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Muscle synergies reveal impaired trunk muscle coordination strategies in individuals with thoracic spinal cord injury
Abstract
Spinal cord injury (SCI) can result in paralysis of trunk muscles, which can affect sitting balance. The objective of this study was to analyze trunk muscle coordination of individuals with thoracic SCI and compare it to able-body individuals. A total of 27 individuals were recruited and subdivided into: (a) high thoracic SCI; (b) low thoracic SCI; and (c) able-body groups. Participants were seated and asked to lean their trunk in eight directions while trunk muscle activity was recorded. Muscle coordination was assessed using the non-negative matrix factorization (NMF) method to extract muscle modules, which are the synergistic trunk muscle activations, and their directional activation patterns. Our results showed that individuals with SCI used less muscle modules, more co-contractions, and less directional tuning, compared to able-bodied people. These results suggest impaired and simplified muscle coordination due to the loss of supraspinal input after SCI. Observed variability in muscle coordination within SCI groups also suggests that other mechanisms such as spasticity and muscle stretch reflexes or individual factors such as experience and training contributed to the postural muscle synergies. Overall, muscle coordination deficits revealed impaired neuromuscular strategies which provide implications for rehabilitation of trunk muscles during sitting balance after SCI.
... The trunk muscles, including the abdominals and paraspinals, play a key role in facilitating seated balance by positioning the upper-body over the base of support. 1 After sustaining a spinal cord injury (SCI), denervation of trunk muscles can dramatically impair seated balance control and severely limit range of stability. [1][2][3][4] For many individuals with SCI, this impairment in seated balance function can drastically interfere with their ability to complete seated activities of daily living such as preparing food, dressing, grooming, and transferring. ...
... The trunk muscles, including the abdominals and paraspinals, play a key role in facilitating seated balance by positioning the upper-body over the base of support. 1 After sustaining a spinal cord injury (SCI), denervation of trunk muscles can dramatically impair seated balance control and severely limit range of stability. [1][2][3][4] For many individuals with SCI, this impairment in seated balance function can drastically interfere with their ability to complete seated activities of daily living such as preparing food, dressing, grooming, and transferring. Indeed, effective seated balance is key for mobility, independence, and overall quality of life for the majority of the SCI population. ...
Context
Recovery of seated balance is a rehabilitation priority for people with motor-complete spinal cord injury (mcSCI). Previous research has demonstrated that people with mcSCI can voluntarily engage their trunk muscles during different exercise programs that have the potential to improve seated balance control. Boxing and battle rope exercises could offer another opportunity to improve seated balance for people with mcSCI, but it is unknown if this type of exercise engages trunk musculature and challenges seated balance.
Objective
To describe the movement patterns of people with mcSCI compared to controls by characterizing the muscle activation patterns and kinematics of the trunk and upper-body during boxing and battle rope exercise.
Design
Cross-sectional study.
Participants
4 males with mcSCI between C7-T9, and 4 able-bodied controls.
Methods
Participants performed different boxing and battle rope exercises while kinematics and electromyography (EMG) from the trunk and arms were recorded.
Outcome Measures
Trunk EMG amplitude, trunk and arm joint angles, and trunk curvature.
Results
Boxing and battle ropes elicited higher relative EMG activity in people with mcSCI compared to controls (P < 0.001). Participants with mcSCI had similar upper-limb kinematics during the exercises to controls, but demonstrated reduced trunk rotation and increased trunk curvature.
Conclusions
These findings suggest that boxing and battle rope can elicit trunk activity in people with mcSCI, though they may adopt increased trunk curvatures. Future research should explore if such exercise programs may improve seated balance in people with mcSCI.
... In wheelchair-bound paraplegics, all normal functional activities depend on trunk control for movement. Thus, postural control and balance reactions in the sitting position should simultaneously provide stability and mobility in the activities of daily living (ADL), such as eating, dressing and wheelchair-to-bed transfers [4][5][6]. ...
... In individuals with SCI, dynamic and static instability to recruit the straight, transverse abdominal, quadratus lumborum and erector spinae muscles may lead to compensatory strategies using non-postural muscles such as the latissimus dorsi, trapezius and pectoralis major. As such, paraplegic patients develop new postural control processes to maintain stability while sitting, which may result in posterior pelvic tilt and an increase in thoracolumbar kyphoscoliosis [4]. ...
Introduction:
Due to motivation and immediate feedback during activities, exergame-based physical therapy may improve trunk balance and functionality in individuals with spinal cord injury (SCI).
Objective:
evaluate the effects of exergames on the trunk control of paraplegics with spinal cord injury or meningomyelocele.
Method:
case series involving four paraplegic patients, with SCI or meningomyelocele. Participants underwent a rehabilitation protocol using the exergame Nintendo Wii®, attending one weekly session for 4 weeks. Patients were encouraged to perform trunk movements in the sitting position using the Swordplay and Canoeing games. Data were collected before and after the intervention by applying the functional reach test adapted for trunk control evaluation, and transfer time and propulsion tests for functional assessment.
Results:
The intervention increased trunk control in 75% of the patients, with improvement varying between 6.4 and 25%. In the propulsion test, the intervention led to a decrease in half of the patients. For the cadence variable, in the same test, there was a reduction in the number of propulsions in 75% of the cases. In the transfer test, the intervention led to reduced chair-to-bed transfer time in all patients.
Conclusion:
Rehabilitation of paraplegics with the use of exergames can be considered viable, innovative and effective. However, future research with greater methodological rigor should be conducted in order to analyze the clinical applicability of this approach.
... In this way, the neural control of locomotion can be reduced to activating groups of muscles rather than individual muscles. Muscle synergy analysis has proven useful in clinical studies to understand how individuals improve their walking performance while recovering from a stroke (Clark et al., 2010) and how persons with spinal cord injury can recover reaching movements (Milosevic et al., 2017;Seelen et al., 1998). Although multiple studies suggest low back pain alters muscle activation patterns (Falla and Hodges, 2017;Hanada et al., 2011;van den Hoorn et al., 2015;van Dieën et al., 2017), no studies to date have examined muscle activation strategies of individuals with SIJD during gait. ...
... In this study, active and passive tensioning of the latissimus dorsi caused lateral rotation in the contralateral hip (Carvalhais et al., 2013) Moreover, van Wingerden and colleagues (2004) demonstrated that the muscular actions of the gluteus maximus significantly contribute to force closure by compressing the SIJ and preventing excessive shear forces. The reduction in muscle weights for the synergy involving gluteus maximus on the affected side and contralateral latissimus dorsi may compromise pelvic stability and alter kinematics by limiting force closure of the joint (McCrory et al., 2001;Milosevic et al., 2017). The lack of synergist activity between these muscles across the affected joint side in individuals with SIJD likely enables slight displacements (Kibsgård et al., 2017(Kibsgård et al., , 2012 between the two joint surfaces, contributing to pain. ...
... It has previously been shown that frequency dispersion was inversely related to the stiffness of the inverted pendulum [15]. Moreover, individuals with high-thoracic SCI used more trunk muscle co-contractions during sitting compared to those with low-thoracic SCI [16]. Therefore, it seems that individuals with high-thoracic SCI utilize a stiffness balance control strategy, which could be related to use of non-postural muscles [4,5] or to the spasticity after SCI [17]. ...
... Overall, large destabilizing effect during sitting with arms extended in individuals with high-thoracic SCI suggests that clinical assessments of sitting balance should include arms extended posture to gain an understanding of the impairment severity. Moreover, our results imply that individuals with high-and low-thoracic SCI use different postural regulatory strategies during sitting balance, confirming that the trunk neuromuscular impairment in those with high-thoracic SCI [16] results in suboptimal posture during sitting. Therefore, rehabilitation strategies should focus on recovering trunk function to improve sitting balance in individuals with thoracic SCI. ...
Thoracic spinal cord injury (SCI) can have significant negative consequences, which can affect the ability to maintain unsupported sitting. The objectives of this study were to compare postural control of individuals with high- and low-thoracic SCI to able-bodied people and evaluate the effects of upper-limb support on postural control during quiet sitting. Twenty-five individuals were recruited into: (a) high-thoracic SCI; (b) low-thoracic SCI; and (c) able-body subgroups. Participants were seated and asked to maintain a steady balance in the following postures: (1) both hands resting on thighs; (2) both arms crossed over the chest; and (3) both arms extended. Center of pressure (COP) fluctuations were evaluated to compare postural performance between groups and different postures. Results showed that individuals with high- and low-thoracic SCI swayed more compared to the able-bodied group regardless of upper-limb support. No differences between the two SCI groups were observed, but the neurological level of injury was correlated to postural performance implying that those with higher injuries swayed more and faster. Unsupported sitting was more unstable in comparison to supported sitting posture, especially in the anterior-posterior direction. The velocity of postural sway was not different between groups, but the results suggest that postural regulation had unique effect during different postures in different groups. These results imply reduced postural stability after thoracic SCI. Overall, the way individuals with high-thoracic SCI achieved stability was different from that of individuals with low-thoracic SCI, suggesting different postural regulation strategies.
... Muscle synergies or modules have been proposed as a possible mechanism for the nervous system to reduce the number of control signals required to perform movements (17, 18). These synergies have been identified in able-bodied individuals (19-21) and even observed to be preserved in some form after incomplete SCI (22,23). With the synergy method, Razavian et al. reduced six stimulation channels to four synergies, which was able to control reaching in two dimensions in able-bodied individuals. ...
Spinal cord injury (SCI) can cause paralysis of trunk and hip musculature that negatively impacts seated balance and ability to lean away from an upright posture and interact fully with the environment. Constant levels of electrical stimulation of peripheral nerves can activate typically paralyzed muscles and aid in maintaining a single upright seated posture. However, in the absence of a feedback controller, such seated postures and leaning motions are inherently unstable and unable to respond to perturbations. Three individuals with motor complete SCI who had previously received a neuroprosthesis capable of activating the hip and trunk musculature volunteered for this study. Subject-specific muscle synergies were identified through system identification of the lumbar moments produced via neural stimulation. Synergy-based calculations determined the real-time stimulation parameters required to assume leaning postures. When combined with a proportional, integral, derivative (PID) feedback controller and an accelerometer to infer trunk orientation, all individuals were able to assume non-erect postures of 30–40° flexion and 15° lateral bending. Leaning postures increased forward reaching capabilities by 10.2, 46.7, and 16 cm respectively for each subject when compared with no stimulation. Additionally, the leaning controllers were able to resist perturbations of up to 90 N, and all subjects perceived the leaning postures as moderately to very stable. Implementation of leaning controllers for neuroprostheses have the potential of expanding workspaces, increasing independence, and facilitating activities of daily living for individuals with paralysis.
