Perception threshold of locomotor symmetry while walking on a split-belt treadmill in healthy elderly individuals

Gait analysis of leprosy patients with foot drop using principal component analysis

BACKGROUND

Peripheral nerve injury caused by leprosy can lead to foot drop, resulting in an altered gait pattern that has not been previously described using 3D gait analysis.

METHODS

Gait kinematics and dynamics were analyzed in 12 patients with unilateral foot drop caused by leprosy and in 15 healthy controls. Biomechanical data from patients' affected and unaffected limbs were compared with controls using inferential statistics and a standard distance, based on principal components analysis (PCA).

FINDINGS

Patients walked slower than controls (0.8 ± 0.2 vs. 1.1 ± 0.2 m/s, p = 0.003), with a reduced stance and increased swing percentage. The affected limb increased (p < 0.05) plantar flexion at the initial contact (-16.8^o ± 8.3), terminal stance (-29.1^o ± 11.5), and swing (-12.4^o ± 6.2) in the affected limb compared to unaffected (-6.6^o ± 10.3; -14.6^o ± 11.6; 2.4^o ± 7.6) and controls (-5.4^o ± 2.5; -18.8^o ± 5.8; -1.4^o ± 3.9). Increased pelvic tilt and knee adduction/abduction range, with lower hip adduction, were observed. The second peak of ground reaction force (98.6 ± 5.2 %BW), ankle torque (0.99 ± 0.33 Nm/kg), and net ankle work in stance (-0.03 ± 5.4 J/Kg) decreased in the affected limb compared to controls (104.1 ± 5.5 %BW; 1.24 ± 0.4 Nm/kg; -4.58 ± 5.19 J/kg; p < 0.05). There were decreasing multivariate standard distances in the affected limb compared with the unaffected and controls. PCA loading factors highlighted the major differences between groups.

INTERPRETATION

Leprosy patients with foot drop presented altered gait patterns in affected and unaffected limbs. There were remarkable differences in ankle kinematics and dynamics. Rehabilitation devices, such as ankle foot orthosis or tendon transfer surgeries to increase ankle dorsiflexion, could benefit these patients and reduce deviations from normal gait.

On Nonlinear Regression for Trends in Split-Belt Treadmill Training

Single and double exponential models fitted to step length symmetry series are used to evaluate the timecourse of adaptation and de-adaptation in instrumented split-belt treadmill tasks. Whilst the nonlinear regression literature has developed substantially over time, the split-belt treadmill training literature has not been fully utilising the fruits of these developments. In this research area, the current methods of model fitting and evaluation have three significant limitations: (i) optimisation algorithms that are used for model fitting require a good initial guess for regression parameters; (ii) the coefficient of determination (R2) is used for comparing and evaluating models, yet it is considered to be an inadequate measure of fit for nonlinear regression; and, (iii) inference is based on comparison of the confidence intervals for the regression parameters that are obtained under the untested assumption that the nonlinear model has a good linear approximation. In this research, we propose a transformed set of parameters with a common language interpretation that is relevant to split-belt treadmill training for both the single and double exponential models. We propose parameter bounds for the exponential models which allow the use of particle swarm optimisation for model fitting without an initial guess for the regression parameters. For model evaluation and comparison, we propose the use of residual plots and Akaike's information criterion (AIC). A method for obtaining confidence intervals that does not require the assumption of a good linear approximation is also suggested. A set of MATLAB (MathWorks, Inc., Natick, MA, USA) functions developed in order to apply these methods are also presented. Single and double exponential models are fitted to both the group-averaged and participant step length symmetry series in an experimental dataset generating new insights into split-belt treadmill training. The proposed methods may be useful for research involving analysis of gait symmetry with instrumented split-belt treadmills. Moreover, the demonstration of the suggested statistical methods on an experimental dataset may help the uptake of these methods by a wider community of researchers that are interested in timecourse of motor training.

The Effect of One Session Split-Belt Treadmill Training on Gait Adaptation in People With Parkinson's Disease and Freezing of Gait

BACKGROUND

Freezing of gait (FOG) in Parkinson's disease (PD) is associated with gait asymmetry and switching difficulty. A split-belt treadmill may potentially address those deficits.

OBJECTIVE

To investigate the immediate and retention effects of one-session split-belt treadmill training (SBT) in contrast to regular tied-belt treadmill training (TBT) on gait asymmetry and adaptation in people with PD and FOG (PD + FOG) and healthy controls (HC). Additionally, to investigate differential effects of 3 SBT protocols and compare different gait adaptation outcomes.

