The effect of velocity on the strategies used during gait termination

Effects of direction cue time and walking speed on spatial-temporal gait adaptations in healthy older and young adults upon approach of turns

BACKGROUND

Hurrying and turning are each associated with falls in older adults. Losing balance sideways when turning increases the likelihood of hip fracture. Yet 99 % of failures when turning unexpectedly have been traced to an inability to curb forward momentum regardless of age.

RESEARCH QUESTION

Do age-based differences exist in spatial-temporal gait adaptations related to medial-lateral (M-L) balance and posterior-anterior (P-A) propulsion upon approach of turns relative to continuing straight, across walking speeds and whether direction is known in advance?

METHODS

Healthy young (n=10) and older adults (n = 10) walked at preferred and fast test speeds while randomly cued for direction either early upon initiating gait or late 1-2 steps before entering a spatially defined turning area. An instrumented 4.6 m carpet recorded spatial-temporal changes up to the penultimate footfall prior to turning 900 or continuing straight.

RESULTS

When approaching the turning zone across interactions of walking test speed, cue time and direction, other than stride-length being shorter in older adults, both age-groups showed similar adjustments in gait speed and stride-length in managing P-A deceleration perturbations, and similar adaptations in right and left heel-to-heel base of support (BOS) in managing M-L balance destabilizing forces. A three-way interaction (p<.027) suggests a similar foot strategy of BOS narrowing may be used approaching turns relative to straight walks when direction is cued early walking fast (p<.020) and late walking preferred speed (p<.014).

SIGNIFICANCE

The findings were interpreted within the context of regulating center of mass acceleration and processing environmental regulatory conditions to maintain a personal space safety margin. The study supports that in otherwise healthy older adults, gait training for turns include practice to not only manage perturbations which accelerate the body sideways but also those which decelerate forward progression.

Biomechanical Analysis of Unplanned Gait Termination According to a Stop-Signal Task Performance: A Preliminary Study

There is a correlation between cognitive inhibition and compensatory balance response; however, the correlation between response inhibition and gait termination is not clear.

OBJECTIVES

The purpose of this study was to investigate the gait parameters of the lower extremity that occurred during unplanned gait termination (UGT) in two groups classified by the stop-signal reaction time (SSRT).

METHODS

Twenty young adults performed a stop-signal task and an unplanned gait termination separately. UGT required subjects to stop on hearing an auditory cue during randomly selected trials. The spatiotemporal and kinematic gait parameters were compared between the groups during UGT.

RESULTS

In phase one, the fast group had a significantly greater angle and angular velocity of knee flexion and ankle plantar flexion than the slow group (p < 0.05). Phase two showed that the fast group had a significantly greater angle and angular velocity of knee extension than the slow group (p < 0.05). Concerning the correlation analysis, the angle and angular velocity of knee flexion and ankle plantar flexion showed a negative correlation with the SSRT during UGT in phase one (p < 0.05). Phase two showed that the angle and angular velocity of knee extension was negatively correlated with the SSRT during UGT (p < 0.05).

CONCLUSION

The shorter the SSRT, the greater the angle and joint angular velocity of the ankle or knee joint that were prepared and adjusted for gait termination. The correlation between the SSRT and UGT suggests that a participant's capacity to inhibit an incipient finger response is associated with their ability to make a corrective gait pattern in a choice-demanding environment.

Evaluation of Lower-Limb Kinematics during Timed Up and Go (TUG) Test in Subjects with Locomotive Syndrome (LS) Using Wearable Gait Sensors (H-Gait System)

Few studies have dealt with lower-limb kinematics during the timed up and go (TUG) test in subjects with locomotive syndrome (LS). This study aimed to evaluate the characteristics of lower-limb kinematics during the TUG test in subjects with LS using the wearable sensor-based H-Gait system. A total of 140 participants were divided into the non-LS (n = 28), the LS-stage 1 (n = 78), and LS-stage 2 (n = 34) groups based on the LS risk test. Compared with the non-LS group, the LS-stage 1 and LS-stage 2 groups showed significantly smaller angular velocity of hip and knee extension during the sit-to-stand phase. The LS-stage 2 group showed significantly smaller peak angles of hip extension and flexion during the walking-out phase compared to the non-LS group. These findings indicate that the evaluation of the lower-limb kinematics during the TUG test using the H-Gait system is highly sensitive to detect LS, compared with the evaluation of the lower-limb kinematics when simply walking.

