The effect of the visual characteristics of obstacles on risk of tripping and gait parameters during locomotion

The effect of visual sensory interference during multitask obstacle crossing in younger and older adults

When older adults step over obstacles during multitasking, their performance is impaired; the impairment results from central and/or sensory interference. The purpose was to determine if sensory interference alters performance under low levels of cognitive, temporal, and gait demand, and if the change in performance is different for younger versus older adults. Participants included 17 younger adults (20.9±1.9 years) and 14 older adults (69.7±5.4 years). The concurrent task was a single, simple reaction time (RT) task: depress button in response to light cue. The gait task was stepping over an obstacle (8 m walkway) in three conditions: (1) no sensory interference (no RT task), (2) low sensory interference (light cue on obstacle, allowed concurrent foveation of cue and obstacle), or (3) high sensory interference (light cue away from obstacle, prevented concurrent foveation of cue and obstacle). When standing, the light cue location was not relevant (no sensory interference). An interaction (sensory interference by task, p<0.01) indicated that RT was longer for high sensory interference during walking, but RT was not altered for standing, confirming that sensory interference increased RT during obstacle approach. An interaction (sensory interference by age, p<0.01) was observed for foot placement before the obstacle: With high sensory interference, younger adults placed the trail foot closer to the obstacle while older adults placed it farther back from the obstacle. The change increases the likelihood of tripping with the trail foot for younger adults, but with the lead limb for older adults. Recovery from a lead limb trip is more difficult due to shorter time for corrective actions. Overall, visual sensory interference impaired both RT and gait behavior with low levels of multitask demand. Changes in foot placement increased trip risk for both ages, but for different limbs, reducing the likelihood of balance recovery in older adults.

Effect of auditory deprivation on adaptive locomotion: Interaction with lower visual field occlusion

Auditory stimuli have been suggested to play a role in adequately controlling movement; however, their influence is not fully understood, particularly regarding dynamic behaviors, such as adaptive locomotion. This study aimed to investigate whether auditory deprivation affects adaptive locomotion. In particular, we aimed to elucidate the role of the auditory sense in obstacle avoidance by manipulating the visual field, which provides crucial sensory information for movement control. Sixteen participants approached a 15-cm obstacle located 6 m away and stepped over it under four different conditions that combined two factors: the hearing condition controlled by wearing earmuffs with and without holes, and the lower visual field condition controlled by carrying opaque white and transparent boards. Spatiotemporal variables during the approach to the obstacle were measured using an electronic walkway, whereas foot clearance over the obstacle was assessed using a motion-capture system. Participants who experienced auditory deprivation and lower visual field occlusion demonstrated greater variability in step length when approaching the obstacle compared with the other conditions. The leading and trailing foot clearances were higher under lower visual field occlusion conditions. Furthermore, when participants were under conditions of auditory deprivation, greater variability was observed in the clearance of the leading foot. These results suggest that auditory information contributes to movement stabilization during adaptive locomotion. Our findings provide evidence that auditory and visual senses complement each other during motor actions, indicating that adaptive locomotion can be influenced by the integration of multiple sensory inputs.

Children with Duchenne muscular dystrophy display specific kinematic strategies during obstacle-crossing

Duchenne muscular dystrophy (DMD) is a genetic disease characterized by progressive muscle weakness with increased neuromechanical challenge and fall risks, especially during obstructed locomotion. This study aimed to identify the kinematic strategies for obstacle-crossing in DMD via synthesizing the changes in the joint kinematics and associated end-point control. Fourteen boys with DMD (age: 9.0 ± 2.5 years) and fourteen typically developed controls (age: 9.0 ± 2.8 years) each crossed obstacles of three different heights (10%, 20% and 30% of leg length) while the angular motions of the trunk-pelvis-leg apparatus and foot-obstacle clearances were measured. Two-way analyses of variance were used to analyze group and obstacle height effects. Compared to the controls, the DMD group crossed obstacles with significantly increased step width, but decreased crossing speed, crossing step length, trailing toe-obstacle clearance and leading heel-obstacle horizontal distance (p < 0.05). When the leading toe was above the obstacle, the patients showed significantly increased pelvic hiking, pelvic and trunk anterior tilt and ankle plantarflexion, but decreased hip flexion in both limbs (p < 0.05). Similar kinematic changes were found during trailing-limb crossing, except for an additional increase in swing-hip abduction and decrease in contralateral trunk side-bending and stance-knee flexion. Patients with DMD crossed obstacles via a specific kinematic strategy with altered end-point control, predisposing them to a greater risk of tripping during trailing-limb crossing. These results suggest that crossing kinematics in DMD should be monitored-especially in the proximal segments of the pelvis-leg apparatus-that may lead to an increased risk of falling.

