Head motion in humans alternating between straight and curved walking path: combination of stabilizing and anticipatory orienting mechanisms

Mobility Requirements and Joint Loading during Straight Walking and 90° Turns in Healthy Older People and Those with Hip Osteoarthritis

Background/Objectives: Hip mobility and joint loading in hip osteoarthritis (HOA) patients are mostly assessed during straight walking. Yet, mobility limitations in the frontal and transverse planes are rarely found during this task in subjects with mild-to-moderate symptoms. Turning movements are frequently encountered during everyday life and might require larger hip mobility compared to straight walking, especially in the frontal and transverse planes. Thus, hip mobility and hip loading during straight walking and 90° turns in persons with HOA and healthy older adults were compared in this study. Methods: A retrospective analysis was conducted on 21 subjects with mild-to-moderate HOA and 21 healthy controls. Hip angles and moments were assessed during straight walking and 90° step and spin turns. Gait analysis was conducted using a motion capture system and a force plate. Group and movement task differences were assessed with a mixed-model ANOVA. Results: Peak abduction and adduction angles were largest during the step and spin turn, respectively, as were the group differences between HOA subjects and healthy subjects. Both turns require a greater transverse hip range of motion compared to straight walking. Limitations in transverse hip mobility in the HOA group were especially prominent during the step turn. Both turns cause higher joint moments than straight walking. Conclusions: The additional inclusion of 90° step and spin turns into gait analysis can enhance early identification of hip mobility limitations in the frontal and transverse planes in subjects with mild-to-moderate hip osteoarthritis. Early diagnosis is crucial for the timely application of conservative treatment strategies.

Gait asymmetry and symptom laterality in Parkinson's disease: two of a kind?

BACKGROUND

The laterality of motor symptoms is considered a key feature of Parkinson's disease (PD). Here, we investigated whether gait and turning asymmetry coincided with symptom laterality as determined by the MDS-UPRDS part III and whether it was increased compared to healthy controls (HC).

METHODS

We analyzed the asymmetry of gait and turning with and without a cognitive dual task (DT) using motion capture systems and wearable sensors in 97 PD patients mostly from Hoehn & Yahr stage II and III and 36 age-matched HC. We also assessed motor symptom asymmetry using the bilateral sub-items of the MDS-UPDRS-III. Finally, we examined the strength of the association between gait asymmetry and symptom laterality.

RESULTS

Participants with PD had increased gait but not more turning asymmetry compared to HC (p < 0.05). Only 53.7% of patients had a shorter step length on the more affected body side as determined by the MDS-UPDRS-III. Also, 54% took more time and 29% more steps during turns toward the more affected side. The degree of asymmetry in the different domains did not correlate with each other and was not influenced by DT-load.

CONCLUSIONS

We found a striking mismatch between the side and the degree of asymmetry in different motor domains, i.e., in gait, turning, and distal symptom severity in individuals with PD. We speculate that motor execution in different body parts relies on different neural control mechanisms. Our findings warrant further investigation to understand the complexity of gait asymmetry in PD.

NONAN GaitPrint: An IMU gait database of healthy young adults

An ongoing thrust of research focused on human gait pertains to identifying individuals based on gait patterns. However, no existing gait database supports modeling efforts to assess gait patterns unique to individuals. Hence, we introduce the Nonlinear Analysis Core (NONAN) GaitPrint database containing whole body kinematics and foot placement during self-paced overground walking on a 200-meter looping indoor track. Noraxon Ultium MotionTM inertial measurement unit (IMU) sensors sampled the motion of 35 healthy young adults (19-35 years old; 18 men and 17 women; mean ± 1 s.d. age: 24.6 ± 2.7 years; height: 1.73 ± 0.78 m; body mass: 72.44 ± 15.04 kg) over 18 4-min trials across two days. Continuous variables include acceleration, velocity, position, and the acceleration, velocity, position, orientation, and rotational velocity of each corresponding body segment, and the angle of each respective joint. The discrete variables include an exhaustive set of gait parameters derived from the spatiotemporal dynamics of foot placement. We technically validate our data using continuous relative phase, Lyapunov exponent, and Hurst exponent-nonlinear metrics quantifying different aspects of healthy human gait.

Head control and head-trunk coordination as a function of anticipation in sidestepping

Head reorientation precedes body reorientation during direction change to facilitate gaze realignment, thus enhancing perceptual awareness. Whole body kinematics are dependent on the available planning time. The purpose of this study was to assess the role of anticipation on head control and head-trunk coordination during sidestepping tasks. Fourteen male collegiate athletes performed anticipated and unanticipated sidestepping tasks. Transverse plane head, trunk and heading direction, as well as head-trunk coordination were assessed. During change of direction tasks, we observed greater head orientation towards the new travel direction, followed by heading direction and then trunk direction during both anticipated and unanticipated tasks. With reduced planning time, heading in the preparatory phase and trunk rotation in the preparatory and stance phases were significantly less oriented towards the new travel direction, with no differences in head rotation. During anticipated sidestepping, significantly greater in-phase coordination was observed during the preparatory phase compared to unanticipated sidestepping. Head reorientation facilitates gaze realignment and may be prioritized irrespective of planning time during sidestepping tasks. During anticipated trials, the head and trunk move more synchronously compared to unanticipated sidestepping, highlighting the potential benefits of aligning the degrees of freedom earlier in the change of direction stride and optimizing perceptual awareness.

Evaluation of movement and brain activity

Clinical neurophysiology studies can contribute important information about the physiology of human movement and the pathophysiology and diagnosis of different movement disorders. Some techniques can be accomplished in a routine clinical neurophysiology laboratory and others require some special equipment. This review, initiating a series of articles on this topic, focuses on the methods and techniques. The methods reviewed include EMG, EEG, MEG, evoked potentials, coherence, accelerometry, posturography (balance), gait, and sleep studies. Functional MRI (fMRI) is also reviewed as a physiological method that can be used independently or together with other methods. A few applications to patients with movement disorders are discussed as examples, but the detailed applications will be the subject of other articles.

