanics of the bipedal gait cycle and the eye movements that gather the information needed to guide foot placement. However, little is known about how the visual and locomotor systems work together to support movement through the world. We developed a system to simultaneously record gaze and full-body kinematics during locomotion over different outdoor terrains. We found that not only do walkers tune their gaze behavior to the specific information needed to traverse paths of varying complexity but that they do so while maintaining a constant temporal look-ahead window across all terrains. This strategy allows walkers to use gaze to tailor their energetically optimal preferred gait cycle to the upcoming path in order to balance between the drive to move efficiently and the need to place the feet in stable locations. Eye movements and locomotion are intimately linked in a way that reflects the integration of energetic costs, environmental uncertainty, and momentary informational demands of the locomotor task. Thus, the relationship between gaze and gait reveals the structure of the sensorimotor decisions that support successful performance in the face of the varying demands of the natural world.

Route previewing results in altered gaze behaviour, increased self-confidence and improved stepping safety in both young and older adults during adaptive locomotion

Older adults with falls risk tend to look away prematurely from targets for safe foot placement to view future hazards; behaviour associated with increased anxiety and stepping inaccuracies. We aimed to determine the effectiveness of route previewing in reducing anxiety and optimizing gaze behaviour and stepping performance of younger and older adults. Nine younger and nine older adults completed six walks with three task complexities over two sessions. Each trial used either an isolated stepping target, or a target followed by either one or two obstacles. Participants with eyes closed, on hearing a signal, opened their eyes and initiated walking (go trials) or stood previewing the route for 10 s before starting (preview trials). Kinematic data were collected using a Vicon motion analysis system. Gaze behaviour was recorded using a Dikablis eye tracker. On average, both older and younger adults fixated the target for significantly longer during walking when they had previewed the route than when they had not. Self-confidence scores were also significantly higher following ‘preview trials’ than ‘go trials’. Stepping performance significantly improved following route previewing (reduced Medial lateral foot placement variability for both groups and reduced anterior/posterior foot placement error in older adults only). These findings implicate route previewing as a potential intervention to increase self-confidence and reduce the risk of tripping in older adults.

Adaptive control of dynamic balance in human gait on a split-belt treadmill

Human bipedal gait is inherently unstable and staying upright requires adaptive control of dynamic balance. Little is known about adaptive control of dynamic balance in reaction to long-term, continuous perturbations. We examined how dynamic balance control adapts to a continuous perturbation in gait, by letting people walk faster with one leg than the other on a treadmill with two belts (i.e. split-belt walking). In addition, we assessed whether changes in mediolateral dynamic balance control coincide with changes in energy use during split-belt adaptation. In nine minutes of split-belt gait, mediolateral margins of stability and mediolateral foot roll-off changed during adaptation to the imposed gait asymmetry, especially on the fast side, and returned to baseline during washout. Interestingly, no changes in mediolateral foot placement (i.e. step width) were found during split-belt adaptation. Furthermore, the initial margin of stability and subsequent mediolateral foot roll-off were strongly coupled to maintain mediolateral dynamic balance throughout the gait cycle. Consistent with previous results net metabolic power was reduced during split-belt adaptation, but changes in mediolateral dynamic balance control were not correlated with the reduction of net metabolic power during split-belt adaptation. Overall, this study has shown that a complementary mechanism of relative foot positioning and mediolateral foot roll-off adapts to continuously imposed gait asymmetry to maintain dynamic balance in human bipedal gait.

A Backward Walking Training Program to Improve Balance and Mobility in Acute Stroke: A Pilot Randomized Controlled Trial

BACKGROUND AND PURPOSE

Strategies to address gait and balance deficits early poststroke are minimal. The postural and motor control requirements of Backward Walking Training (BWT) may provide benefits to improve balance and walking speed in this population. This pilot study (1) determined the feasibility of administering BWT during inpatient rehabilitation and (2) compared the effectiveness of BWT to Standing Balance Training (SBT) on walking speed, balance, and balance-related efficacy in acute stroke.

METHODS

Eighteen individuals 1-week poststroke were randomized to eight, 30-minute sessions of BWT or SBT in addition to scheduled therapy. Five-Meter Walk Test, 3-Meter Backward Walk Test, Activities-Specific Balance Confidence Scale, Berg Balance Scale, Sensory Organization Test, and Function Independence Measure-Mobility were assessed pre- and postintervention and at 3 months poststroke.