A registered report of a crossover study on the effects of face masks on walking adaptability in people with Parkinson's disease and multiple sclerosis

BACKGROUND

Face masks protrude into the lower visual field causing reduced perception of visual stimuli, potentially making obstacle avoidance during walking more difficult and increasing fall risk. Recommendations on walking and mask wearing for older adults have been debated, with no clear consensus on the various factors interacting and influencing walking safety while wearing a face mask. It is particularly important to address this issue in populations at an increased risk of falls. Therefore, this study aims to investigate the effects of mask-wearing on objectively measured walking adaptability in people with Parkinson's disease and Multiple Sclerosis.

METHODS

50 patients with either Parkinson's disease or Multiple Sclerosis attending inpatient neurorehabilitation will be recruited to participate in this crossover study. Performance during a standardized gait adaptability (C-Gait) test on a VR-based treadmill (C-Mill+VR), as well as during clinical mobility tests (10-meter walk test, Timed Up & Go test, and stair ambulation) will be measured with and without an FFP2- mask (order randomized). In addition, participants will be asked about their perceived performance and perceived safety during the tests with and without a mask. Performance on the seven C-Gait subtests is based on centre of pressure-derived measures of foot placement in relation to the different tasks. These are averaged and added to a cognitive C-Gait task to give the overall composite score (primary outcome). Secondary outcomes will include the different subscores and clinical mobility tests.

POTENTIAL SIGNIFICANCE

This study will make an important contribution to an ongoing debate regarding recommendations persons with and without a neurological disease should be given regarding wearing a face mask while walking. Furthermore, the study will complement the existing scientific discourse with clinical data from people with a neurological disease for whom falls, mobility deficits and mask wearing may be more frequent, which can help inform evidence-based recommendations.

TRIAL REGISTRATION

German clinical trial register: DRKS00030207.

Salient Targets and Fear of Falling Changed the Gait Pattern and Joint Kinematic of Older Adults

BACKGROUND

Fear of falling and environmental barriers in the home are two major factors that cause the incidence of falling. Poor visibility at night is one of the key environmental barriers that contribute to falls among older adult residents. Ensuring their visual perception of the surroundings, therefore, becomes vital to prevent falling injuries. However, there are limited works in the literature investigating the impact of the visibility of the target on older adults' walking destinations and how that impact differs across them with different levels of fear of falling.

OBJECTIVE

The purpose of the study was to examine the effects of target salience on older adults' walking performance and investigate whether older adults with varying levels of fear of falling behave differently.

METHODS

The salient target was constructed with LED strips around the destination of walking. Fifteen older adults (aged 75 years old and above), seven with low fear of falling and eight with high fear of falling, volunteered for the study. Participants walked from the designated origin (i.e., near their beds) to the destination (i.e., near the bathroom entrance), with the target turned on or off around the destination of the walking trials. Spatiotemporal gait variables and lower-body kinematics were recorded by inertial sensors and compared by using analysis of variance methods.

RESULTS

Data from inertial sensors showed that a more salient target at the destination increased older adults' gait speed and improved their walking stability. These changes were accompanied by less hip flexion at heel strikes and toe offs during walking. In addition, older adults with low fear of falling showed more substantial lower-body posture adjustments with the salient target presented in the environment.

CONCLUSIONS

Older adults with a low fear of falling can potentially benefit from a more salient target at their walking destination, whereas those with a high fear of falling were advised to implement a more straightforward falling intervention in their living areas.

The effect of COVID-19 pandemic and wearing face masks on ophthalmology practice: What is known so far? A narrative review

Face masks, along with other preventive measures, can help slow the spread of COVID-19. Despite the positive effect of the mask in combating the virus, it has some negative effects on the human body that must be followed up on and reduced. In this study, we discuss the impact of wearing face masks on the eye and the common issues associated with using them. The literature search was conducted using electronic databases such as PubMed and Google Scholar. Only articles published in English were included. A total of 39 relevant articles were deemed eligible. After the duplicate articles were removed, the titles and abstracts of 20 papers underwent full-text screening. The review comprised both prospective and retrospective investigations, case reports, and a series of reporting ocular symptoms following the use of face masks. The COVID-19 pandemic affected ophthalmology practices in managing patients. New factors must be considered, especially when dealing with anti-VEGF injections, such as the risk of endophthalmitis, tests and symptoms of patients with glaucoma, and the emerging symptoms associated with the COVID-19 vaccination. The use of face masks and breathing aids seemed to influence the tear film.