... The ndings of the present study also showed that there is a difference between the EMG activity and onset and offset of the erector spinae and external oblique muscles in the two studied groups, in such a way that people with complete spinal cord injury have a later onset and earlier offset and less EMG activity. This difference could be due to the complete loss of sensorimotor ability, reduced ability to maintain sitting balance, and reduced neuromuscular control ability in individuals with complete spinal cord injury compared to individuals with incomplete spinal cord injury [11,29,[36][37][38][39][40]. The deltoid and biceps muscles play a signi cant role in this sport due to the various shoulder and elbow joint movements involved, and coordinated trunk muscle activity is crucial for distal stability and smooth performance. ...
Background
Para table tennis is a popular sport among individuals with disabilities, and each Paralympic sport has its own classification system. This classification aims to minimize the impact of impairments caused by disability on athletic performance. In the present study, the electromyographic variables of the muscles involved in performing the forehand loop and backhand techniques of elite para table tennis players with complete and incomplete spinal cord injuries in the class 5 category were compared.
Methods
In this study, there were 20 male participants at the national level. According to the ASIA scale, the participants were divided into two groups of 10 people. The first group had complete spinal cord injury, while the second group had incomplete spinal cord injury. After they entered the laboratory, the electrodes were connected to their deltoid, biceps, external oblique, and erector spinae muscles. After connecting the electrodes, the tasks were performed and muscles’ EMG activity, as well as their onset and offset contraction were monitored.
Results
The findings revealed that there are significant differences in the amount of EMG activity as well as the timing of the onset and offset of contraction of selected muscles in two groups of complete and incomplete spinal cord injuries.
Conclusion
The findings suggest that athletes with incomplete spinal cord injuries may perform better than those in the complete group. However, current para table tennis classification rules place both groups in the same class, which could impact the outcome of matches.
... The different body positions for delivery of transspinal stimulation compare efficacy when (1) ongoing neuronal activity is adjusted continuously (standing vs. supine) and (2) upright posture regulation is needed in the presence or absence of transspinal stimulation (active vs. sham during standing). Upright posture regulation, which is greatly affected after SCI, is one of the key elements of locomotor control [55][56][57][58][59][60]. During standing, local spinal inhibitory circuits continuously adjust the soleus H-reflex amplitude based on body sway amplitude [61]. ...
Background
The seemingly simple tasks of standing and walking require continuous integration of complex spinal reflex circuits between descending motor commands and ascending sensory inputs. Spinal cord injury greatly impairs standing and walking ability, but both improve with locomotor training. However, even after multiple locomotor training sessions, abnormal muscle activity and coordination persist. Thus, locomotor training alone cannot fully optimize the neuronal plasticity required to strengthen the synapses connecting the brain, spinal cord, and local circuits and potentiate neuronal activity based on need. Transcutaneous spinal cord (transspinal) stimulation alters motoneuron excitability over multiple segments by bringing motoneurons closer to threshold, a prerequisite for effectively promoting spinal locomotor network neuromodulation and strengthening neural connectivity of the injured human spinal cord. Importantly, whether concurrent treatment with transspinal stimulation and locomotor training maximizes motor recovery after spinal cord injury is unknown.
Methods
Forty-five individuals with chronic spinal cord injury are receiving 40 sessions of robotic gait training primed with 30 Hz transspinal stimulation at the Thoracic 10 vertebral level. Participants are randomized to receive 30 min of active or sham transspinal stimulation during standing or active transspinal stimulation while supine followed by 30 min of robotic gait training. Over the course of locomotor training, the body weight support, treadmill speed, and leg guidance force are adjusted as needed for each participant based on absence of knee buckling during the stance phase and toe dragging during the swing phase. At baseline and after completion of all therapeutic sessions, neurophysiological recordings registering corticospinal and spinal neural excitability changes along with clinical assessment measures of standing and walking, and autonomic function via questionnaires regarding bowel, bladder, and sexual function are taken.
Discussion
The results of this mechanistic randomized clinical trial will demonstrate that tonic transspinal stimulation strengthens corticomotoneuronal connectivity and dynamic neuromodulation through posture-dependent corticospinal and spinal neuroplasticity. We anticipate that this mechanistic clinical trial will greatly impact clinical practice because, in real-world clinical settings, noninvasive transspinal stimulation can be more easily and widely implemented than invasive epidural stimulation. Additionally, by applying multiple interventions to accelerate motor recovery, we are employing a treatment regimen that reflects a true clinical approach.
Trial registration
ClinicalTrials.gov NCT04807764 . Registered on March 19, 2021.
... The different body positions for delivery of transspinal stimulation compare e cacy when 1) ongoing neuronal activity is adjusted continuously (standing vs. supine), and 2) upright posture regulation is needed in presence or absence of transspinal stimulation (active vs. sham during standing). Upright posture regulation, which is greatly affected after SCI, is one of the key elements of locomotor control[55][56][57][58][59][60]. During standing, local spinal inhibitory circuits continuously adjust the soleus H-re ex amplitude based on body sway amplitude [61]. ...
Background: The seemingly simple tasks of standing and walking require continuous integration of complex spinal reflex circuits between descending motor commands and ascending sensory inputs. Spinal cord injury greatly impairs standing and walking ability, but both improve with locomotor training. However, even after multiple locomotor training sessions, abnormal muscle activity and coordination persist. Thus, locomotor training alone cannot fully optimize the neuronal plasticity required to strengthen the synapses connecting the brain, spinal cord, and local circuits and potentiate neuronal activity based on need. Transcutaneous spinal cord (transspinal) stimulation alters motoneuron excitability over multiple segments by bringing motoneurons closer to threshold, a prerequisite for effectively promoting spinal locomotor network neuromodulation and strengthening neural connectivity of the injured human spinal cord. Importantly, whether concurrent treatment with transspinal stimulation and locomotor training maximizes motor recovery after spinal cord injury is unknown.
Methods: Forty-five individuals with chronic spinal cord injury are receiving 40 sessions of robotic gait training primed with 30 Hz transspinal stimulation at the Thoracic 10 vertebral level. Participants are randomized to receive 30-minutes of active or sham transspinal stimulation during standing or active transspinal stimulation while supine followed by 30-minutes of robotic gait training. Over the course of locomotor training, the body weight support, treadmill speed, and leg guidance force are adjusted as needed for each participant based on absence of knee buckling during the stance phase and toe dragging during the swing phase. At baseline and after completion of all therapeutic sessions, neurophysiological recordings registering corticospinal and spinal neural excitability changes along with clinical assessment measures of standing and walking, and autonomic function via questionnaires regarding bowel, bladder and sexual function are taken.
Discussion: The results of this mechanistic randomized clinical trial will demonstrate that tonic transspinal stimulation strengthens corticomotoneuronal connectivity and dynamic neuromodulation through posture-dependent corticospinal and spinal neuroplasticity. We anticipate that this mechanistic clinical trial will greatly impact clinical practice because in real-world clinical settings, noninvasive transspinal stimulation can be more easily and widely implemented than invasive epidural stimulation. Additionally, by applying multiple interventions to accelerate motor recovery, we are employing a treatment regimen that reflects a true clinical approach.
Trial registration: ClinicalTrials.gov: NCT04807764; Registered on March 19, 2021.
... Furthermore, our previous study included 11 functional tasks of multidirectional trunk movements and several of the four positional tasks that require trunk stability 10 . Each motor task has largely been utilized in research and clinical fields to evaluate and improve motor control [14][15][16][17][18] . Therefore, the cluster of trunk motor tasks increases the likelihood of revealing the motor control strategies in a target population that may have diverse features of altered trunk motor control 14 and help to interpret several meaningful daily and sports activities 10 . ...
Muscle synergy analysis is useful for investigating trunk coordination patterns based on the assumption that the central nervous system reduces the dimensionality of muscle activation to simplify movement. This study aimed to quantify the variability in trunk muscle synergy during various trunk motor tasks in healthy participants to provide reference data for evaluating trunk control strategies in patients and athletes. Sixteen healthy individuals performed 11 trunk movement and stability tasks with electromyography (EMG) recording of their spinal and abdominal muscles (6 bilaterally). Non-negative matrix factorization applied to the concatenated EMG of all tasks identified the five trunk muscle synergies (W) with their corresponding temporal patterns (C). The medians of within-cluster similarity defined by scalar products in W and r max coefficient using the cross-correlation function in C were 0.73–0.86 and 0.64–0.75, respectively, while the inter-session similarities were 0.81–0.96 and 0.74–0.84, respectively. However, the lowest and highest values of both similarity indices were broad, reflecting the musculoskeletal system’s redundancy within and between participants. Furthermore, the significant differences in the degree of variability between the trunk synergies may represent the different neural features of synergy organization and strategies to overcome the various mechanical demands of a motor task.
... In athletes 1, 2 and 3 of this research, not only is there a history of traumatic spinal cord injury but there is also a long time of evolution of the pathology-more than eight years-This led to think that the changes in postural control after the development of the proposed exercise program would be minimal. However, significant improvements in trunk displacement were evidenced in these three subjects, which can be explained by the existence of neuromuscular plasticity that allows individuals with spinal cord injury to generate new muscular synergies when the patient is subjected to repetitive multidirectional training [34]. In addition to the aforementioned results, the athletes stated that the best effect for them was the ability to stand during the sessions and the decrease in spasticity and clonus associated with their pathology. ...
Introducción: El deporte paralímpico se originó como parte de procesos de rehabilitación para personas que tuvieran discapacidad. Durante la ejecución de las disciplinas paralímpicas el control motor en la región del tronco y en especial del abdomen es de gran importancia para prevenir lesiones y mejorar el registro de la marca deportiva. Son muchas las herramientas utilizadas por los entrenadores deportivos para mejorar la fuerza muscular y por consiguiente la estabilidad de tronco, buscando disminuir el riesgo en el ámbito deportivo. Sin embargo, las investigaciones sobre el uso de realidad virtual, junto con plataformas de estabilometría para el entrenamiento de deportistas paralímpicos con lesiones físicas, son escasos.
