Obstacle crossing in Parkinson's disease: mediolateral sway of the centre of mass during level-ground walking and obstacle crossing

BACKGROUND

Falls are common in idiopathic Parkinson's disease (PD) and frequently occur when walking and crossing obstacles.

OBJECTIVE

To determine whether people with mild to moderately severe PD have abnormal centre of mass (CoM) motion in response to the perturbations of level-ground walking and obstacle crossing.

METHOD

Mediolateral excursion and velocity of the CoM were measured using three-dimensional motion analysis and force platforms in 20 people with mild to moderately severe PD at the peak dose of their PD medication, and 20 age and sex matched healthy control participants.

RESULTS

People with PD had greater sideways sway than healthy older adults when walking, particularly when walking over obstacles. People with PD also maintained their CoM more medial to their stance foot throughout the swing phase of gait compared to controls. The severity of motor symptoms in people with PD, measured using the UPDRS-III, was associated with faster sideways CoM motion but not increased CoM excursions.

CONCLUSIONS

Environmental hazards, such as ground-based obstacles, may accentuate postural instability in people with PD. Increased mediolateral sway might be due to impaired postural responses or kinematic compensations to increase foot clearance. Fall prevention programs could benefit from inclusion of components educating people with PD about the risks associated with obstacle crossing when walking.

Measuring the effects of a visual or auditory Stroop task on dual-task costs during obstacle crossing

Successful planning and execution of motor strategies while concurrently performing a cognitive task has been previously examined, but unfortunately the varied and numerous cognitive tasks studied has limited our fundamental understanding of how the central nervous system successfully integrates and executes these tasks simultaneously. To gain a better understanding of these mechanisms we used a set of cognitive tasks requiring similar central executive function processes and response outputs but requiring different perceptual mechanisms to perform the motor task. Thirteen healthy young adults (20.6±1.6years old) were instrumented with kinematic markers (60Hz) and completed 5 practice, 10 single-task obstacle walking trials and two 40 trial experimental blocks. Each block contained 20 trials of seated (single-task) trials followed by 20 cognitive and obstacle (30% lower leg length) crossing trials (dual-task). Blocks were randomly presented and included either an auditory Stroop task (AST; central interference only) or a visual Stroop task (VST; combined central and structural interference). Higher accuracy rates and shorter response times were observed for the VST versus AST single-task trials (p<0.05). Conversely, for the obstacle stepping performance, larger dual task costs were observed for the VST as compared to the AST for clearance measures (the VST induced larger clearance values for both the leading and trailing feet), indicating VST tasks caused greater interference for obstacle crossing (p<0.05). These results supported the hypothesis that structural interference has a larger effect on motor performance in a dual-task situation compared to cognitive tasks that pose interference at only the central processing stage.

Relation between frontal plane center of mass position stability and foot elevation during obstacle crossing

High foot elevation during obstacle crossing is viewed as a conservative strategy in older adults, but excessive foot elevation may result in large mediolateral center of mass (CoM) displacement. Since an incorrect transfer of CoM can lead to balance loss during locomotion, both appropriate foot elevation and CoM position must be controlled and coordinated by adjusting body segment positions. However, no studies have revealed time profiles of CoM position by coordinated segment movements and the relation of foot elevation with CoM position during obstacle crossing. Twenty-five healthy older adults crossed an obstacle (depth: 1 cm, width: 60 cm, height: 8 cm) during comfortable-speed walking. Synergy indices were calculated during lead- and trail-limb swing using uncontrolled manifold analysis. High synergy index values indicate a strong multi-joint kinematic synergy, or co-fluctuations in segment movements, to control CoM position. The maximum foot heights of the swing limbs were calculated as the maximum vertical distance between the most distal foot point and the ground. In the mediolateral direction, synergy index values during early lead-limb swing were significantly greater than during early trail-limb swing, and in the vertical direction, large synergy index values were found during early- and mid-swing phases. Moreover, maximum trail-foot height was correlated to vertical synergy index during early phase. CoM position was not well controlled by a kinematic synergy during trail-limb swing and the low control of CoM position was observed with great trail-foot height. The results suggest that a conservative strategy with great trail-foot height would not always be helpful for successful obstacle crossing.