Investigating Temporal Kinematic Differences Caused by Unexpected Stimulation during Gait Termination through the Waveform-Level Variance Equality Test

The efficacy of the variance equality test in steady-state gait analysis is well documented; however, temporal information on where differences in variability occur during gait subtasks, especially during gait termination caused by unexpected stimulation, is poorly understood. Therefore, the purpose of the current study was to further verify the efficacy of the waveform-level variance equality test in gait subtasks by comparing temporal kinematical variability between planned gait termination (PGT) and unplanned gait termination (UGT) caused by unexpected stimulation. Thirty-two asymptomatic male subjects were recruited to participate in the study. A Vicon motion capture system was utilized to measure lower extremity kinematics during gait termination tasks with and without unexpected stimulation conditions. The F-statistic for each interval of the temporal kinematic waveform was compared to the critical value using a variance equality test to identify significant differences in the waveform. Comparative tests between two types of gait terminations found that subjects may exhibit greater kinematics variance in most lower limb joints during UGT caused by unexpected stimulation (especially at stimulus delay and reaction phases). Significant greater variances during PGT were exhibited only in the MPJ sagittal and frontal planes at the early stimulus delay phase (4-15% and 1-15%). This recorded dataset of temporal kinematic changes caused by unexpected stimuli during gait termination is essential for interpreting lower limb biomechanical function and injury prediction in relation to UGT. Given the complexity of the gait termination task, which involves both internal and external variability, the variance equality test can be used as a valuable method to compare temporal differences in the variability of biomechanical variables.

Evaluation of gait termination strategy in individuals with Essential Tremor and Parkinson's disease

INTRODUCTION

Gait termination (GT) is a challenging transitory task involving converting from a dynamic state of motion to a static state. These transitional locomotor tasks are particularly troublesome for populations with postural deficits, i.e., Parkinson's disease (PD) and Essential Tremor (ET). They demand greater postural control and intricate integration of the neuromuscular system. The mechanisms involved in GT in these populations have not been well studied despite the safety concerns and potential risk for falls. The purpose of this investigation was to examine the different control strategies utilized during GT between individuals with ET and PD.

METHODS

Twenty-four individuals with ET (66 ± 8 yrs), twenty-four individuals with PD (64 ± 8 yrs), and twenty healthy older adults (HOA: 63 ± 9 yrs) participated in this study. Average self-selected gait velocity for each group was collected during the GT trial walking portion. Ground reaction force (GRF) data were used to calculate braking and propulsive forces from the last two steps during GT. GRF data measured the dynamic postural stability index (DPSI), defined as an individual's ability to maintain balance while transitioning from a dynamic to a stable state.

RESULTS

Persons with ET had a significantly slower approach velocity (0.63 m/s) when compared to HOA (0.92 m/s) and PD (0.77 m/s). Persons with PD had significantly slower approach velocity when compared to HOA. Examination of GRF data found that those with ET generated significantly smaller propulsive and braking forces (p < .05). Forces increased in those with PD and then even more in the HOA group. Postural stability analysis revealed that ET had significantly worse stability scores than PD and HOA (p < .05).

CONCLUSION

Individuals with PD and ET utilize different control strategies for planned GT, which suggests both the cerebellum and the basal ganglia play central yet potentially different roles in anticipatory control during self-directed activities.

Influence of kyphosis posture on postural control and lower limb mechanical load immediately after stopping walking

[Purpose] This study aimed to clarify the characteristics of joint moment and force for postural control performance after stopping walking under two conditions. [Participants and Methods] A total of 18 healthy males participated in this study. The joint moment and power were compared between the normal and kyphosis postures after stopping walking based on the critical time interval as calculated by stabilogram diffusion analysis. [Results] The polarity of the joint moment in both postures was different in the knee and hip extension–flexion directions, the absolute value being higher in the kyphosis posture than in the normal one. The hip and knee joint powers were negative in the normal posture but positive in the kyphosis posture; these values were higher in the kyphosis posture than the normal one. [Conclusion] The polarity of the joint moment of the hip and knee joints in the direction of flexion and extension differed from the normal one due to the postural changes caused by the kyphosis posture. The postural controls between the two conditions were considered different. The leading limb was thought to be an important braking action in stopping walking.

Tails, Flails, and Sails: How Appendages Improve Terrestrial Maneuverability by Improving Stability

Trade-offs in maneuverability and stability are essential in ecologically relevant situations with respect to robustness of locomotion, with multiple strategies apparent in animal model systems depending on their habitat and ecology. Free appendages such as tails and ungrounded limbs may assist in navigating this trade-off by assisting with balance, thereby increasing the acceleration that can be achieved without destabilizing the body. This comparative analysis explores the inertial mechanisms and, in some cases, fluid dynamic mechanisms by which appendages contribute to the stabilization of gait and perturbation response behaviors in a wide variety of animals. Following a broad review of examples from nature and bio-inspired robotics that illustrate the importance of appendages to the control of body orientation, two specific cases are examined through preliminary experiments: the role of arm motion in bipedal gait termination is explored using trajectory optimization, and the role of the cheetah’s tail during a deceleration maneuver is analyzed based on motion capture data. In both these examples, forward rotation of the appendage in question is found to counteract the unwanted forward pitch caused by the braking forces. It is theorized that this stabilizing action may facilitate more rapid deceleration by allowing larger or longer-acting braking forces to be applied safely.