Objetivo: Establecer el efecto de un programa de entrenamiento del tronco apoyado en realidad virtual en deportistas de alto rendimiento paralímpicos, lanzadores de bala y jabalina con lesiones físicas y que compiten en sillas de lanzamiento.
Materiales y método: La investigación fue diseñada como un estudio cuasiexperimental intrasujeto. Se evaluaron cinco sujetos deportistas paralímpicos de alto rendimiento con discapacidad física. Se empleó un software de realidad virtual que incluye patrones y juegos lúdicos ajustables en tiempo e intensidad y una plataforma de bipedestación dinámico como parte del equipo de intervención, ajustable al paciente, que permite reeducar el equilibrio, la propiocepción, fortalecer y lograr el control del tronco. Las variables de análisis fueron el nivel del desplazamiento anteroposterior y lateral del tronco y los cambios en el volumen de acción. Se realizó una evaluación inicial, una intervención que duró de seis semanas y la evaluación final.
Resultados: En las evaluaciones iniciales de todos los atletas se observó una tendencia al desplazamiento en sentido posterior. En la evaluación final, los rangos de desplazamiento aumentan en casi todos los sujetos con excepción del sujeto 5, cuyos valores permanecen casi estables tanto en las evaluaciones iniciales como las finales. La diferencia en el desplazamiento entre la prueba inicial y final en promedio de los participantes fue de 6.26 grados.
Conclusiones: los resultados positivos del entrenamiento del tronco apoyado en realidad virtual para los participantes constituyen un aporte al conocimiento sobre el tema y abren la posibilidad de incluir esta tecnología en protocolos de entrenamiento en deporte paralímpico.
... On the other hand, the importance of trunk function has been reported. It is confirmed that there are various types of trunk muscle coordination in patients with paraplegia, independent of AIS and NLI [2]. And the relationship between trunk function and ADL in patients with spinal cord injury has also been reported [3]. ...
Background: In the rehabilitation for patients with spinal cord injury, we often use developmental movement patterns of infants and Activity-Based Therapy. They include quadruped movement, but no reports of movement analysis on quadruped movement in patients with spinal cord injury. Objective: This study aimed to analyze quadruped movement in patients with paraplegia, and to summarize its characteristics. Methods: The quadruped movement of 3 patients with complete paraplegia were measured using a three-dimensional motion analyzer, and their characteristics were summarized. Results: All cases showed an ipsilateral rotation of the pelvis when moving the lower limbs. Case A rose the contralateral upper and lower limbs simultaneously. Cases B and C moved one limb at a time. Conclusions: Our results suggested that patients with spinal cord injury have an ipsilateral rotation of the pelvis when moving the lower limbs in quadruped movement. Also, it seems that, depending on the degree of disability, some cases were able to move the contralateral upper and lower limbs simultaneously, while others moved one limb at a time
... Furthermore, our previous study included 11 functional tasks of multidirectional trunk movements and several of the four positional tasks that require trunk stability 9 . Each motor task has largely been utilized in research and clinical elds to evaluate and improve motor control [12][13][14][15][16] . Therefore, the cluster of trunk motor tasks increases the likelihood of revealing the motor control strategies in a target population that may have diverse features of altered trunk motor control 12 and help to interpret several meaningful daily and sports activities 9 . ...
Muscle synergy analysis is a useful approach for investigating the nature of trunk coordination patterns based on the assumption that the central nervous system reduces the dimensionality of muscle activation to simplify movement. This study aimed to quantify the variability in trunk muscle synergy during 11 trunk motor tasks in healthy participants to provide reference data for evaluating trunk control strategies in patients and athletes. Even in a highly variable task context, the five trunk muscle synergies with their temporal patterns presented well-reconstructed original electromyography data. While the variability in trunk synergies between participants and sessions were comparable to those for other body parts in previous studies, these metrics had a broad range, reflecting some level of redundancy of the musculoskeletal system in healthy individuals. Furthermore, the significant differences in the degree of variability between the trunk synergies may reflect the different neural features of trunk synergy organization and strategies to overcome the various mechanical demands of a motor task. The quantification of the variability of trunk muscle synergy may guide the assessment of stereotypes or diverse features of trunk control strategies and the interpretation of adaptability in the presence of diseases or the process of motor training in future research.
... Interventions on trunk function are commonly used in the rehabilitation of individuals with SCI [4]. It has also been reported that trunk function in individuals with SCI is related to sitting balance, walking ability, and activities of daily living [5][6][7]. Several tools are available for assessing sitting balance and trunk function in individuals with SCI [8][9][10][11][12][13]. Among them, the Trunk Control Test for individuals with SCI (TCT-SCI), developed by Quinzaños et al., has been confirmed its reliability and validity in Mexico [6,7]. ...
Study design:
Cross-sectional study.
Objectives:
To evaluate the reliability and calculate the measurement error of the Trunk Assessment Scale for Spinal Cord Injury (TASS) and trunk control test (TCT-SCI) in individuals with spinal cord injury (SCI).
Setting:
Rehabilitation Hospital in Japan.
Methods:
The evaluations of TASS and TCT-SCI for individuals with SCI were video-recorded. The inter-rater reliability (two physiotherapists) was confirmed using the videos. ICC (2,1), kappa coefficient (κ) were used to determine the reliability of the total score and each item. Each minimal detectable change (MDC) was calculated.
Results:
The TASS and TCT-SCI total scores showed excellent inter-rater reliability (ICC = 0.99, and 1.00). The kappa coefficients of TASS were acceptable to excellent for 8 items (κ = 0.76-1.00), below acceptable for 1 item (κ = 0.62). The kappa coefficients of TCT-SCI were excellent for 12 items (κ = 0.83-1.00), below acceptable for 1 item (κ = 0.68). The inter-rater MDC of the TASS total score was 4.07 points, and the MDC of the TCT-SCI total score was 1.13 points. The intra-rater MDC of the TASS total score was 3.86 points.
Conclusion:
Both TASS and TCT-SCI showed high reliability. Differences of less than four points in TASS and one point in TCT-SCI were interpreted as measurement errors between the two raters.
... Synergy 1 cannot, therefore, be similarly discounted as a motor module. Some studies (28,67,68) have found synergies or motor modules encoded in the spinal cord. The cortical involvement in synergy encoding also cannot be ruled out (27,69), but our results suggest that motor modules might be modulated by proprioceptive input at the level of the spinal cord. ...
The influence of proprioceptive feedback on muscle activity during isometric tasks is the subject of conflicting studies. We performed an isometric knee extension task experiment based on two common clinical tests for mobility and flexibility. The task was carried out at four pre-set angles of the knee and we recorded from five muscles for two different hip positions. We applied muscle synergy analysis using non-negative matrix factorisation on surface electromyograph recordings to identify patterns in the data which changed with internal knee angle, suggesting a link between proprioception and muscle activity. We hypothesised that such patterns arise from the way proprioceptive and cortical signals are integrated in neural circuits of the spinal cord. Using the MIIND neural simulation platform, we developed a computational model based on current understanding of spinal circuits with an adjustable afferent input. The model produces the same synergy trends as observed in the data, driven by changes in the afferent input. In order to match the activation patterns from each knee angle and position of the experiment, the model predicts the need for three distinct inputs: two to control a non-linear bias towards the extensors and against the flexors, and a further input to control additional inhibition of rectus femoris. The results show that proprioception may be involved in modulating muscle synergies encoded in cortical or spinal neural circuits.
... In contrast, lower extremity muscle activity during the swing phase was greater than a typical gait pattern for both walking conditions for our participants with SCI. The presence of increased muscle activity in the swing phase suggests more co-contractions and less muscle coordination in people with the SCI (Milosevic et al., 2017). Further, this increased muscle activity during the swing phase was not immediately responsive to the mechanical constraints or software programming of the robotic exoskeleton. ...
Background:
Robotic exoskeleton (RE) enables individuals with lower extremity weakness or paralysis to stand and walk in a stereotypical pattern.
Objective:
Examine whether people with chronic incomplete spinal cord injury (SCI) demonstrate a more typical gait pattern when walking overground in a RE than when walking without.
Methods:
Motion analysis system synchronized with a surface electromyographic (EMG) was used to obtain temporospatial gait parameters, lower extremity kinematics, and muscle activity in ambulatory individuals with SCI and healthy adults.
Results:
Temporospatial parameters and kinematics for participants with SCI (n = 12; age 41.4±12.5 years) with and without RE were significantly different than a typical gait (healthy adults: n = 15; age 26.2±8.3 years). EMG amplitudes during the stance phase of a typical gait were similar to those with SCI with and without RE, except the right rectus femoris (p = 0.005) and left gluteus medius (p = 0.014) when participants with SCI walked with RE. EMG amplitudes of participants with SCI during the swing phase were significantly greater compared to those of a typical gait, except for left medial hamstring with (p = 0.025) and without (p = 0.196) RE.
Conclusions:
First-time walking in a RE does not appear to produce a typical gait pattern in people with incomplete SCI.
... Most of these studies rely on motion capture technologies to record movement kinematics and then measure trunk orientation, trunk excursion, limits of stability, maximum reaching distance, or movement velocity, among other parameters [4,14]. Surface electromyography (EMG) has also been proposed as an assessment tool to measure trunk muscle activity and coordination in patients with SCI [15][16][17]. Other studies have measured reaction forces and changes in the center of pressure (COP) with force plates on the seating surface, to investigate postural control and the limits of stability in individuals with SCI [14,17,18]. ...
Objective:
Impaired trunk stability is frequent in spinal cord injury (SCI), but there is a lack of quantitative measures for assessing trunk function. Our objectives were to: 1) evaluate trunk muscle activity and movement patterns during a reaching task in SCI patients, 2) compare the impact of cervical (cSCI) and thoracic (tSCI) injuries in trunk function, and 3) investigate the effects of a startling acoustic stimulus (SAS) in these patients.
Approach:
Electromyographic (EMG) and smartphone accelerometer data were recorded from 15 cSCI patients, 9 tSCI patients, and 24 healthy controls, during a reaching task requiring trunk tilting. We calculated the response time (RespT) until pressing a target button, EMG onset latencies and amplitudes, and trunk tilt, lateral deviation, and other movement features from accelerometry. Statistical analysis was applied to analyze the effects of group (cSCI, tSCI, control) and condition (SAS, non-SAS) in each outcome measure.
