RESUMO
There has been much debate concerning whether startling sensory stimuli can activate a fast-neural pathway for movement triggering (StartReact) which is different from that of voluntary movements. Activity in sternocleidomastoid (SCM) electromyogram is suggested to indicate activation of this pathway. We evaluated whether SCM activity can accurately identify trials which may differ in their neurophysiological triggering and assessed the use of cumulative distribution functions (CDFs) of reaction time (RT) data to identify trials with the shortest RTs for analysis. Using recent data sets from the StartReact literature, we examined the relationship between RT and SCM activity. We categorised data into short/longer RT bins using CDFs and used linear mixed-effects models to compare potential conclusions that can be drawn when categorising data on the basis of RT versus on the basis of SCM activity. The capacity of SCM to predict RT is task-specific, making it an unreliable indicator of distinct neurophysiological mechanisms. Classification of trials using CDFs is capable of capturing potential task- or muscle-related differences in triggering whilst avoiding the pitfalls of the traditional SCM activity-based classification method. We conclude that SCM activity is not always evident on trials that show the early triggering of movements seen in the StartReact phenomenon. We further propose that a more comprehensive analysis of data may be achieved through the inclusion of CDF analyses. These findings have implications for future research investigating movement triggering as well as for potential therapeutic applications of StartReact.
Assuntos
Movimento , Reflexo de Sobressalto , Estimulação Acústica , Eletromiografia , Músculos do Pescoço , Tempo de ReaçãoRESUMO
When movements of individuals with stroke (iwS) are elicited by startling acoustic stimulus (SAS), reaching movements are faster, further, and directed away from the body. However, these startle-evoked movements also elicit task-inappropriate flexor activity, raising concerns that chronic exposure to startle might also induce heightened flexor activity during voluntarily elicited movement. The objective of this study is to evaluate the impact of startle exposure on voluntary movements during point-to-point reaching in individuals with moderate and severe stroke. We hypothesize that startle exposure will increase task-inappropriate activity in flexor muscles, which will be associated with worse voluntarily initiated reaching performance (e.g. decreased distance, displacement, and final accuracy). Eleven individuals with moderate-to-severe stroke (UEFM = 8-41/66 and MAS = 0-4/4) performed voluntary point-to-point reaching with 1/3 of trials elicited by an SAS. We used electromyography to measure activity in brachioradialis (BR), biceps (BIC), triceps lateral head (TRI), pectoralis (PEC), anterior deltoid (AD), and posterior deltoid (PD). Conversely to our hypothesis, exposure to startle did not increase abnormal flexion but rather antagonist activity in the elbow flexors and shoulder horizontal adductors decreased, suggesting that abnormal flexor/extensor co-contraction was reduced. This reduction of flexion led to increased reaching distance (18.2% farther), movement onset (8.6% faster), and final accuracy (16.1% more accurate) by the end of the session. This study offers the first evidence that exposure to startle in iwS does not negatively impact voluntary movement; moreover, exposure may improve volitionally activated reaching movements by decreasing abnormal flexion activity.
Assuntos
Braço , Acidente Vascular Cerebral , Adulto , Idoso , Cotovelo , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Movimento , Músculo Esquelético , Reflexo de Sobressalto , Adulto JovemRESUMO
StartReact elicits faster, larger, and more appropriate muscle activation in stroke survivors but has been only cursorily studied to date during multi-jointed reaching. Our objective was to evaluate StartReact on unrestricted, two-dimensional point-to-point reaching tasks post-stroke. Data from 23 individuals with stroke were collected during point-to-point reaching. Voluntary and StartReact trials were compared between mild, severe/moderate, and the unimpaired arm. StartReact showed an increase in probability of muscle activity, larger muscle activity amplitude, and faster muscle activity onset. Despite changes in muscle activity, metrics of movement (distance, final error, linear deviation) were not different between StartReact and Voluntary trials except in severe/moderate stroke who had larger reaching distances during StartReact. While StartReact impacted many metrics of muscle activity, the most profound effect was on the probability of muscle activity increasing 34% compared to voluntary which allowed severe/moderate subjects to increase reaching distance but did not translate to decrease in final error suggesting that the additional movement was not always directed towards the appropriate target. These results indicate that SR has the capacity to activate paralyzed muscle in severe/moderate patients, but future studies are needed to explore the possible use of SR in the rehabilitation.