Visuospatial working memory and obstacle crossing in young and older people

Obstacle crossing requires visuospatial working memory to guide the trailing leg trajectory when vision in unavailable. Visuospatial working memory, as assessed with neuropsychological tests, declines with age, however, this remains to be investigated functionally in obstacle crossing. There is also evidence that visuospatial encoding during a secondary task interferes with balance control during stepping and walking in older people. Here, we studied the interaction effects of age by delay (study 1) and age by secondary visuospatial task (study 2) conditions on obstacle clearance in a visuospatial working memory -guided obstacle crossing task. Healthy young adults aged 19 to 36 years (n = 20 in study 1 and n = 17 in study 2) and healthy older adults aged 66 to 83 years (n = 29 in study 1 and n = 21 in study 2) were instructed to step over an obstacle with their leading leg and straddle it for a delay period before completing the crossing with their trailing leg. In study 1, two obstacle height conditions (12 cm, 18 cm) and two delay durations (20 s, 60 s) were presented in random order. In study 2, participants were required to attend to either no secondary task (control), a visuospatial secondary (star movement) task, or a nonspatial secondary (arithmetic) task, while straddling the obstacle for a delay duration of 20 s, at obstacle heights of 12 cm and 18 cm, randomly presented. Trailing leg kinematics (mean and variability of maximum toe clearance over the obstacle) were determined via motion capture. There were no statistically significant age by delay or age by secondary task interactions. In study 1, toe clearance variability was significantly greater in young adults and increased with increasing delay duration in both groups. In study 2, compared with the control condition, toe clearance variability was significantly greater in the non-spatial secondary task condition but not in the visuospatial condition. Contrary to our hypotheses, these findings suggest that young and older adults alike can store an obstacle representation via visuospatial working memory for durations of at least 60 s and use this information to safely scale their trailing leg over an obstacle. However, the increase in trailing leg toe clearance variability with delay duration suggests that obstacle representation starts to deteriorate even within the first 20 s regardless of age. The finding that undertaking a concurrent arithmetic task impaired visuospatial working memory-guided obstacle clearance suggests a potential increased risk of tripping during obstacle crossing while dual-tasking in both young and older people.

Use of the Azure Kinect to measure foot clearance during obstacle crossing: A validation study

Obstacle crossing is typical adaptive locomotion known to be related to the risk of falls. Previous conventional studies have used elaborate and costly optical motion capture systems, which not only represent a considerable expense but also require participants to visit a laboratory. To overcome these shortcomings, we aimed to develop a practical and inexpensive solution for measuring obstacle-crossing behavior by using the Microsoft Azure Kinect, one of the most promising markerless motion capture systems. We validated the Azure Kinect as a tool to measure foot clearance and compared its performance to that of an optical motion capture system (Qualisys). We also determined the effect of the Kinect sensor placement on measurement performance. Sixteen healthy young men crossed obstacles of different heights (50, 150, and 250 mm). Kinect sensors were placed in front of and beside the obstacle as well as diagonally between those positions. As indices of measurement quality, we counted the number of measurement failures and calculated the systematic and random errors between the foot clearance measured by the Kinect and Qualisys. We also calculated the Pearson correlation coefficients between the Kinect and Qualisys measurements. The number of measurement failures and the systematic and random error were minimized when the Kinect was placed diagonally in front of the obstacle on the same side as the trail limb. The high correlation coefficient (r > 0.890) observed between the Kinect and Qualisys measurements suggest that the Azure Kinect has excellent potential for measuring foot clearance during obstacle-crossing tasks.

Visuomotor control of leaping over a raised obstacle is sensitive to small baseline displacements

The limb kinematics used for stepping or leaping over an obstacle are determined primarily by visual sensing of obstacle position and geometry. In this study, we demonstrate that changes are induced in limb kinematics even when obstacle geometry is manipulated in a way that does not introduce a mechanical requirement for a change of limb trajectory nor increase risk of collision. Human participants performed a running leap over a single raised obstacle bar. Kinematic changes were measured when an identical second bar was introduced at a ground level underneath the obstacle and displaced by a functionally insignificant distance along the axis of travel. The presence or absence of a baseline directly beneath the highest extremity had no significant effect on limb kinematics. However, displacing the baseline horizontally induced a horizontal translation of limb trajectory in the direction of the displacement. These results show that systematic changes to limb trajectories can occur in the absence of a change in sensed mechanical constraints or optimization. The nature of visuomotor control of human leaping may involve a continuous mapping of sensory input to kinematic output rather than one responsive only to information perceived to be mechanically relevant.