Main results:
SCI patients, especially those with cSCI, presented significantly longer RespT and EMG onset latencies than controls. Moreover, in SCI patients, forward trunk tilt was accompanied by significant lateral deviation. RespT and EMG latencies were remarkably shortened by the SAS (the so-called StartReact effect) in tSCI patients and controls, but not in cSCI patients, who also showed higher variability.
Significance:
The combination of EMG and smartphone accelerometer data can provide quantitative measures for the assessment of trunk function in SCI. Our results show deficits in postural control and compensatory strategies employed by SCI patients, including delayed responses and higher lateral deviations, possibly to improve sitting balance. This is the first study investigating the StartReact responses in trunk muscles in SCI patients and shows that the SAS significantly accelerates RespT in tSCI, but not in cSCI, suggesting an increased cortical control exerted by these patients.
... In the evaluation of the trunk balance of wheelchair basketball players with the modified functional reach test, a significant difference was found between eyes open and closed measurement values [26]. When poliomyelitis sequelae, amputated and spinal cord injured players were compared, it was found that there was a statistically significant difference between the groups in terms of the bilateral reach test values [27]. In their study, Korkmaz et al. evaluated 49 patients with relapsing-remitting multiple sclerosis and 49 healthy individuals in terms of upper extremity functionality. ...
Background
Archery is defined as a static sport that requires postural control, upper body strength and balance ability to achieve high scores.
Purpose
The aim of this study was to compare the trunk stabilization, body perception, and quality of life of professional physically disabled and able-bodied archers.
Methods
Twenty professional archers aged between 18 and 55 years were included in the study. The individuals were divided into two groups as physically disabled archers (n = 10) and able-bodied archers (n = 10). All athletes were evaluated with anthropometric measurements of upper extremity, normal range of motion (ROM) of shoulder, manual muscle strength of upper extremity, and endurance of trunk flexion and extension for trunk stabilization, with modified functional reach, lateral reach and bilateral reach tests for body balance, with Body Perception Scale (BPS) for body perception, and with Short Form 36 (SF-36) for quality of life.
Results
Statistically significant differences were found in all reach tests, physical role difficulties and physical function sub-scores of SF-36, and left horizontal adduction and right internal rotation ROM in favor of the able-bodied group. There was a statistically significant difference in arm circumference measurements in favor of the disabled group. No significant difference was there between the groups in endurance of trunk flexion and extension, and BPS.
Conclusion
In conclusion, it has been observed that the able-bodied archers have better body balance and quality of life than disabled archers and there is no difference between disabled and able-bodied athletes in terms of trunk stabilization and body perception.
... A reduction in strength and neuromuscular coordination are associated with injury (Wilson et al. 2020;Harput et al. 2020;Ward et al. 2015) and disease (Milosevic et al. 2017;Stock et al. 2019), whilst strength is a key quality of athletic performance (Joffe and Tallent 2020). Consequently, the enhancement of strength and neuromuscular coordination through maximising neurological adaptation is vital. ...
Optimal strategies for enhancing strength and improving motor skills are vital in athletic performance and clinical rehabilitation. Initial increases in strength and the acquisition of new motor skills have long been attributed to neurological adaptations. However, early increases in strength may be predominantly due to improvements in inter-muscular coordination rather than the force generating capacity of the muscle. Despite the plethora of research investigating neurological adaptations from motor skill or resistance training in isolation, little effort has been made in consolidating this research to compare motor skill and resistance training adaptations. The findings of this review demonstrated that motor skill and resistance training adaptations show similar short-term mechanisms of adaptations, particularly at a cortical level. Increases in corticospinal excitability and a release in short-interval cortical inhibition occur as a result of the commencement of both resistance and motor skill training. Spinal changes show evidence of task-specific adaptations from the acquired motor skill, with an increase or decrease in spinal reflex excitability, dependant on the motor task. An increase in synaptic efficacy of the reticulospinal projections is likely to be a prominent mechanism for driving strength adaptations at the subcortical level, though more research is needed. Transcranial electric stimulation has been shown to increase corticospinal excitability and augment motor skill adaptations, but limited evidence exists for further enhancing strength adaptations from resistance training. Despite the logistical challenges, future work should compare the longitudinal adaptations between motor skill and resistance training to further optimise exercise programming.
... Since the spinal cord [16] and cerebral cortex [17] are involved in the recruitment of muscle synergy, many previous studies have focused on neurological disorders [18][19][20][21]. Contrarily, muscle co-ordination patterns and muscle synergy are constrained by the biomechanics of the musculoskeletal system [22][23][24]. ...
Objective:
To clarify whether there are any muscle synergy changes in individuals with knee osteoarthritis, and to determine whether muscle synergy analysis could be applied to other musculoskeletal diseases.
Methods:
Subjects in this study included 11 young controls (YC), 10 elderly controls (EC), and 10 knee osteoarthritis patients (KOA). Gait was assessed on a split-belt treadmill at 3 km/h. A non-negative matrix factorization (NNMF) was applied to the electromyogram data matrix to extract muscle synergies. To assess the similarity of each module, we performed the NNMF analysis assuming four modules for all of the participants. Further, we calculated joint angles to compare the kinematic data between the module groups.
Results:
The number of muscle modules was significantly lower in the EC (2-3) and KOA (2-3) groups than in the YC group (3-4), which reflects the merging of late swing and early stance modules. The EC and KOA groups also showed greater knee flexion angles in the early stance phase. Contrarily, by focusing on the module structure, we found that the merging of early and late stance modules is characteristic in KOA.
Conclusion:
The lower number of modules in the EC and KOA groups was due to the muscle co-contraction with increased knee flexion angle. Contrarily, the merging of early and late stance modules are modular structures specific to KOA and may be biomarkers for detecting KOA.
Significance:
Describing the changes in multiple muscle control associated with musculoskeletal degeneration can serve as a fundamental biomarker in joint disease.
... For instance, abnormal muscle synergy patterns have been widely reported in poststroke survivors during locomotion [18], arm isometric contractions [19], and voluntary reaching movements [20]- [23]. Muscle synergies have also been explored in subjects with spinal cord injury, revealing substantial differences to healthy individuals during different motor tasks: hand grip function [24], different locomotor tasks in children [25], postural balance [26], [27], gait [28], and standing protocols under spinal cord stimulation [29]. All this evidence supports that muscle synergies can be a powerful tool for characterizing motor behavior and providing physiological markers to assess motor function in injured patients. ...
Reaching and grasping (R&G) is a skilled voluntary movement which is critical for animals. In this work, we aim to identify muscle synergy patterns from R&G movements in rats and show how these patterns can be used to characterize such movements and investigate their consistency and repeatability. For that purpose, we analyzed the electromyographic (EMG) activity of five forelimb muscles recorded while the animals were engaged in R&G tasks. Our dataset included 200 R&G attempts from three different rats. Non-negative matrix factorization was used to decompose EMG signals and extract muscle synergies. We compared all pairs of attempts and created cross-validated models to study intra- and inter-subject variability. We found that three synergies were enough to accurately reconstruct the EMG envelopes. These muscle synergies and their corresponding activation coefficients were very similar for all the attempts in the database, providing a general pattern to describe the movement. Results suggested that the movement strategy adopted by an individual in its different attempts was highly repetitive, but also resembled the strategies adopted by the other animals. Inter-subject variability was not much higher than intra-subject variability. This study is a proof-of-concept, but the proposed approaches can help to establish whether there is a stereotyped pattern of neuromuscular activity in R&G movement in healthy rats, and the changes that occur in animal models of acute neurological injuries. Research on muscle synergies could elucidate motor control mechanisms, and lead to quantitative tools for evaluating upper limb motor impairment after an injury.
... However, Sosnoff et al. [11] quantified muscle properties using electromyography (EMG) recordings, which is a limitation of this work since such recordings cannot directly evaluate muscular characteristics. Similarly, Shin and Sosnoff [12] tested whether Trembling fluctuations could reflect impairment levels in individuals with spinal cord injury (SCI) during sitting balance, with the underlying hypothesis that people with different levels of SCI are more spastic compared to the control group due to increased stiffness [13,14]. However, there were no differences in Rambling and Trembling fluctuations between people with SCI compared to control subjects. ...
The rambling and trembling analysis separates the center of pressure (COP) fluctuations into two components: rambling (supraspinal contribution) and trembling (muscle stiffness / reflexive properties contribution). We examined whether the trembling component is correlated to the contractile properties (muscle stiffness and contraction time) of lower limb superficial skeletal muscles to experimentally test the rambling and trembling hypothesis. We hypothesized that muscle stiffness and contraction time, would be: (a) more correlated with; and (b) have a greater impact on the trembling component compared to the rambling component. Thirty-two healthy young adults were recruited for the study and tensiomyography was used to assess mechanical muscle responses to a single electrical stimulus to calculate muscle stiffness and contraction time based on radial muscle belly displacement measurements of lower limb muscles unilaterally. Moreover, upright postural control was assessed using a force plate to record ground reaction forces and moments and calculate the COP fluctuations during two 30 seconds trials. From the COP fluctuations, rambling and trembling time series were extracted, and all fluctuation time series were described using a number of different time-domain and frequency-domain parameters in both the anterior-posterior and medial-lateral directions. Our results demonstrated that both muscle stiffness and contraction time were moderately correlated with time-domain and frequency-domain parameters of the trembling component, as compared with those of the rambling component which was not as well correlated. Moreover, they also predicted the trembling component better. Overall, these results imply that postural control during quiet stance is, in part, related to intrinsic muscle stiffness in the lower extremities. Moreover, we showed that the rambling and trembling hypothesis is effective in separating postural sway fluctuations during upright posture to extract the contributions of muscle stiffness / reflexive properties (trembling), and likely the supraspinal contribution (rambling).
... Series: Journal of Physics: Conf. Series 1176 (2019) 052024 IOP Publishing doi:10.1088/1742-6596/1176/5/052024 2 movement and do work, we should take the specific movement corresponding to the original muscle group as the object of piezoelectric signal collection, so as to better reflect the corresponding motion intention of the knee joint [3][4][5][6] . ...
