Fear of Falling Alters Anticipatory Postural Control during Cued Gait Initiation

Neurological gait assessment

Gait disorders are a common feature of neurological disease. The gait examination is an essential part of the neurological clinical assessment, providing valuable clues to a myriad of causes. Understanding how to examine gait is not only essential for neurological diagnosis but also for treatment and prognosis. Here, we review aspects of the clinical history and examination of neurological gait to help guide gait disorder assessment. We focus particularly on how to differentiate between common gait abnormalities and highlight the characteristic features of the more prevalent neurological gait patterns such as ataxia, waddling, steppage, spastic gait, Parkinson's disease and functional gait disorders. We also offer diagnostic clues for some unusual gait presentations, such as dystonic, stiff-person and choreiform gait, along with red flags that help differentiate atypical parkinsonism from Parkinson's disease.

Effects of postural threat on the scaling of anticipatory postural adjustments in young and older adults

Introduction

The ability to scale anticipatory postural adjustments (APAs) according to the predicted size of the upcoming movement is reduced with aging. While age-related changes in central set may be one reason for this effect, an individual's emotional state might also contribute to changes in anticipatory postural control. Therefore, the purpose of this study was to determine whether an altered emotional state, as elicited through postural threat, alters the scaling of APAs during a handle pull movement in young and older adults. It was hypothesized that the presence of postural threat would lead to more homogenous APAs (i.e., less scaling of APAs) across a range of pulling forces.

Methods

Young (n = 23) and older adults (n = 16) stood on top of a force plate that was mounted to a motorized platform. From this position, participants performed a series of handle pull trials without (no threat) or with (threat) the possibility of receiving a postural perturbation in the form of an unpredictable surface translation. Handle pulls were performed at force levels between 50 and 90% of maximum force. For each trial, the magnitude and timing of the APA were quantified from center of pressure (COP) recordings as well as electromyographic (EMG) activity of the soleus and medial gastrocnemius. The scaling of APAs with respect to force exertion was then determined through regression analyses and by comparing APAs during pulls of lower versus higher force.

Results and discussion

As evidenced by their smaller slope of the regression line between various dependent measures (i.e., COP velocity, soleus EMG onset latency, and soleus EMG amplitude) and the pulled forces, older adults demonstrated less scaling of APAs than the young. However, increases in arousal, anxiety and fear of falling due to postural threat, only minimally altered the scaling of APAs. Regardless of age, the slope of the regressions for none of the measures were affected by threat while only the soleus and medial gastrocnemius EMG onsets demonstrated significant force × threat interaction effects. These results suggest that the decreased ability to scale APAs with aging is unlikely to be due to changes in emotional state.

Anticipatory postural adjustments mediate the changes in fear-related behaviors in individuals with chronic low back pain

OBJECTIVES

The role(s) of anticipatory postural adjustments (APAs) in changes in subsequent motor and postural controls in response to movement perturbations are unclear in individuals with chronic low back pain (CLBP). This study aimed to clarify the relationships among kinesiophobia, APAs, lumbar kinematic output, and postural control associated with lumbar movement in individuals with CLBP.

METHODS

CLBP participants (n=48) and healthy controls (HCs) without CLBP (n=22) performed a bend-forward task using their lumbar region on a force platform and returned upright. Each participant's lumbar movements were recorded using an electrogoniometer. We calculated the APA duration, the duration of lumbar direction changes from forward to backward, and the center of pressure (COP) position after lumbar movement tasks completion.

RESULTS

Compared with the HCs, the duration of direction changes in lumbar movement and the APA duration in CLBP participants were prolonged, and the COP position was shifted forward. The mediation analysis revealed that the duration of lumbar direction changes in the CLBP group was subjected to a significant indirect effect of APAs and a direct effect of kinesiophobia, and the COP position was subjected to a significant indirect effect of kinesiophobia through APAs.

CONCLUSIONS

APAs partially mediate the relationship between kinesiophobia and changes in lumbar motor control and mediate the relationship between kinesiophobia and postural control in response to movement perturbations. These findings expand our understanding of APAs in altered subsequent movement and postural controls due to kinesiophobia in individuals with CLBP.