Sensitivity of the Toe Height to Multijoint Angular Changes in the Lower Limbs During Unobstructed and Obstructed Gait

Tripping while walking is a main contributor to falls across the adult lifespan. Trip risk is proportional to variability in toe clearance. To determine the sources of this variability, the authors computed for 10 young adults the sensitivity of toe clearance to 10 bilateral lower limb joint angles during unobstructed and obstructed walking when the lead and the trail limb crossed the obstacle. The authors computed a novel measure-singular value of the appropriate Jacobian-as the combined toe clearance sensitivity to 4 groups of angles: all sagittal and all frontal plane angles and all swing and all stance limb angles. Toe clearance was most sensitive to the stance hip ab/adduction for unobstructed gait. For obstructed gait, sensitivity to other joints increased and matched the sensitivity to stance hip ab/adduction. Combined sensitivities revealed critical information that was not evident in the sensitivities to individual angles. The combined sensitivity to stance limb angles was 84% higher than swing limb angles. The combined sensitivity to the sagittal plane angles was lower than the sensitivity to the frontal plane angles during unobstructed gait, and this relation was reversed during obstacle crossing. The results highlight the importance of the stance limb joints and indicate that frontal plane angles should not be ignored.

Age-related changes in postural control in older women: transitional tasks in step initiation

Background

Aging, being a natural process, involves many functional and structural changes within the body. Identifying the age-related postural changes will provide insight into the role of aging on postural control during locomotion. The aim of this study was to identify age-related postural changes during a transitional task under different conditions.

Methods

Sixty healthy females divided into three age groups: A (50-60 y/o), B (60-70 y/o), and C (70-80 y/o). The transitional task was measured by two force platforms. The procedure consisted of three phases: quiet standing, transfer onto a second platform, and quiet standing on the second platform. Four different conditions were applied: unperturbed transfer, obstacle crossing, step-up, and step-down. Double-support time, transit time, and stability time before and after the step task were analyzed.

Results

The transit time was longer by 30% for subjects over 70 y/o. The double-support time was longer by 11% among adults 60-70 y/o, while in people over 70 y/o it was longer by almost 50% compared to the 50-60 y/o subjects. The stability time before the transitional task was longer by 17% among adults over 60 y/o compared to middle-age subjects. The stability times before and after the transitional task were longer for adults in the 50-60 y/o category.

Conclusion

The proposed procedure is adequate for assessing age-related changes in postural control while undergoing a transitional task. An analysis of the double-support time and stability time before and after the step task enabled the detection of early signs of balance changes in middle-age adults. Independent of age, the transitional task parameters changed with the increasing difficulty of the tasks.

Enhanced Obstacle Contrast to Promote Visual Scanning in Fallers with Parkinson's Disease: Role of Executive Function

The ability to perceive differences in environmental contrast is critical for navigating complex environments safely. People with Parkinson's disease (PD) report a multitude of visual and cognitive deficits which may impede safe obstacle negotiation and increase fall risk. Enhancing obstacle contrast may influence the content of visual information acquired within complex environments and thus target environmental fall risk factors. 17 PD with a history of falls and 18 controls walked over an obstacle covered in a high and low contrast material in separate trials whilst eye movements were recorded. Measures of visual function and cognition were obtained. Gaze location was extracted during the approach phase. PD spent longer looking at the obstacle compared to controls regardless of contrast (p < .05), however group differences were largest for the low contrast obstacle. When accounting for group differences in approach time, PD spent longer looking at the low contrast obstacle and less time looking at the ground beyond the low contrast obstacle compared to controls (p < .05). The response to obstacle contrast in PD (high-low) was significantly associated with executive function. Better executive function was associated with spending longer looking at the low contrast obstacle and at the ground beyond the high contrast obstacle. Enhancing the contrast of ground-based trip hazards may improve visual processing of environmental cues in PD, particularly for individuals with better executive function. Manipulating contrast to attract visual attention is already in use in the public domain, however its utility for reducing fall risk in PD is yet to be formally tested in habitual settings.