Aiming at the human body exoskeleton motion intention recognition process, based on the pressure signals of muscle groups of control, building joint motion information acquisition system, the application of multi-sensor information fusion technique based on neural network, based on the piezoelectric signal muscle as input and output of the joint angle trajectory motion intention model, calculate the joint exercise intention and angle track. Finally, the knee flexion and extension movement as the main object of study, through calculation and practical test, the ideal results are obtained. It shows that the motion signals of the knee joint can be reflected by the piezoelectric signals collected during the motion of the knee joint.
... The application of a clustering algorithm for diagnosing gait disorder is discussed in a later section. Patients with thoracic spinal cord injury revealed lesser modules, higher cocontraction and, less directional tuning in relation to healthy individuals [46]. It is likely that the number of dimensional space was affected due to the choice of preprocessing [47]. ...
Electromyography (EMG) is a commonly used technique to record myoelectric signals, i.e., motor neuron signals that originate from the central nervous system (CNS) and synergistically activate groups of muscles resulting in movement. EMG patterns underlying movement, recorded using surface or needle electrodes, can be used to detect movement and gait abnormalities. In this review article, we examine EMG signal processing techniques that have been applied for diagnosing gait disorders. These techniques span from traditional statistical tests to complex machine learning algorithms. We particularly emphasize those techniques are promising for clinical applications. This study is pertinent to both medical and engineering research communities and is potentially helpful in advancing diagnostics and designing rehabilitation devices.
... Therefore, a fatigue-induced reduction in the ST's ability to mediate eccentric knee extension demands (Ono et al., 2010(Ono et al., , 2011) is likely to elevate imposed demands upon its synergists in a disproportionate fashion. While the ability to access the wealth of strategies within motor abundance is seen to be a representation of a robust movement system (Milosevic et al., 2017), a muscle less structurally tolerant or mechanically advantaged to mediate such imposed demands would indeed appear more vulnerable. This perspective suggests that while any potential strategy to the accommodation of the demands of terminal swing are welcome, some may possess greater risk than others. ...
A synergistic algebra appears to be at play in the body, sustaining an athlete's performance in the face of competing demands, yet these may be associated with risk. Akin to the employment of redundancy within engineering sciences, we suggest this phenomenon can be strategically harnessed through careful consideration of programme scheduling, contraction profiles and exercise design to share the work amongst other tissues and access the plasticity evident within the movement system.
Tabled 1
SynergistsPrimary Focus
Biceps Femoris Long Head, Semimembranosus
Sagittal plane, eccentric force production, fascicle elongation
Semitendinosus, Biceps Femoris Short Head, Popliteus
Sagittal and transverse plane fatigue tolerance
Gluteus Maximus
Sagittal plane, concentric force production and fascicle shortening
Adductor Magnus
Tri-planar eccentric force production, fascicle elongation
Gastrocnemius
Increased stiffness facilitating enhanced force transfer and tendon contribution
Oblique abdominals
Tri-planar eccentric force production within small amplitudes of muscle length around lumbo-pelvic neutral alignment
Specific muscles in the management of hamstring injuries for repeat sprint athletes (footballers).
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Objective:
To confirm the structural validity of the Trunk Assessment Scale for Spinal Cord Injury (TASS).
Participants and methods:
We evaluated 104 Japanese individuals with a spinal cord injury (SCI) (age 63.5 ± 12.2 years; 64 with tetraplegia) with the TASS 1-3 times. We conducted a Rasch analysis to assess the TASS' unidimensionality, fit statistics, category probability curve, ceiling/floor effects, local independence, reliability, and difference item function (DIF).
Results:
The TASS was observed to be a unidimensional and highly reproducible scale of item difficulty hierarchy that sufficiently identifies the superiority of the examinee's ability. The TASS was easy for the participants of this study. One TASS item was a misfit based on the infit and outfit mean square; another item also showed a DIF contrast for age. Several items were found to require a synthesis or modification of the content. The TASS showed a floor effect, and most of the non-scorers were individuals with a complete SCI.
Conclusion:
Our findings clarify the structural validity of the TASS, and our analyses revealed that the TASS includes an unfitness item and was less challenging for individuals with SCIs. The improvements suggested by these results provide important information for modifying the TASS to a more useful instrument.
Arm cycling is used for cardiorespiratory rehabilitation but its therapeutic effects on the neural control of the trunk after spinal cord injury (SCI) remain unclear. We investigated the effects of single session of arm cycling on corticospinal excitability, and the feasibility of home-based arm cycling exercise training on volitional control of the erector spinae (ES) in individuals with incomplete SCI. Using transcranial magnetic stimulation, we assessed motor evoked potentials (MEPs) in the ES before and after 30 minutes of arm cycling in 15 individuals with SCI and 15 able-bodied controls (Experiment 1). Both groups showed increased ES MEP size after the arm cycling. The participants with SCI subsequently underwent a six-week home-based arm cycling exercise training (Experiment 2). MEP amplitudes and activity of the ES, and movements of the trunk during reaching, self-initiated rapid shoulder flexion, and predicted external perturbation tasks were measured. After the training, individuals with SCI reached further and improved trajectory of the trunk during the rapid shoulder flexion task, accompanied by increased ES activity and MEP amplitudes. Exercise adherence was excellent. We demonstrate preserved corticospinal drive after single arm cycling session and feasible home-based arm cycling exercise training for individuals with SCI for trunk rehabilitation.
Background:
The Trunk Assessment Scale for Spinal Cord Injury (TASS) and the Trunk Control Test for individuals with a Spinal Cord Injury (TCT-SCI) are highly reliable assessment tools for evaluating the trunk function of individuals with SCIs. However, the potential differences in the validity of these two scales are unclear.
Objectives:
To evaluate the criterion validity of the TASS and the construct validity of the TASS and TCT-SCI.
Participants and methods:
We evaluated 30 individuals with SCIs (age 63.8 ± 10.7 yrs, 17 with tetraplegia). To evaluate criterion validity, we calculated Spearman's rho between the TASS and the gold standard (the TCT-SCI). To determine construct validity, we used the following hypothesis testing approaches: (i) calculating Spearman's rho between each scale and the upper and lower extremity motor scores (UEMS, LEMS), the Walking Index for SCI-II (WISCI-II), and the motor score of the Functional Independence Measure (mFIM); and (ii) determining the cut-off point for identifying ambulators with SCIs (≥ 3 points on item 12 of Spinal Cord Independent Measure III) by a receiver operating characteristics analysis.
Results:
A moderate correlation was confirmed between the TASS and the TCT-SCI (r = 0.68). Construct validity was supported by six of the eight prior hypotheses. The cut-off points for identifying ambulators with SCIs were 26 points (TASS) and 18 points (TCT-SCI).
Conclusion:
Our results indicate that the contents of the TASS and the TCT-SCI might reflect the epidemiological characteristics of the populations in which they were developed.
Over the past several decades, many scholars have investigated muscle synergy as a promising tool for evaluating motor function. However, it is challenging to obtain favorable robustness using the general muscle synergy identification algorithms, namely non-negative matrix factorization (NMF), independent component analysis (ICA), and factor analysis (FA). Some scholars have proposed improved muscle synergy identification algorithms to overcome the shortcomings of these approaches, such as singular value decomposition NMF (SVD-NMF), sparse NMF (S-NMF), and multivariate curve resolution-alternating least squares (MCR-ALS). However, performance comparisons of these algorithms are seldom conducted. In this study, experimental electromyography (EMG) data collected from healthy individuals and stroke survivors were applied to assess the repeatability and intra-subject consistency of NMF, SVD-NMF, S-NMF, ICA, FA, and MCR-ALS. MCR-ALS presented higher repeatability and intra-subject consistencies than the other algorithms. More synergies and lower intra-subject consistencies were observed in stroke survivors than in healthy individuals. Thus, MCR-ALS is considered a favorable muscle synergy identification algorithm for patients with neural system disorders.
Upper- and lower-limb neuromuscular electrical stimulation (NMES) is known to modulate the excitability of the neural motor circuits. However, it remains unclear whether short-duration trunk muscle NMES could achieve similar neuromodulation effects. We assessed motor evoked potentials (MEPs) elicited through transcranial magnetic stimulation of the primary motor cortex representation of the trunk extensor muscles to evaluate corticospinal excitability. Moreover, cervicomedullary motor evoked potentials (CMEPs) were assessed through cervicomedullary junction magnetic stimulation to evaluate subcortical excitability. Twelve able-bodied individuals participated in the MEP study, and another twelve in the CMEP study. During the interventions, NMES was applied bilaterally to activate the erector spinae muscle and produce intermittent contractions (20 s ON/20 s OFF) for a total of 20 min while participants remained seated. Assessments were performed: (i) before; (ii) during (in brief periods when NMES was OFF); and (iii) immediately after the interventions to compare MEP or CMEP excitability. Our results showed that MEP responses were not affected by trunk NMES, while CMEP responses were facilitated for approximately 8 min during the intervention, and returned to baseline before the end of the 20 min stimulating period. Our findings therefore suggest that short-duration NMES of the trunk extensor muscles likely does not affect the corticospinal excitability, but it has a potential to facilitate subcortical neural circuits immediately after starting the intervention. These findings indicate that short-duration application of NEMS may be helpful in rehabilitation to enhance neuromodulation of the trunk subcortical neural motor circuits.
Background:
Assessing co-activation characteristics in knee osteoarthritis (knee OA) using method of quantification of the activity ratio (such as the co-contraction index (CCI) or the directed co-activation ratios (DCAR)) for surface electromyography (EMG) has been reported. However, no studies have discussed the differences in results between non-negative matrix factorization (NNMF) and the DCAR.
Research question:
Does DCAR or NNMF reflect the characteristic co-activation pattern of knee OA while using EMG normalized by the peak dynamic method?
Methods:
Ten elderly control participants (EC) and ten knee OA patients (KOA) volunteered to participate in this study. EMG data from 20 participants were obtained from our previous study. Patients with knee OA were recruited from a local orthopedic clinic. The DCAR of agonist and antagonist muscles and the number of modules using NNMF were calculated to evaluate multiple muscle co-activations. An independent t-test statistical parametric mapping approach was used to compare the DCAR between the two groups. The difference in the number of modules between EC and KOA was evaluated using the Wilcoxon rank-sum test.
Results:
There was no significant difference in the DCAR between the two groups. However, NNMF had significantly fewer modules with KOA than with EC.