Assuntos
Braço/fisiopatologia , Atividade Motora/fisiologia , Músculo Esquelético/fisiopatologia , Desempenho Psicomotor/fisiologia , Reflexo de Sobressalto/fisiologia , Reabilitação do Acidente Vascular Cerebral/instrumentação , Acidente Vascular Cerebral/fisiopatologia , Acidente Vascular Cerebral/terapia , Adulto , Idoso , Idoso de 80 Anos ou mais , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Índice de Gravidade de Doença , Reabilitação do Acidente Vascular Cerebral/métodos , Adulto JovemRESUMO
StartReact is the ability of the startle reflex to involuntarily release a planned movement in the presence of a loud acoustic stimulus resulting in muscle activity patterns and kinematics that are tightly regulated and scaled with the intended action. Previous studies demonstrated startReact's robustness during simple single-joint reaching tasks and found no difference between startReact and voluntary movements for movement kinematics and muscle activation patterns. However, startReact has not been evaluated during multi-joint reaching movements with multiple degrees of freedom. It is unclear if startReact would evoke accurate and precise multi-joint reaching movements in an unrestricted workspace. Furthermore, if tested more rigorously, multi-joint startReact movement kinematics and muscle activation patterns might not be truly equivalent despite showing no difference through traditional ANOVAs. A previous study found multi-joint startReact was possible during unrestricted elbow and shoulder movement when reaching to a forward target. Therefore, we hypothesized that startReact would evoke similar multi-joint reaching movements for movement accuracy and muscle activation patterns when compared to voluntary movements in a multi-directional workspace. Expanding upon the previous study, our study uses a larger workspace and fully evaluates movement kinematics and muscle activations patterns. Results confirmed our hypothesis and found startReact movements were readily evoked in all directions. StartReact responses presented stereotypically earlier muscle activation, but the relative timing of agonist/antagonist firing pairs between startReact and voluntary movements remained similar. Results demonstrate that startReact is robustly present and equivalent in multi-joint reaching tasks and has potential clinical use for evaluating healthy and impaired movement.
Assuntos
Potencial Evocado Motor/fisiologia , Articulações/inervação , Movimento/fisiologia , Músculo Esquelético/fisiologia , Desempenho Psicomotor/fisiologia , Reflexo de Sobressalto/fisiologia , Análise de Variância , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino , Adulto JovemRESUMO
Humans and cats respond to balance challenges, delivered via horizontal support surface perturbations, with directionally selective muscle recruitment and constrained ground reaction forces. It has been suggested that this postural strategy arises from an interaction of limb biomechanics and proprioceptive networks in the spinal cord. A critical experimental validation of this hypothesis is to test the prediction that the principal directions of muscular activation oppose the directions responding muscles exert their forces on the environment. Therefore, our objective was to quantify the endpoint forces of a diverse set of cat hindlimb muscles and compare them with the directionally sensitive muscle activation patterns generated in the intact and decerebrate cat. We hypothesized that muscles are activated based on their mechanical advantage. Our primary expectation was that the principal direction of muscle activation during postural perturbations will be directed oppositely (180°) from the muscle endpoint ground reaction force. We found that muscle activation during postural perturbations was indeed directed oppositely to the endpoint reaction forces of that muscle. These observations indicate that muscle recruitment during balance challenges is driven, at least in part, by limb architecture. This suggests that sensory sources that provide feedback about the mechanical environment of the limb are likely important to appropriate and effective responses during balance challenges. Finally, we extended the analysis to three dimensions and different stance widths, laying the groundwork for a more comprehensive study of postural regulation than was possible with measurements confined to the horizontal plane and a single stance configuration.