Gait characteristics during inadvertent obstacle contacts in young, middle-aged and older adults

BACKGROUND

When stepping over obstacles, analyses have focused on the successful trials to understand adaptive gait. However, examination of the inadvertent trips that occasionally occur in the laboratory can provide a rich source of information regarding the gait characteristics underlying trip-related falls.

RESEARCH QUESTION

What gait variables during obstacle crossing are associated with inadvertent obstacle contacts, and are these variables different across the lifespan?

METHODS

Three age groups included: young adults (20-35 years, N = 20), middle-aged adults (50-64 years, N = 15), and older adults (65-79 years, N = 19). A stationary, visible obstacle (26 cm tall) was placed in the middle of a walkway. Foot trajectories and head angles were compared between contact and non-contact trials.

RESULTS

Twelve participants contacted the obstacle: seven young adults (3.5% of young adult trials), two middle-aged adults (1.3%), and three older adults (1.6%). Young and middle-aged adults contacted primarily with the trail limb, while older adults contacted primarily with the lead limb. Contacts occurred for different reasons: Most young adult contact trials had appropriate foot placement, but inadequate elevation; middle-aged and older adults demonstrated inappropriate foot placement before the obstacle, leading to foot contact during the swing phase.

SIGNIFICANCE

Lower contact rates in the middle-aged and older adults indicates that the cautious strategies adopted during obstacle crossing are effective. Higher contact rates in young adults may indicate trial-and-error exploratory behavior. Inappropriate foot placement in the middle-aged and older adults may indicate impaired ability to gather obstacle position information during the approach phase.

Avoiding 3D Obstacles in Mixed Reality: Does It Differ from Negotiating Real Obstacles?

Mixed-reality technologies are evolving rapidly, allowing for gradually more realistic interaction with digital content while moving freely in real-world environments. In this study, we examined the suitability of the Microsoft HoloLens mixed-reality headset for creating locomotor interactions in real-world environments enriched with 3D holographic obstacles. In Experiment 1, we compared the obstacle-avoidance maneuvers of 12 participants stepping over either real or holographic obstacles of different heights and depths. Participants' avoidance maneuvers were recorded with three spatially and temporally integrated Kinect v2 sensors. Similar to real obstacles, holographic obstacles elicited obstacle-avoidance maneuvers that scaled with obstacle dimensions. However, with holographic obstacles, some participants showed dissimilar trail or lead foot obstacle-avoidance maneuvers compared to real obstacles: they either consistently failed to raise their trail foot or crossed the obstacle with extreme lead-foot margins. In Experiment 2, we examined the efficacy of mixed-reality video feedback in altering such dissimilar avoidance maneuvers. Participants quickly adjusted their trail-foot crossing height and gradually lowered extreme lead-foot crossing heights in the course of mixed-reality video feedback trials, and these improvements were largely retained in subsequent trials without feedback. Participant-specific differences in real and holographic obstacle avoidance notwithstanding, the present results suggest that 3D holographic obstacles supplemented with mixed-reality video feedback may be used for studying and perhaps also training 3D obstacle avoidance.

Interdependence of balance mechanisms during bipedal locomotion

Our main interest is to identify how humans maintain upright while walking. Balance during standing and walking is different, primarily due to a gait cycle which the nervous system must contend with a variety of body configurations and frequent perturbations (i.e., heel-strike). We have identified three mechanisms that healthy young adults use to respond to a visually perceived fall to the side. The lateral ankle mechanism and the foot placement mechanism are used to shift the center of pressure in the direction of the perceived fall, and the center of mass away from the perceived fall. The push-off mechanism, a systematic change in ankle plantarflexion angle in the trailing leg, results in fine adjustments to medial-lateral balance near the end of double stance. The focus here is to understand how the three basic balance mechanisms are coordinated to produce an overall balance response. The results indicate that lateral ankle and foot placement mechanisms are inversely related. Larger lateral ankle responses lead to smaller foot placement changes. Correlations involving the push-off mechanism, while significant, were weak. However, the consistency of the correlations across stimulus conditions suggest the push-off mechanism has the role of small adjustments to medial-lateral movement near the end of the balance response. This verifies that a fundamental feature of human bipedal gait is a highly flexible balance system that recruits and coordinates multiple mechanisms to maintain upright balance during walking to accommodate extreme changes in body configuration and frequent perturbations.