The role of enhanced plantar-surface sensory feedback on lower limb EMG during planned gait termination

Purpose/aim of the study: Generation of smooth movement relies on the central nervous system (CNS) having information from the visual, vestibular and somatosensory systems to effectively execute motor behaviour. Recently, cutaneous afferent inputs have been linked to lower leg motorneuron pools, resulting in a growing interest of adding texture to the plantar foot sole interface as a novel method to facilitate cutaneous feedback. The aim of this study was to characterize the changes in magnitude and temporal organization of muscle activity, and to investigate motor output changes from enhanced tactile feedback during perturbed gait termination.Materials and methods: Thirty young adults experienced an unpredictable platform perturbation when completing planned gait termination. The study manipulated two experimental variables: 1) direction of platform tilt (anterior, posterior, medial, lateral), and 2) foot sensory facilitation (non-facilitated, facilitated). Upper and lower leg EMG onset, cessation time and integrated EMG (iEMG) were measured in addition to common gait parameters (walking velocity, step length, step width).Results: Gait termination over a textured surface resulted in significantly earlier upper leg EMG onset times and modified iEMG of rectus femoris, vastus medialis and biceps femoris muscles.Conclusions: Results of this study suggest that the addition of cutaneous feedback under the plantar-surface of the foot increases the ability to generate an earlier muscle response, consequently improving response ability to an unexpected perturbation. Secondly, enhanced tactile feedback appears to inform the CNS of the magnitude of the threat to the balance control system, providing additional insight into how the CNS uses enhanced tactile feedback during a gait termination task.

A Comparative Biomechanical Analysis during Planned and Unplanned Gait Termination in Individuals with Different Arch Stiffnesses

Although values of arch stiffness index (ASI) have been used to evaluate arch structure and injury susceptibility, investigations are limited regarding the influence of ASI on biomechanical characteristics during gait termination, which involves a challenging balance transition from walking to standing. This study aimed to explore plantar pressure distribution and lower extremity joint kinematic differences between individuals with both a stiff and flexible arch (SA and FA, respectively) during planned and unplanned gait termination (PGT and UGT, respectively). Following the calculation of ASI, sixty-five asymptomatic male subjects were classified and participated in two types of gait termination tests to acquire kinematic and plantar pressure data. Parameters were compared between SA and FA using a two-way ANOVA during PGT and UGT, respectively. UGT was found to have a larger range of motion on the hip joint in the sagittal plane and the knee joint in the transverse plane when compared with PGT. The differences in the kinematic characteristics of the lower limb joints caused by the difference in arch stiffness are mainly concentrated in the ankle and metatarsophalangeal joints. Plantar pressure data, represented by the maximum pressure, showed significant differences in the forefoot and rearfoot areas. These results suggest that ASI could change freedom of motion of the lower limb joints, and UGT tends to conduct a compensatory adjustment for the lower extremity kinetic chain. An understanding of the biomechanical characteristics of arch structures may provide additional insights into foot function and injury prediction during gait termination.

Non-specific chronic low back pain elicits kinematic and neuromuscular changes in walking and gait termination

BACKGROUND

Chronic low back pain (CLBP) is associated with an increased trunk stiffness and muscle coactivation during walking. However, it is still unclear whether CLBP individuals are unable to control neuromechanically their upper body motion during a sudden termination of gait (GT), which involves a challenging balance transition from walking to standing.

RESEARCH QUESTION

Does CLBP elicit neuromuscular and kinematic changes which are specific to walking and GT?.

METHODS

Eleven individuals with non-specific CLBP and 11 healthy controls performed walking and sudden GT in response to an external visual cue. 3D kinematic characteristics of thorax, lumbar and pelvis were obtained, with measures of range of motion (ROM) and intra-subject variability of segmental movement being calculated. Electromyographic activity of lumbar and abdominal muscles was recorded to calculate bilateral as well as dorsoventral muscle coactivation.

RESULTS

CLBP group reported greater transverse ROM of the lumbar segment during walking and GT compared to healthy controls. Thorax sagittal ROM was higher in CLBP than healthy participants during GT. Greater overall movement variability in the transverse plane was observed in the CLBP group while walking, whereas GT produced greater variability of lumbar frontal motion. CLBP participants showed higher bilateral lumbar coactivation compared to healthy participants after the stopping stimulus delivery during GT.

SIGNIFICANCE

These results suggest that CLBP can elicit a wider and more variable movement of the upper body during walking and GT, especially in the transverse plane and at lumbar level. Alterations in upper body motor control appeared to depend on task, plane of motion and segmental level. Therefore, these findings should be considered by practitioners when screening before planning specific training interventions for recovery of motor control patterns in CLBP population.