How does the extent of central visual field loss affect adaptive gait?

Visual impairment is one of the most important clinical risk factors associated with falls. Currently it remains unclear whether adaptive gait is progressively affected as the extent of central visual field loss (CFL) increases, or when CFL exceeds a certain size. 10 participants (aged 22 ± 3 years) negotiated a floor based obstacle in full vision (no occlusion) and wearing custom made contact lenses which simulated 10° CFL and 20° CFL. Movement kinematics assessed the period immediately prior to and during obstacle crossing. In the 20° CFL condition, participants exhibited adaptations in gait which were consistent with being more cautious and more variable during the approach to and crossing of the obstacle, when compared to both 10° CFL and full vision conditions. Specifically, in the 20° CFL condition participants placed their lead foot further from the obstacle, lifted both their lead and trail feet higher and slower over the obstacle, and took longer to negotiate the obstacle when compared to the 10° CFL and full vision conditions. Data highlights differences in adaptive gait as a function of the extent of CFL when compared to full vision. More importantly, these adaptations were only associated with loss of the central 20° of the visual field, suggesting that gait is compromised only after central visual field loss exceeds a certain level.

Biomechanical risk factors for tripping during obstacle--Crossing with the trailing limb in patients with type II diabetes mellitus

People with type II diabetes mellitus (DM) are at a high risk of falling especially during more challenging locomotor tasks such as obstacle-crossing. The current study aimed to identify the risk factors for tripping in these patients during trailing-limb obstacle-crossing. Fourteen patients with type II DM with or without mild peripheral neuropathy (PN) and 14 healthy controls walked and crossed obstacles of three different heights while their motion data were measured using a motion capture system and two forceplates. The DM group was found to cross obstacles with significantly reduced trailing toe clearance (p<0.05), increasing the probability of the foot hitting the obstacle, and thus the risk of tripping. This altered end-point control was associated with significantly reduced knee flexion and hip adduction of the trailing swing limb (p<0.05), as well as significantly increased ankle plantarflexor moments in the leading stance limb (p<0.05). Therefore, reduced knee flexion and hip adduction of the swing limb are identified as risk factors for tripping during obstacle-crossing. Increased mechanical demands on the ankle plantarflexors suggest that weakness of these muscles may further reduce the already compromised performance of obstacle-crossing in these patients. The current results showed that obstacle-crossing can be used to detect gait deviations and to identify the associated risk of tripping in patients with type II DM without or at an early stage of PN.

The Correlation between Dynamic Balance Measures and Stance Sub-phase COP Displacement Time in Older Adults during Obstacle Crossing

[Purpose] This study examined the relationship between the center of pressure (COP) displacement time during the stance subphases and dynamic balance ability when elderly cross obstacles 0, 10, and 40 cm in height. [Subjects] Fifteen older adults were enrolled in this study (≥65 years of age). [Methods] An F-Scan System was used to measure the COP displacement time when subjects crossed obstacles 0, 10, and 40 cm in height, and the Dynamic Gait Index, Berg Balance Scale, and Four Square Step Test were used to measure dynamic balance ability. [Results] The Dynamic Gait Index, Berg Balance Scale, and Four Square Step Test were correlated with each other. Dynamic balance tests were correlated with the COP displacement time during the stance phase. At obstacle heights of 10 and 40 cm during loading response and at all heights during pre-swing, there were correlations with dynamic balance ability. However, dynamic balance ability did not affect the COP displacement time during mid-stance and terminal stance. [Conclusion] People with a lower dynamic balance ability show a larger COP displacement time during loading response and pre-swing. Therefore, dynamic balance ability can be predicted by measuring the COP displacement time.

The relationship between lower limb proprioceptive sense and locomotor skill acquisition

Sensorimotor integration is essential for controlling movement and acquiring new motor tasks in humans. The aim of this project was to understand how lower limb proprioceptive sense contributes to the acquisition of a skilled walking task. We assessed lower limb joint position and movement detection sense in healthy human subjects using the Lokomat robotic exoskeleton. Subjects walked on a treadmill to practice a skilled motor task (200 trials) requiring them to match their foot height during the swing phase to the height of a virtual obstacle displayed on a monitor in front of them. Subjects were given visual feedback on their error relative to the obstacle height after it was crossed. Lower limb joint position sense was related to the final performance error, but not the learning rate of the skilled walking task. The findings from this study support the role of lower limb proprioceptive sense on locomotor skill performance in healthy adult subjects.