Assessment of an augmented reality apparatus for the study of visually guided walking and obstacle crossing

To walk through the cluttered natural environment requires visually guided and anticipatory adjustments to gait in advance of upcoming obstacles. However, scientific investigation of visual contributions to obstacle crossing have historically been limited by the practical issues involved with the repeated presentation of multiple obstacles upon a ground plane. This study evaluates an approach in which the perception of a 3D obstacle is generated from 2D projection onto the ground plane with perspective correction based on the subject's motion-tracked head position. The perception of depth is further reinforced with the use of stereoscopic goggles. To evaluate the validity of this approach, behavior was compared between approaches to two types of obstacles in a blocked design: physical obstacles, and the augmented reality (AR) obstacles projected upon the ground plane. In addition, obstacle height, defined in units of leg length (LL), was varied on each trial (0.15, 0.25, 0.35 LL). Approaches to ended with collision on 0.8% of trials with physical obstacles per subject, and on 1.4% trials with AR obstacles. Collisions were signaled by auditory feedback. Linear changes in the height of both AR and physical obstacles produced linear changes in maximum step height, preserving a constant clearance magnitude across changes in obstacle height. However, for AR obstacles, approach speed was slower, the crossing step peaked higher above the obstacle, and there was greater clearance between the lead toe and the obstacle. These results suggest that subjects were more cautious when approaching and stepping over AR obstacles.

Gaze diversion affects cognitive and motor performance in young adults when stepping over obstacles

BACKGROUND

In many common multi-tasks, vision is used for two or more of the tasks, such as viewing cars, traffic signals, and the sidewalk curb at a crosswalk.

RESEARCH QUESTION

How does gaze diversion affect adaptive locomotion in young adults?

METHODS

Seventeen young adults completed a simple reaction time (RT) task while (1) standing and (2) during the approach to an obstacle on an 8 m walkway. Participants pressed a remote switch in response to a light cue (activated once during approach phase). The light cue was located either (1) on the obstacle (gaze diverted to obstacle) or (2) at eye level (gaze diverted away from obstacle). A gait baseline task with no RT task was included.

RESULTS

An interaction was observed (task (standing versus walking) by gaze location (on versus away from obstacle), p = 0.01), where RT was not affected by the gaze location in the standing task, but RT was longer when gaze was diverted away from the obstacle in the gait task. Furthermore, trail foot placement was closer to the obstacle when the gaze was diverted away from the obstacle (p = 0.002), which increased risk of tripping.

SIGNIFICANCE

Gaze diversion did not affect cognitive performance in the standing task, as information regarding the obstacle was not relevant for the standing task. However, completing a simple discrete visual cognitive task during obstacle crossing impaired both cognitive and gait performance, but only when gaze was diverted away from the obstacle. The impaired performance is likely due to the larger amount of structural interference when gaze was diverted away from the obstacle. These findings highlight the critical role of vision during the approach phase to an obstacle.

Changes in the control of obstacle crossing in middle age become evident as gait task difficulty increases

BACKGROUND

Age-associated physiological changes result in modified gait, such as slower speed, for older adults. Identifying the onset of age-related gait changes will provide insight into the role of aging on locomotor control. It is expected that a more challenging gait task (obstacle crossing) puts more demands on physiological systems, and may reveal gait modifications in a middle-aged group that are not evident in an easier gait task (level walking).

RESEARCH QUESTION

To identify the effect of advancing age on gait as a function of increasing locomotor challenge during an obstacle crossing task.

METHODS

Three age groups (young, middle-aged, and older adults) stepped over an obstacle placed in a 15 m walkway. Task challenge ranged from low to high in four conditions: unobstructed gait, 3, 10, and 26 cm obstacles. Gait measures were calculated during the approach and crossing steps.

RESULTS

Significant interactions were observed for gait speed (age by height by step, p < 0.01), foot placement variability (age by step, p < 0.01) and foot clearance (age by height, p = 0.05). Relative to young adults, older adults walked slower in all conditions and had higher foot clearances for the 10 and 26 cm obstacles. Middle-aged adults walked with speeds and foot clearances that were not different from young adults in the lower gait challenge conditions, and changed to values that were not different from older adults in the highest gait challenge conditions. Foot placement variability was greater for the middle-aged and older groups, but only in the last two steps before the obstacle.

SIGNIFICANCE

Multiple gait changes were observed as early as middle-age, and changes in speed and foot clearance became more evident as task difficulty increased. The increased gait challenge placed more demands on the neuromuscular system, revealing age-related gait modifications that were not evident in the level walking gait task.