METHODS

PD + FOG (n = 45) and HC (n = 36) were randomized to 1 of 3 SBT groups (belt speeds' ratio 0.75:1; 0.5:1 or changing ratios) or TBT group. Participants were tested at Pre, Post, and Retention after one treadmill training session. Gait asymmetry was measured during a standardized adaptation test on the split-belt treadmill.

RESULTS

SBT proved beneficial for gait adaptation in PD + FOG and HC (P < .0001); however, HC improved more. SBT with changing ratios demonstrated significant effects on gait adaptation from Pre to Post in PD + FOG, supported by strong effect sizes (d = 1.14) and improvements being retained for 24 hours. Mean step length asymmetry during initial exposure was lower in HC compared with PD + FOG (P = .035) and differentiated best between the groups.

CONCLUSIONS

PD + FOG improved gait adaptation after a single SBT session although effects were smaller than in HC. SBT with changing ratios was the most effective to ameliorate gait adaptation in PD + FOG. These promising results warrant future study on whether long-term SBT strengthens adaptation in PD + FOG and has potential to induce a better resilience to FOG. Clinical trial ID: NCT03725215.

Increased intramuscular coherence is associated with temporal gait symmetry during split-belt locomotor adaptation

When walking on a split-belt treadmill where one belt moves faster than the other, the nervous system consistently attempts to maintain symmetry between legs, quantified as deviation from double support time or step length symmetry. It is known that the cerebellum plays a critical role in locomotor adaptation. Less is known about the role of corticospinal drive in maintaining this type of proprioceptive-driven locomotor adaptation. The objective of this study was to examine the functional role of oscillatory drive in relation to changes in spatiotemporal gait parameters during split-belt walking adaptation. Eighteen healthy participants adapted and deadapted on a split-belt treadmill; 13 out of 18 participants repeated the paradigm two more times to examine the effects of reexposure. Coherence analysis was used to quantify the coupling between electromyography (EMG) from the proximal (TAprox) and distal tibialis anterior (TAdist) muscle during the swing phase of walking. EMG-EMG coherence was examined within the alpha (8–15 Hz), beta (15–30 Hz), and gamma (30–45 Hz) frequencies. Our results showed that 1) beta- and gamma-band coherence (markers of corticospinal drive) increased during early split-belt walking compared with baseline walking in the slow leg, 2) beta-band coherence decreased from early to late split-belt adaptation in the fast leg, 3) alpha-, beta-, and gamma-band coherence decreased from first to third split-belt exposure in the fast leg, and 4) there was a relationship between higher beta coherence in the slow leg TA and smaller double support asymmetry. Our results suggest that corticospinal drive may play a functional role in the temporal control of split-belt walking adaptation.

NEW & NOTEWORTHY This is the first study to examine the functional role of intramuscular coherence in relation to changes in spatiotemporal gait parameters during split-belt walking adaptation. We found that the corticospinal drive measured by intramuscular coherence in tibialis anterior changes with adaptation and that the corticospinal drive is related to temporal but not spatial parameters. This study may give insight as to the specific role of the motor cortex during gait.

Limping on split-belt treadmills implies opposite kinematic and dynamic lower limb asymmetries

Walking on a split-belt treadmill (each of the two belts running at a different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise. However, the scarcity of dynamic investigations challenges the validity of the available findings. The aim of the present study was to investigate the dynamic asymmetries of lower limbs of healthy adults during adaptation to gait on a split-belt treadmill. Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('tied' condition) or at different speeds ('split' condition, 0.4 vs. 0.8 or 0.8 vs. 1.2 m/s). The sagittal power and work provided by ankle, knee and hip joints, joint rotations, muscle lengthening, and surface electromyography were recorded simultaneously. Various tied/split walking sequences were requested. In the split condition a marked asymmetry between the parameters recorded from each of the two lower limbs, in particular from the ankle joint, was recorded. The work provided by the ankle (the main engine of body propulsion) was 4.8 and 2.2 times higher (in the 0.4 vs. 0.8, and 0.8 vs. 1.2 m/s conditions, respectively) compared with the slower side, and 1.2 and 1.1 times higher compared with the same speed in the tied condition. Compared with overground gait in hemiplegia, split gait entails an opposite spatial and dynamic asymmetry. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view. These differences challenge the proposed protocols of split gait as forms of therapeutic exercise.

Different Error Size During Locomotor Adaptation Affects Transfer to Overground Walking Poststroke

BACKGROUND

Studies in neurologically intact subjects suggest that the gradual presentation of small perturbations (errors) during learning results in better transfer of a newly learned walking pattern to overground walking. Whether the same result would be true after stroke is not known.

OBJECTIVE

To determine whether introducing gradual perturbations, during locomotor learning using a split-belt treadmill influences learning the novel walking pattern or transfer to overground walking poststroke.