Prospective dynamic balance control during the swing phase of walking: stability boundaries and time-to-contact analysis

This study examined the prospective control of the swing phase in young healthy adults while walking at preferred speed over unobstructed ground and during obstacle clearance. Three aspects of swing were examined: (1) the relation of the body Center of Mass (CoM) to the stability boundaries at the base of support; (2) a dynamic time-to-contact analysis of the CoM and swing foot to these boundaries; and (3) the role of head movements in the prospective control of gait and field of view assessment. The time-to-contact analysis of CoM and swing foot showed less stable swing dynamics in the trail foot compared to the lead foot in the approach to the unstable equilibrium, with the CoM leading the swing foot and crossing the anterior stability boundary before the swing foot. Compensations in temporal coupling occurred in the trail limb during the late swing phase. Time-to-contact analysis of head movement showed stronger prospective control of the lead foot, while fixation of the field of view occurred earlier in swing and was closer to the body in the obstacle condition compared to unobstructed walking. The dynamic time-to-contact analysis offers a new approach to assessing the unstable swing phase of walking in different populations.

The effects of object height and visual information on the control of obstacle crossing during locomotion in healthy older adults

In order to safely avoid obstacles, humans must rely on visual information regarding the position and shape of the object obtained in advance. The present study aimed to reveal the duration of obstacle visibility necessary for appropriate visuomotor control during obstacle avoidance in healthy older adults. Participants included 13 healthy young women (mean age: 21.5±1.4years) and 15 healthy older women (mean age: 68.5±3.5years) who were instructed to cross over an obstacle along a pressure-sensitive pathway at a self-selected pace while wearing liquid crystal shutter goggles. Participants were evaluated during three visual occlusion conditions: (i) full visibility, (ii) occlusion at T-1 step (T: time of obstacle crossing), and (iii) occlusion at T-2 steps. Toe clearances of both the lead and trail limb (LTC and TTC) were calculated. LTC in the occlusion at T-2 steps condition was significantly greater than that in other conditions. Furthermore, a significant correlation was observed between LTC and TTC in both groups, regardless of the condition or obstacle height. In the older adult group alone, step width in the occlusion at T-2 steps condition increased relative to that in full visibility conditions. The results of the present study suggest that there is no difference in the characteristics of visuomotor control for appropriate obstacle crossing based on age. However, older adults may exhibit increased dependence on visual information for postural stability; they may also need an increased step width when lacking information regarding their positional relationship to obstacles.

Contribution of vision and its age-related changes to postural stability in obstacle crossing during locomotion

BACKGROUND

Obstacle crossing requires sufficient toe clearance for trip and fall prevention for which postural stability is a prerequisite. It is thought that the upper visual field plays an important role in the maintenance of postural stability, but its influence and age-dependence have not been investigated yet.

RESEARCH QUESTION

What is the role of the visual fields in maintaining postural stability during crossing an obstacle in young and older adults?.

METHODS

This study included 14 young adults and 14 older adults. The participants, wearing an accelerometer and liquid crystal shutter goggles, were asked to cross an obstacle under the following three conditions (i) full vision; (ii) total visual field occlusion at two steps before the obstacle, and (iii) lower visual field occlusion at two steps before the obstacle. The root mean square ratio in the mediolateral direction (RMSR_ML) for the three sections (i.e., approach to the obstacle, lead limb crossing, and trail limb crossing), as well as the root mean square in the mediolateral direction (RMS_ML) for each section were calculated.

RESULTS

RMS_ML during lead limb crossing was significantly increased in older adults compared to young adults (p < 0.01). There was no significant main effect of visual condition and age group on RMSR_ML for the three steps.

SIGNIFICANCE

The study results suggest postural lateral instability in older adults with poor balance ability during lead limb crossing. Regardless of age, the peripheral visual information appears to contribute minimally to the maintenance of postural lateral stability at least from two steps before the obstacle, when the participants perceived the surrounding environment and the size of the obstacle while approaching it.

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.