Significance:
The NNMF with the ratio of the amplitude of each muscle and duration of activity as variables reflected the co-activation of KOA, characterized by the high synchronous and prolonged activity of each muscle. Therefore, the NNMF is suitable for extracting characteristic muscle activity patterns of knee OA independent of the normalization method.
Background: A substantial proportion of individuals with incomplete spinal cord injury (SCI) exhibit reduced volitional control of trunk muscles due to damage of the corticospinal tract, resulting in impaired postural control and function. Studies using conventional bipolar electromyography (EMG) showed altered activity of the trunk muscles in people with SCI. However, the spatial distribution of trunk muscle activity remains unknown. Therefore, this study aimed to investigate the spatial distribution of the erector spinae (ES) below the level of injury in individuals with incomplete SCI during postural tasks and multidirectional reaching tasks using high-density EMG.
Methods: Twenty-one individuals with incomplete SCI and 21 age-matched healthy controls performed two postural tasks (rapid shoulder flexion and external perturbation tasks) and multidirectional reaching tasks. EMG amplitude of the thoracic ES and displacement of the arm, trunk, and centre of pressure were recorded during the tasks.
Results: Overall, the EMG amplitude of the ES was lower, and activation was distributed more in the caudal part of the ES in individuals with SCI compared with the controls during the postural and reaching tasks. EMG amplitude was greater during reaching forward than returning to the upright posture in the controls; however, this phase-dependent difference in the EMG amplitude was not present in individuals with SCI.
Conclusions: Our findings demonstrate alterations in regional activation of the thoracic ES during postural and reaching tasks after SCI, suggesting a loss of selective control from the central nervous system to the trunk muscles.
Objective:
To confirm the responsiveness and minimal clinically important differences (MCIDs) of the Trunk Assessment Scale for Spinal Cord Injury (TASS).
Participants and methods:
We evaluated 48 Japanese individuals with spinal cord injury (SCI) (age 64.1 ± 10.4 yrs, 28 with tetraplegia) admitted to two institutions at admission, at 1 month of hospitalization, and at discharge with the TASS, the Trunk Control Test in individuals with an SCI (TCT-SCI) motor score, the Functional Independence Measure motor score (mFIM), and the Global Rating of Change Scale (GRCS). We assessed the TASS responsiveness by determining the correlation coefficients for the changes in the TASS' and other assessments' scores. We calculated the MCIDs by five anchor-based methods.
Results:
The changes in the TASS and those in the other assessments were weakly correlated at 1 month and moderately correlated at discharge. The TASS MCIDs were observed at 1 month and at discharge.
Conclusion:
Our findings confirmed that the change in TASS scores had weak-to-moderate correlations with the changes in the participants' upper- and lower-limb function and activities of daily living. Using the MCID for the TASS determined by anchor-based methods may lead to a better interpretation of changes in the trunk function of individuals with SCIs.
Manipulations require complex upper-limb movements in which the central nervous system (CNS) must deal with many degrees of freedom. Evidence suggests that the CNS utilizes motor primitives called muscle synergies to simplify the production of movements. However, the exact neural mechanism underlying muscle synergies to control a wide array of manipulations is not fully understood. Here, we tested whether there are basic units of muscle synergies that can explain a diverse range of manipulations. We measured the electromyographic activities of 20 muscles across the shoulder, elbow, and wrist and fingers during 24 manipulation tasks. As a result, non-negative matrix factorization identified nine basic units of muscle synergies derived from the upper limb muscles that are shared across all tasks. The high similarity between muscle synergies of each of the 24 tasks and various combinations of nine basic unit muscle synergies in a single and/or merging state provides evidence that the CNS flexibly selects and modifies the degree of contribution of the nine basic units of muscle synergies to overcome different mechanical demands of tasks.
Context: Although neuromuscular deficits in people with chronic ankle instability (CAI) have been identified, previous studies mostly investigated the activation of multiple muscles in isolation. Investigating muscle synergies in people with CAI would provide information about the coordination and control of neuromuscular activation strategies and could hold important information for understanding and rehabilitating neuromuscular deficits in this population.
Objective: The purpose of this study was to investigate muscle synergies in people with CAI and healthy controls as they perform different cutting tasks.
Design: Cross-sectional study
Setting: Laboratory
Participants: Eleven people with CAI (22 ± 3 years, 1.68 ± 0.11 m, 69.0 ± 19.1 kg) and 11 healthy controls (CON) (23 ± 4 years, 1.74 ± 0.11 m, 66.8 ± 15.5 kg) participated in the current study.
Main Outcome Measures: Muscle synergies were extracted from the EMG of the soleus, medial gastrocnemius, lateral gastrocnemius, tibialis anterior, and fibularis longus muscles during anticipated and unanticipated cutting tasks. The number of synergies, activation coefficients, and muscle-specific weighting coefficients were compared between groups and across tasks.
Results: The number of muscle synergies were the same for each group and task. The CAI group exhibited significantly greater (p = 0.023) tibialis anterior weighting coefficients within Synergy 1 compared to the CON group. In addition, both groups exhibited greater fibularis longus (p = 0.029) weighting coefficients within Synergy 2 during unanticipated cutting compared to anticipated cutting.
Conclusion: These results suggest that while both groups used a neuromuscular control strategy of similar complexity / dimensionality to perform the cutting tasks, people with CAI exhibited different muscle-specific weightings characterized by greater emphasis on tibialis anterior function within Synergy 1, which may reflect an effort to increase joint stability to compensate for the presence of ankle instability.
Background
Postural strategies are enabled by rapid muscle activation sequences to prevent a fall. Intralimb muscular couplings underlie these postural strategies are likely impaired after incomplete spinal cord injury (iSCI), leading to inappropriate postural reactions and increased fall risk; yet, the nature of these changes is unknown.
Research question
Identify changes occurring in intralimb coupling following a perturbation in individuals with iSCI.
Methods
Ten men with iSCI and eight age-matched controls (CTRL) stood on a force-platform that was randomly tilted forward or backward. Electromyographic (EMG) activity of the lower limb muscles was recorded, and coactivation or simultaneous facilitation/suppression between pairs of muscles was analyzed. Onset and duration of coupling latency, intralimb coupling delay, and amplitude ratios were measured in the distal (soleus [SOL]/tibialis anterior [TA]), proximal (biceps femoris [BF]/vastus lateralis [VL]), anterior (TA-VL), and posterior (SOL-BF) muscle couplings.
Results
In forward tilt, the main coupling was TA-SOL co-contraction for both groups, but the latency was longer and the duration shorter in SCI participants. In backward tilt, the TA-VL co-activation was the main coupling in CTRL (88%), although it was also expressed by 60% of SCI participant with a delayed latency. The facilitation/suppression of TA-SOL was the main coupling in SCI group (80% vs 63% in CTRL). Delayed coupling latencies were more pronounced in individuals with cervical iSCI and were correlated with the strength of lower limbs.
Significance
Similar muscular couplings are present in both groups but are delayed, which might contribute to postural reaction deficits in individuals with iSCI.
The central nervous system (CNS) may produce coordinated motor outputs via the combination of motor modules representable as muscle synergies. Identification of muscle synergies has hitherto relied on applying factorization algorithms to multi-muscle electromyographic data (EMGs) recorded during motor behaviors. Recent studies have attempted to validate the neural basis of the muscle synergies identified by independently retrieving the muscle synergies through CNS manipulations and analytic techniques such as spike-triggered averaging of EMGs. Experimental data have demonstrated the pivotal role of the spinal premotor interneurons in the synergies' organization and the presence of motor cortical loci whose stimulations offer access to the synergies, but whether the motor cortex is also involved in organizing the synergies has remained unsettled. We argue that one difficulty inherent in current approaches to probing the synergies' neural basis is that the EMG generative model based on linear combination of synergies and the decomposition algorithms used for synergy identification are not grounded on enough prior knowledge from neurophysiology. Progress may be facilitated by constraining or updating the model and algorithms with knowledge derived directly from CNS manipulations or recordings. An investigative framework based on evaluating the relevance of neurophysiologically constrained models of muscle synergies to natural motor behaviors will allow a more sophisticated understanding of motor modularity, which will help the community move forward from the current debate on the neural versus non-neural origin of muscle synergies.
Recent work suggests that kinematics-based electrical stimulation may restore dynamic trunk stability following spinal cord injury. However, to ensure fatigue-resistant control, knowledge of the relation between body motion and the activity of relevant muscles during non-impaired, unstable sitting may be beneficial. Therefore, our objective was to quantify the spatial and temporal relationships between (1) characteristic angular kinematics (i.e., the kinematics characterizing trunk stabilization) and (2) trunk and upper leg muscle activity in unstable sitting as elicited via a wobble board. Wobble board motion and bilateral electromyograms from fourteen trunk and upper leg muscles were recorded in fifteen non-disabled participants (i.e., individuals with no history of neurological or musculoskeletal impairments or pain, gait or balance difficulties, or use of a walking aid) sitting on a wobble board. The relationship between wobble board tilt and the electromyograms was quantified using cross-correlation analysis. During unstable sitting, the trunk was stabilized through direction-specific activation of the trunk and upper leg muscles, preceding wobble board displacement by 110 to 230 ms. Direction-specific activation implies the presence of active neural control, while preceding activation may be needed to account for known torque generation time delays. Furthermore, the specific muscles activated for each direction of wobble board displacement suggest the use of stiffness control in the anterior-posterior, but not medial-lateral direction. Future work will use the gained insights in defining the muscle stimulation patterns of kinematics-based neuroprostheses that can restore trunk stability following impairment.
The aim of this study was to quantify and compare the inter-limb muscle coordination during crawling between typically developing infants and infants with developmental delay. Typically developing (TD, $\text{N}=$20) infants and infants with at risk of developmental delay (ARDD, $\textbf{N}=$33) or confirmed developmental delayCDD, N=14) participated in this study. Surface electromyography of eight muscles from arms and legs and the corresponding joint kinematic data were collected while they were crawling on hands and knees at their self-selected velocity. The number of used inter-limb muscle synergies during crawling was identified by nonnegative matrix factorization algorithm. Our results showed that there was no significant difference in the number of used muscle synergies between ARDD and TD infants during crawling. However, a reduced number of synergies were identified in infants with CDD, as compared to that in TD and ARDD infants, indicating constrained neuromuscular control strategy during crawling in developmental delayed infants. The absence of inter-limb muscle synergies may be one of the mechanisms underlying the impairments of crawling in developmental delayed infants, who are at high risk of cerebral palsy. This result also suggests that the metrics of muscle synergy during infant crawling, such as the number of synergy, may be feasible as a biomarker for early diagnosis of infants with cerebral palsy.