The quality of visual information about the lower extremities influences visuomotor coordination during virtual obstacle negotiation

Successful negotiation of obstacles during walking relies on the integration of visual information about the environment with ongoing locomotor commands. When information about the body and the environment is removed through occlusion of the lower visual field, individuals increase downward head pitch angle, reduce foot placement precision, and increase safety margins during crossing. However, whether these effects are mediated by loss of visual information about the lower extremities, the obstacle, or both remains to be seen. Here we used a fully immersive, virtual obstacle negotiation task to investigate how visual information about the lower extremities is integrated with information about the environment to facilitate skillful obstacle negotiation. Participants stepped over virtual obstacles while walking on a treadmill with one of three types of visual feedback about the lower extremities: no feedback, end-point feedback, and a link-segment model. We found that absence of visual information about the lower extremities led to an increase in the variability of leading foot placement after crossing. The presence of a visual representation of the lower extremities promoted greater downward head pitch angle during the approach to and subsequent crossing of an obstacle. In addition, having greater downward head pitch was associated with closer placement of the trailing foot to the obstacle, further placement of the leading foot after the obstacle, and higher trailing foot clearance. These results demonstrate that the fidelity of visual information about the lower extremities influences both feedforward and feedback aspects of visuomotor coordination during obstacle negotiation. NEW & NOTEWORTHY Here we demonstrate that visual information about the lower extremities is utilized for precise foot placement and control of safety margins during obstacle negotiation. We also found that when a visual representation of the lower extremities is present, this information is used in the online control of foot trajectory. Together, our results highlight how visual information about the body and the environment is integrated with motor commands for planning and online control of obstacle negotiation.

Examining Transfer Effects of Dual-Task Training Protocols for a Complex Locomotor Task

Training protocols designed to improve dual-task performance of an obstacle crossing and auditory Stroop task (OBS+Stroop) were tested. In Experiment  1 , following baseline collection of OBS+Stroop trials, proximally related walking training was performed, and participants were then retested on the OBS+Stroop test. After training, participants adopted a more cautious obstacle crossing strategy, indicating a potentially safer navigation strategy. Transfer effects from distally related training were then examined (Experiment  2 ); a computer game training paradigm was examined using the same testing protocol as Experiment  1 . Computer training demonstrated improved dual-task performance on some measures, but did not induce a more cautious stepping strategy. Results indicate that dual-task training needs to be similar to targeted tasks to yield reliable, positive training outcomes.

Do characteristics of a stationary obstacle lead to adjustments in obstacle stepping strategies?

Navigating cluttered and complex environments increases the risk of falling. To decrease this risk, it is important to understand the influence of obstacle visual cues on stepping parameters, however the specific obstacle characteristics that have the greatest influence on avoidance strategies is still under debate. The purpose of the current work is to provide further insight on the relationship between obstacle appearance in the environment and modulation of stepping parameters. Healthy young adults (N=8) first stepped over an obstacle with one visible top edge ("floating"; 8 trials) followed by trials where experimenters randomly altered the location of a ground reference object to one of 7 different positions (8 trials per location), which ranged from 6cm in front of, directly under, or up to 6cm behind the floating obstacle (at 2cm intervals). Mean take-off and landing distance as well as minimum foot clearance values were unchanged across different positions of the ground reference object; a consistent stepping trajectory was observed for all experimental conditions. Contrary to our hypotheses, results of this study indicate that ground based visual cues are not essential for the planning of stepping and clearance strategies. The simultaneous presentation of both floating and ground based objects may have provided critical information that lead to the adoption of a consistent strategy for clearing the top edge of the obstacle. The invariant foot placement observed here may be an appropriate stepping strategy for young adults, however this may not be the case across the lifespan or in special populations.

How does visual manipulation affect obstacle avoidance strategies used by athletes?

Research examining our ability to avoid obstacles in our path has stressed the importance of visual input. The aim of this study was to determine if athletes playing varsity-level field sports, who rely on visual input to guide motor behaviour, are more able to guide their foot over obstacles compared to recreational individuals. While wearing kinematic markers, eight varsity athletes and eight age-matched controls (aged 18-25) walked along a walkway and stepped over stationary obstacles (180° motion arc). Visual input was manipulated using PLATO visual goggles three or two steps pre-obstacle crossing and compared to trials where vision was given throughout. A main effect between groups for peak trail toe elevation was shown with greater values generated by the controls for all crossing conditions during full vision trials only. This may be interpreted as athletes not perceiving this obstacle as an increased threat to their postural stability. Collectively, findings suggest the athletic group is able to transfer their abilities to non-specific conditions during full vision trials; however, varsity-level athletes were equally reliant on visual cues for these visually guided stepping tasks as their performance was similar to the controls when vision is removed.

