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Rectified EMG level comparisons between groups for levels of activity for the main agonist (TA; a) and antagonist (soleus; b) during posterior perturbations. Note that raw-rectified EMG levels have been log-transformed. The prolonged contraction of TA in Group 1 PD patients was probably a consequence of their inability to compensate for the applied perturbation
Source publication
We studied 12 patients with Parkinson’s disease (PD): 6 with postural instability (Hoehn and Yahr Stage 3) and 6 without (Stage 2 or 2.5), using a quantitative test based on the clinical pull test. Their findings were compared with those for 12 healthy controls. The patients on their usual medications were pulled either forwards or backwards at the...
Citations
... Backward pulls have been applied at the shoulders [7,8] similar to the clinical pull-test, but also at the chest [6,9] and waist [10]. The response to the pull-test has been quantified using force plates [7,[9][10][11], EMG [7,10,11], electromagnetic sensors [8], and video capture equipment [10]. Most of these studies had participants wear a harness for safety [6][7][8][9][10] which could affect participant response on the test. ...
... Backward pulls have been applied at the shoulders [7,8] similar to the clinical pull-test, but also at the chest [6,9] and waist [10]. The response to the pull-test has been quantified using force plates [7,[9][10][11], EMG [7,10,11], electromagnetic sensors [8], and video capture equipment [10]. Most of these studies had participants wear a harness for safety [6][7][8][9][10] which could affect participant response on the test. ...
Background:
Postural instability can occur in the later-stages of Parkinson's disease (PD). The clinical pull-test is scored on a 0-4 scale on the Unified Parkinson's disease rating scale (UPDRS), with postural instability scored 2 or higher. This ordinal scale does not adequately track progression in early-PD or predict development of postural instability.
Research question:
To develop a test that quantifiably measured the backward stepping response on the pull-test in early-PD.
Methods:
Participants (35 controls and 79 PD participants) were prospectively enrolled in this study. Participants stepped backwards with each shoulder pull at four strengths on an instrumented gait mat. Four spatiotemporal parameters (reaction-time, step-back-time, step-back-distance, step-back-velocity) were quantified using Protokinetics Movement Analysis Software. Spatiotemporal pull-test parameters were compared to standard PD measures using linear regression and correlation coefficients. Repeated measures analysis was used to determine group differences in pull-test parameters. In a subset of participants repeated testing was performed and Bland-Altman plots were used to determine reproducibility of the pull-test parameters.
Result:
Step-back-distance and step-back-velocity were inversely related to motor UPDRS and freezing of gait questionnaire scores. PD participants had shorter step-back-distance than controls adjusted for age and sex. Repeat assessments in 16 participants, on average 0.7 years apart, showed good agreement on most of the quantified parameters.
Significance:
The backward stepping response in PD participants was quantifiable, reproducible, and related to disease severity and could be used to quantify progression towards postural instability in early-PD.
... This may be attributed to a combination of the large inertial properties of the trunk, and neurodegeneration in PD leading to pathological mechanisms producing rigidity (e.g., axial hypertonicity- Wright et al. 2007) and alterations in brainstem-mediated postural control (Craig et al. 2020). Critically, deficits in static and dynamic balance are thought to be directly linked to reduced trunk mobility (Cano-de-la-Cuerda et al. 2017Colebatch and Govender 2019;Di Giulio et al. 2016;Horak et al. 2005;Phan et al. 2018;Khobkhun et al. 2020;Wright et al. 2007). The influence of trunk motion on postural control as an independent measure has been used diagnostically as an objective biomarker for classifying pre-clinical stages in PD progression (Mancini et al. 2012) and for predicting fall risk (Kerr et al. 2010). ...
