A coactivation strategy in anticipatory postural adjustments during voluntary unilateral arm movement while standing in individuals with bilateral spastic cerebral palsy.

Individuals with bilateral spastic cerebral palsy (BSCP) reportedly has problems with anticipatory postural adjustments (APAs) while standing. However, the use of coactivation strategy in APAs in individuals with BSCP has conflicting evidence. Hence, this study aimed to investigate postural muscle activities in BSCP during unilateral arm flexion task in which postural perturbations occur in the sagittal, frontal, and horizontal planes. We included 10 individuals with BSCP with level II on the Gross Motor Function Classification System (BSCP group) and 10 individuals without disability (control group). The participants stood on a force platform and rapidly flexed a shoulder from 0° to 90° at their own timing. Surface electromyograms were recorded from the rectus femoris, medial hamstring, tibialis anterior, and medial gastrocnemius. The control group showed a mixture of anticipatory activation and inhibition of postural muscles, whereas the BSCP group predominantly exhibited anticipatory activation with slight anticipatory inhibition. Compared with the control group, the BSCP group tended to activate the ipsilateral and contralateral postural muscles and the agonist-antagonist muscle pairs. The BSCP group had a larger disturbance in postural equilibrium, quantified by the peak displacement of center of pressure during the unilateral arm flexion, than those without disability. Individuals with BSCP may use coactivation strategy, mainly the anticipatory activation of postural muscle activity, during a task that requires a selective postural muscle activity to maintain stable posture.

I-BaR: integrated balance rehabilitation framework.

Neurological diseases are observed in approximately 1 billion people worldwide. A further increase is foreseen at the global level as a result of population growth and aging. Individuals with neurological disorders often experience cognitive, motor, sensory, and lower extremity dysfunctions. Thus, the possibility of falling and balance problems arise due to the postural control deficiencies that occur as a result of the deterioration in the integration of multi-sensory information. We propose a novel rehabilitation framework, Integrated Balance Rehabilitation (I-BaR), to improve the effectiveness of the rehabilitation with objective assessment, individualized therapy, convenience with different disability levels and adoption of assist-as-needed paradigm and, with integrated rehabilitation process as whole, that is, ankle-foot preparation, balance, and stepping phases, respectively. Integrated Balance Rehabilitation allows patients to improve their balance ability by providing multi-modal feedback: visual via utilization of virtual reality; vestibular via anteroposterior and mediolateral perturbations with the robotic platform; proprioceptive via haptic feedback.

The effects of combined transcranial brain stimulation and a 4-week visuomotor stepping training on voluntary step initiation in persons with chronic stroke-a pilot study.

Purpose: Evidence suggests that transcranial direct current stimulation (tDCS) can enhance motor performance and learning of hand tasks in persons with chronic stroke (PCS). However, the effects of tDCS on the locomotor tasks in PCS are unclear. This pilot study aimed to: (1) determine aggregate effects of anodal tDCS combined with step training on improvements of the neural and biomechanical attributes of stepping initiation in a small cohort of persons with chronic stroke (PCS) over a 4-week training program; and (2) assess the feasibility and efficacy of this novel approach for improving voluntary stepping initiation in PCS. Methods: A total of 10 PCS were randomly assigned to one of two training groups, consisting of either 12 sessions of VST paired with a-tDCS (n = 6) or sham tDCS (s-tDCS, n = 4) over 4 weeks, with step initiation (SI) tests at pre-training, post-training, 1-week and 1-month follow-ups. Primary outcomes were: baseline vertical ground reaction force (B-vGRF), response time (RT) to initiate anticipatory postural adjustment (APA), and the retention of B-VGRF and RT. Results: a-tDCS paired with a 4-week VST program results in a significant increase in paretic weight loading at 1-week follow up. Furthermore, a-tDCS in combination with VST led to significantly greater retention of paretic BWB compared with the sham group at 1 week post-training. Clinical implications: The preliminary findings suggest a 4-week VST results in improved paretic limb weight bearing (WB) during SI in PCS. Furthermore, VST combined with a-tDCS may lead to better retention of gait improvements (NCT04437251) (https://classic.clinicaltrials.gov/ct2/show/NCT04437251).

Mesencephalic Locomotor Region and Presynaptic Inhibition during Anticipatory Postural Adjustments in People with Parkinson's Disease.