On the mechanical contribution of head stabilization to passive dynamics of anthropometric walkers

During the steady gait, humans stabilize their head around the vertical orientation. Although there are sensori-cognitive explanations for this phenomenon, its mechanical effect on the body dynamics remains unexplored. In this study, we take profit from the similarities that human steady gait shares with the locomotion of passive-dynamics robots. We introduce a simplified anthropometric 2D model to reproduce a broad walking dynamics. In a previous study, we showed heuristically that the presence of a stabilized head–neck system has a significant influence on the dynamics of walking. This article gives new insights that lead to understanding this mechanical effect. In particular, we introduce an original cart upper-body model that allows to better understand the mechanical interest of head stabilization when walking, and we study how this effect is sensitive to the choice of control parameters.

Walking Along Curved Trajectories. Changes With Age and Parkinson's Disease. Hints to Rehabilitation

In this review, we briefly recall the fundamental processes allowing us to change locomotion trajectory and keep walking along a curved path and provide a review of contemporary literature on turning in older adults and people with Parkinson's Disease (PD). The first part briefly summarizes the way the body exploits the physical laws to produce a curved walking trajectory. Then, the changes in muscle and brain activation underpinning this task, and the promoting role of proprioception, are briefly considered. Another section is devoted to the gait changes occurring in curved walking and steering with aging. Further, freezing during turning and rehabilitation of curved walking in patients with PD is mentioned in the last part. Obviously, as the research on body steering while walking or turning has boomed in the last 10 years, the relevant critical issues have been tackled and ways to improve this locomotor task proposed. Rationale and evidences for successful training procedures are available, to potentially reduce the risk of falling in both older adults and patients with PD. A better understanding of the pathophysiology of steering, of the subtle but vital interaction between posture, balance, and progression along non-linear trajectories, and of the residual motor learning capacities in these cohorts may provide solid bases for new rehabilitative approaches.

Neck posture is influenced by anticipation of stepping

BACKGROUND

Postural deviations such as forward head posture (FHP) are associated with adverse health effects. The causes of these deviations are poorly understood. We hypothesized that anticipating target-directed movement could cause the head to get "ahead of" the body, interfering with optimal head/neck posture, and that the effect may be exacerbated by task difficulty and/or poor inhibitory control.

METHOD

We assessed posture in 45 healthy young adults standing quietly and when they anticipated walking to place a tray: in a simple condition and in conditions requiring that they bend low or balance an object on the tray. We defined FHP as neck angle relative to torso; we also measured head angle relative to neck and total neck length. We assessed inhibitory control using a Go/No-Go task, Stroop task, and Mindful Attention Awareness Scale (MAAS).

RESULTS

FHP increased when participants anticipated movement, particularly for more difficult movements. Worse Stroop performance and lower MAAS scores correlated with higher FHP. False alarms on the Go/No-Go task correlated with a more extended head relative to the neck and with shortening of the neck when anticipating movement.

CONCLUSIONS

Maintaining neutral posture may require inhibition of an impulse to put the head forward of the body when anticipating target-directed movement.

Do Adolescents With Idiopathic Scoliosis Have an Erroneous Perception of the Gravitational Vertical?

STUDY DESIGN

Multicenter, case-control study.

OBJECTIVES

Demonstrate altered perception of verticality in AIS compared with matched controls.

SUMMARY OF BACKGROUND DATA

The cause of adolescent idiopathic scoliosis (AIS) remains to be found. AIS is associated with neurosensorial anomalies, in particular, altered control of orthostatic posture. During kinetic activity, the upright posture, in humans, is determined in reference to the gravitational vertical (GV). We hypothesized that in AIS, there is a discordance in the perception of the GV and the true GV. In AIS, the longitudinal axis of the body would thus be misoriented because of an erroneous perception of the GV.

METHODS

Thirty adolescents with right thoracic AIS (age 14.23 ± 1.75 years; Cobb angle 31.97°± 12.83°) and 30 controls matched for age (13.93 ± 1.85 years), body mass index, Tanner stage, and handedness were compared for subjective visual vertical (SVV) measured in static and dynamic (optokinetic stimulation) conditions, and subjective postural vertical (SPV).

RESULTS

There was no difference in the two groups, AIS and controls, for SVV. The SPV was significantly different between the two groups (p = .00023). The SPV was shifted to the right for most of the AIS patients (2.13°± 2.22°) compared with controls (-0.08°±1.40°). There was a significant correlation between SPV and clinical frontal tilt in the AIS patients.

CONCLUSION

Our findings demonstrate that patients with right thoracic AIS have an erroneous perception of the GV. In most AIS patients, SPV was shifted to the right, with no alteration of the SVV. AIS might be the consequence of a reoriented longitudinal body axis aligned with an erroneous vertical reference. The underlying mechanism might involve dysfunction of trunk graviceptors. The primary or secondary nature of this dysfunction remains an open question.

Analytical CPG model driven by limb velocity input generates accurate temporal locomotor dynamics

The ability of vertebrates to generate rhythm within their spinal neural networks is essential for walking, running, and other rhythmic behaviors. The central pattern generator (CPG) network responsible for these behaviors is well-characterized with experimental and theoretical studies, and it can be formulated as a nonlinear dynamical system. The underlying mechanism responsible for locomotor behavior can be expressed as the process of leaky integration with resetting states generating appropriate phases for changing body velocity. The low-dimensional input to the CPG model generates the bilateral pattern of swing and stance modulation for each limb and is consistent with the desired limb speed as the input command. To test the minimal configuration of required parameters for this model, we reduced the system of equations representing CPG for a single limb and provided the analytical solution with two complementary methods. The analytical and empirical cycle durations were similar (R 2 = 0.99) for the full range of walking speeds. The structure of solution is consistent with the use of limb speed as the input domain for the CPG network. Moreover, the reciprocal interaction between two leaky integration processes representing a CPG for two limbs was sufficient to capture fundamental experimental dynamics associated with the control of heading direction. This analysis provides further support for the embedded velocity or limb speed representation within spinal neural pathways involved in rhythm generation.