Obstacle crossing following stroke improves over one month when the unaffected limb leads, but not when the affected limb leads

While it is well established that obstacle crossing is impaired following stroke, it is not known whether obstacle crossing improves as gait improves following stroke. The purpose of this study was to determine whether obstacle crossing changed over a one month time period in people with a recent stroke. Twenty participants receiving rehabilitation following a recent stroke were tested on two occasions one month apart. Participants received usual care rehabilitation, including physiotherapy, between the tests. The main outcome measure was obstacle crossing speed as participants stepped over a 4-cm high obstacle. Secondary measures were spatiotemporal variables. Data were collected via a three dimensional motion analysis system. When leading with the affected limb no changes in obstacle crossing speed or spatiotemporal variables were observed over the one month period. When leading with the unaffected limb, crossing speed significantly increased (p=.002), and affected trail limb swing time (p=.03) and crossing step double support time reduced (p=.016). While not significant, the lead and trail limb pre-obstacle distance increased (p=.08), and lead swing time (p=.052) reduced. Change in obstacle crossing speed did not correlate with change in level gait speed. Obstacle crossing does not necessarily improve over a one month time period in people receiving rehabilitation following stroke. These findings suggest that there may be a need for more targeted training of obstacle crossing, particularly when leading with the affected limb.

Effects of simulated firefighting and asymmetric load carriage on firefighter obstacle crossing performance

Slips, trips, and falls (STF) of firefighters may occur while traversing stationary obstacles. STF risk may be amplified by fatigue from firefighting and carrying an asymmetric load. Vertical and horizontal clearances of the lead (VCL, HCL) and trailing (VCT, HCT) foot and contact with a 30 cm obstacle were examined in 24 firefighters. We examined the impact on obstacle crossing performance due to three exercise protocols (treadmill walking or simulated firefighting in an environmental chamber, and simulated firefighting in a live-fire burn building) and carrying a hose load on the right shoulder. Post-activity fatigue resulted in significant decreases in HCL and VCT. Adding a hose load did not affect choice of lead/trailing foot, but did significantly decreased HCL and increased VCL. The hose load amplified acute fatigue effects by causing a sharper decrease in both VCL and VCT. Clearances were significantly impacted by interaction effects of exercise protocol type and acute fatigue. HCL decreased and VCL remained consistent following both simulated firefighting tasks, but HCL remained unchanged and VCL increased following the treadmill protocol. Contact errors increased with fatigue and load, and more errors occurred following simulated firefighting task protocols compared to treadmill walking. Our findings suggest that both acute fatigue and carrying an additional load can cause decrements in firefighter movement, which may place a firefighter at greater STF risk. Simulated firefighting testing protocols may have greater impact on movement performance than treadmill walking. Knowledge of these results may assist in the development of a reliable, laboratory based, and standardizable simulated firefighting exercise protocol.

Virtual obstacle crossing: Reliability and differences in stroke survivors who prospectively experienced falls or no falls

INTRODUCTION

Stroke survivors often fall during walking. To reduce fall risk, gait testing and training with avoidance of virtual obstacles is gaining popularity. However, it is unknown whether and how virtual obstacle crossing is associated with fall risk.

AIM

The present study assessed whether obstacle crossing characteristics are reliable and assessed differences in stroke survivors who prospectively experienced falls or no falls.

METHOD

We recruited twenty-nine community dwelling chronic stroke survivors. Participants crossed five virtual obstacles with increasing lengths. After a break, the test was repeated to assess test-retest reliability. For each obstacle length and trial, we determined; success rate, leading limb preference, pre and post obstacle distance, margins of stability, toe clearance, and crossing step length and speed. Subsequently, fall incidence was monitored using a fall calendar and monthly phone calls over a six-month period.

RESULTS

Test-retest reliability was poor, but improved with increasing obstacle-length. Twelve participants reported at least one fall. No association of fall incidence with any of the obstacle crossing characteristics was found.

DISCUSSION

Given the absence of height of the virtual obstacles, obstacle avoidance may have been relatively easy, allowing participants to cross obstacles in multiple ways, increasing variability of crossing characteristics and reducing the association with fall risk.

CONCLUSION

These finding cast some doubt on current protocols for testing and training of obstacle avoidance in stroke rehabilitation.