Trunk control and postural instability remain critical markers of functional status in Parkinson’s Disease (PD). As pharmacological and invasive neuro-stimulation interventions provide only limited benefits for trunk and postural control, exercise-based interventions may provide the only effective path to improving functional outcomes for balance in PD. We describe the framework for a virtual reality (VR) graded exercise-based intervention focused on improving trunk mobility and control, including preliminary outcomes on perceptions and motion capabilities of individuals with PD. The study collected whole-body motion capture from 11 PD participants (8M, 3F; H&Y Stage I–III) as they performed tasks within a custom-designed set of VR therapies. Therapies involved static interactions (e.g., matching a cube sequence set to anthropometrically relevant locations to elicit specific trunk motions—Matchality), and more dynamic tasks (e.g., intercepting virtual fish jumping from a lake—Fishality, or a virtual session of dodgeball—Dodgeality). Participants were able to safely complete all tasks while performing trunk excursions requiring functionally relevant ranges of motion, and which altered across VR environment (F(1,10) = 8.319, p = 0.016). Overall, satisfaction with the MoVR therapy suite was high with 96% of responses showing agreement to questions relating to ‘immersion,’ ‘fun,’ and elements of player engagement. These results provide early safety, usability, and feasibility outcomes for VR interventions that require specific trunk excursions. Future work should confirm the effectiveness of VR interventions longitudinally on PD-specific trunk outcomes (e.g., trunk rigidity) and global balance/mobility measures associated with improved functional status.
... The 53 eligible articles had sample sizes ranging from 9 to 170 participants. Experimental studies compared postural reflexes in people with and without multiple sclerosis (n = 7) [17][18][19][20][21][22][23], Parkinson's disease (n = 10) [24][25][26][27][28][29][30][31][32][33], history of stroke (n = 10) [34][35][36][37][38][39][40][41][42][43], cerebellar dysfunction (n = 4) [44][45][46][47], diabetes (n = 2) [5,48], HIV (n = 3) [49][50][51], iSCI (n = 2) [52,53] and pain (n = 7) [15,[54][55][56][57][58][59]. Seven intervention studies examined adaptation of postural reflexes to exercise interventions in people with Parkinson's disease (n = 3) [31,32,60], stroke (n = 3) [61][62][63] and cerebellar dysfunction (n = 1) [47]. ...
... The results of the risk of bias assessment are shown in Appendices A.3 and A.4. Most articles (57%, n = 30) [15,[17][18][19][20][21][22][23][24]26,28,29,31,36,39,[46][47][48][52][53][54][55][56][57][59][60][61][62][63][64] compared similar groups in terms of age and gender, however, few studies reported standardized instructions regarding responses to perturbations (43%, n = 23) [5,10,15,22,25,27,28,30,31,33,39,41,43,46,47,49,50,53,55,56,60,63,66]. ...
... For EMG characteristics, only 19% (n = 10) [30,35,36,38,43,53,56,58,62,65] reported adhering to the SENIAM guidelines or specifically described the location of electrode placement, with 23% (n = 12) [5,15,17,26,27,34,39,54,55,57,59,64] providing a brief description of location (e.g. muscle belly), and the remaining articles only stating the muscle used for EMG recording (58%, n = 31). ...
Background
Pathological conditions can impair responses to postural perturbations and increase risk of falls. Research question
To what extent are postural reflexes impaired in people with pathological conditions and can exercise interventions shorten postural reflexes?
Methods
MEDLINE, EMBASE, Scopus, SportDiscus and Web of Science were systematically searched for articles comparing muscle activation onset latency in people with pathological conditions to healthy controls following unpredictable perturbations including the effect of exercise interventions (registration: CRD42020170861).