The effect of walking path configuration on gait in adults with Alzheimer's dementia

BACKGROUND

Walking is a cognition intensive activity and impaired walking is associated with an increased fall risk in people with Alzheimer's dementia (AD). Walking in a curved path configuration increases complexity of the task, reflects real-life environments and situations when falls occur. The effect of walking path task complexity has not been evaluated in people with AD.

RESEARCH QUESTION

The purpose was 1) to assess the utility of a curved path walking task to detect differences in gait performance between people with AD and healthy controls and 2) to assess the relationship of cognitive function to gait performance on straight path and curved path walking.

METHODS

Participants with AD (n = 14, mean age ± SD = 73.08 ± 9.22) and age and sex matched controls (n = 14, mean age = 72.86 ± 9.53) were recruited. Time to complete a 6-meter straight path and a curved path (Figure of 8 Test) walking task was recorded. Steps taken, accuracy and qualitative measures of smoothness were rated for curved-path walking. Measures of global cognition (MMSE, MoCA) and executive function (Trail making A and B, Digit Span forwards and backwards) were assessed.

RESULTS

Gait was significantly slower in people with AD for both the straight-path (AD = 6.05 ± 1.26 s, Control = 5.09 ± 0.76 s, p = 0.02) and curved-path walking (AD = 11.25 ± 4.87 s, Control = 8.28 ± 2.44 s, p =  0.05). In addition, smoothness scores were significantly lower for people with AD (AD = 1.93±1.26; Control = 3.00±0.00, p = 0.004).

SIGNIFICANCE

Walking in a curved path resulted in a significant deterioration in gait quality in the people with AD. Executive function was related only to curved path walking, in which lower executive function scores were associated with longer time to walk.

Quantifying the impact on navigation performance in visually impaired: Auditory information loss versus information gain enabled through electronic travel aids

This study’s purpose was to analyze and quantify the impact of auditory information loss versus information gain provided by electronic travel aids (ETAs) on navigation performance in people with low vision. Navigation performance of ten subjects (age: 54.9±11.2 years) with visual acuities >1.0 LogMAR was assessed via the Graz Mobility Test (GMT). Subjects passed through a maze in three different modalities: ‘Normal’ with visual and auditory information available, ‘Auditory Information Loss’ with artificially reduced hearing (leaving only visual information), and ‘ETA’ with a vibrating ETA based on ultrasonic waves, thereby facilitating visual, auditory, and tactile information. Main performance measures comprised passage time and number of contacts. Additionally, head tracking was used to relate head movements to motion direction. When comparing ‘Auditory Information Loss’ to ‘Normal’, subjects needed significantly more time (p<0.001), made more contacts (p<0.001), had higher relative viewing angles (p = 0.002), and a higher percentage of orientation losses (p = 0.011). The only significant difference when comparing ‘ETA’ to ‘Normal’ was a reduced number of contacts (p<0.001). Our study provides objective, quantifiable measures of the impact of reduced hearing on the navigation performance in low vision subjects. Significant effects of ‘Auditory Information Loss’ were found for all measures; for example, passage time increased by 17.4%. These findings show that low vision subjects rely on auditory information for navigation. In contrast, the impact of the ETA was not significant but further analysis of head movements revealed two different coping strategies: half of the subjects used the ETA to increase speed, whereas the other half aimed at avoiding contacts.

The Yoyo-Man

The paper reports on two results issued from a multidisciplinary research action exploring the motor synergies of anthropomorphic walking. By combining the biomechanical, neurophysiology, and robotics perspectives, it is intended to better understand human locomotion with the ambition to better design bipedal robot architectures. The motivation of the research starts from the simple observation that humans may stumble when following a simple reflex-based locomotion on uneven terrains. The rationale combines two well established results in robotics and neuroscience, respectively:

passive robot walkers, which are very efficient in terms of energy consumption, can be modeled by a simple rotating rimless wheel; humans and animals stabilize their head when moving.

The seminal hypothesis is then to consider a wheel equipped with a stabilized mass on top of it as a plausible model of bipedal walking. The two results presented in the paper support the hypothesis.

From a motion capture data basis of twelve human walkers, we show that the motions of the feet are organized around a geometric center, which is the center of mass, and is surprisingly not at the hip. After introducing a ground texture model that allows us to quantify the stability performance of walker control schemes, we show how compass-like passive walkers are better controlled when equipped with a stabilized 2-degree-of-freedom moving mass on top of them.

The center of mass and head then play complementary roles that define what we call the Yoyo-Man. Beyond the two results presented in the paper, the Yoyo-Man model opens new perspectives to explore the computational foundations of anthropomorphic walking.

Anticipatory detection of turning in humans for intuitive control of robotic mobility assistance

Many wearable lower-limb robots for walking assistance have been developed in recent years. However, it remains unclear how they can be commanded in an intuitive and efficient way by their user. In particular, providing robotic assistance to neurologically impaired individuals in turning remains a significant challenge. The control should be safe to the users and their environment, yet yield sufficient performance and enable natural human-machine interaction. Here, we propose using the head and trunk anticipatory behaviour in order to detect the intention to turn in a natural, non-intrusive way, and use it for triggering turning movement in a robot for walking assistance. We therefore study head and trunk orientation during locomotion of healthy adults, and investigate upper body anticipatory behaviour during turning. The collected walking and turning kinematics data are clustered using the k-means algorithm and cross-validation tests and k-nearest neighbours method are used to evaluate the performance of turning detection during locomotion. Tests with seven subjects exhibited accurate turning detection. Head anticipated turning by more than 400-500 ms in average across all subjects. Overall, the proposed method detected turning 300 ms after its initiation and 1230 ms before the turning movement was completed. Using head anticipatory behaviour enabled to detect turning faster by about 100 ms, compared to turning detection using only pelvis orientation measurements. Finally, it was demonstrated that the proposed turning detection can improve the quality of human-robot interaction by improving the control accuracy and transparency.