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

Background

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

Methods

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

Results

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

Conclusion

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

Quantification of spatiotemporal parameter behavior during walking speed transitions

The biomechanics of constant speed walking have been well quantified, but little is known about transitions between walking speeds. Spatiotemporal behavior (step time, length, and speed) has been investigated in starting, stopping, and walking to running transitions, but speed transitions during walking have yet to be investigated. This study quantified the spatiotemporal parameter behavior during walking speed transitions with a range of magnitudes (or differences between pre- and post-transition normalized speeds ranging from 0.03 to 0.13, or approximately 1.18 m/s to 1.58 m/s). 23 healthy adults walked on a treadmill at five different constant speeds for one minute each to establish a baseline. They then performed walking speed transitions, in which they walked on the treadmill as it randomly changed between the five speeds. Linear mixed effect models showed that subjects converged to slightly different post-transition step time and step length averages than established in the constant speed baseline, but the differences are likely too small to be meaningful (on the order of 0.01 s and 0.01 m). When diverging from the pre-transition speed, subjects either diverged in only step time (with step length remaining the same), only step length (with step time remaining the same), or both step time and step length to reach the post-transition speed, with the behavior strongly tied to the magnitude of the speed transition (p<0.001). Step time often overshot the new value before converging. The number of steps required for each parameter to converge increased with increasing transition magnitude (p<0.001) and was consistently higher at all magnitudes for speed than step time and length (p<0.001). In summary, transition magnitude affected the spatiotemporal behavior during walking speed transitions. Further, step time, length, and speed all exhibited slightly different divergence and convergence behavior during transitions.

Unplanned gait termination in individuals with multiple sclerosis

Despite the pervasive nature of gait impairment in multiple sclerosis (MS), there is limited information concerning the control of gait termination in individuals with MS. The purpose of this investigation was to examine unplanned gait termination with and without cognitive distractors in individuals with MS compared to healthy controls. Thirty-one individuals with MS and 14 healthy controls completed a series of unplanned gait termination tasks over a pressure sensitive walkway under distracting and non-distracting conditions. Individuals with MS were further broken down into groups based on assistive device use: (no assistive device (MS_noAD) n=18; and assistive device (MS_AD) n=13). Individuals with MS who walked with an assistive device (MS_AD: 67.8±15.1cm/s) walked slower than individuals without an assistive device (MS_noAD: 110.4±32.3cm/s, p<0.01) and controls (120.0±30.0cm/s; p<0.01). There was a significant reduction in velocity in the cognitively distracting condition (93.4±32.1cm/s) compared to the normal condition [108.8±36.2cm/s; F(1,43)=3.4, p=0.04]. All participants took longer to stop during the distracting condition (1.7±0.6s) than the non-distracting condition (1.4±0.4s; U=673.0 p<0.01). After controlling for gait velocity, post-hoc analysis revealed the MS_AD group took significantly longer to stop compared to the control group (p=0.05). Further research investigating the control of unplanned gait termination in MS is warranted.

GAIT ANALYSIS: SYSTEMS, TECHNOLOGIES, AND IMPORTANCE

Human gait is the identity of a person's style and quality of life. Reliable cognition of gait properties over time, continuous monitoring, accuracy of evaluation, and proper analysis of human gait characteristics have demonstrated their importance not only in clinical and medical studies, but also in the field of sports, rehabilitation, training, and robotics research. Focusing on walking gait, this study presents an overview on gait mechanisms, common technologies used in gait analysis, and importance of this particular field of research. Firstly, available technologies that involved in gait analysis are briefly introduced in this paper by concentrating on the usability and limitations of the systems. Secondly, key gait parameters and motion characteristics are elucidated from four angles of views; one: gait phases and gait properties; two: center of mass and center of pressure (CoM-CoP) tracking profile; three: Ground Reaction Force (GRF) and impact, and four: muscle activation. Thirdly, the study focuses on the clinical observations of gait patterns in diagnosing gait abnormalities of impaired patients. The presentation also shows the importance of gait analysis in sports to improve performance as well as to avoid risk of injuries of sports personnel. Significance of gait analysis in robotic research is also illustrated in this part where the study focuses on robot assisted systems and its possible applicability in clinical rehabilitation and sports training.

Biomechanical analysis of gait termination in 11-17year old youth at preferred and fast walking speeds

In populations where walking and/or stopping can be difficult, such as in children with cerebral palsy, the ability to quickly stop walking may be beyond the child's capabilities. Gait termination may be improved with physical therapy. However, without a greater understanding of the mechanical requirements of this skill, treatment planning is difficult. The purpose of this study was to understand how healthy children successfully terminate gait in one step when walking quickly, which can be challenging even for healthy children. Lower extremity kinematic and kinetic data were collected from 15 youth as they performed walking, planned, and unplanned stopping tasks. Each stopping task was performed as the subject walked at his/her preferred speed and a fast speed. The most significant changes in mechanics between speed conditions (preferred and fast) of the same stopping task were greater knee flexion angles (unplanned: +16.49±0.54°, p=0.00; planned: +15.75±1.1°, p=0.00) and knee extension moments (unplanned: +0.67±0.02N/kgm, p=0.00; planned: +0.57±0.23N/kgm, p=0.00) at faster speeds. The extra range of motion in the joints and extra muscle strength required to maintain the stopping position suggests that stretching and strengthening the muscles surrounding the joints of the lower extremity, particularly the knee, may be a useful intervention.