Individuals with Parkinson's disease (PD) and freezing of gait (FOG) have a loss of presynaptic inhibition (PSI) during anticipatory postural adjustments (APAs) for step initiation. The mesencephalic locomotor region (MLR) has connections to the reticulospinal tract that mediates inhibitory interneurons responsible for modulating PSI and APAs. Here, we hypothesized that MLR activity during step initiation would explain the loss of PSI during APAs for step initiation in FOG (freezers). Freezers (n = 34) were assessed in the ON-medication state. We assessed the beta of blood oxygenation level-dependent signal change of areas known to initiate and pace gait (e.g., MLR) during a functional magnetic resonance imaging protocol of an APA task. In addition, we assessed the PSI of the soleus muscle during APA for step initiation, and clinical (e.g., disease duration) and behavioral (e.g., FOG severity and APA amplitude for step initiation) variables. A linear multiple regression model showed that MLR activity (R2 = 0.32, p = 0.0006) and APA amplitude (R2 = 0.13, p = 0.0097) explained together 45% of the loss of PSI during step initiation in freezers. Decreased MLR activity during a simulated APA task is related to a higher loss of PSI during APA for step initiation. Deficits in central and spinal inhibitions during APA may be related to FOG pathophysiology.

Corticomotor Control of Lumbar Erector Spinae in Postural and Voluntary Tasks: The Influence of Transcranial Magnetic Stimulation Current Direction.

Lumbar erector spinae (LES) contribute to spine postural and voluntary control. Transcranial magnetic stimulation (TMS) preferentially depolarizes different neural circuits depending on the direction of electrical currents evoked in the brain. Posteroanterior current (PA-TMS) and anteroposterior (AP-TMS) current would, respectively, depolarize neurons in the primary motor cortex (M1) and the premotor cortex. These regions may contribute differently to LES control. This study examined whether responses evoked by PA- and AP-TMS are different during the preparation and execution of LES voluntary and postural tasks. Participants performed a reaction time task. A Warning signal indicated to prepare to flex shoulders (postural; n = 15) or to tilt the pelvis (voluntary; n = 13) at the Go signal. Single- and paired-pulse TMS (short-interval intracortical inhibition-SICI) were applied using PA- and AP-TMS before the Warning signal (baseline), between the Warning and Go signals (preparation), or 30 ms before the LES onset (execution). Changes from baseline during preparation and execution were calculated in AP/PA-TMS. In the postural task, MEP amplitude was higher during the execution than that during preparation independently of the current direction (p = 0.0002). In the voluntary task, AP-MEP amplitude was higher during execution than that during preparation (p = 0.016). More PA inhibition (SICI) was observed in execution than that in preparation (p = 0.028). Different neural circuits are preferentially involved in the two motor tasks assessed, as suggested by different patterns of change in execution of the voluntary task (AP-TMS, increase; PA-TMS, no change). Considering that PA-TMS preferentially depolarize neurons in M1, it questions their importance in LES voluntary control.

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.

Gait control by the frontal lobe.

The frontal lobe is crucial and contributes to controlling truncal motion, postural responses, and maintaining equilibrium and locomotion. The rich repertoire of frontal gait disorders gives some indication of this complexity. For human walking, it is necessary to simultaneously achieve at least two tasks, such as maintaining a bipedal upright posture and locomotion. Particularly, postural control plays an extremely significant role in enabling the subject to maintain stable gait behaviors to adapt to the environment. To achieve these requirements, the frontal cortex (1) uses cognitive information from the parietal, temporal, and occipital cortices, (2) creates plans and programs of gait behaviors, and (3) acts on the brainstem and spinal cord, where the core posture-gait mechanisms exist. Moreover, the frontal cortex enables one to achieve a variety of gait patterns in response to environmental changes by switching gait patterns from automatic routine to intentionally controlled and learning the new paradigms of gait strategy via networks with the basal ganglia, cerebellum, and limbic structures. This chapter discusses the role of each area of the frontal cortex in behavioral control and attempts to explain how frontal lobe controls walking with special reference to postural control.

Comparative Study of Anticipatory Postural Adjustments between Normal and Cervical Myelopathy Patients.

Patients with cervical spondylotic myelopathy or ossification of the posterior longitudinal ligament have been considered to be prone to falls due to lower extremity dysfunction and gait instability. Anticipatory postural adjustments (APAs) are unconscious muscular activities to counterbalance perturbation. To date, there are no reports on APAs in cervical myelopathy patients, and quantification of postural control remains difficult. Thirty participants were enrolled, of which 15 were cervical myelopathy patients and 15 were normal age- and sex-matched controls. A three-dimensional motion capture system with force plates was used, and the APA phase was defined as the time between start of movement at the center of pressure and heel-off of the step leg. The APA phase (0.47 vs. 0.39 s, p < 0.05) and turning time (2.27 vs. 1.83 s, p < 0.01) were significantly longer, whereas step length tended to be shorter (305.18 vs. 361.04 mm, p = 0.06) in cervical myelopathy patients. There was a significant correlation between Japanese Orthopaedic Association lower extremity motor dysfunction scores and step length (p < 0.01). Cervical myelopathy patients are prone to falls due to longer APA phases with shorter step lengths. Analysis of the APA phase aids the visualization and quantification of postural control during initial gait in cervical myelopathy patients.

