Anticipatory Postural Adjustments Research Articles

Postural adjustment in standing position when catching a ball under unpredictable conditions of the direction to be caught

BackgroundBalanced postural control of the body is associated with two mechanisms: anticipatory postural adjustment and compensatory postural adjustment. Previous studies reported changes in body postural control under unpredictable conditions (interference with closed eyes). Research questionTo ascertain whether in contrast with predictable disturbances, there is a difference in muscle activity and center of pressure displacement changes when the direction of the disturbance is unpredictable. MethodsThree examiners stood at 45° to the left, the front, and 45° to the right of the participant to throw the ball to him. 11 healthy young participants were required to maintain their balance in the standing position after receiving the ball in conditions with and without known catching directions. The anticipatory postural adjustment and compensatory postural adjustment integral changes of the muscle activity in the lower limbs and trunk bilaterally and at the center of pressure displacement in the known and unknown conditions were observed. Two-way ANOVA was used to compare the differences in muscle activity and displacement changes. ResultsResults showed that the center of pressure in the anticipatory postural adjustment and compensatory postural adjustment in the posterior direction with known catching direction was significantly shorter than those without. Integration of electromyogram in anticipatory postural adjustment of the right soleus (p = 0.023) was associated with higher muscle activities in the unknown than known conditions. Integration of electromyogram in compensatory postural adjustment of the right tibial anterior (p = 0.004), right rectus femoris (p = 0.023) and left rectus abdominis (p = 0.038) in unknown catching direction had significantly greater muscle activity than those without. When the direction of the perturbation is unpredictable, the central nervous system may initiate and induce greater center of pressure changes in the posterior direction with changes in several muscular activities to ensure postural control.

Reliability and validity of quantitative evaluation of anticipatory postural adjustments using smartphones.

[Purpose] This study aimed to investigate the reliability and validity of the quantitative evaluation of anticipatory postural adjustments using smartphones. [Participants and Methods] The study included 10 young control participants who underwent a one-legged stance with an accelerometer and a smartphone that were simultaneously attached to their lower back (L5). Acceleration was measured as the mediolateral component of the lumbar movement toward the stance side. The peak value of the time (peak latency) and the amount of displacement (peak magnitude) in the stance side direction of the lumbar acceleration were analyzed as anticipatory postural adjustment features. Intra-rater reliability was calculated for both accelerometer and smartphone measurements, while inter-rater reliability was calculated for smartphone measurements by two examiners. Validity was determined for both accelerometer and smartphone measurements. [Results] In this study, the intra-rater reliability of the peak latency and peak magnitude in accelerometer and smartphone measurements was confirmed, as was the inter-rater reliability in smartphone measurements. The intra-rater reliability was confirmed through re-testing, while the validity of the accelerometer and smartphone measurements was also confirmed. [Conclusion] The findings of this study suggest that the use of smartphones to measure anticipatory postural adjustments is highly reliable and valid, making it a useful clinical balance index. The method is simple and can be used for continuous patient monitoring.

Influência do excesso de peso sobre o equilíbrio postural e a mobilidade de candidatos à cirurgia bariátrica

Abstract Obesity is considered a risk factor to health and besides generating metabolic and cardiovascular alterations, it is related to mechanical complications. Since stability may be altered due to anthropometric and biomechanical factors, studies investigating the relationship of excess weight on the mobility and balance of obese adults are still scarce. The research aimed to evaluate the postural balance and mobility of obese individuals who are waiting for bariatric surgery. This is a cross-sectional and descriptive study, conducted at the Hospital das Clínicas of the Universidade Federal de Pernambuco. The sample consisted of 97 individuals, 81 women, 16 men, age 38.39 ± 10.60 years and body mass index 47.5 ± 6.9 kg/m2. The Timed Up and Go test, which evaluates the mobility, resulted in 7.6 ± 1.7 seconds as the average of the longest times spent to perform the test. Regarding the evaluation of dynamic balance and mobility, it was found that the domains of anticipatory postural adjustments, necessary to prevent postural disturbances (median 5, 95%CI 5-6) and the domain of dynamic movement, which corresponds to the balance necessary to walk (median 8, 95%CI 7-9) are the most impaired in the subjects with obesity. Positive correlations were found between weight and dynamic balance. The findings indicate that excess body fat interferes with dynamic balance.