Constraints on perception of information from obstacles during foot clearance in people with chronic stroke

The aim of this study was to examine effects of different types of task constraints on coupling of perception and action in people with chronic stroke when crossing obstacles during a walking task. Ten participants with hemiplegic chronic stroke volunteered to walk over a static obstacle under two distinct task constraints: simple and dual tasks. Under simple task constraints, without specific instructions, participants walked at their preferred speed and crossed over an obstacle. Under dual task constraints, the same individuals were required to subtract numbers whilst walking. Under both distinct task constraints, we examined emergent values of foot distance when clearing a static obstacle in both affected and unaffected legs, measured by a 3D motion tracking system. Principal component analysis was used to quantify task performance, and discriminant analysis was used to compare gait performance between task constraints. Results suggested that patients, regardless of affected body side, demonstrated differences in perception of distance information from the obstacle, which constrained gait differences in initial swing, mid-swing, and crossing phases. Furthermore, dual task constraints, rather than hemiplegic body side, were a significant discriminator in patients' perceptions of distance and height information to the obstacle. These findings suggested how performance of additional cognitive tasks might constrain perception of information from an obstacle in people with chronic stroke during different phases of obstacle crossing, and thus may impair their adaptive ability to successfully manoeuvre around objects.

Effects of a 12-week online Tai Chi intervention on gait and postural stability in individuals with Parkinson's disease

Parkinson's disease (PD) affects gait and postural stability. Tai Chi (TC) is recommended for PD for management of the condition, however biomechanical understanding to its effects on gait and postural stability is limited. This study aimed to examine the effects of an online 12-week biomechanical-based TC intervention on gait and posture in people with PD. Fifteen individuals in early-stage PD were recruited (Hoehn & Yahr stages 1-2). The TC intervention program was 60 ​min session, three times weekly for 12 weeks. The pre- and post-intervention test in obstacle crossing, timed-up-and-go (TUG) test, and single leg standing (SLS) with eyes open (EO) and closed (EC) were conducted. Gait speed, crossing stride length, clearance height of the heel and toe, anterior-posterior (AP) and medial-lateral (ML) displacement and velocity of the center of mass (COM) and separation of the COM-center of pressure (COP) were analyzed. The participants significantly improved their pre-vs. post-TC intervention performance on TUG test (p ​= ​0.002). During obstacle crossing, the participants significantly increased crossing stride length of the trailing foot, increased AP COM displacement and decreased ML COM-COP separation (p ​< ​0.05); the maximal dorsiflexion angle of the leading limb significantly increased and maximal plantarflexion angle of the trailing limb significantly decreased (p ​< ​0.05). A 12-week biomechanical-based online TC training was effective towards improvement of gait and postural stability among people in the early-stage of PD. The TC program and online training could be applied for management of PD.

The effects of laterality on obstacle crossing performance in unilateral trans-tibial amputees

BACKGROUND

Unilateral trans-tibial amputees have bilaterally reduced toe clearance, and an increased risk of foot contact, while crossing obstacles compared to the able-bodied. While the able-bodied tend to lead with a 'preferred' limb it is equivocal whether amputees prefer to lead with the intact or prosthetic limb. This study determined the effects of laterality, compared to side of amputation, on amputees' obstacle crossing performance. To help understand why laterality could affect performance we also assessed knee proprioception for both limbs.

METHODS

Foot placement and toe clearance parameters were recorded while nine amputees crossed obstacles of varying heights leading with both their intact and prosthetic limbs. Joint-position sense was also assessed. Participants self-reported which limb was their preferred (dominant) limb.

FINDINGS

There were no significant differences in foot placements or toe clearance variability across lead-limb conditions. There were no significant differences in toe clearance between intact and prosthetic lead-limbs (p=0.28) but toe clearance was significantly higher when amputees led with their preferred compared to non-preferred limb (p=0.025). There was no difference in joint-position sense between the intact and residual knees (p=0.34) but joint-position sense tended to be more accurate for the preferred, compared to non-preferred limb (p=0.08).

INTERPRETATION

Findings suggest that, despite the mechanical constraints imposed by use of a prosthesis, laterality may be as important in lower-limb amputees as it is in the able bodied. This suggests that amputees should be encouraged to cross obstacles leading with their preferred limb.