Hands-and-knees-crawling is an important motor developmental milestone and a unique window into the development of central nervous system (CNS). Mobility during crawling is regularly used in clinical assessments to identify delays in motor development. However, possible contribution from CNS impairments to motor development delay is still unknown. The aim of this study was to quantify and compare inter-limb muscle synergy and kinematics during crawling among infants at a similar developmental age, however, clinically determined to be typically developing (TD, N = 20) infants, infants at risk of developmental delay (ARDD, N = 33), or infants with confirmed developmental delay (CDD, N = 13). We hypothesized that even though all of the groups are at a similar developmental age, there would be differences in kinematic measures during crawling, and such differences would be associated with CNS impairment as measured by electromyography (EMG) features. Surface EMG of eight arm and leg muscles and the corresponding joint kinematic data were collected while participants crawled on hands and knees at their self-selected velocity. Temporal-spatial parameters and normalized Jerk-Cost (JC) function (i.e., smoothness of movement) were computed from the measured kinematics. The inter-limb muscle synergy and the number of co-activating muscles per synergy were measured using EMGs. We found that the infants with CDD demonstrated higher normalized JC values (less movement smoothness), fewer muscle synergies, and more co-activating muscles per synergy, compared to infants with TD (p < 0.05) and ARDD (p < 0.05). Furthermore, the normalized JC values were correlated (p < 0.05) with the number of co-activation muscles per synergy. Our results suggest a constrained neuromuscular control strategy due to neurological injury in infants with CDD, and such constrain may contribute to the reduced movement smoothness in infant crawling.
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In humans, trunk muscles have an essential role in postural control as well as walking. However, little is known about the mechanisms of interaction with different muscles, especially related to how trunk muscles interact with the limbs. Contraction of muscles can modulate the corticospinal excitability not only of the contracted muscle, but also of other muscles even in the remote segments of the body. However, "remote effect" mechanism has only been examined for inter-limb interactions. The aim of our current study was to test if there are trunk-limb interactions in the corticospinal pathways. We examined corticospinal excitability of: (a) trunk muscles at rest when hands, legs and jaw muscles were contracted and; (b) hand, leg, and jaw muscles at rest when trunk muscles were contracted. We measured motor evoked potentials elicited using transcranial magnetic stimulation in the rectus abdominis, flexor digitorum superficialis, masseter, tibialis anterior muscles under the following experimental conditions: (1) participants remained relaxed (Rest); (2) during trunk contraction (Trunk); (3) during bilateral hand clenching (Hands); (4) during jaw clenching (Jaw); and (5) during bilateral ankle dorsiflexion (Legs). Each condition was performed at three different stimulation intensities and conditions were randomized between participants. We found that voluntary contraction of trunk muscle facilitated the corticospinal excitability of upper-limb and lower-limb muscles during rest state. Furthermore, voluntary contraction of upper-limb muscle also facilitated the corticospinal excitability of trunk muscles during rest state. Overall, these results suggest the existence of trunk-limb interaction in the corticospinal pathway, which is likely depended on proximity of the trunk and limb representation in the motor cortex.
Trunk muscles are responsible for maintaining trunk stability during sitting. However, the effects of anticipation of perturbation on trunk muscle responses are not well understood. The objectives of this study were to identify the responses of trunk muscles to sudden support surface translations and quantify the effects of anticipation of direction and time of perturbation on the trunk neuromuscular responses. Twelve able-bodied individuals participated in the study. Participants were seated on a kneeling chair and support surface translations were applied in the forward and backward directions with and without direction and time of perturbation cues. The trunk started moving on average approximately 40 ms after the perturbation. During unanticipated perturbations, average latencies of the trunk muscle contractions were in the range between 103.4 and 117.4 ms. When participants anticipated the perturbations, trunk muscle latencies were reduced by 16.8 ± 10.0 ms and the time it took the trunk to reach maximum velocity was also reduced, suggesting a biomechanical advantage caused by faster muscle responses. These results suggested that trunk muscles have medium latency responses and use reflexive mechanisms. Moreover, anticipation of perturbation decreased trunk muscles latencies, suggesting that the central nervous system modulated readiness of the trunk based on anticipatory information.
Background:
The purpose of this study was to examine the impact of functional electrical stimulation (FES) induced co-activation of trunk muscles during quiet sitting. We hypothesized that FES applied to the trunk muscles will increase trunk stiffness. The objectives of this study were to: 1) compare the center of pressure (COP) fluctuations during unsupported and FES-assisted quiet sitting - an experimental study and; 2) investigate how FES influences sitting balance - an analytical (simulation) study.
Methods:
The experimental study involved 15 able-bodied individuals who were seated on an instrumented chair. During the experiment, COP of the body projected on the seating surface was calculated to compare sitting stability of participants during unsupported and FES-assisted quiet sitting. The analytical (simulation) study examined dynamics of quiet sitting using an inverted pendulum model, representing the body, and a proportional-derivative (PD) controller, representing the central nervous system control. This model was used to analyze the relationship between increased trunk stiffness and COP fluctuations.
Results:
In the experimental study, the COP fluctuations showed that: i) the mean velocity, mean frequency and the power frequency were higher during FES-assisted sitting; ii) the frequency dispersion for anterior-posterior fluctuations was smaller during FES-assisted sitting; and iii) the mean distance, range and centroidal frequency did not change during FES-assisted sitting. The analytical (simulation) study showed that increased mechanical stiffness of the trunk had the same effect on COP fluctuations as the FES.
Conclusions:
The results of this study suggest that FES applied to the key trunk muscles increases the speed of the COP fluctuations by increasing the trunk stiffness during quiet sitting.
This chapter examines methodologies for dimensional analysis and linear decomposition of multivariate data sets, and discusses their implicit hypotheses and interpretations for muscle coordination of movement. It presents tutorials to compare how two common methods-principal components analysis (PCA) and non-negative matrix factorization (NMF)-decompose electromyographic signals into underlying components. To facilitate the integration of such mathematical techniques with physiological hypothesis testing, the chapter focuses on developing an intuitive understanding to the two techniques. It provides a simple two-dimensional tutorial, focusing on how orthogonality constraints in PCA and non-negativity constraints in NMF impact the resulting data decomposition and physiological relevance. Examples are presented using real data sets from human balance control and locomotion. The chapter examines the structure of the resulting components, their robustness across tasks, and their implications for various muscle synergy hypotheses. The chapter addresses practical issues and caveats in organizing datasets, the selection of the appropriate number of components, and considerations and pitfalls of experimental design and analysis, as well as offering suggestions and cautions for interpreting results. Based on these comparisons and on the work in the visual system over the last decade, evidence is presented for the increased neurophysiological relevance of the factors derived from NMF compared to PCA.
Neuromechanical principles define the properties and problems that shape neural solutions for movement. Although the theoretical and experimental evidence is debated, we present arguments for consistent structures in motor patterns, i.e., motor modules, that are neuromechanical solutions for movement particular to an individual and shaped by evolutionary, developmental, and learning processes. As a consequence, motor modules may be useful in assessing sensorimotor deficits specific to an individual and define targets for the rational development of novel rehabilitation therapies that enhance neural plasticity and sculpt motor recovery. We propose that motor module organization is disrupted and may be improved by therapy in spinal cord injury, stroke, and Parkinson's disease. Recent studies provide insights into the yet-unknown underlying neural mechanisms of motor modules, motor impairment, and motor learning and may lead to better understanding of the causal nature of modularity and its underlying neural substrates.
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Although cats that have been spinalized can also be trained to stand and step with full weight support, directionally-appropriate long-latency responses to perturbations are impaired, suggesting that these behaviors are mediated by distinct neural mechanisms. However, it remains unclear whether these responses reflect an attenuated postural response using the appropriate muscular coordination patterns for balance, or are due to fundamentally different neural mechanisms such as increased muscular co-contraction, or short-latency stretch responses. Here we used muscle synergy analysis on previously collected data to identify whether there are changes in the spatial organization of muscle activity for balance within an animal following spinalization. We hypothesized that the modular organization of muscle activity for balance control is disrupted by spinal cord transection. In each of 4 animals, muscle synergies were extracted from postural muscle activity both before and after spinalization using non-negative matrix factorization. Muscle synergy number was reduced post-spinalization in 3 animals, and increased in 1 animal. However, muscle synergy structure was greatly altered post-spinalization with reduced direction tuning, suggesting little consistent organization of muscle activity. Further, muscle synergy recruitment was correlated to subsequent force production in the intact but not spinalized condition. Our results demonstrate that the modular structure of sensorimotor feedback responses for balance control are severely disrupted post-spinalization, suggesting that the muscle synergies for balance control are not accessible by spinal circuits alone. Moreover, we demonstrate that spinal mechanisms underlying weight support are distinct from brainstem mechanisms underlying directional balance control. -
A module is a functional unit of the nervous system that specifies functionally-relevant patterns of muscle activation. In adults, 4-5 modules account for muscle activation during walking. Neurologic injury alters modular control and is associated with walking impairments. The effect of neurologic injury on modular control in children is unknown and may differ from adults due to their immature and developing nervous systems. We examined modular control of locomotor tasks in children with incomplete spinal cord injuries (ISCIs) and control children. Five controls (8.6 ± 2.7 years) and five children with ISCIs (8.6 ± 3.7 years) performed treadmill walking, overground walking, pedaling, supine lower extremity flexion/extension, stair climbing, and crawling. Electromyograms (EMGs) were recorded in bilateral leg muscles. Non-negative matrix factorization was applied and the minimum number of modules required to achieve 90% of the "variance accounted for" (VAF) was calculated. On average, 3.5 modules explained muscle activation in the controls; whereas, 2.4 modules were required in the children with ISCIs. To determine if control is similar across tasks, the module weightings identified from treadmill walking were used to reconstruct the EMGs from each of the other tasks. This resulted in VAF values exceeding 86% for each child and each locomotor task. Our results suggest that 1) modularity is constrained in children with ISCIs; 2) for each child, similar neural control mechanisms are used across locomotor tasks. These findings suggest that interventions that activate the neuromuscular system to enhance walking also may influence the control of other locomotor tasks.