Visuo-locomotor control in persons with spinal cord injury in a manual or power wheelchair for direction change and obstacle circumvention

Many individuals, such as persons with spinal cord injury (SCI), rely on wheeled locomotion involving manual (MWC) or power (PWC) wheelchairs to navigate their environments. Yet, visuo-locomotor control underlying WC navigation in experienced users is not well understood. The objective of this study was to compare the visuo-locomotor control between MWC and PWC in individuals with SCI while changing direction and circumventing an obstacle. Participants with SCI using a MWC (n = 12, 38.5 ± 10.7 years) or a PWC (n = 10, 47.8 ± 8.6 years) were asked to maneuver their chair straight ahead, while changing direction 45° to the right, and while circumventing an obstacle to the right, all at self-selected speeds. Speed, minimal clearance, point of deviation, temporal body and WC coordination, relative timing of segment rotations and visual behavior were analyzed. There was no main effect of group for speed, clearance and point of deviation. During direction change, the head always led body and wheelchair reorientation while an "en bloc" strategy was used for circumventing obstacle for both groups. In straight-ahead locomotion, participants predominantly fixed their gaze on the end target. During direction change and obstacle circumvention, participants fixated more on the future path and the obstacle for both WC modes. Overall, specific gaze behavior depended on environmental demands. While MWC and PWC users adopt similar navigational strategies and visuo-locomotor coordination while changing direction and circumventing obstacle, there were some differences in the amount of head rotation that could be related to a counter-movement used more by PWC users.

Stroke Affects the Coordination of Gaze and Posture During Preplanned Turns While Walking

Background In healthy subjects, the act of walking and turning is accomplished by a sequential horizontal reorientation of gaze, head, and body toward the direction of the turn. Subjects with stroke, however, have difficulty altering their walking direction and present with loss of balance when performing a head turn or whole body rotation.

Objective. To study, in a pilot case study, the spatial and temporal coordination of gaze and posture during preplanned turns executed while walking in severely disabled and mildly disabled subjects with stroke as compared to a healthy control walking at slow speed.

Methods. Horizontal plane orientations of gaze, head, thorax, pelvis, and feet as well as the body’s center of mass (CoM) trajectory were analyzed as subjects were walking straight or executing a 90-deg turn.

Results. Subjects with stroke revealed altered orientation and sequencing of gaze body segments. These alterations were more pronounced in the most severely disabled subject with stroke, especially when turning to the nonparetic side as compared to the paretic side.

Conclusions. These findings suggest an altered coordination of gaze and posture during steering of locomotion in subjects with stroke. This altered coordination is likely due to a complex interaction of motor, sensory, and biomechanical factors that may explain the poor balance and poor control of heading direction during walking and turning in stroke.

Cervicocephalic relocation test to evaluate cervical proprioception in adolescent idiopathic scoliosis

PURPOSE

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of the spine associated with disturbed postural control. Cervical proprioception participates in controlling orthostatic posture via its influence on head stabilization. We hypothesized that patients with AIS exhibit altered cervical proprioception.

METHODS

We conducted a case-control study to evaluate cervical proprioception using the cervicocephalic relocation test (CRT) in 30 adolescents with AIS (15.5 ± 1.5 years; Cobb 24.8° ± 9.5°) versus 14 non-scoliotic controls (14.6 ± 2.0 years). CRT evaluates cervical proprioception by measuring the capacity to relocate the head on the trunk after active rotation of the head in the transversal plane without visual control. Each subject performed ten right and then ten left head rotations.

RESULTS

The CRT results were pathological in 12 AIS patients (40 %). The CRT mean was significantly different between AIS patients with a pathological CRT (5° ± 1.4° for right rotation; 4.2° ± 0.9° for left rotation) compared with AIS patients with a normal CRT (2.7° ± 0.6° for right rotation; 2.9° ± 0.8° for left rotation) or with the control group (3.5° ± 2.1° for right rotation; 3.1° ± 1.2° for left rotation).

CONCLUSION

Cervical proprioception is impaired in certain AIS patients. This anomaly may worsen the prognosis of AIS (headache; balance disorders; worsened spinal deformity; complication after spinal fusion). We recommend systematic screening for altered cervical proprioception in AIS patients.

Walking paths to and from a goal differ: on the role of bearing angle in the formation of human locomotion paths

The path that humans take while walking to a goal is the result of a cognitive process modulated by the perception of the environment and physiological constraints. The path shape and timing implicitly embeds aspects of the architecture behind this process. Here, locomotion paths were investigated during a simple task of walking to and from a goal, by looking at the evolution of the position of the human on a horizontal (x,y) plane. We found that the path while walking to a goal was not the same as that while returning from it. Forward-return paths were systematically separated by 0.5-1.9m, or about 5% of the goal distance. We show that this path separation occurs as a consequence of anticipating the desired body orientation at the goal while keeping the target in view. The magnitude of this separation was strongly influenced by the bearing angle (difference between body orientation and angle to goal) and the final orientation imposed at the goal. This phenomenon highlights the impact of a trade-off between a directional perceptual apparatus—eyes in the head on the shoulders—and and physiological limitations, in the formation of human locomotion paths. Our results give an insight into the influence of environmental and perceptual variables on human locomotion and provide a basis for further mathematical study of these mechanisms.