RESULTS

Forward gait speed change (BWT: 0.75 m/s; SBT: 0.41 m/s), assessed by the 5-Meter Walk Test, and backward gait speed change (BWT: 0.53 m/s; SBT: 0.23 m/s), assessed by the 3-Meter Backward Walk Test, preintervention to 1-month retention were greater for BWT than for SBT (P < 0.05). Group difference effect size from preintervention to 1-month retention was large for Activities-Specific Balance Confidence Scale, moderate for Berg Balance Scale and Function Independence Measure-Mobility, and small for Sensory Organization Test.

DISCUSSION AND CONCLUSIONS

Individuals 1-week poststroke tolerated 30 min/d of additional therapy. At 1-month postintervention, BWT resulted in greater improvements in both forward and backward walking speed than SBT. Backward walking training is a feasible important addition to acute stroke rehabilitation. Future areas of inquiry should examine BWT as a preventative modality for future fall incidence.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A193).

Voluntary steps and gait initiation

This chapter explores mechanisms that control goal-directed steps for the purpose of reorienting the body or initiating gait. A key issue concerns the control of balance. We argue that standing balance is relinquished while the stepping foot is in the air thus allowing the body to fall under gravity. The falling body's trajectory is largely controlled by motor activity that occurs before the stepping foot leaves the ground (the throw), and is finely tuned to where and when the foot is planned to land (the catch). This close coupling between the throw and catch is paramount for achieving the stepping goal while simultaneously ensuring balance is regained at the end of the step. Nonetheless, there is some scope for making midstep adjustments by modifying the body's trajectory and/or the stepping leg's movement. The magnitude of midstep adjustment is severely limited by mechanical and balance constraints, but can occur at remarkably short latency in response to new visual information, possibly controlled by subcortical neural networks. We conclude that taking a step is a highly predictive and coordinated action that is vulnerable to errors leading to falls, particularly in the face of neural and muscular degeneration associated with aging or neurologic disease.

Sensorimotor anatomy of gait, balance, and falls

The review demonstrates that control of posture and locomotion is provided by systems across the caudal-to-rostral extent of the neuraxis. A common feature of the neuroanatomic organization of the postural and locomotor control systems is the presence of key nodes for convergent input of multisensory feedback in conjunction with efferent copies of the motor command. These nodes include the vestibular and reticular nuclei and interneurons in the intermediate zone of the spinal cord (Rexed's laminae VI-VIII). This organization provides both spatial and temporal coordination of the various goals of the system and ensures that the large repertoire of voluntary movements is appropriately coupled to either anticipatory or reactive postural adjustments that ensure stability and provide the framework to support the intended action. Redundancies in the system allow adaptation and compensation when sensory modalities are impaired. These alterations in behavior are learned through reward- and error-based learning processes implemented through basal ganglia and cerebellar pathways respectively. However, neurodegenerative processes or lesions of these systems can greatly compromise the capacity to sufficiently adapt and sometimes leads to maladaptive changes that impair movement control. When these impairments occur, the risk of falls can be significantly increased and interventions are required to reduce morbidity.

Gait adaptability

Our activities of daily living inherently involve interacting with the physical environment. This interaction involves both reactive (feedback) and proactive (feedforward) gait adaptations. Reactive adaptations involve responses to mechanical perturbations and occur, for instance, when we stumble over a doorstep or slip on an icy spot on the pavement. Examples of proactive adaptations in response to visual stimuli include stepping over an obstacle, targeting precise foot placements when walking on rough terrain, stepping up to the pavement, or making a turn for going around a corner. These adaptations have to be implemented in our steady-state gait pattern, thus posing a challenge to center-of-mass control and maintenance of forward progression. Yet, despite the apparent complexity of adaptive bipedal walking, we commonly do this with remarkable ease. This chapter will provide a comprehensive overview of the behavioral strategies and control mechanisms that we apply for executing these common, yet complex, gait adaptations. In addition, how we use visual information for guiding proactive gait adaptations and path selection will be discussed. Finally, cognitive involvement during gait adaptations will also be addressed.