Longitudinal kinematic and kinetic adaptations to obstacle crossing in recent lower limb amputees

BACKGROUND

Obstacle crossing is an important activity of daily living, necessary to avoid tripping or falling, although it is not fully understood how transtibial amputees adapt to performing this activity of daily living following discharge from rehabilitation.

OBJECTIVES

The objective of this study was to investigate the longitudinal adaptations in obstacle crossing in transtibial amputees post-discharge from rehabilitation.

STUDY DESIGN

Longitudinal repeated measures.

METHODS

Seven unilateral transtibial amputees crossed an obstacle 0.1m high positioned along a walkway while kinematic and kinetic data were recorded at 1, 3 and 6 months post-discharge.

RESULTS

At 6 months post-discharge, walking velocity had increased (0.17 m.s(-1)) with most participants self-selecting an intact lead limb preference. During swing phase, peak knee flexion (p = 0.03) and peak knee power absorption (K4; p = 0.01) were greater with an intact versus affected lead limb preference. Having crossed the obstacle, intact limb peak ankle power generation in pre-swing (A2; p = 0.01) and knee power absorption (K3; p = 0.05) during stance phase were greater when compared to the affected limb.

CONCLUSIONS

Obstacle crossing improved, although a greater reliance on intact limb function was highlighted. Results suggested that further improvements to locomotor performance may be obtained by increasing affected limb knee range of motion and concentric and eccentric strength of the knee extensors and flexors.

CLINICAL RELEVANCE

The novel objective data from this study establish an understanding of how recent transtibial amputees adapt to performing obstacle crossing following discharge from rehabilitation. This allows for evidence-based clinical interventions to be developed, aimed at optimising biomechanical function, thus improving overall locomotor performance and perhaps subsequent quality of life.

Reduced gait and postural stability under challenging conditions in fallers with upper limb fracture

BACKGROUND

While most fractures are caused by falls, not all falls result in fractures. Risk factors for falls are well established, but only weak associations have been demonstrated for risk factors for fractures. Conflicting results on the implication of bone mineral density (BMD) suggest that other risk factors should be studied, such as gait and balance disorders.

AIMS

Gait and postural stability in challenging conditions were, therefore, compared between fallers with and without fracture.

METHODS

We enrolled 80 adults aged 55 and older who fell in the previous year. We compared gait and posture after obstacle crossing between fallers with an upper-limb fracture (n = 38), and fallers without fracture (n = 42). Data on BMD, body mass index, handgrip strength, fear of falling, number of comorbidities, number of falls, global cognition, executive functioning and education level were collected.

RESULTS

Compared to fallers without fracture, fallers with fracture had significant lower gait velocity (Likelihood-Ratio = 4.93; P = 0.03) and lower postural stability during stabilization after obstacle crossing (Likelihood-Ratio = 10.99; P < 0.001). In addition, fallers with fracture had lower handgrip strength (Likelihood-Ratio = 9.92; P = 0.002), lower education level (Likelihood-Ratio = 8.32; P = 0.004), poorer executive functions (Likelihood-Ratio = 5.81; P = 0.02, higher fear of falling (Likelihood-Ratio = 5.55; P = 0.02) and were more likely women (Likelihood-Ratio = 17.55; P < 0.001), compared to fallers without fracture.

DISCUSSION

This study demonstrated that the main difference between fallers with upper-limb fracture and fallers without fracture is mobility in dynamic condition. Poor executive function and low muscular strength could also be involved.

CONCLUSIONS

These factors should be taken into account when assessing risk factors for fracture and implementing preventive programs.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov. NCT02292316.

Effects of simulated trunk flexion contracture on the margin of stability during obstacle crossing in elderly individuals

BACKGROUND

Trunk flexion contracture is an abnormal posture in elderly individuals with lumbar kyphosis. It is unclear whether this posture affects locomotor stability (margin of stability [MoS]) during obstacle crossing, which is a common trigger for falls in elderly people.

RESEARCH QUESTION

Does trunk flexion contracture negatively affect MoS during obstacle crossing in elderly people?