From normal to fast walking: Impact of cadence and stride length on lower extremity joint moments

This study aimed to clarify the influence of various speeding strategies (i.e. adjustments of cadence and stride length) on external joint moments. This study investigated the gait of 52 healthy subjects who performed self-selected normal and fast speed walking trials in a motion analysis laboratory. Subjects were classified into three separate groups based on how they increased their speed from normal to fast walking: (i) subjects who increased their cadence, (ii) subjects who increased their stride length and (iii) subjects who simultaneously increased both stride length and cadence. Joint moments were calculated using inverse dynamics and then compared between normal and fast speed trials within and between three groups using spatial parameter mapping. Individuals who increased cadence, but not stride length, to walk faster did not experience a significant increase in the lower limb joint moments. Conversely, subjects who increased their stride length or both stride length and cadence, experienced a significant increase in all joint moments. Additionally, our findings revealed that increasing the stride length had a higher impact on joint moments in the sagittal plane than those in the frontal plane. However, both sagittal and frontal plane moments were still more responsive to the gait speed change than transverse plane moments. This study suggests that the role of speed in altering the joint moment patterns depends on the individual's speed-regulating strategy, i.e. an increase in cadence or stride length. Since the confounding effect of walking speed is a major consideration in human gait research, future studies may investigate whether stride length is the confounding variable of interest.

Biomechanical alterations of gait termination in middle-aged and elderly women

[Purpose] The purpose of this study was to analyze the biomechanical changes and patterns of the lower extremities after gait termination in middle-aged and elderly women. [Subjects] The study population comprised an elderly group and middle-aged group. [Methods] To collect kinematic and kinetic data related to gait termination, six infrared cameras and one force platform were used, and variables were calculated by using Visual 3D. [Results] During the termination phase, the elderly group generated less braking force than the middle-aged group. During initiation of the termination phase and after the center of gravity completely stopped moving, there was a difference between the two groups in the hip joint angle. During the termination phase, the maximum angular velocity and extension moment of the ankle joint and those of the knee joint were higher in the elderly group than in the middle-aged group. [Conclusion] In contrast to the middle-aged group that showed a rapid increase and then decrease of the initial extension moment during gait termination, the maximum extension moment that was created during the early stage of the termination phase in the elderly group continued until the center of gravity completely stopped.

Dynamic stability during running gait termination: Differences in strategies between children and adults to control forward momentum

Rapid deceleration during running is key for successful participation in most childhood activities and sports; this requires modulation of body momentum and consequent challenges to postural equilibrium. The purpose of this study was to investigate the strategies employed by adults and children to control forward momentum and terminate running gait. Sixteen young adults and 15 pre-pubertal children completed two tasks as fast as possible: an unobstructed run (RUN) and a run and stop (STOP) at a pre-determined location. For STOP, center of mass (COM) approach velocity and momentum prior to deceleration and spatiotemporal characteristics and COM position during deceleration were compared between groups. Position and velocity variables were normalized to height and maximum velocity during RUN, respectively. Children used fewer steps with relatively longer step length to decelerate over a relatively longer distance and longer time than adults. Children approached at higher relative velocity than adults, but adults approached with greater momentum. Adults positioned their COM lower and more posterior than children throughout deceleration. Our results suggest that pre-pubertal children and young adults employ different strategies to modulate body momentum, with adults exhibiting mechanics characteristic of a more stable strategy. Despite less stable mechanics, children and adults achieved similar success.

Gait deviations in children with autism spectrum disorders: a review

In recent years, it has become clear that children with autism spectrum disorders (ASDs) have difficulty with gross motor function and coordination, factors which influence gait. Knowledge of gait abnormalities may be useful for assessment and treatment planning. This paper reviews the literature assessing gait deviations in children with ASD. Five online databases were searched using keywords “gait” and “autism,” and 11 studies were found which examined gait in childhood ASD. Children with ASD tend to augment their walking stability with a reduced stride length, increased step width and therefore wider base of support, and increased time in the stance phase. Children with ASD have reduced range of motion at the ankle and knee during gait, with increased hip flexion. Decreased peak hip flexor and ankle plantar flexor moments in children with ASD may imply weakness around these joints, which is further exhibited by a reduction in ground reaction forces at toe-off in children with ASD. Children with ASD have altered gait patterns to healthy controls, widened base of support, and reduced range of motion. Several studies refer to cerebellar and basal ganglia involvement as the patterns described suggest alterations in those areas of the brain. Further research should compare children with ASD to other clinical groups to improve assessment and treatment planning.