Ground Reaction Forces of the Lead and Trail Limbs when Stepping Over an Obstacle

BACKGROUND

Precise force generation and absorption during stepping over different obstacles need to be quantified for task accomplishment. This study aimed to quantify how the lead limb (LL) and trail limb (TL) generate and absorb forces while stepping over obstacle of various heights.

MATERIAL AND METHODS

Thirteen healthy young women participated in the study. Force data were collected from 2 force plates when participants stepped over obstacles. Two limbs (right LL and left TL) and 4 conditions of stepping (no obstacle, stepping over 5 cm, 20 cm, and 30 cm obstacle heights) were tested for main effect and interaction effect by 2-way ANOVA. Paired t-test and 1-way repeated-measure ANOVA were used to compare differences of variables between limbs and among stepping conditions, respectively. The main effects on the limb were found in first peak vertical force, minimum vertical force, propulsive peak force, and propulsive impulse.

RESULTS

Significant main effects of condition were found in time to minimum force, time to the second peak force, time to propulsive peak force, first peak vertical force, braking peak force, propulsive peak force, vertical impulse, braking impulse, and propulsive impulse. Interaction effects of limb and condition were found in first peak vertical force, propulsive peak force, braking impulse, and propulsive impulse.

CONCLUSIONS

Adaptations of force generation in the LL and TL were found to involve adaptability to altered external environment during stepping in healthy young adults.

Proactive gait strategies to mitigate risk of obstacle contact are more prevalent with advancing age

The purposes of this study were to determine if healthy older adults adopt strategies to decrease the likelihood of obstacle contact, and to determine how these strategies are modified as a function of advancing age. Three age groups were examined: 20-25 yo (N = 19), 65-79 yo (N = 11), and 80-91 yo (N = 18). Participants stepped over a stationary, visible obstacle on a walkway. Step length and gait speed progressively decreased with advancing age; the shorter step length resulted in closer foot placement to the obstacle and an associated increased risk of obstacle contact. Lead (first limb to cross the obstacle) and trail (second) limb trajectories were examined for behavior that mitigated the risk of contact. (1) Consistent trail foot placement before the obstacle across all ages allowed space and time for the trail foot to clear the obstacle. (2) To avoid lead limb contact due to closer foot placement before and after the obstacle, the lead toe was raised more vertically after toe-off, and then the foot was extended beyond the landing position (termed lead overshoot) and retracted backwards to achieve the shortened step length. Lead overshoot progressively increased with advancing age. (3) Head angle was progressively lower with advancing age, an apparent attempt to gather more visual information during approach. Overall, a series of proactive strategies were adopted to mitigate risk of contact. However, the larger, more abrupt movements associated with a more vertical foot trajectory and lead overshoot may compromise whole body balance, indicating a possible trade-off between risk of contact and stability.

Factors leading to obstacle contact during adaptive locomotion

During everyday life, healthy adults occasionally trip over an obstacle that they knew was there. These 'spontaneous' trips can provide insight into the circumstances leading to trips and falls. The goal of this study was to describe the errors in foot placement and/or foot elevation that resulted in a spontaneous contact with a fixed, visible obstacle in young, healthy adults. Fifteen subjects stepped over an obstacle (height set to 25 % leg length) placed in the middle of an 8 m walkway, up to 300 times. Three subjects never contacted the obstacle and 12 subjects contacted the obstacle 1-4 times, totaling 24 contacts in 3,843 trials (0.6 %). Most of the contacts (92 %) were with the trail limb. Minimum foot clearance of the trail limb (trail MFC) decreased linearly (average slope of -1 mm/trial) with repeated trials. The majority of subjects (70 %) continued the linear decrease of trail MFC until they contacted the obstacle. The remaining contacts resulted from an apparent misjudgment of foot placement and/or foot elevation. Following contact, trail MFC increased 75 % in the subsequent trials and remained elevated at least up to 30 trials post-contact, but the trajectory of the unperturbed lead limb did not change, further supporting the idea of independent control for the lead and trail limbs during obstacle crossing. Possible causes of the progressive decrease in trail MFC until obstacle contact are considered.