External and internal focus of attention differentially modulate corticospinal excitability in anticipatory postural adjustments

Whether attentional focus modulates the corticospinal excitability of the lower limb muscles in anticipatory postural adjustments (APAs) when performing a ballistic movement of the upper limb remains unclear. The present study used transcranial magnetic stimulation (TMS) to examine the corticospinal excitability of the lower limb muscles along with the kinematic profiles during dart throwing with different attentional foci, external focus (EF) and internal focus (IF). In 13 healthy participants, TMS was applied immediately before electromyographic onset of the tibialis anterior (TA) muscle, and the motor evoked potential (MEP) was recorded in the TA and soleus (SOL) muscles. The performance accuracy was significantly higher in the EF condition than in the IF condition. In both EF and IF conditions, MEP amplitude in the TA muscle, but not the SOL muscle, was significantly higher immediately before TA muscle onset (− 100, − 50, and 0 ms) compared to the control. In particular, the MEP increment in the TA muscle before TA muscle onset (− 50 and 0 ms) was significantly larger in the EF condition than in the IF condition. Our findings provide the first evidence for the modulation of corticospinal excitability in APA by changing attentional focus.

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

ObjectiveFreezing 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. MethodsThirty 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. ResultsThe 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. ConclusionsThe neural capacity to prepare the spatial and temporal components of gait initiation remains intact in PD individuals with and without FOG. SignificanceThe 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.

Correlations between the EMG Structure of Movement Patterns and Activity of Postural Muscles in Able-Bodied and Wheelchair Fencers.

The study involved Paralympic wheelchair fencers (N = 7) in two disability categories, and able-bodied female epee fencers (N = 7), members of the polish paralympic fencing teams. The performance of postural muscles and sword arm muscles in both groups of fencers, and of the front and rear leg muscles in the able-bodied fencers, was examined using surface electromyography with an accelerometer and the OptiTrack motion analysis system, as well as ground force reaction platforms. The activation sequence of individual muscles was determined and the structure of movement patterns in able-bodied and wheelchair fencers was formulated. A statistically significant correlation was found between the complex motor reaction time and latissimus dorsi muscle activation (p = 0.039, Z = -2.062) in wheelchair fencers. High correlations between the vertical force and EMG signal values of the gastrocnemius caput laterale muscle (0.85 for p = 0.022) were found in able-bodied fencers. A heuristic analysis indicated the significance of postural muscles in the movement patterns of wheelchair and able-bodied fencers. These muscles play a crucial role in the anticipatory postural adjustment of the trunk during technical fencing actions, including attacks on the opponent's body.

The feasibility of using an auditory cue to elicit anticipatory postural adjustments for a posterior perturbation

When humans are exposed to a predictable external perturbation, they usually generate anticipatory postural adjustments (APAs), which reduce the effect of potential body disturbance. However, when an external perturbation comes from behind and as such unpredicted, no APAs are generated, which challenges postural control. The aim of this study was to examine whether humans exposed to unpredictable perturbations could generate APAs using an auditory cue. Ten young adults were exposed to external perturbations hitting their shoulders from behind with or without an auditory cue prior to the physical impact. Electromyography (EMG) activities of eight trunk and leg muscles and center-of-pressure (COP) displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results showed that young adults were able to rely on an auditory cue to generate APAs prior to external perturbations coming from behind, and they demonstrated stronger APAs with training. Moreover, they utilized co-contraction of ventral and dorsal muscles as their APA response. The outcome provides a foundation for future studies aiming at using auditory cues to facilitate the generation of APAs and improve postural control in people with impaired balance while exposed to perturbations.

Assessment of balance in people with mild traumatic brain injury using a balance systems model approach

PurposeMeasuring persistent imbalance after mTBI is challenging and may include subjective symptom-reporting as well as clinical scales. Clinical assessments for quantifying balance following mTBI have focused on sensory orientation. It is theorized that balance control goes beyond sensory orientation and also includes subdomains of anticipatory postural adjustments, reactive postural control, and dynamic gait. The Mini Balance Evaluation Systems Test (Mini-BESTest) is a validated balance test that measures balance according to these subdomains for a more comprehensive assessment. The purpose of this study was to compare Mini-BESTest total and subdomain scores after subacute mTBI with healthy controls. MethodsSymptomatic mTBI (n = 90, 20 % male, age=36.0 ± 12.0, 46.3.4 ± 22.1 days since injury) and healthy control (n = 45, 20 % male, age=35.4 ± 12.5) participants completed the Mini-BESTest for balance. Mini-BESTest between-group differences were evaluated using Wilcoxon rank-sum tests. ResultsThe mTBI group (Median[minimum,maximum]) had a significantly worse Mini-BESTest total score than the healthy controls (24[18,28] vs 27[23–28], p < 0.001). The mTBI group performed significantly worse in 3 of the 4 subdomains compared to the healthy controls: reactive postural control: 5[2–6] vs 6[3–6], p = 0.003; sensory orientation: 6[5,6] vs 6[6], p = 0.005; dynamic gait: 8[5–10] vs 9[8–10], p < 0.001. There was no significance difference between groups in the anticipatory postural adjustments domain (5[3–6] vs 5[3–6], p = 0.12). ConclusionsThe Mini-BESTest identified deficits in people with subacute mTBI in the total score and 3 out of 4 subdomains, suggesting it may be helpful to use in the clinic to identify balance subdomain deficits in the subacute mTBI population. In combination with self-reported assessments, the mini-BESTest may identify balance domain deficits in the subacute mTBI population and help guide treatment for this population.