Automated detection of gait initiation and termination using wearable sensors

This paper presents algorithms for detection of gait initiation and termination using wearable inertial measurement units and pressure-sensitive insoles. Body joint angles, joint angular velocities, ground reaction force and center of plantar pressure of each foot are obtained from these sensors and input into supervised machine learning algorithms. The proposed initiation detection method recognizes two events: gait onset (an anticipatory movement preceding foot lifting) and toe-off. The termination detection algorithm segments gait into steps, measures the signals over a buffer at the beginning of each step, and determines whether this measurement belongs to the final step. The approach is validated with 10 subjects at two gait speeds, using within-subject and subject-independent cross-validation. Results show that gait initiation can be detected timely and accurately, with few errors in the case of within-subject cross-validation and overall good performance in subject-independent cross-validation. Gait termination can be predicted in over 80% of trials well before the subject comes to a complete stop. Results also show that the two sensor types are equivalent in predicting gait initiation while inertial measurement units are generally superior in predicting gait termination. Potential use of the algorithms is foreseen primarily with assistive devices such as prostheses and exoskeletons.

Altered gait termination strategies following a concussion

The purpose was to determine if planned gait termination can identify acute and lingering motor control strategy alterations in post-concussion individuals. Controls completed two standard gait and five planned gait termination trials once while concussed individuals were tested on Day-1 and Day-10 post-concussion. Dependent variables included gait velocity and normalized, relative to standard gait, peak propulsive and braking forces. Control and only Day-1 post-concussion gait velocity differed. Normalized peak propulsive and braking forces were altered on both Day-1 and Day-10. Altered propulsive and braking forces persisted despite all concussion participants achieving their baseline values on standard concussion clinical tests. Thus gait termination can detect both acute and lingering motor control strategy alterations following concussion.

Effects of repeated optic flow stimulation on gait termination in humans

CONCLUSIONS

Because the basic strategies to stop walking are stored as motor programs, visual stimulation may have little influence on body deviation during gait termination and its time course. Walking velocity, however, demonstrated dynamic flexible changes, which may subserve the stable process of gait termination under variable circumstantial changes such as optic flow.

OBJECTIVE

The aim of this study was to examine the effect of repeated optic flow on body deviation and walking velocity during gait termination, which may be more complicated than continuous standing or walking.

METHODS

Twenty-three healthy subjects were instructed to start walking upon an acoustic cue and to stop walking when the scenery changed in a virtual reality environment. Subjects underwent eight control trials without optic flow and three sets of optic flow conditions including four trials each of optic horizontal and rotational movement randomly.

RESULTS

Repeated optic flow caused no significant change of body deviation or the time course of the gait termination process in comparison with that in the control. The walking velocity at the start of the termination process showed short-term flexibility that denoted a gradual increase over the trial for within-set and long-term flexibility that denoted a gradual decrease for between-set.

Kinematic and kinetic analysis of planned and unplanned gait termination in children

Gait termination is a task which requires people to alter momentum and stabilize the body. To date, many of the kinematic and kinetic characteristics of gait termination have not been reported, making it difficult for clinicians to design interventions to improve the ability to terminate gait quickly and efficiently. Therefore, the purpose of this study was to describe the lower body mechanics of healthy children as they performed walking trials, planned stopping trials, and unplanned stopping trials. Kinematic and kinetic data were collected from 15 healthy children between the ages of 11 and 17 years (14.3±2.1 years). The timing and magnitude of peak sagittal plane joint angles and moments were compared across the three conditions for the leg that led the stop step. Most differences were found when comparing unplanned stopping to both walking and planned stopping. During unplanned stopping, most subjects used either a hip/knee extension strategy or hip/knee flexion strategy to stabilize and perform the stopping task. The magnitudes of the peak hip extension moment and peak knee flexion angle were significantly greater, while the peak plantarflexion moment was significantly smaller during unplanned stopping than walking and planned stopping. The peak plantarflexion moment occurred significantly earlier during the stop stance phase of planned and unplanned stopping than during walking. This suggests that the ability to create sufficient joint moments in a short period of time is essential to be able to stop quickly and safely. Therefore, possible treatments/interventions should focus on ensuring that patients have appropriate strength, power, and range of motion.

Stepping strategies for regulating gait adaptability and stability

Besides a stable gait pattern, gait in daily life requires the capability to adapt this pattern in response to environmental conditions. The purpose of this study was to elucidate the anticipatory strategies used by able-bodied people to attain an adaptive gait pattern, and how these strategies interact with strategies used to maintain gait stability. Ten healthy subjects walked in a Computer Assisted Rehabilitation ENvironment (CAREN). To provoke an adaptive gait pattern, subjects had to hit virtual targets, with markers guided by their knees, while walking on a self-paced treadmill. The effects of walking with and without this task on walking speed, step length, step frequency, step width and the margins of stability (MoS) were assessed. Furthermore, these trials were performed with and without additional continuous ML platform translations. When an adaptive gait pattern was required, subjects decreased step length (p<0.01), tended to increase step width (p=0.074), and decreased walking speed while maintaining similar step frequency compared to unconstrained walking. These adaptations resulted in the preservation of equal MoS between trials, despite the disturbing influence of the gait adaptability task. When the gait adaptability task was combined with the balance perturbation subjects further decreased step length, as evidenced by a significant interaction between both manipulations (p=0.012). In conclusion, able-bodied people reduce step length and increase step width during walking conditions requiring a high level of both stability and adaptability. Although an increase in step frequency has previously been found to enhance stability, a faster movement, which would coincide with a higher step frequency, hampers accuracy and may consequently limit gait adaptability.