METHODS

Twenty-six chronic stroke survivors participated and completed the following walking testing paradigm: baseline overground walking; baseline treadmill walking; split-belt treadmill/adaptation period (belts moving at different speeds); catch trial (belts at same speed); post overground walking. Subjects were randomly assigned to the Gradual group (gradual changes in treadmill belts speed during adaptation) or the Abrupt group (a single, large, abrupt change during adaptation). Step length asymmetry adaptation response on the treadmill and transfer of learning to overground walking was assessed.

RESULTS

Step length asymmetry during the catch trial was the same between groups ( P = .195) confirming that both groups learned a similar amount. The magnitude of transfer to overground walking was greater in the Gradual than in the Abrupt group ( P = .041).

CONCLUSIONS

The introduction of gradual perturbations (small errors), compared with abrupt (larger errors), during a locomotor adaptation task seems to improve transfer of the newly learned walking pattern to overground walking poststroke. However, given the limited magnitude of transfer, future studies should examine other factors that could impact locomotor learning and transfer poststroke.

Freezing-related perception deficits of asymmetrical walking in Parkinson's disease

Patients with Parkinson's disease (PD), and especially those with freezing of gait (FOG), are known to experience impairments in gait rhythmicity, symmetry, and bilateral coordination between both legs. In the current study, we investigated whether deficits in perception of gait speed between limbs were more pronounced in freezers than in non-freezers and could explain some of these gait impairments. We also assessed cognitive ability and proprioception. Twenty-five PD patients (13 freezers, 12 non-freezers) and 12 healthy controls walked on a split-belt treadmill, while the speed of one of the belts was gradually increased. Participants had to indicate the moment at which they perceived belt speeds to be different. The main outcome variables were the number of correct responses (perception accuracy) and the difference in belt speeds at the moment the participants perceived belt speeds to be different (perception threshold). In addition, gait characteristics during both split- and tied-belt walking were determined. Results showed significantly lower perception accuracy in freezers, whereas the perception threshold did not differ between groups. During tied-belt walking, freezers exhibited more asymmetrical step lengths and limb excursions than non-freezers and healthy controls. Greater step length and limb excursions were associated with better perception, whereas more variable gait was associated with more impaired perception. The results confirm the hypothesis that freezers have impaired perception of locomotor asymmetry. While proprioceptive and cognitive ability did not explain these findings, the possible causal link with the occurrence of FOG needs further corroboration.

Perception of Gait Asymmetry During Split-Belt Walking

Optimization of gait rehabilitation using split-belt treadmills critically depends on our understanding of the roles of somatosensory perception and sensorimotor recalibration in perceiving gait asymmetry and adapting to split-belt walking. Recent evidence justifies the hypothesis that perception of gait asymmetry is based mainly on detection of temporal mismatches between afferent inputs at the spinal level.

Perception of symmetry and asymmetry in individuals with anterior cruciate ligament reconstruction

BACKGROUND

Changes in the quantity, quality and integration of sensory information are thought to persist long after anterior cruciate ligament reconstruction and completion of physical therapy. Our purpose was to investigate the ability of individuals with anterior cruciate ligament reconstruction to perceive imposed asymmetry and symmetry while walking.

METHODS

Twenty participants with anterior cruciate ligament reconstruction and 20 controls walked on a split-belt treadmill while we assessed the ability to detect symmetry and asymmetry at fast and slow speeds. Detection scores and spatiotemporal data during asymmetric and symmetric tasks in which the belts were coupled or decoupled over time were recorded.

FINDINGS

The ability to detect symmetry and asymmetry was not altered in individuals with anterior cruciate ligament reconstruction compared to healthy young adults. The belt-speed ratio at detection also correlated to asymmetry for step length, stride length, double support time, and stance time. However, the anterior cruciate ligament reconstruction group appeared to utilize unique information to determine detection. When asked to detect symmetry at a fast speed, no asymmetry scores significantly correlated with belt-speed ratio in the anterior cruciate ligament reconstruction group. Conversely, asymmetry in stride length, step length, and stance time all significantly correlated with belt-speed ratio at detection in the control group.

INTERPRETATION

Specific sensory cues arising from the speed of the leg may also augment perception of symmetry. This strategy may be necessary in order to successfully execute the motor task, and could develop due to altered sensory information from the reconstructed knee at faster walking speeds.

Individuals Poststroke Do Not Perceive Their Spatiotemporal Gait Asymmetries as Abnormal

BACKGROUND

Following stroke, spatiotemporal gait asymmetries persist into the chronic phases, despite the neuromuscular capacity to produce symmetric walking patterns. This persistence of gait asymmetry may be due to deficits in perception, as the newly established asymmetric gait pattern is perceived as normal.