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

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. 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. 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. 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.

Anticipatory postural adjustments in older versus young adults: a systematic review and meta-analysis

BackgroundAnticipatory postural adjustments (APAs) are a feedforward mechanism triggered in advance to a predictable perturbation, to help the individual counteract mechanical effects that the disturbance may cause. Whether or not this strategy is compromised in the elderly is not a consensus in the literature.MethodsIn this systematic review with meta-analysis, we investigated aging effects on postural control, based on anticipatory postural adjustments (APAs). We selected 11 eligible articles of the following databases: Lilacs, SciELO, PubMed, Cochrane Central, Embase, and CINAHL, involving 324 research participants, assessing their methodological quality and extracting electromyographic, posturographic, and kinematic measurements. We included studies that investigated the occurrence of APAs in healthy younger and older adults, published before 10th August 2022, in English. Studies involving participant with conditions that may affect balance or that did not report measures of onset or amplitude of electromyography (EMG), COP, or kinematics were excluded. To analyze the aggregated results from these studies, we performed the analysis based on the outcome measures (EMG, COP, or kinematic measures) used in individual studies. We calculated differences between younger and older adult groups as the mean differences between the groups and the estimated effect. Egger’s test was conducted to evaluate whether this meta-analysis had publication bias.ResultsThrough this review, older adults showed no significant difference in the velocity to perform a movement compared to the younger adults (MD 0.95, 95% CI −0.86, 2.76, I2 = 82%), but both muscle onset and center of pressure (COP) onset were significantly more delayed in older than in younger adults: erector spinae (MD −31.44, 95% CI −61.79, −1.09, I2 = 95%); rectus abdominis (RA) (MD −31.51, 95% CI −70.58, −3.57, I2 = 85%); tibialis anterior (TA) (MD −44.70, 95% CI −94.30, 4.91, I2 = 63%); soleus (SOL) (MD −37.74, 95% CI −65.43, −10.05, I2 = 91%); gastrocnemius (GAS) (MD −120.59, 95% CI −206.70, −34.49, I2 = 94%); quadriceps (Q) (MD −17.42, 95% CI −34.73, −0.12, I2 = 0%); biceps femoris (BF) (MD −117.47, 95% CI −192.55, −42.70, I2 = 97%); COP onset (MD −45.28, 95% CI −89.57, −0.98, I2 = 93%), and COP apa (COPapa) (MD 2.35, 95% CI −0.09, 4.79, I2 = 64%). These changes did not seem to be linked to the speed of movement but possibly to age-related physiological changes that indicated decreased motor control during APAs in older adults.ConclusionsOlder adults use different postural strategies that aim to increase the safety margin and stabilize the body to perform the movement, according to the requirements imposed, and this should be considered in rehabilitation protocols.Systematic review registrationPROSPERO CRD420119143198

Neurophysiological mechanisms of gait disturbance in advanced Parkinson's disease patients

AbstractThis review considers pathophysiological mechanisms of posture‐gait disturbances in Parkinson's disease (PD). Clinical studies have shown that posture‐gait disturbance attributes to the dysfunction of the whole neuraxis in addition to the musculoskeletal system. The cerebral cortex, basal ganglia (BG), cerebellum, brainstem, and spinal cord temporally and spatially integrate and coordinate multisensory feedback and efferent copies of the motor command. Therefore, the extensive repertoire of voluntary movements can be coupled with anticipatory and reactive postural adjustments to provide the framework for supporting and stabilizing the goal‐directed gait activity. Redundancies in the system allow adaptation and compensation through reward‐oriented and error‐based learning processes implemented through the BG and cerebellar pathways, respectively. However, the impairment of these systems in PD may considerably compromise the capacity to adapt and lead to maladaptive changes impairing posture‐gait control. When these impairments occur, the risk of falls can significantly increase, and interventions are required to reduce morbidity. The damage in dopamine (DA) neurons is the primary cause of PD. Insufficient DA supply in the striatum disturbs the operation of intrinsic networks in the BG. This also pathologically increases GABAergic BG output to the cerebral cortex and brainstem, resulting in functional disconnection of other structures from the BG. The disconnection makes PD patients disable to achieve habitually acquired automatized gait control. Moreover, Lewy body degeneration in most brain areas, particularly in cholinergic and other monoaminergic systems vulnerable to neurodegeneration, further disturbs posture‐gait control and alters non‐motor symptoms of PD.