Gait termination strategies differ between those with and without ankle instability

BACKGROUND

Chronic ankle instability is a common occurrence after an ankle sprain. Yet, some people (copers) possess a mechanism that limits recurrent injury and disability. During gait termination, those with chronic ankle instability exhibit altered feed-forward and feedback control but little is known about alterations in copers. Therefore, the purpose of this investigation was to determine the biomechanical control alterations present in controls, copers, and those with chronic ankle instability during planned and unplanned gait termination.

METHODS

Twenty subjects with chronic ankle instability, 20 copers, and 20 uninjured controls completed planned and unplanned gait termination tasks. Unplanned gait termination required subjects to stop, when cued, during randomly selected trials. Planned gait termination required intended stopping. A total of 10 trials were recorded for each condition. Normalized propulsive and braking force magnitudes and dynamic postural stability indices were calculated and compared among the groups.

FINDINGS

Normalized maximum braking forces were significantly higher in the chronic ankle instability group (Mean: 2.82 SD: 0.93N/kg), relative to copers (Mean: 2.59 SD: 0.84N/kg) and controls (Mean: 2.51 SD: 0.78N/kg). Similarly, the antero-posterior postural stability index revealed higher scores in the chronic ankle instability group (Mean: 0.15 SD: 0.03) compared to the coper (Mean: 0.14 SD: 0.02) and control group (Mean: 0.14 SD: 0.02). Copers did not differ from controls.

INTERPRETATION

The findings suggest that the ability of copers to terminate gait in a manner similar to uninjured controls may represent part of the underlying mechanism that limits recurrent injury and disability in copers.

Real-time feedback as a method of monitoring walking velocity during gait analysis

When quantifying the mechanics of gait, it is important to ensure that subjects maintain a consistent walking velocity during gait analysis trials. Most methods of measuring walking velocity do not produce data until after the subject has completed the trial. This often results in discarding completed trials from analysis because the subject's velocity was not within an acceptable range. Real-time feedback of position data can be used to help subjects adjust their walking velocity during the trial, when necessary. Results from 14 subjects who participated in gait analysis using real-time feedback to monitor their walking velocity show that they were able to stay within an acceptable range of their target walking velocities (each subject's preferred velocity and 150% of their preferred velocity) during 90% and 80% of trials, respectively. This method allows for accurate and efficient data collections without the use of additional equipment.

Planned stopping in people with Parkinson

The aim of this study was to quantify gait termination in people with Parkinson (PwP) as the basis for understanding the underlying pathophysiology of stopping difficulties. Fourteen PwP and 14 age- and gender-matched comparisons completed five trials each of four walking tasks: preferred walk, preferred walk with secondary motor task, coming to a planned stop, and planned stop with a secondary motor task. Spatio-temporal data of walks were compared to steady state walking in stopping trials. Results showed that PwP walked with shorter step length, slower speed, yet similar cadence to comparisons. Both groups decreased step length and step speed when performing a secondary task. Neither group showed changes of gait characteristics in steady state walking prior to stopping. For stopping trials, the number of steps, time, and distance taken to stop were compared for PwP and controls. In planned stops PwP used more steps and took a longer time to stop, but both groups stopped within a similar distance. A secondary motor task did not alter stopping distance or number of steps to stop, but stopping time increased in the comparisons. The results indicate that central control mechanisms regulating planned stopping appear to be intact in people with mild to moderate Parkinson.

Postural control in isometric ramp pushes: the role of Consecutive Postural Adjustments (CPAs)

Postural adjustments, which occur after the end of a voluntary movement (termed Consecutive Postural Adjustments: CPAs), were studied and compared to the corresponding Anticipatory Postural Adjustments (APAs). Seven right-handed male adults were asked to perform horizontal two-handed maximal ramp pushes as quickly as possible, while sitting. A dynamometric bar measured the reaction to push force (Fx) and a custom-designed device measured the resultant reaction forces along the antero-posterior axis (Rx). Two ischio-femoral contacts (100 BP: full ischio-femoral contact of the ischio-femoral length; and 30BP: one-third contact) were considered. Each session consisted of ten pushes. The reaction forces, as well as push force, increased continuously, displaying similar time course profiles. However, Rx continued to increase after the end of push rise, which ascertained CPAs. CPAs were showed to be consistent kinetic phenomena, using a biomechanical analysis, based on time courses of reaction forces and CoG kinematics. Their coherence was checked precisely, by comparing theoretical and experimental occurrences of remarkable points (extrema and zero crossings). CPA durations and peak amplitudes (dCPA and pCPA) were significantly greater than the corresponding APA values (dAPA and pAPA). Moreover, dAPAs and dCPAs increased (p < 0.001), as did pCPAs (p<0.001) and pAPAs (p < 0.05) when the peak push force was greater (30 BP), showing that the probability of finding a statistically significant difference is greater for APA duration than amplitude, unlike CPAs. Finally, the present results were discussed in relation to the hypothesis according to which the focal and the postural components are parts of the same motor program.