Results
Fifty-three articles were included for systematic review. Significant delays in muscle activity onset following perturbations were evident in people with multiple sclerosis (n=7, mean difference [MD]: 22ms, 95% confidence interval [CI]: 11, 33), stroke (n=10, MD: 34ms, 95% CI: 19, 49), diabetes (n=2, MD: 19ms, 95% CI: 10, 27), HIV (n=3, MD: 9ms, 95% CI: 4, 14), incomplete spinal cord injury (n=2, MD: 57ms, 95% CI: 33, 80) and back and knee pain (n=7, MD: 12ms, 95% CI: 6, 18), but not in people with Parkinson’s disease (n=10) or cerebellar dysfunction (n=4). Following exercise interventions, the paretic limb of stroke survivors (n=3) displayed significantly faster muscle activation onset latency compared to pre-exercise (MD: -13ms, 95% CI: -24, -4), with no significant changes in Parkinson’s disease (n=3).
Conclusions
This systematic review demonstrated that postural reflexes are significantly delayed in people with multiple sclerosis (+22ms), stroke (+34ms), diabetes (+19ms), HIV (+9ms), incomplete spinal cord injury (+57ms), back and knee pain (+12ms); pathological conditions characterized by impaired sensation or neural function. In contrast, timing of postural reflexes was not impaired in people with Parkinson’s disease and cerebellar dysfunction, confirming the limited involvement of supraspinal structures. The meta-analysis showed exercise interventions can significantly shorten postural reflex latencies in stroke survivors (-14ms), but more research is needed to confirm this finding and in people with other pathological conditions.
... Moreover, PD patients often have limb and axial rigidity (stiffness). While this stiffening reduces the area of sway (21), it does prevent the use of flexible responses, thereby aggravating the deterioration of postural reflexes (22,23). PD patients with postural instability and gait difficulty are more likely to suffer falls compared to PD patients without postural instability or gait difficulty (24). ...
... It could be that the PD patients are not able to adapt their sway much because of their bradykinesia and rigidity. However, it is also known that rigidity can increase postural sway by preventing the use of flexible responses and thereby aggravating the deterioration of postural reflexes (22,23). MS patients increased their sway a lot, especially area, acceleration and jerk, when adapting to the most complex task. ...
Neurological diseases are associated with static postural instability. Differences in postural sway between neurological diseases could include “conceptual” information about how certain symptoms affect static postural stability. This information might have the potential to become a helpful aid during the process of finding the most appropriate treatment and training program. Therefore, this study investigated static postural sway performance of Parkinson's disease (PD) and multiple sclerosis (MS) patients, as well as of a cohort of healthy adults. Three increasingly difficult static postural tasks were performed, in order to determine whether the postural strategies of the two disease groups differ in response to the increased complexity of the balance task. Participants had to perform three stance tasks (side-by-side, semi-tandem and tandem stance) and maintain these positions for 10 s. Seven static sway parameters were extracted from an inertial measurement unit that participants wore on the lower back. Data of 47 healthy adults, 14 PD patients and 8 MS patients were analyzed. Both healthy adults and MS patients showed a substantial increase in several static sway parameters with increasingly complex stance tasks, whereas PD patients did not. In the MS patients, the observed substantial change was driven by large increases from semi-tandem and tandem stance. This study revealed differences in static sway adaptations between PD and MS patients to increasingly complex stance tasks. Therefore, PD and MS patients might require different training programs to improve their static postural stability. Moreover, this study indicates, at least indirectly, that rigidity/bradykinesia and spasticity lead to different adaptive processes in static sway.
... However, the precise identification of the input variable that better correlates with the CoP response could facilitate the interpretation of the results and the design of appropriate postural tests. Significantly, it could enhance testing of patients affected with disorders in which the normal PR may be compromised (Grassi et al. 2017;Colebatch and Govender 2019). ...