Comparison of gait velocity and center of mass during square and semicircular turning gaits between groups of elderly people with differing visual acuity

[Purpose] The purpose of this study was to investigate gait velocity and center of mass (COM) during square and semicircular turning gaits between two groups of elderly people with differing visual acuity. [Subjects] Twenty elderly Korean women who could walk independently and who lived in the community were recruited. [Methods] We measured gait velocity and COM using an accelerometer during two different turning gaits. [Results] The velocity during square and semicircular turning gaits of participants with good binocular visual acuity (GBVA) was significantly higher than that of participants with poor binocular visual acuity (PBVA). The COM during square and semicircular turning gaits of the GBVA group was significantly decreased compared with that of the PBVA group. [Conclusion] These findings suggest that visual acuity affects velocity and COM during square and semicircular turning gaits of elderly people.

Reproducibility of spatio-temporal and dynamic parameters in various, daily occurring, turning conditions

OBJECTIVE

This study aims to assess the test-retest reproducibility of specific spatio-temporal (foot placement, foot contact time) and dynamic (resultant horizontal and vertical ground reaction force) gait parameters of three different, everyday occurring, turning conditions. The subjects were tested at two subsequent days. Out of this setting the purpose of this study is to clarify, if turning locomotion is stable when performed at different test occurrences.

METHODS

Eight subjects completed three different daily occurring turning conditions along turns with a given walking velocity of 5 km/h (± 10%). Subjects had to complete the turns three times clockwise and counter clockwise. The measurements were recorded with a 3D motion analysis system (Vicon(®)) and two force sensitive platforms (AMTI(®)), connected to the motion analysis system.

RESULTS

The analysis yields for most of the parameters and turning conditions ICCs from good (r = 0.72; p = .06) to high (r = 0.96; p < .01) magnitude for the measured spatio-temporal and dynamic parameters.

CONCLUSIONS

Based on our findings it can be assumed that locomotion strategies, related to the measured gait parameters of common daily turning tasks, are stable and reproducible.

Simulated visual field loss does not alter turning coordination in healthy young adults

Turning, while walking, is an important component of adaptive locomotion. Current hypotheses regarding the motor control of body segment coordination during turning suggest heavy influence of visual information. The authors aimed to examine whether visual field impairment (central loss or peripheral loss) affects body segment coordination during walking turns in healthy young adults. No significant differences in the onset time of segments or intersegment coordination were observed because of visual field occlusion. These results suggest that healthy young adults can use visual information obtained from central and peripheral visual fields interchangeably, pointing to flexibility of visuomotor control in healthy young adults. Further study in populations with chronic visual impairment and those with turning difficulties are warranted.

Kinematics of turning during walking over ground and on a rotating treadmill

Background

After neurological injury, gait rehabilitation typically focuses on task oriented training with many repetitions of a particular movement. Modern rehabilitation devices, including treadmills, augment gait rehabilitation. However, they typically provide gait training only in the forward direction of walking, hence the mechanisms associated with changing direction during turning are not practiced. A regular treadmill extended with the addition of rotation around the vertical axis is a simple device that may enable the practice of turning during walking. The objective of this study was to investigate to what extent pelvis and torso rotations in the transversal plane, as well as stride lengths while walking on the proposed rotating treadmill, resemble those in over ground turning.

Methods

Ten neurologically and orthopedically intact subjects participated in the study. We recorded pelvis and torso rotations in the transversal plane and the stride lengths during over ground turning and while walking on a rotating treadmill in four experimental conditions of turning. The similarity between pelvis and torso rotations in over ground turning and pair-matching walking on the rotating treadmill was assessed using intra-class correlation coefficient (ICC - two-way mixed single measure model). Finally, left and right stride lengths in over ground turning as well as while walking on the rotating treadmill were compared using a paired t-test for each experimental condition.

Results

An agreement analysis showed average ICC ranging between 0.9405 and 0.9806 for pelvis and torso rotation trajectories respectively, across all experimental conditions and directions of turning. The results of the paired t-tests comparing left and right stride lengths showed that the stride of the outer leg was longer than the stride of the inner leg during over ground turning as well as when walking on the rotating treadmill. In all experimental conditions these differences were statistically significant.

Conclusions

In this study we found that pelvis rotation and torso rotation are similar when turning over ground as compared to walking on a rotating treadmill. Additionally, in both modes of turning, we found that the stride length of the outer leg is significantly longer than the stride length of the inner leg.

Electronic supplementary material

The online version of this article (doi:10.1186/1743-0003-11-127) contains supplementary material, which is available to authorized users.

Kinematic variability of the head, lumbar spine and knee during the "walk and turn to sit down" task in older and young adults

This study investigates the kinematic variability of the head, lumbar spine and knee during the various walk and turn to sit phases in older and young adults. Sixteen older adults and eighteen young adults were recruited for this study. Each subject performed the "Walk and turn to sit down" test. A 16-channel telemetry system with electrogoniometers and an inclinometer was used to record the kinematic data. The turning step was divided into braking, mid-stance, swing and terminal load phases for kinematic analysis. The results showed that the older adults had a lower displacement angle and velocity of the lumbar spine, head and knee during different turning phases than the young adults. However, older adults performed turning with a higher variability in angular velocity of head flexion than the young adults during the turning step. The onset of lumbar movement and lateral flexion of the head occurred significantly earlier in older adults than in the young adults during turning.

CONCLUSION

Older adults more cautiously control their motion by changing their trunk movement amplitude, velocity and timing in relation to their lower extremity movements during turning. The larger variability in angular velocity of head flexion may imply that older adults cannot precisely estimate the required movement for smooth turning.

Kinematics and muscle activity of the head, lumbar and knee joints during 180° turning and sitting down task in older adults

BACKGROUND

The "180° turning and sitting down task" is a very conscious movement that requires focusing on turning at the exact moment, and very few studies address on this topic in older adults. The purpose of the study was to compare kinematics and electromyography of the head, lumbar and knee joints during 180°turning in older and young adults.

METHODS

Twenty older adults and 20 younger adults were assessed. A 16-channel telemetry electromyography system with electrogoniometers and an inclinometer were used to record the head, lumbar and knee joint kinematic and electromyography data during the 180° turning. This movement had been further divided into 4 phases (braking, mid-stance, swing, and terminal loading) for analysis.