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.

Gait Initiation Impairment in Patients with Parkinson’s Disease and Freezing of Gait

Freezing of gait (FOG) is a sudden episodic inability to produce effective stepping despite the intention to walk. It typically occurs during gait initiation (GI) or modulation and may lead to falls. We studied the anticipatory postural adjustments (imbalance, unloading, and stepping phase) at GI in 23 patients with Parkinson's disease (PD) and FOG (PDF), 20 patients with PD and no previous history of FOG (PDNF), and 23 healthy controls (HCs). Patients performed the task when off dopaminergic medications. The center of pressure (CoP) displacement and velocity during imbalance showed significant impairment in both PDNF and PDF, more prominent in the latter patients. Several measurements were specifically impaired in PDF patients, especially the CoP displacement along the anteroposterior axis during unloading. The pattern of segmental center of mass (SCoM) movements did not show differences between groups. The standing postural profile preceding GI did not correlate with outcome measurements. We have shown impaired motor programming at GI in Parkinsonian patients. The more prominent deterioration of unloading in PDF patients might suggest impaired processing and integration of somatosensory information subserving GI. The unaltered temporal movement sequencing of SCoM might indicate some compensatory cerebellar mechanisms triggering time-locked models of body mechanics in PD.

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.

Can the balance evaluation systems test be used to identify system-specific postural control impairments in older adults with chronic neck pain?

Older adults with chronic neck pain (CNP) demonstrate impaired postural control. The Balance Evaluation Systems Test (BESTest) is used to assess systems underlying postural control impairments, but its use in CNP has not been reported. This study assessed whether the BESTest can identify postural control impairments in CNP as well as the level of BESTest item difficulty by Rasch analysis. This cross-sectional study recruited thirty young adults (YOUNG) aged 20-40 years and eighty older adults aged 60 years or older [without neck pain (OLD) = 60, with chronic neck pain (CNP) = 20]. Questionnaires were administered to collect demographic data, intensity of neck pain (VAS), patient's self-rated neck pain and disability (NDI), and balance confidence in daily activities (ABC). The BESTest was used to assess postural control. The CNP group showed the lowest ABC scores. Compared to the YOUNG group, the BESTest score was significantly lower in the OLD group, while the CNP group showed the lowest score, suggesting that balance control deteriorated from the normal aging process and further declined in the CNP group, especially in biomechanical constraints, transitions-anticipatory postural adjustment, and reactive postural response (p < 0.05). Using scores from these three sections, the BESTest was accurate at the cutoff score of 48.5 out of 51 for differentiating the older adults whose daily life are affected by neck problems (using the NDI as a reference) with a high AUC (0.79), sensitivity (72%), and specificity (69%). The Rasch analysis revealed that the Timed Up and Go with dual task test was the most difficult BESTest item for all groups, whereas 14 items showed more difficulty for the CNP group. The BESTest can be used to identify postural control impairments in CNP patients, even those with moderate pain and mild disability with a high level of physical functioning. The combined score of biomechanical constraints, transitions-anticipatory postural adjustment, and reactive postural response domains was suggested for the detection of older adults whose daily lives are affected by neck problems. This will also help clinicians consider the management of neck pain to prevent falls in CNP.

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

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. 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. 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. 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.

Detecting differences in gait initiation between older adult fallers and non-fallers through multivariate functional principal component analysis

Gait initiation (GI) is an important locomotor transition task that includes anticipatory postural adjustments and the joint propulsion necessary for the first step of walking. Discrete variable analysis between GI of fallers and non-fallers has shown important between-group differences. More complex time series analysis, such as functional principal component analysis (FPCA) may highlight group differences not detectable using discrete comparisons alone. This study aims to characterize the differences between fallers and non-fallers by examining the kinematics and kinetics of gait initiation using multivariate FPCA (mFPCA). A sample of 56 community-dwelling older adults completed five walking trials where GI was measured by force platforms. mFPCA of center of pressure kinematics and kinetics was conducted and functional principal component scores were compared between groups. Overall mFPCA provided a comprehensive assessment of GI that supports and enhances previous findings with respect to differences between faller and non-faller cohorts. During weight transfer and forward progress, fallers demonstrate a greater range of mediolateral movement and lower lateral force than non-fallers. During the first step, fallers have a more gradual rise in vertical force, as well as a greater lateral movement toward the edge of their base of support. Fallers also demonstrate a shorter step length, indicating an altered approach to GI, where mediolateral and anteroposterior stability may be prioritized over forward advancement.