Assuntos
Membro Posterior/fisiologia , Músculo Esquelético/fisiologia , Postura/fisiologia , Animais , Gatos , Equilíbrio Postural/fisiologiaRESUMO
Long-latency responses elicited by postural perturbation are modulated by how a subject is instructed to respond to the perturbation, yet the neural pathways responsible for this modulation remain unclear. The goal of this study was to determine whether instruction-dependent modulation is associated with activity in brainstem pathways contributing to startle. Our hypothesis was that elbow perturbations can evoked startle, indicated by activity in the sternocleidomastoid muscle (SCM). Perturbation responses were compared to those elicited by a loud acoustic stimulus, known to elicit startle. Postural perturbations and startling acoustic stimuli both evoked SCM activity, but only when a ballistic elbow extension movement was planned. Both stimuli triggered SCM activity with the same probability. When SCM activity was present, there was an associated early onset of triceps electromyographic (EMG), as required for the planned movement. This early EMG onset occurred at a time often attributed to long-latency stretch reflexes (75-100 ms). The nature of the perturbation-triggered EMG (excitatory or inhibitory) was independent of the perturbation direction (flexion or extension) indicating that it was not a feedback response appropriate for returning the limb to its original position. The net EMG response to perturbations delivered after a movement had been planned could be explained as the sum of a stretch reflex opposing the perturbation and a startle-evoked response associated with the prepared movement. These results demonstrate that rapid perturbations can trigger early release of a planned ballistic movement, and that this release is associated with activity in the brainstem pathways contributing to startle reflexes.
Assuntos
Reflexo de Sobressalto/fisiologia , Reflexo de Estiramento/fisiologia , Estimulação Acústica , Adulto , Braço/inervação , Braço/fisiologia , Interpretação Estatística de Dados , Articulação do Cotovelo/fisiologia , Eletromiografia , Feminino , Humanos , Modelos Lineares , Masculino , Movimento/fisiologia , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Estimulação Luminosa , Desempenho Psicomotor/fisiologia , Adulto JovemRESUMO
PURPOSE: This prospective, single-blinded, parallel, stratified, randomized clinical trial via telehealth aimed to investigate the impact of Startle Adjuvant Rehabilitation Therapy (START) on aphasia, apraxia of speech (AOS), and quality of life in individuals with chronic stroke. The study hypothesized that START would have a greater effect on AOS-related measures and more severe individuals. METHOD: Forty-two participants with poststroke aphasia, AOS, or both were randomly assigned to the START or control group. Both groups received 77-dB GET READY and GO cues during a word repetition task for three 1-hr sessions on consecutive days. The START group additionally received 105-dB white noise GO cues during one third of trials. The Western Aphasia Battery-Revised, Apraxia Battery for Adults, Stroke Impact Scale, and Communication Outcomes After Stroke scale were administered at Day 1, Day 5, and 1-month follow-up. RESULTS: START improved performance on some subtests of the Western Aphasia Battery (Comprehension, Repetition, Reading) and measures of AOS (Diadochokinetic Rate, Increasing Word Length) in individuals with moderate/severe aphasia, whereas moderate/severe controls saw no changes. Individuals with mild aphasia receiving START had improved Reading, whereas mild controls saw improved Comprehension. The START group had increased mood and perceived communication recovery by Day 5, whereas controls saw no changes in quality of life. CONCLUSIONS: This study is the first to evaluate the impact of training with startling acoustic stimuli on clinical measures of aphasia and AOS. Our findings suggest START can enhance both nontrained speech production and receptive speech tasks in moderate/severe aphasia, possibly by reducing poststroke cortical inhibition. Our findings should be considered carefully, as our limitations include small effect sizes, within-group variability, and low completion rates for quality-of-life assessments and follow-up visits. Future studies should explore a mechanism of action, conduct larger and longer Phase 2 clinical trials, and evaluate long-term retention. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.24093519.