Effects of cadence on energy generation and absorption at lower extremity joints during gait

BACKGROUND

Information regarding kinetic changes associated with walking speed is important for identifying alterations in locomotor disorders caused by pathological processes, as opposed to those arising solely from altered speeds.

METHODS

Fourteen healthy subjects were assessed walking at both natural and imposed cadences of 60, 80, and 120 steps/min. A 3D motion analysis system, force platforms, and related software were used to obtain kinematic and kinetic data. Net joint powers were calculated across cycles and the area under the positive and negative phases of the power curves provided the mechanical work generated and absorbed at the hip, knee, and ankle. The relative contributions to the total positive and negative work across the four cadences were calculated for each joint. ANOVAs followed by planned contrasts were used to assess the effects of laterality, joint, and cadence.

FINDINGS

Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by walking cadence, independent of laterality. The ankle, knee, and hip contributions to the total limb generation and absorption at the lowest cadence were 53%, 21%, and 26%, and at the highest cadence, the corresponding values were 34%, 33%, and 33%, respectively.

INTERPRETATION

Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by the walking cadence, independent of laterality. These findings will be helpful for identifying walking strategies and adaptations in populations with gait disorders.

Kinetic mechanisms to alter walking speed

A mechanism to modulate speed during human walking has not yet been proposed in the literature, even though changing walking speed is likely a necessary attribute of everyday ambulation. To understand how joint kinetics modulate walking speed 12 normal adults walked Fast (1.4m/s), Slow (1.0m/s), Accel (1.0-1.4m/s) and Decel (1.4-1.0m/s) trials while full body 3D kinematics and kinetics were collected. Reduced sagittal ankle plantarflexor moments were observed in Accel trials during early single limb stance (p<0.001) and increased sagittal plantarflexor moments were seen in Decel trials during early single limb stance (p<0.001) compared to steady speed walking. Modulating the sagittal ankle moment altered the center of pressure location and either attenuated (Accel) or accentuated (Decel) the early stance braking impulse to accelerate or decelerate the center of mass. The onset of walking speed changes occurred at approximately 15% of the gait cycle and did not support the concept of "controlled falling". Sagittal ankle push-off power appears a consequence of increased walking speed, but not the causative factor to increase walking speed.

Gait termination in lower limb amputees

OBJECTIVE

To study the limitations in function and adjustment strategies of lower limb amputees in gait termination.

DESIGN

Observational cohort study.

SETTING

University Medical Centre.

PARTICIPANTS

Unilateral transfemoral and transtibial amputees, and able-bodied control subjects.

MAIN OUTCOME MEASURES

Leading limb preference, temporal variables, lower limb joint angles, ground reaction forces, and centre of pressure shift.

RESULTS

Compared to able-bodied subjects, amputees showed a decreased peak braking ground reaction force in the prosthetic limb, no anterior centre of pressure shift during leading with the prosthetic limb and an increased mediolateral centre of pressure shift. Amputees used several adjustment strategies to compensate for the limitations in function; leading limb preference for the non-affected limb, longer production of braking force in the non-affected limb, decreased gait termination velocity and more weight-bearing on the non-affected limb.

CONCLUSION

Limitations in function and adjustment strategies were mainly similar in transfemoral and transtibial amputees. Due to the lack of active ankle function, amputees were not able to increase the braking force and to shift the centre of pressure anteriorly. Leading with the non-affected limb is favourable for adequate deceleration and balance control, but in daily life not always applicable. It is important that amputees are trained in gait termination during rehabilitation and prosthetic design should focus on a more active role of the prosthetic foot and knee.

Do people with Parkinson's disease change strategy during unplanned gait termination?

In light of the movement control problems reported for patients with Parkinson's disease (PD), we examined the lower extremity control strategies used by these subjects to stop walking in planned and unplanned situations. We compared how patients with PD and age and gender-matched control subjects modulated lower extremity muscular activity and ground reaction forces during planned and unplanned stoppings. The main findings were that control subjects did not alter muscle activation from planned to unplanned stopping, relative to stance limb kinetic events; they just increased the amplitude of the response (by approximately 800%). We speculate that these data provide preliminary evidence in support of a stereotypical sequence of muscle activation for gait termination whether planned or unplanned. In contrast, subjects with PD appeared to adopt a different strategy when stopping unexpectedly compared to planned stopping. Additional data show that subjects with PD required additional steps to stop walking when stopping unexpectedly as compared to control subjects.