Movement kinematic and postural control differences when performing a visuomotor skill in real and virtual environments

Immersive technologies, like virtual and mixed reality, pose a novel challenge for our sensorimotor systems as they deliver simulated sensory inputs that may not match those of the natural environment. These include reduced fields of view, missing or inaccurate haptic information, and distortions of 3D space; differences that may impact the control of motor actions. For instance, reach-to-grasp movements without end-point haptic feedback are characterised by slower and more exaggerated movements. A general uncertainty about sensory input may also induce a more conscious form of movement control. We tested whether a more complex skill like golf putting was also characterized by more consciously controlled movement. In a repeated-measures design, kinematics of the putter swing and postural control were compared between (i) real-world putting, (ii) VR putting, and (iii) VR putting with haptic feedback from a real ball (i.e., mixed reality). Differences in putter swing were observed both between the real world and VR, and between VR conditions with and without haptic information. Further, clear differences in postural control emerged between real and virtual putting, with both VR conditions characterised by larger postural movements, which were more regular and less complex, suggesting a more conscious form of balance control. Conversely, participants actually reported less conscious awareness of their movements in VR. These findings highlight how fundamental movement differences may exist between virtual and natural environments, which may pose challenges for transfer of learning within applications to motor rehabilitation and sport.

Impairment and characteristics of postural control sub-components in people with COPD: a scoping review

Purpose: Impairment of postural control is common in people with COPD. However, the precise characteristics of this alteration are not clearly known. The "Systems Framework for Postural Control" which define postural control sub-components, represents an interesting tool to explore this field. The main aim of this review was to identify which postural control sub-components are impaired in people with COPD and to summarise characteristics for each sub-component. A secondary aim was to precise the relation between postural control and activities of daily living (ADL).Materials and methods: A scoping review was conducted, according to the JBI methodology. Medline, Cochrane Library, Scielo, Google Scholar, OpenGrey, and HAL were searched from inception to May 2022. The search was performed in English and French.Results: Eighty-nine articles were included. There was evidence of a potential impairment for most of the postural control sub-components. Characteristics of every sub-component alteration were heterogeneous. Reduced postural control could be associated with difficulties in ADL.Conclusions: People with COPD may have impairment in a wide range of postural control sub-components. Further research is needed to clarify if a common pattern of modification exits for this alteration and to precise the link with ADL.Implications for rehabilitationImpairment of postural control is a common extra-respiratory manifestation in people with COPD and so clinicians must include it in their clinical reasoning.Numerous postural control sub-components could be altered in people with COPD, suggesting that postural control assessment must be holistic.This scoping review shows that characteristics of postural control impairment are varied and that there may be no common pattern at the COPD population level.The relationship between impaired postural control and activities of daily living remains unclear, but clinicians should be alert to potential negative interactions between these two areas.

Apathy in Parkinson’s Disease: Defining the Park Apathy Subtype

Apathy is a neurobehavioural symptom affecting Parkinson’s disease patients of all disease stages. Apathy seems to be associated with a specific underlying non-motor disease subtype and reflects dysfunction of separate neural networks with distinct neurotransmitter systems. Due to the complicated neuropsychiatric aetiology of apathy, clinical assessment of this invalidating non-motor symptom remains challenging. We aim to summarize the current findings on apathy in Parkinson’s disease and highlight knowledge gaps. We will discuss the prevalence rates across the different disease stages and suggest screening tools for clinically relevant apathetic symptoms. We will approach the fundamental knowledge on the neural networks implicated in apathy in a practical manner and formulate recommendations on patient-tailored treatment. We will discuss the Park apathy phenotype in detail, shedding light on different clinical manifestations and implications for prognosis. With this review, we strive to distil the vast available theoretical knowledge into a clinical and patient-oriented perspective.

Does visual cueing improve gait initiation in people with Parkinson's disease?