Assuntos
Afasia , Apraxias , Reabilitação do Acidente Vascular Cerebral , Acidente Vascular Cerebral , Adulto , Humanos , Método Simples-Cego , Estudos Prospectivos , Qualidade de Vida , Afasia/terapia , Distúrbios da Fala , FalaRESUMO
Intact cats and humans respond to support surface perturbations with broadly tuned, directionally sensitive muscle activation. These muscle responses are further sensitive to initial stance widths (distance between feet) and perturbation velocity. The sensory origins driving these responses are not known, and conflicting hypotheses are prevalent in the literature. We hypothesize that the direction-, stance-width-, and velocity-sensitive muscle response during support surface perturbations is driven largely by rapid autogenic proprioceptive pathways. The primary objective of this study was to obtain direct evidence for our hypothesis by establishing that muscle spindle receptors in the intact limb can provide appropriate information to drive the muscle response to whole body postural perturbations. Our second objective was to determine if spindle recordings from the intact limb generate the heightened sensitivity to small perturbations that has been reported in isolated muscle experiments. Maintenance of this heightened sensitivity would indicate that muscle spindles are highly proficient at detecting even small disturbances, suggesting they can provide efficient feedback about changing postural conditions. We performed intraaxonal recordings from muscle spindles in anesthetized cats during horizontal, hindlimb perturbations. We indeed found that muscle spindle afferents in the intact limb generate broadly tuned but directionally sensitive activation patterns. These afferents were also sensitive to initial stance widths and perturbation velocities. Finally, we found that afferents in the intact limb have heightened sensitivity to small perturbations. We conclude that muscle spindle afferents provide an array of important information about biomechanics and perturbation characteristics highlighting their potential importance in generating appropriate muscular response during a postural disturbance.
Assuntos
Anestesia , Retroalimentação Fisiológica/fisiologia , Fusos Musculares/fisiologia , Equilíbrio Postural/fisiologia , Postura/fisiologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Analgésicos/farmacologia , Animais , Fenômenos Biomecânicos , Gatos , Eletromiografia , Extremidades/inervação , Extremidades/fisiologia , Retroalimentação Fisiológica/efeitos dos fármacos , Feminino , Membro Posterior/efeitos dos fármacos , Membro Posterior/fisiologia , Ketamina/farmacologia , Fusos Musculares/efeitos dos fármacos , Orientação , Equilíbrio Postural/efeitos dos fármacos , Tempo de Reação/fisiologia , Xilazina/farmacologiaRESUMO
BACKGROUND: Ankle-foot-orthoses (AFOs) and functional electrical stimulators (FES) are commonly prescribed to treat foot-drop in individuals with stroke. Despite well-established positive impacts of AFO and FES devices on balance and gait, AFO and FES-users still fall at a high rate. OBJECTIVE: The objective of this study was to investigate 1) the underlying biomechanical mechanisms leading to a fall in long-term AFO and FES-users with chronic stroke and 2) the impacts of AFOs and FES devices on fall outcomes and compensatory stepping response of long-term users with chronic stroke. METHODS: Fall outcomes as well as kinematics and kinetics of compensatory stepping response of 42 individuals with chronic stroke (14 AFO-users, 10 FES-users, 18 Non-users) were evaluated during trip-like treadmill perturbations. AFO and FES-users were evaluated with and without their device. RESULTS: Chronic AFO and FES-users fell 2.50 and 2.77 times more than Non-users. The most robust differences between AFO/FES-users and Non-users were 1) Reduced capacity to stabilize the trunk through reduction in forward whole-body angular momentum and 2) diminished capability to prepare and generate a second step using the paretic leg. Provocatively, the removal of AFO and FES devices did not decease/increase falls or change kinematics. SIGNIFICANCE: It is well-established that AFOs/FES devices have a positive impact on static balance and decrease community falls by increasing toe clearance thus preventing trips/stumbles. However, our results suggest that once a trip occurs, these devices do not adequately assist recovery of balance. Specifically, current AFO and FES devices do not assist with second step generation or trunk control. Future studies should explore new devices or training paradigms that target enhancing trunk control and paretic compensatory stepping to decrease falls in this population.