A cross sectional study investigating dynamic balance when stepping to targets in children with cerebral palsy compared to typically developing children.

BACKGROUND: Children with Cerebral Palsy (CP) have altered anticipatory postural adjustments (APAs) during gait initiation. These APAs may affect dynamic balance in tasks such as stepping. RESEARCH QUESTIONS: How are APAs in children with CP affected during stepping to precise targets? How do children with CP modulate APAs when stepping to medial and lateral targets? What is the association between APAs and symptom severity, movement quality and impairment profile? METHOD: Children undertook a stepping task to laterally and medially placed targets with either leg, in a randomised order. Movement of the centre of pressure (COP) and markers at the pelvis and foot were measured via a force plate and 3D motion analysis. Motion of the centre of mass (COM) was estimated via pelvic markers. APAs were assessed prior to leading leg lift-off in medio-lateral and antero-posterior directions. Stepping error was calculated. Baseline characteristics of children with CP included Gross Motor Function Measure (GMFM), Quality Function Measure (QFM), leg muscle hypertonia (Tardieu test) and strength (manual dynamometry). RESULTS: Sixteen ambulant children with CP (12.2 years ± 2.2) and 14 typically developing (TD) children (11.6 years ± 2.9) were assessed. In children with CP, APAs in the medio-lateral direction were 20-30% smaller. Children with CP were less able to modulate their APAs with steps to medial and laterally placed targets, than TD children. Medio-lateral COP motion was associated with movement quality assessed by QFM subsections, GMFM (correlation coefficient r = 0.66-0.80) and hip abductor strength (r = 0.75). Antero-posterior APAs were significantly smaller when stepping with the non-paretic leg in children with CP. APA size was positively related to the length of the contralateral, paretic gastrocnemius (r = 0.77). Stepping error was higher in children with CP and inversely correlated to the size of the medio-lateral APA. DISCUSSION: Children with CP show smaller medio-lateral APAs especially when stepping to medially placed targets. APA size may be limited by proximal muscle strength and gastrocnemius length.

Startle-induced rapid release of a gait initiation sequence in Parkinson's disease with freezing of gait.

OBJECTIVE: Freezing of gait (FOG) in Parkinson's disease (PD) is characterized by the inability to initiate stepping, despite the intention to do so. This study used a startling acoustic stimulus paradigm to examine if the capacity to select, prepare and initiate gait under simple and choice reaction time conditions are impaired in people with PD and FOG. METHODS: Thirty individuals (10 PD with FOG, 10 PD without FOG, and 10 controls) performed an instructed-delay gait initiation task under simple and choice reaction time conditions. In a subset of trials, a startle stimulus (124 dB) was presented 500 ms before the time of the imperative go-cue. Anticipatory postural adjustments preceding and accompanying gait initiation were quantified. RESULTS: The presentation of a startling acoustic stimulus resulted in the rapid initiation of an anticipatory postural adjustment sequence during both the simple and choice reaction time tasks in all groups. CONCLUSIONS: The neural capacity to prepare the spatial and temporal components of gait initiation remains intact in PD individuals with and without FOG. SIGNIFICANCE: The retained capacity to prepare anticipatory postural adjustments in advance may explain why external sensory cues are effective in the facilitation of gait initiation in people with PD with FOG.

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.

Accuracy and effort costs together lead to temporal asynchrony of multiple motor commands.