Anticipatory postural adjustments (APAs) prior to gait initiation are impaired in people with Parkinson's disease (PD), particularly in those who report Freezing of Gait (FOG). External cues can improve gait parameters in people with PD, but the effects of visual cues on gait initiation are poorly known. The study aimed to (i) assess differences, during gait initiation, between people with PD with (FOG+) and without FOG (FOG-) and healthy controls (HC), (ii) explore the effect of disease severity on gait initiation and (iii) investigate the acute effect of visual cueing on gait initiation and straight-ahead gait. Twenty FOG- and twenty FOG+, and eighteen HC participated in this study. Participants were asked to perform self-initiated gait with and without visual cues presented as transverse taped lines on the floor. Gait initiation and gait were characterized with wireless inertial measurement units. Results showed that FOG+ had smaller APAs than HC and FOG-; although no differences were detected between FOG+ and FOG- when taking into account disease severity. Significant correlations between MDS-UPDRS III scores and gait initiation/straight-ahead gait variables confirmed that differences between FOG+ and FOG- were driven by disease severity. In gait initiation, visual cues elicited different behaviors in people with and without PD. Particularly, people with PD showed smaller and longer APAs, whereas HC showed longer first step durations, compared to baseline. However, the adopted visual cues improved gait speed and stride length in all individuals. These results suggest that people with PD, despite the presence of FOG, utilize different motor strategies, compared to HC, to adapt to the new biomechanical requirements of gait initiation dictated by the visual cues.

Validity and Reliability of Smartphone App for Evaluating Postural Adjustments during Step Initiation

The evaluation of anticipatory postural adjustments (APAs) requires high-cost and complex handling systems, only available at research laboratories. New alternative methods are being developed in this field, on the other hand, to solve this issue and allow applicability in clinic, sport and hospital environments. The objective of this study was to validate an app for mobile devices to measure the APAs during gait initiation by comparing the signals obtained from cell phones using the Momentum app with measurements made by a kinematic system. The center-of-mass accelerations of a total of 20 healthy subjects were measured by the above app, which read the inertial sensors of the smartphones, and by kinematics, with a reflective marker positioned on their lumbar spine. The subjects took a step forward after hearing a command from an experimenter. The variables of the anticipatory phase, prior to the heel-off and the step phase, were measured. In the anticipatory phase, the linear correlation of all variables measured by the two measurement techniques was significant and indicated a high correlation between the devices (APAonset: r = 0.95, p < 0.0001; APAamp: r = 0.71, p = 0.003, and PEAKtime: r = 0.95, p < 0.0001). The linear correlation between the two measurement techniques for the step phase variables measured by ques was also significant (STEPinterval: r = 0.56, p = 0.008; STEPpeak1: r = 0.79, p < 0.0001; and STEPpeak2: r = 0.64, p < 0.0001). The Bland−Altman graphs indicated agreement between instruments with similar behavior as well as subjects within confidence limits and low dispersion. Thus, using the Momentum cell phone application is valid for the assessment of APAs during gait initiation compared to the gold standard instrument (kinematics), proving to be a useful, less complex, and less costly alternative for the assessment of healthy individuals.

Postural threat influences the coupling between anticipatory and compensatory postural adjustments in response to an external perturbation

Fear of falling increases conscious control of balance and postural threat warrants accurate anticipatory motor commands for keeping a safe body posture. This study examines the anticipatory (APAs) and compensatory (CPAs) postural adjustments generated in response to an external perturbation while individuals are positioned at two different altitudes (2 cm and 80 cm) from the floor level. The main result indicates that due to the perceived emotional threat, different agonist and antagonist muscles synergies (R and C-Indexes) are manifested, particularly during the anticipatory phase. The results suggest that the CNS sends central commands for anticipating postural adjustments by adopting primarily a muscle reciprocal activation instead of a muscle co-activation strategy. Interestingly, the APAs strategies were modified under different postural threats by controlling the agonist-antagonist muscles at different joints of lower extremity. For CPAs the reciprocal activation was less applied compared to muscles co-activation to unsure larger margin for compensatory adjustments as needed and re-establish the postural stability. The results indicate that when facing to a postural threat, the CNS modulates the anticipatory and compensatory phases of postural adjustments to minimize the risk of falling.