Assuntos
Terapia por Estimulação Elétrica , Órtoses do Pé , Transtornos Neurológicos da Marcha , Reabilitação do Acidente Vascular Cerebral , Acidente Vascular Cerebral , Tornozelo , Fenômenos Biomecânicos , Marcha/fisiologia , Transtornos Neurológicos da Marcha/etiologia , Transtornos Neurológicos da Marcha/terapia , Humanos , Acidente Vascular Cerebral/complicaçõesRESUMO
PURPOSE: The StartReact effect, whereby movements are elicited by loud, startling acoustic stimuli (SAS), allows the evaluation of movements when initiated through involuntary circuitry, before auditory feedback. When StartReact is applied during poststroke upper extremity movements, individuals exhibit increased muscle recruitment, reaction times, and reaching distances. StartReact releases unimpaired speech with similar increases in muscle recruitment and reaction time. However, as poststroke communication disorders have divergent neural circuitry from upper extremity tasks, it is unclear if StartReact will enhance speech poststroke. Our objective is to determine if (a) StartReact is present in individuals with poststroke aphasia and apraxia and (b) SAS exposure enhances speech intelligibility. METHOD: We remotely delivered startling, 105-dB white noise bursts (SAS) and quiet, non-SAS cues to 15 individuals with poststroke aphasia and apraxia during repetition of six words. We evaluated average word intensity, pitch, pitch trajectories, vowel formants F1 and F2 (first and second formants), phonemic error rate, and percent incidence of each SAS versus non-SAS-elicited phoneme produced under each cue type. RESULTS: For SAS trials compared to non-SAS, speech intensity increased (∆ + 0.6 dB), speech pitch increased (∆ + 22.7 Hz), and formants (F1 and F2) changed, resulting in a smaller vowel space after SAS. SAS affected pitch trajectories for some, but not all, words. Non-SAS trials had more stops (∆ + 4.7 utterances) while SAS trials had more sustained phonemes (fricatives, glides, affricates, liquids; ∆ + 5.4 utterances). SAS trials had fewer distortion errors but no change in substitution errors or overall error rate compared to non-SAS trials. CONCLUSIONS: We show that stroke-impaired speech is susceptible to StartReact, evidenced by decreased intelligibility due to altered formants, pitch trajectories, and articulation, including increased incidence of sounds that could not be produced without SAS. Future studies should examine the impact of SAS on voluntary speech intelligibility and clinical measures of aphasia and apraxia.
Assuntos
Afasia , Apraxias , Acidente Vascular Cerebral , Acústica , Afasia/etiologia , Apraxias/etiologia , Humanos , Reflexo de Sobressalto/fisiologia , Inteligibilidade da Fala , Acidente Vascular Cerebral/complicaçõesRESUMO
Learning declines with age. Recent evidence indicates that the brainstem may play an important role in learning and motor skill acquisition. Our objective was to determine if delays in the reticular formation, measured via the startle reflex, correspond to age-related deficits in learning and retention. We hypothesized that delays in the startle reflex would be linearly correlated to learning and retention deficits in older adults. To determine if associations were unique to the reticulospinal system, we also evaluated corticospinal contributions with transcranial magnetic stimulation. Our results showed a linear relationship between startle onset latency and percent learning and retention but no relationship between active or passive motor-evoked potential onsets or peak-to-peak amplitude. These results lay the foundation for further study to evaluate if (1) the reticular formation is a subcortical facilitator of skill acquisition and (2) processing delays in the reticular formation contribute to age-related learning deficits.
Assuntos
Potencial Evocado Motor , Estimulação Magnética Transcraniana , Potencial Evocado Motor/fisiologia , Aprendizagem/fisiologia , Reflexo de Sobressalto/fisiologia , Formação Reticular/fisiologiaRESUMO
Motor skill acquisition utilizes a wide array of neural structures; however, few articles evaluate how the relative contributions of these structures shift over the course of learning. Recent evidence from rodents and songbirds suggests there is a transfer from cortical to subcortical structures following intense, repetitive training. Evidence from humans indicate that the reticulospinal system is modulated over the course of skill acquisition and may be a subcortical facilitator of learning. The objective of this study was to evaluate how reticulospinal contributions are modulated by task expertise. Reticulospinal contributions were assessed using StartReact (SR). We hypothesized that expert typists would show SR during an individuated, keystroke task but SR would be absent in novices. Expert (75.2 ± 9.8 WPM) and novice typists (41.6 ± 8.2 WPM) were evaluated during an individuated, keystroke movements. In experts, SR was present but was absent in novices. Together, these results suggest that experts use reticulospinal contributions more for movement than novices indicating that the reticular formation becomes increasingly important for movement execution in highly trained, skilled tasks even those that require individuated movement of the fingers.