The timing of motor commands is critical for task performance. A well-known example is rapidly raising the arm while standing upright. Here, reaction forces from the arm movement to the body are countered by leg and trunk muscle activity starting before any sensory feedback from the perturbation and often before the onset of arm muscle activity. Despite decades of research on the patterns, modifiability, and neural basis of these "anticipatory postural adjustments," it remains unclear why asynchronous motor commands occur. Simple accuracy considerations appear unlikely since temporally advanced motor commands displace the body from its initial position. Effort is a credible and overlooked factor that has successfully explained coordination patterns of many behaviors including gait and reaching. We provide the first use of optimal control to address this question. Feedforward commands were applied to a body mass mechanically linked to a rapidly moving limb mass. We determined the feedforward actions with the lowest cost according to an explicit criterion, accuracy alone versus accuracy + effort. Accuracy costs alone led to synchronous activation of the body and limb controllers. Adding effort to the cost resulted in body commands preceding limb commands. This sequence takes advantage of the body's momentum in one direction to counter the limb's reaction force in the opposite direction, allowing a lower peak command and lower integral. With a combined accuracy + effort cost, temporal advancement was further impacted by various task goals and plant dynamics, replicating previous findings and suggesting further studies using optimal control principles.NEW & NOTEWORTHY An important goal in the fields of sensorimotor neuroscience and biomechanics is to explain the timing of different muscles during behavior. Here, we propose that energy and accuracy considerations underlie the asynchronous onset of postural and arm muscles during rapid movement. Our novel model-based framework replicates a broad range of observations across varying task demands and plant dynamics and offers a new perspective to study motor timing.

Freezing of gait, gait initiation, and gait automaticity share a similar neural substrate in Parkinson's disease.

Individuals with Parkinson's disease (PD) and freezing of gait (FOG) have difficulty initiating and maintaining a healthy gait pattern; however, the relationship among FOG severity, gait initiation, and gait automaticity, in addition to the neural substrate of this relationship has not been investigated. This study investigated the association among FOG severity during turning (FOG-ratio), gait initiation (anticipatory postural adjustment [APA]), and gait automaticity (dual-task cost [DTC]), and the neural substrates of these associations. Thirty-four individuals with FOG of PD were assessed in the ON-medication state. FOG-ratio during a turning test, gait automaticity using DTC on stride length and gait speed, and APA during an event-related functional magnetic resonance imaging protocol to assess brain activity from the regions of interest (e.g., dorsolateral prefrontal cortex [DLPFC] and mesencephalic locomotor region [MLR]) were assessed in separated days. Results showed that FOG-ratio, APA amplitude, and DTC on stride length are negatively associated among them (P < 0.05). APA amplitude and DTC on stride length explained 59% of the FOG-ratio variance (P < 0.05). Although the activity of the right DLPFC and right MLR explained 55% of the FOG-ratio variance (P < 0.05) and 30% of the DTC on stride length variance (P ≤ 0.05), only the activity of the right MLR explained 23% of the APA amplitude (P < 0.05). FOG severity during turning, APA amplitude, and stride length automaticity are associated among them and share a similar locomotor substrate, as the MLR activity was a common brain region in explaining the variance of these variables.

Postural Adjustments in HTLV-1 Infected Patients during a Self-Initiated Perturbation.

BACKGROUND: Human T-cell lymphotropic virus type 1 (HTLV-1) infection can be associated with tropical spastic paraparesis (TSP/HAM), which causes neurological myelopathy and sensory and muscle tone alterations, leading to gait and balance impairments. Once trunk perturbation is predicted, the motor control system uses anticipatory and compensatory mechanisms to maintain balance by recruiting postural muscles and displacement of the body's center of mass. METHODS: Twenty-six participants (control or infected) had lower limb muscle onset and center of pressure (COP) displacements assessed prior to perturbation and throughout the entire movement. RESULTS: Semitendinosus (ST) showed delayed onset in the infected group compared to the control group. The percentage of trials with detectable anticipatory postural adjustment was also lower in infected groups in the tibialis anterior and ST. In addition, COP displacement in the infected group was delayed, had a smaller amplitude, and took longer to reach the maximum displacement. CONCLUSIONS: HTLV-1 infected patients have less efficient anticipatory adjustments and greater difficulty recovering their postural control during the compensatory phase. Clinical assessment of this population should consider postural stability during rehabilitation programs.

An increase in relative contribution of compensatory postural adjustments during voluntary movement while standing in adolescents and young adults with bilateral spastic cerebral palsy.

Previous studies have revealed several deficits in anticipatory postural adjustments (APAs) during voluntary movements while standing in individuals with bilateral spastic cerebral palsy (BSCP). However, it remains unclear whether compensatory postural adjustments (CPAs) during movement increase to compensate for APA deficits. We investigated the anticipatory and compensatory activities of postural muscles during voluntary movement while standing in adolescents and young adults with BSCP. The study included seven participants with BSCP with level II on the Gross Motor Function Classification System (GMFCS), seven with BSCP with level III on the GMFCS, and fourteen healthy controls. The participants stood on a force platform and lifted a load under two weight conditions (light and heavy). The electromyographic activities of postural muscles were analyzed at time intervals typical for APAs and CPAs. The percentage of muscle activity in the CPA time epoch against the total muscle activity during the APA and CPA time epochs was higher in the two BSCP groups than in the control group. In the control group, a load-related modulation was observed only in the APA time epoch, whereas in the BSCP-II group, the load-related increase was observed in both the APA and CPA time epochs. No load-related modulations were observed in the BSCP-III group. These findings suggest that adolescents and young adults with BSCP exhibit an increase in the relative contribution of CPAs during voluntary movement and that there exist severity-related differences in the modulation of APAs and CPAs.