FINDINGS

There were significant differences in the joint displacement and muscular activity among the different phases. Comparison between groups showed that the older adults group had less lateral lumbar flexion, less knee flexion and lower velocity of the head and knee flexion compared to young adults during turning. The electromyography data of the left biceps femoris, left gastrocnemius and left erector spinae muscles in the older adults group showed significantly higher levels than in the young adults.

INTERPRETATION

Older adults need to adjust velocities of moving joints and increase the extensor synergy muscles of the back and the stance leg to provide posture stability. Kinematics and neuromuscular modulations of the head, lumbar and knee are required according to the various phases of the turn movements and change with aging.

Compensation to whole body active rotation perturbation

The aim of the present study is the exploration of the compensation mechanisms in healthy adults elicited by superimposing a horizontal perturbation, through a rotation of the support base, during a whole body active rotation around the participant's own vertical body axis. Eight healthy participants stood on a rotating platform while executing 90° whole body rotations under three conditions: no concurrent platform rotation (NP), support surface rotation of ± 45° in the same (45-S) and opposite (45-O) directions. Participants' kinematics and CoP displacements were analyzed with an optoelectronic system and a force platform. In both 45-S and 45-O conditions, there was a tendency for the head to be affected by the external perturbation and to be the last and least perturbed segment while the pelvis was the most perturbed. The observed reduced head perturbation in 45-S and 45-O trials is consistent with a goal-oriented strategy mediated by vision and vestibular information, whereas the tuning of lumbar rotation is consistent with control mechanisms mediated by somato-sensory information.

Gaze anticipation during human locomotion

During locomotion, a top-down organization has been previously demonstrated with the head as a stabilized platform and gaze anticipating the horizontal direction of the trajectory. However, the quantitative assessment of the anticipatory sequence from gaze to trajectory and body segments has not been documented. The present paper provides a detailed investigation into the spatial and temporal anticipatory relationships among the direction of gaze and body segments during locomotion. Participants had to walk along several mentally simulated complex trajectories, without any visual cues indicating the trajectory to follow. The trajectory shapes were presented to the participants on a sheet of paper. Our study includes an analysis of the relationships between horizontal gaze anticipatory behavior direction and the upcoming changes in the trajectory. Our findings confirm the following: 1) The hierarchical ordered organization of gaze and body segment orientations during complex trajectories and free locomotion. Gaze direction anticipates the head orientation, and head orientation anticipates reorientation of the other body segments. 2) The influence of the curvature of the trajectory and constraints of the tasks on the temporal and spatial relationships between gaze and the body segments: Increased curvature resulted in increased time and spatial anticipation. 3) A different sequence of gaze movements at inflection points where gaze plans a much later segment of the trajectory.

Contributions of cognitive function to straight- and curved-path walking in older adults

OBJECTIVE

To determine whether the cognitive function contribution to straight- and curved-path walking differs for older adults.

DESIGN

Cross-sectional observational study.

SETTING

Ambulatory clinical research training center.

PARTICIPANTS

People (N=106) aged 65 to 92 years, able to walk household distances independently with or without an assistive device, and who scored 24 or greater on the Mini-Mental State Examination.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Cognitive function was assessed using the Digit Symbol Substitution Test (DSST) as a measure of psychomotor speed, and Trail Making Test Parts A and B (TMT-A and TMT-B) and the Trail Making Test difference score (TMT-B-A) as executive function measures of complex visual scanning and set shifting. Gait speed recorded over an instrumented walkway was used as the measure of straight-path walking. Curved-path walking was assessed using the Figure-of-8 Walk Test (F8W) and recorded as the total time and number of steps for completion.

RESULTS

Both DSST and TMT-A independently contributed to usual gait speed (P<.001). TMT-A performance contributed to F8W time (P<.001). Neither TMT-B nor TMT-B-A contributed to usual gait speed or time to complete the F8W. For the number of steps taken to complete the F8W, TMT-A, TMT-B, and TMT-B-A (all P<.001) were independent contributors, while DSST performance was not.

CONCLUSIONS

Curved-path walking, as measured by the F8W, involves different cognitive processes compared with straight-path walking. Cognitive flexibility and set-shifting processes uniquely contributed to how individuals navigated curved paths. The measure of curved-path walking provides different and meaningful information about daily life walking ability than usual gait speed alone.

Do walkers follow their heads? Investigating the role of head rotation in locomotor control

Eye and head rotations are normally correlated with changes in walking direction; however, it is unknown whether they play a causal role in the control of steering. The objective of the present study was to answer two questions about the role of head rotations in steering control when walking to a goal. First, are head rotations sufficient to elicit a change in walking direction? Second, are head rotations necessary to initiate a change in walking direction or guide steering to a goal? To answer these questions, participants either walked toward a goal located 7 m away or were cued to steer to the left or right by 37°. On a subset of trials, participants were either cued to voluntarily turn their heads to the left or right, or they underwent an involuntary head perturbation via a head-mounted air jet. The results showed that large voluntary head turns (35°) yielded slight path deviations (1°-2°) in the same or opposite direction as the head turn, depending on conditions, which have alternative explanations. Involuntary head rotations did not elicit path deviations despite comparable head rotation magnitudes. In addition, the walking trajectory when turning toward an eccentric goal was the same regardless of head orientation. Steering can thus be decoupled from head rotation during walking. We conclude that head rotations are neither a sufficient nor a necessary component of steering control, because they do not induce a turn and they are not required to initiate a turn or to guide the locomotor trajectory to a goal.