Assuntos
Aprendizagem/fisiologia , Destreza Motora/fisiologia , Movimento/fisiologia , Aptidão/fisiologia , Eletromiografia , Feminino , Dedos/fisiologia , Humanos , Masculino , Músculo Esquelético/fisiologia , Adulto JovemRESUMO
Cats actively respond to horizontal perturbations of the supporting surface according to the force constraint strategy. In this strategy, the force responses fall into two groups oriented in either rostral and medial directions or caudal and lateral directions, rather than in strict opposition to the direction of perturbation. When the distance between forelimbs and hindlimbs is decreased, the responses are less constrained and directed more in line with the perturbation. We have recently shown that electromyographic responses from limb muscles of the decerebrate cat resemble those obtained in the intact animal. Our objectives here were to determine whether the decerebrate cat preparation would also exhibit the force constraint strategy and whether that strategy would exhibit the characteristic dependence on limb position on the strategy. Horizontal support surface perturbations were delivered and three-dimensional exerted forces were recorded from all four limbs. Clustered force responses were generated by all four limbs and were found to be statistically indistinguishable between animals decerebrated using two different levels of transection. The directionality of the force responses was preserved throughout successive time epochs during the perturbations. In addition, the clustering of force responses increased with distance between forelimbs and hindlimbs. These results indicate that the force constraint strategy used by terrestrial animals to maintain stability can be generated without the assistance of the cerebral cortices and without prior training. This suggests an important role for the lower brain stem and spinal cord in generating an appropriate strategy to maintain stability.
Assuntos
Estado de Descerebração , Membro Posterior , Equilíbrio Postural/fisiologia , Postura/fisiologia , Animais , Fenômenos Biomecânicos , Gatos , Eletromiografia/métodos , Músculo Esquelético/fisiologia , Orientação/fisiologia , Fatores de TempoRESUMO
Quadrupeds and bipeds respond to horizontal perturbations of the support surface with muscular responses that are broadly tuned and directionally sensitive. Since the discovery of this directional sensitivity, interest has turned toward the critical sensory systems necessary to generate these responses. We hypothesize that cutaneous feedback affects the magnitude of muscle responses to postural perturbation but has little effect on the directionality of the muscle response. We developed a modified premammillary decerebrate cat preparation to evaluate the sensory mechanisms driving this directionally sensitive muscle activation in response to support surface perturbation. This preparation allows us the flexibility to isolate the proprioceptive (cutaneous and muscle receptors) system from other sensory influences. We found that loss of cutaneous feedback leads to a significant loss in background activity causing a smaller muscular response to horizontal perturbations. However, the directional properties of the muscular responses remained intact.
Assuntos
Estado de Descerebração/patologia , Estado de Descerebração/fisiopatologia , Retroalimentação Fisiológica/fisiologia , Músculo Esquelético/fisiopatologia , Equilíbrio Postural/fisiologia , Pele/inervação , Potenciais de Ação/fisiologia , Animais , Gatos , Denervação/métodos , Eletromiografia/métodos , Modelos LinearesRESUMO
Ankle-foot-orthoses (AFOs) are commonly prescribed to treat foot drop and enhance walking in fall-prone individuals (e.g. stroke). AFOs improve static balance but AFO-users are still at high fall risk. To our knowledge, no one has studied the biomechanical effect of AFO-use on the compensatory stepping response required to avoid falling during dynamic conditions such as trip, the leading cause of falls. The objective of this study is to evaluate the impact of a semi-rigid thermoplastic AFO on the compensatory stepping response in young healthy individuals following trip-like treadmill perturbations. We found that the AFO on the stepping leg (AFO-step) decreased trunk stability (increased trunk angle and angular velocity), shortened the compensatory step length, and reduced dynamic stability (smaller COM-BOS). AFO on the support leg (AFO-support) was only marginally different from the No-AFO condition. Detrimental changes in compensatory stepping response (e.g. decreased trunk stability) were linearly correlated to diminished propulsive impulse of the step. In summary, AFO-use on the stepping leg is associated with impaired compensatory stepping response (e.g. reduced trunk stability) and decreased propulsive impulse in young adults. It is important to note that AFO-use enhances static stability and decreases the probability of a trip/stumble occurring indicating they are important for fall prevention. Still, our results suggest that AFO-use may impair the compensatory stepping response after a trip/stumble has occurred and may suggest that preserving plantarflexion function may support the compensatory stepping response. Further study of these devices and their impact on compensatory stepping response in fall-prone individuals is warranted.