PurposeMany studies have investigated postural reactions (PR) to body-delivered perturbations. However, attention has been focused on the descriptive variables of the PR rather than on the characterization of the perturbation. This study aimed to test the hypothesis that the impulse rather than the force magnitude of the perturbation mostly affects the PR in terms of displacement of the center of foot pressure (ΔCoP).Methods
Fourteen healthy young adults (7 males and 7 females) received 2 series of 20 perturbations, delivered to the back in the anterior direction, at mid-scapular level, while standing on a force platform. In one series, the perturbations had the same force magnitude (40 N) but different impulse (range: 2–10 Ns). In the other series, the perturbations had the same impulse (5 Ns) but different force magnitude (20–100 N). A simple model of postural control restricted to the sagittal plane was also developed.ResultsThe results showed that ΔCoP and impulse were highly correlated (on average: r = 0.96), while the correlation ΔCoP–force magnitude was poor (r = 0.48) and not statistically significant in most subjects. The normalized response, ΔCoPn = ΔCoP/I, was independent of the perturbation magnitude in a wide range of force amplitude and impulse and exhibited good repeatability across different sets of stimuli (on average: ICC = 0.88). These results were confirmed by simulations.Conclusion
The present findings support the concept that the magnitude of the applied force alone is a poor descriptor of trunk-delivered perturbations and suggest that the impulse should be considered instead.
... This would reflect early changes in inertial body properties related to parkinsonian rigidity (Yelshyna et al., 2016) and/or excessive co-contraction in axial muscles (Dimitrova et al., 2004a(Dimitrova et al., , 2004bHorak et al., 2005;Jacobs et al., 2005;Schoneburg et al., 2013). Rigidity would reduce the body resilience to postural perturbations by affecting the absorption of the applied force as a rotation of the trunk (Colebatch and Govender, 2019). As a result of reduced body resilience, PD patients would manifest increased body axial displacement and falls in the same direction of the imposed perturbation. ...
Objective
Early postural instability (PI) is a red flag for the diagnosis of Parkinson’s disease (PD). Several patients, however, fall within the first three years of disease, particularly when turning. We investigated whether PD patients, without clinically overt PI, manifest abnormal reactive postural responses to ecological perturbations resembling turning.
Methods
Fifteen healthy subjects and 20 patients without clinically overt PI, under and not under L-Dopa, underwent dynamic posturography during axial rotations around the longitudinal axis, provided by a robotic mechatronic platform. We measured reactive postural responses, including body displacement and reciprocal movements of the head, trunk, and pelvis, by using a network of three wearable inertial sensors.
Results
Patients showed higher body displacement of the head, trunk and pelvis, and lower joint movements at the lumbo-sacral junction than controls. Conversely, movements at the cranio-cervical junction were normal in PD. L-Dopa left reactive postural responses unchanged.
Conclusions
Patients with PD without clinically overt PI manifest abnormal reactive postural responses to axial rotations, unresponsive to L-Dopa. The biomechanical model resulting from our experimental approach supports novel pathophysiological hypotheses of abnormal axial rotations in PD.
Significance
PD patients without clinically overt PI present subclinical balance impairment during axial rotations, unresponsive to L-Dopa.
... The pendulum's length could be adjusted according to the subjective shoulders' height, while its weight could be set according to the desired magnitude of the impact, e.g., equal to a certain percentage of the subject's body weight (Chen et al. 2016). An even simpler model has been recently proposed in which the perturbation was manually imparted by the experimenter who had placed his hand on the subject's shoulder and briefly pulled the latter's torso in the anterior or posterior direction (Colebatch et al. 2016;Colebatch and Govender 2019). An important limitation of this experimental design is the poor definition, in terms of onset, magnitude, and time course, of the perturbation. ...
... An important limitation of this experimental design is the poor definition, in terms of onset, magnitude, and time course, of the perturbation. In some case, the ensuing body acceleration has been used as a surrogate (Colebatch et al. 2016;Chen et al. 2017;Colebatch and Govender 2019), although it was actually the output variable of the perturbed system. ...