Neuromuscular strategies in the paretic leg during curved walking in individuals post-stroke

Reduced flexibility over the neuromotor control of paretic leg muscles may impact the extent to which individuals post-stroke modulate their muscle activity patterns to walk along curved paths. The purpose of this study was to compare lower-limb movements and neuromuscular strategies in the paretic leg of individuals with stroke with age-matched controls during curved walking. Participants walked at their preferred walking velocity along four different paths of increasing curvature, while lower-limb kinematics and muscle activity were recorded. A second group of able-bodied individuals walked along the four paths, matching the walking speed of the stroke group. The stroke group showed reduced lower-limb joint excursion and disordered modulation of foot pressure during curved walking, accompanied by reduced modulation of muscle activity patterns. In the inner leg of the curve in control subjects, the posteromedial muscles (medial gastrocnemius and medial hamstrings) showed decreased electromyographic amplitude as path curviture increased. Conversely, activity of the posterolateral musculature of the outer leg was decreased with increasing path curvature. Activity in the tibialis anterior and gluteus medius was also modulated with path curvature. However, in the stroke group, we found reduced modulation of muscle activity in the paretic leg during curved walking. The extent of modulation was also associated with the level of physical impairment due to stroke. The results of this study provide further knowledge about neuromuscular control of locomotor adaptations post-stroke.

Self-motion perception and vestibulo-ocular reflex during whole body yaw rotation in standing subjects: the role of head position and neck proprioception

Self-motion perception and vestibulo-ocular reflex (VOR) were studied during whole body yaw rotation in the dark at different static head positions. Rotations consisted of four cycles of symmetric sinusoidal and asymmetric oscillations. Self-motion perception was evaluated by measuring the ability of subjects to manually track a static remembered target. VOR was recorded separately and the slow phase eye position (SPEP) was computed. Three different head static yaw deviations (active and passive) relative to the trunk (0°, 45° to right and 45° to left) were examined. Active head deviations had a significant effect during asymmetric oscillation: the movement perception was enhanced when the head was kept turned toward the side of body rotation and decreased in the opposite direction. Conversely, passive head deviations had no effect on movement perception. Further, vibration (100 Hz) of the neck muscles splenius capitis and sternocleidomastoideus remarkably influenced perceived rotation during asymmetric oscillation. On the other hand, SPEP of VOR was modulated by active head deviation, but was not influenced by neck muscle vibration. Through its effects on motion perception and reflex gain, head position improved gaze stability and enhanced self-motion perception in the direction of the head deviation.

Dissociable cognitive mechanisms underlying human path integration

Path integration is a fundamental mechanism of spatial navigation. In non-human species, it is assumed to be an online process in which a homing vector is updated continuously during an outward journey. In contrast, human path integration has been conceptualized as a configural process in which travelers store working memory representations of path segments, with the computation of a homing vector only occurring when required. To resolve this apparent discrepancy, we tested whether humans can employ different path integration strategies in the same task. Using a triangle completion paradigm, participants were instructed either to continuously update the start position during locomotion (continuous strategy) or to remember the shape of the outbound path and to calculate home vectors on basis of this representation (configural strategy). While overall homing accuracy was superior in the configural condition, participants were quicker to respond during continuous updating, strongly suggesting that homing vectors were computed online. Corroborating these findings, we observed reliable differences in head orientation during the outbound path: when participants applied the continuous updating strategy, the head deviated significantly from straight ahead in direction of the start place, which can be interpreted as a continuous motor expression of the homing vector. Head orientation-a novel online measure for path integration-can thus inform about the underlying updating mechanism already during locomotion. In addition to demonstrating that humans can employ different cognitive strategies during path integration, our two-systems view helps to resolve recent controversies regarding the role of the medial temporal lobe in human path integration.

Visually evoked whole-body turning responses during stepping in place in a virtual environment

Humans use a specific sequence of reorientation of the eyes, head and body to perform turning and redirections while walking. Gaze (eye and head) rotation in a new direction of travel precedes body rotation by as much as 1.5s and provides a stable reference frame that guides subsequent whole-body redirection. The purpose of the current study was to determine whether a visually presented rotation of the external environment can induce whole-body turning lead by gaze redirection in a new travel direction. Five healthy young adults performed a stepping in place task while watching a virtual scene that moved as if they were walking down a hallway, thus providing participants with a perception of forward self motion. While "forward" stepping, the virtual scene would gradually turn around a 90 degrees corner. As a result the turn could be anticipated by the participants. Significant horizontal eye movements and head and body rotation magnitudes were observed in response to the virtual visual turning cue. Onset of eye, head and body redirection revealed a sequenced order and timing of segment rotation that is characteristic of steering behaviour in real world turning situations. The results of this study provide support for the hypothesis that gaze redirection may be an essential subcomponent to steering behaviour. The link between visual redirection and coordinated body turning implies instability when turning may result from visual and/or oculomotor deficits.

Reduced performance in balance, walking and turning tasks is associated with increased neck tone in Parkinson's disease

Rigidity or hypertonicity is a cardinal symptom of Parkinson's disease (PD). We hypothesized that hypertonicity of the body axis affects functional performance of tasks involving balance, walking and turning. The magnitude of axial postural tone in the neck, trunk and hip segments of 15 subjects with PD (both ON and OFF levodopa) and 15 control subjects was quantified during unsupported standing in an axial twisting device in our laboratory as resistance to torsional rotation. Subjects also performed six functional tests (walking in a figure of eight [Figure of Eight], Timed Up and Go, Berg Balance Scale, supine rolling task [rollover], Functional Reach, and standing 360-deg turn-in-place) in the ON and OFF state. Results showed that PD subjects had increased tone throughout the axis compared to control subjects (p=0.008) and that this increase was most prominent in the neck. In PD subjects, axial tone was related to functional performance, but most strongly for tone at the neck and accounted for an especially large portion of the variability in the performance of the Figure of Eight test (r(OFF)=0.68 and r(ON)=0.74, p<0.05) and the Rollover test (r(OFF)=0.67 and r(ON)=0.55, p<0.05). Our results suggest that neck tone plays a significant role in functional mobility and that abnormally high postural tone may be an important contributor to balance and mobility disorders in individuals with PD.