Assuntos
Acidentes por Quedas/prevenção & controle , Órtoses do Pé , Aparelhos Ortopédicos/estatística & dados numéricos , Adulto , Tornozelo/fisiopatologia , Fenômenos Biomecânicos/fisiologia , Feminino , Marcha/fisiologia , Humanos , Masculino , Aparelhos Ortopédicos/normas , Equilíbrio Postural/fisiologia , Acidente Vascular Cerebral/fisiopatologia , Tronco/fisiopatologia , Caminhada/fisiologia , Adulto JovemRESUMO
BACKGROUND: Individuals with stroke are at significant risk of falling. Trip-specific training is a targeted training approach that has been shown to reduce falls in older adults and amputees by enhancing the compensatory stepping response required to prevent a fall. Still, individuals with stroke have unique deficits (e.g. spasticity) which draws into question if this type of training will be effective for this population. OBJECTIVE: Evaluate if a single session of trip-specific training can modify the compensatory stepping response (trunk movement, step length/duration, reaction time) of individuals with chronic stroke. METHODS: Sixteen individuals with unilateral chronic stroke participated in a single session of trip-specific training consisting of 15 treadmill perturbations. A falls assessment consisting of 3 perturbations was completed before and after training. Recovery step kinematics measured during the pre- and post-test were compared using a repeated measures design. Furthermore, Fallers (those who experienced at least one fall during the pre- or post-test) were compared to Non-fallers. RESULTS: Trip-specific training decreased trunk movement post perturbation. Specifically following training, Trunk flexion was 48 and 19 percent smaller on the small and medium perturbations at the end of the first compensatory step. Fallers (9 out of 16 subjects) post-training resembled Non-Fallers pre-training. Specifically, Trunk flexion at the completion of the first step during small and medium perturbations was not different between Fallers post-training and Non-Fallers pre-training. Still enthusiasm was tempered because Trunk flexion at the largest perturbation (where most falls occurred) was not changed and therefore total falls were not reduced as a result of this training. SIGNIFICANCE: Our results indicate that trip-specific training modifies the dynamic falls response immediately following trip-like treadmill perturbations. However, the incidence of falls was not reduced with a single training session. Further study of the implications and length of the observed intervention effect are warranted.
Assuntos
Acidentes por Quedas/prevenção & controle , Marcha/fisiologia , Equilíbrio Postural/fisiologia , Reabilitação do Acidente Vascular Cerebral/métodos , Acidente Vascular Cerebral/fisiopatologia , Idoso , Fenômenos Biomecânicos , Teste de Esforço , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Tronco/fisiopatologiaRESUMO
OBJECTIVE: Falls are the most common and expensive medical complication following stroke. Hypermetric reflexes have been suggested to impact post-stroke balance but no study has evaluated reflex amplitudes under real conditions of falls in this population. Our objective was to quantify the early reflexive responses during falls induced in the laboratory. METHODS: Sixteen stroke survivors were exposed to posteriorly directed treadmill perturbations that required a forward step to maintain a balance. Perturbations differed in terms of treadmill translation displacement, velocity, and acceleration. EMG amplitudes were compared between Fall/Recovery trials, as well as Fallers/Non-Fallers at two different time windows: 50-75 and 75-100â¯ms. RESULTS: Sixteen of 86 trials resulted in falls by nine subjects (Fallers). While no differences were found between 50 and 75â¯ms, EMG amplitude in the paretic rectus femoris muscle was larger between 75 and 100â¯ms during Fall trials. Further, a bilateral increase in RF activity was seen in Fallers but not Non-Fallers. Interestingly, the bilateral increase was related to perturbation intensity (larger EMG activity with larger perturbations) in Fallers, but again not in Non-Fallers. CONCLUSIONS: Heightened early recovery hip flexor activity between 75 and 100â¯ms is associated with falls and Fallers post-stroke. SIGNIFICANCE: Though requiring replication and expanded subject pools, these preliminary results reflect a possible clinically meaningful relationship between heightened reflexive responses and fall risk. Future work should evaluate the underlying mechanisms driving these heightened reflexes (e.g. stretch, startle) such that future rehabilitation techniques can address this abnormal response.