Aquatic Therapy after Incomplete Spinal Cord Injury: Gait Initiation Analysis Using Inertial Sensors.

Populations with potential damage to somatosensory, vestibular, and visual systems or poor motor control are often studied during gait initiation. Aquatic activity has shown to benefit the functional capacity of incomplete spinal cord injury (iSCI) patients. The present study aimed to evaluate gait initiation in iSCI patients using an easy-to-use protocol employing four wearable inertial sensors. Temporal and acceleration-based anticipatory postural adjustment measures were computed and compared between dry-land and water immersion conditions in 10 iSCI patients. In the aquatic condition, an increased first step duration (median value of 1.44 s vs. 0.70 s in dry-land conditions) and decreased root mean squared accelerations for the upper trunk (0.39 m/s2 vs. 0.72 m/s2 in dry-land conditions) and lower trunk (0.41 m/s2 vs. 0.85 m/s2 in dry-land conditions) were found in the medio-lateral and antero-posterior direction, respectively. The estimation of these parameters, routinely during a therapy session, can provide important information regarding different control strategies adopted in different environments.

Simulated practice effects on the transfer and retention of gait sequences from the upper to the lower extremity.

This study investigated transfer of training from upper extremity limbs (the index fingers) to the lower extremity limbs (the legs) for performance of three gait sequences of different difficulty. Fifteen subjects participated in the study. Subjects in an iPad training group practiced by sequentially moving their left-and right-hand index fingers across tiles to each of three targets displayed on an iPad for 20 trials. Subjects in a gait training group practiced by sequentially walking across tiles to each of the 3 targets displayed on a screen for 20 trials. A no practice group did not receive practice trials. Immediately following practice of each level of difficulty, a transfer test (20 trials) was given for which subjects walked to the target just practiced. A retention test of 36 trials (12 trials at each difficulty level) was administered 20 min following performance of the last transfer test trial. The retention test showed that reaction times were shorter for the iPad training than gait training and no training groups; anticipatory postural adjustment times were equivalent for the iPad and gait training groups, but shorter than for the no training group; and movement times were shorter for the iPad training group than for the gait training and no training groups. These results suggest that iPad training (upper extremity) followed by performance of gait training (lower extremity) had greater benefits for learning (as measured by the delayed retention test) the gait sequences than practicing the actual gait sequences themselves.

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.

Weighting for the Beat: Using a Dance Cue to Facilitate Turning in People with Parkinson's Disease and Freezing of Gait.

Freezing of gait (FOG) can severely compromise daily functioning in people with Parkinson's disease. Inability to initiate a step from FOG is likely underpinned, at least in part, by a deficient preparatory weight-shift. Conscious attempts to weight-shift in preparation to step can improve success of initiating forward steps following FOG. However, FOG often occurs during turning, where weight-shifting is more complex and risk of falling is higher. We explored the effectiveness of a dance-based ('cha-cha') weight-shifting strategy to re-initiate stepping following FOG during turning. Results suggest that this simple movement strategy can enhance turning steps following FOG, without compromising safety.

Vibratory cue training elicits anticipatory postural responses to an external perturbation.

Anticipatory postural adjustments (APAs) represent the feedforward mechanism of neuromuscular control essential for maintaining balance under predictable perturbations. The importance of vision as a distal sensory modality in the generation of APAs is well established. However, the capabilities of external cues in generating APAs are less explored. In the present study, vibratory cue was investigated for its reliability among healthy individuals in generating anticipatory response under external perturbation in the absence of vision. Ten participants, in quiet stance, were provided with external perturbation in the form of pendulum impact in anterior-posterior (AP) direction under conditions of: both vision and vibratory cue absent; vision present but vibratory cue was absent; vision and vibratory cue both were present; only vibratory cue is present with vision being absent. EMG activities of the leg muscles and displacement of center of pressure (COP) in AP direction were recorded. The data were later analyzed and quantified in the time frame of anticipatory and compensatory phases. The results showed that with training, participants were able to generate significant APAs relying on the vibratory cue alone. Improvement in APAs was accompanied by minimizing the need for larger CPA and improved stability (COP displacement) under perturbation. The study outcome indicates the possibility of using vibratory cues for APA-based interventions.