Maneuvers during legged locomotion

Maneuverability is essential for locomotion. For animals in the environment, maneuverability is directly related to survival. For humans, maneuvers such as turning are associated with increased risk for injury, either directly through tissue loading or indirectly through destabilization. Consequently, understanding the mechanics and motor control of maneuverability is a critical part of locomotion research. We briefly review the literature on maneuvering during locomotion with a focus on turning in bipeds. Walking turns can use one of several different strategies. Anticipation can be important to adjust kinematics and dynamics for smooth and stable maneuvers. During running, turns may be substantially constrained by the requirement for body orientation to match movement direction at the end of a turn. A simple mathematical model based on the requirement for rotation to match direction can describe leg forces used by bipeds (humans and ostriches). During running turns, both humans and ostriches control body rotation by generating fore-aft forces. However, whereas humans must generate large braking forces to prevent body over-rotation, ostriches do not. For ostriches, generating the lateral forces necessary to change movement direction results in appropriate body rotation. Although ostriches required smaller braking forces due in part to increased rotational inertia relative to body mass, other movement parameters also played a role. Turning performance resulted from the coordinated behavior of an integrated biomechanical system. Results from preliminary experiments on horizontal-plane stabilization support the hypothesis that controlling body rotation is an important aspect of stable maneuvers. In humans, body orientation relative to movement direction is rapidly stabilized during running turns within the minimum of two steps theoretically required to complete analogous maneuvers. During straight running and cutting turns, humans exhibit spring-mass behavior in the horizontal plane. Changes in the horizontal projection of leg length were linearly related to changes in horizontal-plane leg forces. Consequently, the passive dynamic stabilization associated with spring-mass behavior may contribute to stability during maneuvers in bipeds. Understanding the mechanics of maneuverability will be important for understanding the motor control of maneuvers and also potentially be useful for understanding stability.

Eye-head coupling tendencies in stationary and moving subjects

Humans exhibit considerable individuality in their propensity to make head movements during horizontal saccades. These variations originate in multiple quantifiable characteristics, including individuals' preferred ranges of gaze, eye-in-head, and head-on-neck eccentricity. Such "eye-head tendencies" have been uniformly assessed in seated subjects. It is unknown whether they continue to influence behavior when subjects are in motion. Previous studies of eye-head coordination in subjects ambulating in laboratories would predict that wholly different eye-head tendencies become ascendant when subjects ambulate. We tested this prediction by recording eye and head positions in normal subjects in an outdoor environment as they spontaneously regarded their surroundings while seated, passively riding in a wheelchair, and ambulating. Individuals exhibited the usual subject-to-subject variations in the preferred ranges of eye, head, and gaze position, but their own behavior was similar across the different conditions. While ambulation did affect some of the measured eye-head tendencies, passively riding had similar effects, indicating that these effects relate more to motion through the environment than to the act of walking. In a surprising departure from studies of eye-head coordination in subjects ambulating in laboratory environments, neither head nor gaze was particularly strongly aligned with the direction of travel. Thus, the neural mechanisms of walking do not demand that specific gaze or head orientations be maintained continuously, at least not in the common situation of a non-challenging path that can be negotiated without much attention. In such situations eye and head control is flexible, and the eye-head tendencies manifesting when stationary can emerge.

Gaze and Postural Reorientation in the Control of Locomotor Steering After Stroke

Background. Steering of locomotion is a complex task involving stabilizing and anticipatory orienting behavior essential for the maintenance of balance and for establishing a stable frame of reference for future motor and sensory events. How these mechanisms are affected by stroke remains unknown. Objectives. To compare locomotor steering behavior between stroke and healthy individuals and to determine whether steering abilities are influenced by walking speed, turning direction and walking capacity in stroke individuals. Methods. Gaze and body kinematics were recorded in 8 stroke and 7 healthy individuals while walking and turning in response to a visual cue. Horizontal orientation of gaze, head, thorax, pelvis, and feet with respect to spatial and heading coordinates were examined. Results. Temporal and spatial coordination of gaze and body movements revealed stabilizing and anticipatory orienting mechanisms in the healthy individuals. Changing walking speed affected the onset time but not the sequencing of segment reorientation. In the individuals with stroke, abnormally large and uncoordinated head and gaze motion were observed. The sequence of gaze, head, thorax and pelvis horizontal reorientation also was also disrupted. Alterations in orienting behaviors were more pronounced at the slowest walking speeds and turning to the nonparetic side in 3 of the most severely disabled individuals. Conclusion. The results in this convenience sample of slow and faster walkers suggest that stroke alters the stabilizing and orienting behavior during steering of locomotion. Such alterations are not caused by the inherently slow walking speed, but rather by a combination of biomechanical factors and defective sensorimotor integration, including altered vestibulo-ocular reflexes.

Walking along curved paths of different angles: the relationship between head and trunk turning

Walking along a curved path requires coordinated motor actions of the entire body. Here, we investigate the relationship between head and trunk movements during walking. Previous studies have found that the head systematically turns into turns before the trunk does. This has been found to occur at a constant distance rather than at a constant time before a turn. We tested whether this anticipatory head behavior is spatially invariant for turns of different angles. Head and trunk positions and orientations were measured while participants walked around obstacles in 45 degrees, 90 degrees, 135 degrees or 180 degrees turns. The radius of the turns was either imposed or left free. We found that the head started to turn into the direction of the turn at a constant distance before the obstacle (approximately 1.1 m) for turn angles up to 135 degrees . During turns, the head was consistently oriented more into the direction of the turn than the trunk. This difference increased for larger turning angles and reached its maximum later in the turn for larger turns. Walking speeds decreased monotonically for increasing turn angles. Imposing fixed turn radii only affected the point at which the trunk started to turn into a turn. Our results support the view that anticipatory head movements during turns occur in order to gather advance visual information about the trajectory and potential obstacles.