Assuntos
Acidentes por Quedas , Quadril/fisiopatologia , Músculo Esquelético/fisiologia , Equilíbrio Postural , Acidente Vascular Cerebral/fisiopatologia , Feminino , Quadril/inervação , Quadril/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Contração Muscular , Músculo Esquelético/inervação , Músculo Esquelético/fisiopatologia , ReflexoRESUMO
The ability of the classic startle reflex to evoke voluntarily prepared movement involuntarily has captured the attention of neuroscientists for its wide-ranging functional utility and potential uses in patient populations. To date, there is only one documented task resistant to the startReact phenomenon-index finger abduction. Previous reports have suggested the lack of startReact is due to different neural mechanisms driving individuated finger movement and more proximal joint control (e.g. elbow, wrist movement). However, an alternative hypothesis exists. Though not particularly difficult to execute, isolated index finger abduction is rarely performed during activities of daily living and is not a natural correlate to common individuated finger tasks. We propose that startReact can be evoked during individuated finger movements but only during tasks that are highly trained or familiar. The objective of this study was to determine the impact of a 2-week training regimen on the ability to elicit startReact. We found evidence in support of our hypothesis that following training, individuated movements of the hands (specifically index finger abduction) become susceptible to startReact. This is significant not only because it indicates that individuated finger movements are in fact amenable to startReact, but also that startle has differential response characteristics in novel tasks compared to highly trained tasks suggesting that startle is a measurable behavioral indicator of motor learning.
Assuntos
Aprendizagem , Atividade Motora/fisiologia , Reflexo de Sobressalto/fisiologia , Feminino , Dedos/fisiologia , Humanos , Masculino , Adulto JovemRESUMO
Falls are the most common and expensive medical complication in stroke survivors. There is remarkably little information about what factors lead to a fall in stroke survivors. With few exceptions, the falls literature in stroke has focused on relating metrics of static balance and impairment to fall outcomes in the acute care setting or in community. While informative, these studies provide little information about what specific impairments in a stroke-survivor's response to dynamic balance challenges lead to a fall. We identified the key kinematic characteristics of stroke survivors' stepping responses following a balance disturbance that are associated with a fall following dynamic balance challenges. Stroke survivors were exposed to posteriorly-directed translations of a treadmill belt that elicited a stepping response. Kinematics were compared between successful and failed recovery attempts (i.e. a fall). We found that the ability to arrest and reverse trunk flexion and the ability to perform an appropriate initial compensatory step were the most critical response contributors to a successful recovery. We also identified 2 compensatory strategies utilized by stroke survivors to avoid a fall. Despite significant post-stroke functional impairments, the biomechanical causes of trip-related falls by stroke survivors appear to be similar to those of unimpaired older adults and lower extremity amputees. However, compensatory strategies (pivot, hopping) were observed.
Assuntos
Acidentes por Quedas , Laboratórios , Equilíbrio Postural , Acidente Vascular Cerebral/fisiopatologia , Fenômenos Biomecânicos , Teste de Esforço , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Movimento , Equilíbrio Postural/fisiologia , Amplitude de Movimento Articular , Sobreviventes , Tronco/fisiopatologiaRESUMO
Little attention has been given to how age affects the neural processing of movement within the brainstem. Since the brainstem plays a critical role in motor control throughout the whole body, having a clear understanding of deficits in brainstem function could provide important insights into movement deficits in older adults. A unique property of the startle reflex is its ability to involuntarily elicit planned movements, a phenomenon referred to as startReact. The noninvasive startReact response has previously been used to probe both brainstem utilization and motor planning. Our objective was to evaluate deficits in startReact hand extension movements in older adults. We hypothesized that startReact hand extension will be intact but delayed. Electromyography was recorded from the sternocleidomastoid (SCM) muscle to detect startle and the extensor digitorum communis (EDC) to quantify movement onset in both young (24 ± 1) and older adults (70 ± 11). Subjects were exposed to a startling loud sound when prepared to extend their hand. Trials were split into those where a startle did (SCM+) and did not (SCM-) occur. We found that startReact was intact but delayed in older adults. SCM+ onset latencies were faster than SCM- trials in both the populations, however, SCM+ onset latencies were slower in older adults compared to young (Δ = 8 msec). We conclude that the observed age-related delay in the startReact response most likely arises from central processing delays within the brainstem.