METHODS

Ten healthy elderly individuals performed five trials of obstacle crossing using a comfortable speed under two experimental conditions, namely, with (FLEX) or without (NORMAL) a hard lumbar brace to simulate trunk flexion contracture. The obstacle-crossing motion was captured using an optical motion analysis system in order to calculate the MoS in the anteroposterior direction. The MoS at initial contact (IC) and that when the swing foot was above the obstacle (Obs) was compared between FLEX and NORMAL. A greater MoS suggests greater risk of a forward fall. The trunk and lower limb joint angles were measured at Obs.

RESULTS

FLEX significantly increased the MoS at IC, whereas the MoS at Obs did not differ between the two conditions. FLEX demonstrated a crouch posture characterized by an increased flexion angle of stance-side hip and knee joints at the Obs instant.

SIGNIFICANCE

Forward fall chance might be increased at IC in obstacle crossing with trunk flexion contracture. Meanwhile, the MoS at Obs might be controlled by increasing the crouch posture to offset a forward shift in the CoM position due to the trunk flexion. Because the risk of a stumble on an obstacle and of forward falls should be higher at Obs than at IC, the crouch posture seems to be an effective adaptation that enables elderly people with trunk flexion contracture to safely cross obstacles.

Restricting ankle motion via orthotic bracing reduces toe clearance when walking over obstacles

BACKGROUND

When trans-tibial amputees cross obstacles leading with their prosthesis, foot clearance is achieved using compensatory swing-phase kinematics. Such compensation would suggest able-bodied individuals normally use swing-phase ankle dorsiflexion to attain adequate obstacle clearance; however, direct evidence of such contribution is equivocal. This study determined the contribution of sagittal plane ankle motion in achieving lead-limb clearance during obstacle negotiation.

METHODS

Twelve male able-bodied individuals (ages 18-30) completed obstacle crossing trials while walking on a flat surface. Lead-limb (right) ankle motion was manipulated using a knee-ankle-foot orthosis. Trials were completed with the ankle restricted at a neutral angle or unrestricted (allowing ∼±15° plantar/dorsiflexion).

FINDINGS

Restricted ankle motion caused significant increase in trail-limb foot placement distance before the obstacle (p=0.005); significant decrease in vertical toe clearance (p<0.003), vertical heel clearance (p=0.045), and lead-limb foot placement distance after the obstacle (p=0.045); but no significant changes in knee angle at instant of crossing or in average walking speed.

INTERPRETATION

The shifts in foot placements altered the part of swing that the lead-limb was in when the foot crossed the obstacle, which led to a decrease in clearance. These adaptations may have been due to being unable to dorsiflex the ankle to 'lift' the toes in mid-swing or to plantarflex the ankle during initial contact following crossing, which changed how the lead-limb was to be loaded. These findings suggest individuals using ankle bracing or those with ankle arthrodesis, will have reduced gait safety when negotiating obstacles.

The effect of trial frames on adaptive gait

PURPOSE

Research investigating how vision affects adaptive gait typically tests participants whilst wearing their own spectacles or whilst wearing trial case lenses mounted in a trial frame. Trial frames are temporary frames allowing different lenses to be inserted, permitting different visual conditions to be simulated. Trial frames occlude part of the wearer's peripheral visual field. The current study investigated how use of trial frames affects adaptive gait.

METHODS

Fifteen participants (age 25 ± 5 years) with normal uncorrected vision negotiated a single floor based obstacle habitually (not wearing a trial frame) or wearing trial frames which occluded part of the lower visual field (half-eye) or circumferential peripheral visual field (full aperture). No lenses were used in the trial frames. Analysis assessed visual field occlusion and the kinematics of obstacle crossing.

RESULTS

Visual field was reduced wearing either trial frame. Compared to the habitual condition, participants wearing either type of trial frame lifted their foot significantly higher over the obstacle and increased the time taken to step over the obstacle; a result of uncertainty regarding the precise location (height) of the obstacle due to the occlusion of visual information from the inferior visual field. There were no differences in obstacle crossing between trial frame conditions.

CONCLUSIONS

Wearing either full or half eye trial frames can in itself influence adaptive gait. Whilst consideration needs to be given to the visual correction that participants wear during gait research, the method of mounting these lenses also requires consideration.