PurposePostural reactions (PR) of standing subjects have been mostly investigated in response to platform displacements or body perturbations of fixed magnitude. The objective of this study was to investigate the relationship between PR and the peak force and impulse of the perturbation.Methods
In ten healthy young men, standing balance was challenged by anteriorly directed perturbations (peak force: 20–60 N) delivered to the back, at the lumbar (L) or inter-scapular (IS) level, by means of a manual perturbator equipped with a force sensor. Postural reactions as expressed by the displacement of the center of pressure (CoP) were recorded using a force platform. Two sets of 20 randomly ordered perturbations (10 to each site) were delivered in two separate testing sessions.ResultsThe magnitude of CoP response (∆CoP) was better correlated with the impulse (I) than with the peak force of the perturbation. The normalized response, ∆CoPn = ∆CoP/I, exhibited good reliability (ICCs of 0.93 for IS and 0.82 for L), was higher with IS than with L perturbations (p < 0.01), and was significantly correlated with the latency of CoP response: r = 0.69 and 0.71 for IS and L, respectively.Conclusion
These preliminary findings support the concept that manually delivered perturbations can be used to reliably assess individual PR and that ∆CoPn may effectively express a relevant aspect of postural control.
Objective:
To examine the inter- and intra-rater reliability of the pull test in patients with Parkinson's disease (PD) using the extracted pull force.
Methods:
In this inter- and intra-rater reliability study, two raters performed a pull test on 30 patients with PD. The pull force was quantified using inertial sensors attached to the rater's right hand and the patient's lower trunk. This study calculated the pull force as an extracted three-dimensional vector quantity, the resultant acceleration, and was expressed in m/s2. Inter- and intra-rater reliabilities were analyzed using the interclass correlation coefficient (ICC) for the pull force and Cohen's weighted kappa (κw) for the pull test score. Furthermore, Bland-Altman analysis was used to investigate systematic errors.
Results:
The inter- and intra-rater reliabilities of the pull force were very poor (ICC = 0.033-0.214). Bland-Altman analysis revealed no systematic errors between the pull forces at the two test points. Conversely, κw for the pull test scores were 0.763-0.920, indicating substantial to almost perfect agreement.
Conclusion:
The pull test score was reliable despite variations in the quantified pull force for inter- and intra-rater reliabilities. Our findings suggest that the pull test is a robust tool for evaluating postural instability in patients with PD and that the pull force probably does not affect scoring performance.
Resumen
Objetivos
La enfermedad de Parkinson (EP) genera alta incidencia de caídas, sin embargo, existe poca evidencia de inestabilidades en etapas iniciales. Esta investigación buscó comparar los tiempos de activación muscular en pacientes con EP inicial frente a una alteración postural vs. un grupo control.
Materiales y métodos
Se evaluó la actividad electromiográfica (EMG) de 10 pacientes con EP (61,3 ± 3,8 años) en etapas iniciales y grupo control de 10 adultos (62,2 ±3,0 años). Los participantes fueron tratados mediante una alteración de la superficie, la cual generó una respuesta de estabilización. La prueba se realizó en 2 condiciones: ojos abiertos (OA) vs. ojos cerrados (OC). Se analizó el tiempo de activación de músculos del tronco (erector espinal) y extremidad inferior (sóleo, tibial anterior, peroneo lateral largo, recto femoral, bíceps femoral, glúteo medio y aductor mayor) usando EMG de superficie.
Resultados
El grupo con EP mostró tiempos de respuestas más rápidas en comparación con l grupo control en el músculo sóleo en OC (p = 0,04). Este mismo músculo mostró diferencias al comparar OA vs. OC solo en el grupo con EP (p = 0,04), mostrando un menor tiempo de respuesta en la condición OC. Al comparar el músculo erector espinal el grupo con EP mostró tiempos de respuesta más lentos en la condición de OA (p = 0,02) y OC (p = 0,04) con relación al grupo control.
Conclusiones
Los tiempos de activación muscular muestran que las personas con EP responden con un retraso en la activación en la musculatura del tronco, mientras que a nivel distal responden más rápido que los sujetos controles. En las etapas tempranas las respuestas más lentas a nivel de tronco podrían explicar el inicio de las alteraciones del equilibrio en estos pacientes.