Motor inhibition parameters are reflected in the kinetic and kinematic of gait initiation in a step version of the Stop Signal Task

Interacting with a continuously changing environment may necessitate cancelling a programmed movement, such as a step, after an environmental change to avoid errors and possible falls. This cancellation is successful if it occurs during the few milliseconds from the Anticipatory Postural Adjustments (APA) that precede the step onset, a period in which the center of mass (CoM) and the center of pressure (CoP) can still be aligned. Here we studied the inhibition of steps by the means of Stop Signal Task (SST), a behavioral task matched with a theoretical model developed to study the behavioral and physiological correlates of simple response inhibition [1], e.g., pressing a button. Aim of the present work was investigating if and how the inhibition of a complex multi-effectors movement as in step, accomplishes the assumptions of the model developed for simpler movements and if it is they are reflected in the time evolution of CoM and CoP. 12 healthy subjects (age: 33.3±7.1 y; weight: 69.3±17 kg; height: 169.7±8.2 cm) were required to initiate 300 walks from a stationary position (Go trials; GT) in response to the onset of an ahead pointing arrow (Go signal) on a pc monitor, and to interrupt the movement when in 30% of the trials (Stop trials; ST), a road stop signal (Stop signal) replaced the arrow after a variable time, determined using a behavioral tracking staircase algorithm [2]. A stereo-photogrammetric motion analysis system (SMART-DX 6000: BTS) and eight dynamometer platforms (Kistler 9286B; Kistler) were used to detect the kinematic and dynamic parameters of gait initiation. Ad-hoc analysis algorithms were developed by the MATLAB software (R2019b 9.7; MathWorks) to track the time evolution of CoM and CoP trajectories and capture the related reaction times (RT) for GT, error stop trials (eST), and correct stop trials (cST), and to conduct the statistical analysis. Fig. 1 displays the CoM (left upper panels) and CoP (left lower panels) trajectories in GT, eST, and cST, and the computed corresponding RT (rightmost panels). A repeated measures ANOVA and post-hoc tests detected (p<0.001), for both CoM and CoP, a significantly slowest RTs in cST (CoM=375±53ms; CoP=277±64ms), faster RT in GT (CoM=335±62ms; CoP=253±70ms), and the even faster in RT during the eST (CoM=296±61ms; CoP=213±64ms). By tracking the time evolution of CoM and CoP in a step version of the SST we obtained, during APA, a measure of RT, not only in GT and eST trials, but even in cST, a parameter hidden in the typical experimental setup. With these variables, we detected that the outcome of our version of SST complied with the main assumption of the race model: a movement is successfully cancelled when a stop process wins the race being faster than a go process. Accordingly, here we observed the eST were the trials approaching the race with significantly faster RT than cST. These results provide evidence that our version of SST is a valid tool for studying inhibition of complex movements and the associated kinematic variables.

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.

Asymmetric Influence of Dual-Task Interference on Anticipatory Postural Adjustments in One-Leg Stance.

This study investigated the differences of anticipatory postural adjustments (APAs) in a one-leg stance (OLS) that appear according to lower-extremity dominance and dual-task interference. Thirteen young, healthy, male volunteers performed the OLS task under the following six conditions: (1) dominant leg (DL), single-task; (2) DL, dual-task, with a low level of cognitive load (DT1/2); (3) DL, dual-task, with a high level of cognitive load (DT + 1); (4) non-dominant leg (NDL), single-task; (5) NDL, DT1/2; and (6) NDL, DT + 1. In order to measure the subjects’ APA, we used the medial–lateral displacement of their centers of pressure and gravity from the force plate and the time-series data of joint angular motions, recorded using a 3D motion analysis system. In the NDL under the dual-task condition, the onset of APA was delayed and the amplitude declined, which resulted in an increase in the duration of the APA period. The number of components identified by principal component analysis differed according to the dominant foot, and the change caused by cognitive load was found only in the NDL. As the cognitive load increased, the variance of the principal component decreased. These findings show that dual-task interference asymmetrically influences APA according to limb dominance, which reorganizes the coordination strategy of joints’ angular motion.