OBJECTIVE

The purpose of this study was to determine the effect of usual overground gait asymmetry on the ability to consciously and unconsciously perceive the presence of gait asymmetry in people poststroke.

DESIGN

An observational study was conducted.

METHODS

Thirty people poststroke walked overground and on a split-belt treadmill with the belts moving at different speeds (0%-70% difference) to impose varied step length and stance time asymmetries. Conscious awareness and subconscious detection of imposed gait patterns were determined for each participant, and the asymmetry magnitudes at those points were compared with overground gait.

RESULTS

For both spatial and temporal asymmetry variables, the asymmetry magnitude at the threshold of awareness was significantly greater than the asymmetry present at the threshold of detection or during overground gait. Participants appeared to identify belt speed differences using the type of gait asymmetry they typically exhibited (ie, step length or stance time asymmetries during overground gait).

LIMITATIONS

Very few individuals with severe spatiotemporal asymmetry were tested, and participants were instructed to identify asymmetric belt speeds rather than interlimb movements.

CONCLUSIONS

The data suggest that asymmetry magnitudes need to exceed usual overground levels to reach conscious awareness. Therefore, it is proposed that the spatiotemporal asymmetry that is specific to each participant may need to be augmented beyond what he or she usually has during walking in order to promote awareness of asymmetric gait patterns for long-term correction and learning.

Gait asymmetry during early split-belt walking is related to perception of belt speed difference

Gait adaptation is essential for humans to walk according to the different demands of the environment. Although locomotor adaptation has been studied in different contexts and in various patient populations, the mechanisms behind locomotor adaptation are still not fully understood. The aim of the present study was to test two opposing hypotheses about the control of split-belt walking, one based on avoidance of limping and the other on avoiding limb excursion asymmetry. We assessed how well cerebellar patients with focal lesions and healthy control participants could sense differences between belt speeds during split-belt treadmill walking and correlated this to split-belt adaptation parameters. The ability to perceive differences between belt speeds was similar between the cerebellar patients and the healthy controls. After combining all participants, we observed a significant inverse correlation between stance time symmetry and limb excursion symmetry during the early phase of split-belt walking. Participants who were better able to perceive belt speed differences (e.g., they had a lower threshold and hence were able to detect a smaller speed difference) walked with the smallest asymmetry in stance time and the largest asymmetry in limb excursion. Our data support the hypothesis that humans aim to minimize (temporal) limping rather than (spatial) limb excursion asymmetry when using their perception of belt speed differences in the early phase of adaptation to split-belt walking.

Perception of gait patterns that deviate from normal and symmetric biped locomotion

This study examines the range of gait patterns that are perceived as healthy and human-like with the goal of understanding how much asymmetry is allowable in a gait pattern before other people start to notice a gait impairment. Specifically, this study explores if certain abnormal walking patterns can be dismissed as unimpaired or not uncanny. Altering gait biomechanics is generally done in the fields of prosthetics and rehabilitation, however the perception of gait is often neglected. Although a certain gait can be functional, it may not be considered as normal by observers. On the other hand, an abnormally perceived gait may be more practical or necessary in some situations, such as limping after an injury or stroke and when wearing a prosthesis. This research will help to find the balance between the form and function of gait. Gait patterns are synthetically created using a passive dynamic walker (PDW) model that allows gait patterns to be systematically changed without the confounding influence from human sensorimotor feedback during walking. This standardized method allows the perception of specific changes in gait to be studied. The PDW model was used to produce walking patterns that showed a degree of abnormality in gait cadence, knee height, step length, and swing time created by changing the foot roll-over-shape, knee damping, knee location, and leg masses. The gait patterns were shown to participants who rated them according to separate scales of impairment and uncanniness. The results indicate that some pathological and asymmetric gait patterns are perceived as unimpaired and normal. Step time and step length asymmetries less than 5%, small knee location differences, and gait cadence changes of 25% do not result in a change in perception. The results also show that the parameters of a pathologically or uncanny perceived gait can be beneficially altered by increasing other independent parameters, in some sense masking the initial pathology.

Gait parameters affecting the perception threshold of locomotor symmetry: comment on Lauzière, et al. (2014)

In a recent work on locomotor symmetry while walking on a split-belt treadmill, Lauzière and co-workers determined the perception threshold of gait symmetry in a sample of healthy elderly. In addition, they aimed to determine which particular gait parameters affect the symmetry of the perception threshold. Although only temporal and kinetic gait parameters were measured (and no kinematics), it was suggested that stance time symmetry is an important criterion that participants use to identify the threshold. Here it is argued that several other gait parameters could qualify equally well as main criteria used to identify the threshold and that these parameters should be taken into account in future studies.