Relation between the kinematic synergy controlling swing foot and visual exploration during obstacle crossing

To step over obstacles of varying heights, two distinct ongoing streams of activities-visual exploration of the environment and gait adjustment- were required to occur concurrently without interfering each other. Yet, it remains unclear whether and how the manner of embodied behavior of visual exploration is related to the synergistic control of foot trajectory to negotiate with the irregular terrain. Thus, we aimed to explore that how the synergistic control of the vertical trajectory of the swing foot (i.e., obstacle clearance) crossing an obstacle is related to the manner of visual exploration of the environment during approach. Twenty healthy young adults crossed an obstacle (depth: 1 cm, width: 60 cm, height: 8 cm) during their comfortable-speed walking. The visual exploration was evaluated as the amount of time spent in fixating the vicinity of the obstacle on the floor during the period from two to four steps prior to crossing the obstacle, and the strengths of kinematic synergy to control obstacle clearance were estimated using the uncontrolled manifold approach. We found that the participants with relatively weak synergy spent more time fixating at the vicinity of the obstacle from two to four steps prior to crossing the obstacle, and those participants exhibited greater amount of head flexion movement compared to those with stronger kinematic synergy. Taking advantage of this complex relationship between exploratory activities (e.g. looking movement) and performative activities (e.g. adjustment of ground clearance) would be crucial to adapt walking in a complex environment.

Manipulating sensory information: obstacle crossing strategies between typically developing children and young adults

Individuals constantly adapt their locomotion to navigate through complex environments. However, little known about anticipatory strategies used by children during adaptive locomotion. The purpose of this study was to compare the effects of manipulating visual and somatosensory information during a multiple obstacle crossing task between children and adults. It was hypothesized that compared to young adults, children would have difficulty with anticipatory motor planning and online control during a multiple obstacle crossing task when sensory information was manipulated. Children (N = 16, [Formula: see text] = 9 ± 1.07 years) and young adults (N = 16, [Formula: see text] = 22 ± 0.96 years) walked along a 7 m pathway towards a goal while avoiding stepping on one, or two virtual obstacles placed 5 m from the start. Visual information regarding the number of obstacles was either presented at the start of steady-state locomotion, or two steps prior to the first obstacle. Each participant completed 36 trials, 18 on flat ground and 18 on foam terrain. Results indicated that in comparison to young adults, children's foot positions were significantly closer to the first obstacle when visual information about the obstacle was delayed. On flat ground, children demonstrated similar Trail foot positions relative to the first and second obstacles, suggesting children planned for the avoidance of the obstacles separately. On foam terrain, children performed similar to young adults, such that their Trail foot position relative to the first obstacle was significantly closer to the obstacle compared to their Trial foot position relative to the second obstacle. The results suggest that children plan for the avoidance of multiple obstacles differently compared to young adults. When stability is challenged, maintaining forward progression of locomotion overrides the planning of obstacle crossing, such that children perform similar to young adults. Therefore, it appears that children have difficulties with online control and anticipatory motor strategies during a multiple obstacle crossing task.

Key function for obstacle crossing in hemiplegic persons with varied degrees of spasticity

[Purpose] To evaluate various key functions related to obstacle crossing motions in hemiplegic people based on the paralysis degree. [Subjects and Methods] Thirty-seven patients with maintenance-stage hemiplegia who could independently ambulate outdoors were included. Subjects’ crossing movements were measured using obstacles with heights of 10%, 20%, and 30% of the trochanter length. The relationship among maximal crossing height and isometric knee extension muscle strength, one leg standing time, Trunk Impairment Scale score, disease duration, and subject age was examined, as was the target variable of maximum crossing height and the top four measurement items, to determine the explanatory variables. The participants were grouped based on Brunnstrom Recovery Stages III–IV (severe spasticity) and V–VI (mild spasticity). [Results] The explanatory variables were the Trunk Impairment Scale in the severe spasticity group and unaffected side-knee extension muscle strength in the mild spasticity group (contribution rates: 75.6% and 21.0%, respectively). [Conclusion] Trunk function in the severe spasticity group majorly contributed to crossing obstacles. Furthermore, knee extension muscle strength on the unaffected side in the mild spasticity group moderately contributed to crossing obstacles. Selecting and implementing a physical therapy routine that is aimed at improving function, depending on the severity of paralysis, is necessary.