Objectives: To compare multidirectional seated postural stability between individuals with spinal cord injury and able-bodied- individuals and to evaluate the impact of abdominal and low back muscle paralysis on multidirectional seated stability. Design: Case-control study. Participants: Fifteen individuals with complete or incomplete spinal cord injury affecting various vertebral levels participated in this study and were gender-matched with 15 able-bodied individuals. Methods: Participants were instructed to lean as far as possible in 8 directions, set apart by 45° intervals, while seated on an instrumented chair with their feet placed on force plates. Eight direction-specific stability indices and a global stability index were calculated. Results: The global stability index and all direction-specific indices, except in the anterior and posterior directions, were lower in individuals with spinal cord injury than in able-bodied individuals. However, the individuals with spinal cord injury who had partial or full control of their abdominal and lower trunk muscles obtained a similar global stability index and similar direction-specific indices compared to the able-bodied individuals. Conclusion: Multidirectional seated postural stability is reduced in individuals with SCI who have paralysis of the abdominal and lower back muscles in comparison to able-bodied individuals.
The modular control of muscles in groups, often referred to as muscle synergies, has been proposed to provide a motor repertoire of actions for the robust control of movement. However, it is not clear whether muscle synergies identified in one task are also recruited by different neural pathways subserving other motor behaviors. We tested the hypothesis that voluntary and reactive modifications to walking in humans result from the recruitment of locomotor muscle synergies. We recorded the activity of 16 muscles in the right leg as subjects walked a 7.5 m path at two different speeds. To elicit a second motor behavior, midway through the path we imposed ramp and hold translation perturbations of the support surface in each of four cardinal directions. Variations in the temporal recruitment of locomotor muscle synergies could account for cycle-by-cycle variations in muscle activity across strides. Locomotor muscle synergies were also recruited in atypical phases of gait, accounting for both anticipatory gait modifications before perturbations and reactive feedback responses to perturbations. Our findings are consistent with the idea that a common pool of spatially fixed locomotor muscle synergies can be recruited by different neural pathways, including the central pattern generator for walking, brainstem pathways for balance control, and cortical pathways mediating voluntary gait modifications. Together with electrophysiological studies, our work suggests that muscle synergies may provide a library of motor subtasks that can be flexibly recruited by parallel descending pathways to generate a variety of complex natural movements in the upper and lower limbs.
The experimental findings herein reported are aimed at gaining a perspective on the complex neural events that follow lesions of the motor cortical areas. Cortical damage, whether by trauma or stroke, interferes with the flow of descending signals to the modular interneuronal structures of the spinal cord. These spinal modules subserve normal motor behaviors by activating groups of muscles as individual units (muscle synergies). Damage to the motor cortical areas disrupts the orchestration of the modules, resulting in abnormal movements. To gain insights into this complex process, we recorded myoelectric signals from multiple upper-limb muscles in subjects with cortical lesions. We used a factorization algorithm to identify the muscle synergies. Our factorization analysis revealed, in a quantitative way, three distinct patterns of muscle coordination-including preservation, merging, and fractionation of muscle synergies-that reflect the multiple neural responses that occur after cortical damage. These patterns varied as a function of both the severity of functional impairment and the temporal distance from stroke onset. We think these muscle-synergy patterns can be used as physiological markers of the status of any patient with stroke or trauma, thereby guiding the development of different rehabilitation approaches, as well as future physiological experiments for a further understanding of postinjury mechanisms of motor control and recovery.
The purpose of this study was to demonstrate the use of the self-organizing map (SOM) method for visualization, modeling, and comparison of trunk neuromuscular synergies during perturbed sitting. Thirteen participants were perturbed at the level of the sternum, in eight directions during sitting. Electromyographic (EMG) responses of ten trunk muscles involved in postural control were recorded. The SOM was used to encode the EMG responses on a 2-D projection (i.e., visualization). The result contains similar patterns mapped close together on the plot therefore forming clusters of data. Such visualization of ten EMG responses, following eight directional perturbations, allows for comparisons of direction-dependent postural synergies. Direction-dependent neuromuscular response models for each muscle were then constructed from the SOM visualization. The results demonstrated that the SOM was able to encode neuromuscular responses, and the SOM visualization showed direction-dependent differences in the postural synergies. Moreover, each muscle was modeled using the SOM-based method, and derived models showed that all muscles, except for one, produced a Gaussian fit for direction-dependent responses. Overall, SOM analysis offers a reverse engineering method for exploration and comparison of complex neuromuscular systems, which can describe postural synergies at a glance.
Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis that muscle activation patterns during walking are produced through the variable activation of a small set of motor modules. In 20 healthy control subjects, EMG signals from eight leg muscles were measured across a range of walking speeds. Four motor modules identified through nonnegative matrix factorization were sufficient to account for variability of muscle activation from step to step and across speeds. Next, consistent with the clinical notion of abnormal limb flexion-extension synergies post-stroke, we tested the hypothesis that subjects with post-stroke hemiparesis would have altered motor modules, leading to impaired walking performance. In post-stroke subjects (n = 55), a less complex coordination pattern was shown. Fewer modules were needed to account for muscle activation during walking at preferred speed compared with controls. Fewer modules resulted from merging of the modules observed in healthy controls, suggesting reduced independence of neural control signals. The number of modules was correlated to preferred walking speed, speed modulation, step length asymmetry, and propulsive asymmetry. Our results suggest a common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects. Identification of motor modules may lead to new insight into impaired locomotor coordination and the underlying neural systems.
The following procedure is proposed:
1. An ECG signal should be recorded together with the EMGs. A
good idea is to use a free EMG channel.
2. At the start of each measuring session a recording of about 10 s
should be made with all electrodes attached and the muscles
relaxed as much as possible, e.g. with the subject sitting or
supine.
3. With this ‘resting’ recording the impulse responses of the ECG
filters for each EMG channel are determined.
4. In the actual EMG measurements the filtered ECGs are subtracted
from the unprocessed EMGs.
5. After ECG-subtraction the EMGs are filtered by the usual 20 or
30 Hz high-pass filter.
Is perception of the whole based on perception of its parts? There is psychological and physiological evidence for parts-based representations in the brain, and certain computational theories of object recognition rely on such representations. But little is known about how brains or computers might learn the parts of objects. Here we demonstrate an algorithm for non-negative matrix factorization that is able to learn parts of faces and semantic features of text. This is in contrast to other methods, such as principal components analysis and vector quantization, that learn holistic, not parts-based, representations. Non-negative matrix factorization is distinguished from the other methods by its use of non-negativity constraints. These constraints lead to a parts-based representation because they allow only additive, not subtractive, combinations. When non-negative matrix factorization is implemented as a neural network, parts-based representations emerge by virtue of two properties: the firing rates of neurons are never negative and synaptic strengths do not change sign.
Today, there is accumulating evidence from animal experiments that axonal regeneration and an enhanced level of functional repair can be induced after a spinal cord injury (SCI). Consequently, in the near future, new therapeutic approaches will be developed for the treatment of patients with SCI. The aim of the project presented here is to provide the required clinical basis for the implementation of novel interventional therapies. Refined and combined clinical and neurophysiological measures are needed for a precise qualitative and quantitative assessment of spinal cord function in patients with SCI at an early stage. This represents a basic requirement to recognise any improvement in the recovery of function and to monitor any significant effect of a new treatment. To this aim, five European Spinal Cord Injury Centres involved in the rehabilitation of acute SCI patients have built up a close clinical collaboration to develop a standardised protocol for the assessment of the outcome after SCI and the extent of recovery achieved by actually applied therapies in a larger population of SCI patients. The project's aim is to establish objective, refined tools as a basis for monitoring the effects of new treatment strategies.
Spinal cord modularity impacts on our understanding of reflexes, development, descending systems in normal motor control, and recovery from injury. We used independent component analysis and best-basis or matching pursuit wavepacket analysis to extract the composition and temporal structure of bursts in hindlimb muscles of frogs. These techniques make minimal a priori assumptions about drive and motor pattern structure. We compared premotor drive and burst structures in spinal frogs with less reduced frogs with a fuller repertoire of locomotory, kicking, and scratching behaviors. Six multimuscle drives explain most of the variance of motor patterns (approximately 80%). Each extracted drive was activated with pulses at a single time scale or common duration (approximately 275 msec) burst structure. The data show that complex behaviors in brainstem frogs arise as a result of focusing drives to smaller core groups of muscles. Brainstem drives were subsets of the muscle groups from spinal frogs. The 275 msec burst duration was preserved across all behaviors and was most precise in brainstem frogs. These data support a modular decomposition of frog behaviors into a small collection of unit burst generators and associated muscle drives in spinal cord. Our data also show that the modular organization of drives seen in isolated spinal cord is fine-tuned by descending controls to enable a fuller movement repertoire. The unit burst generators and their associated muscle synergies extracted here link the biomechanical "primitives," described earlier in the frog, rat, and cat, and to the elements of pattern generation examined in fictive preparations.
We recently showed that four muscle synergies can reproduce multiple muscle activation patterns in cats during postural responses to support surface translations. We now test the robustness of functional muscle synergies, which specify muscle groupings and the active force vectors produced during postural responses under several biomechanically distinct conditions. We aimed to determine whether such synergies represent a generalized control strategy for postural control or if they are merely specific to each postural task. Postural responses to multidirectional translations at different fore-hind paw distances and to multidirectional rotations at the preferred stance distance were analyzed. Five synergies were required to adequately reconstruct responses to translation at the preferred stance distance-four were similar to our previous analysis of translation, whereas the fifth accounted for the newly added background activity during quiet stance. These five control synergies could account for > 80% total variability or r2 > 0.6 of the electromyographic and force tuning curves for all other experimental conditions. Forces were successfully reconstructed but only when they were referenced to a coordinate system that rotated with the limb axis as stance distance changed. Finally, most of the functional muscle synergies were similar across all of the six cats in terms of muscle synergy number, synergy activation patterns, and synergy force vectors. The robustness of synergy organization across perturbation types, postures, and animals suggests that muscle synergies controlling task-variables are a general construct used by the CNS for balance control.
Postural control is a natural behavior that requires the spatial and temporal coordination of multiple muscles. Complex muscle activation patterns characterizing postural responses suggest the need for independent muscle control. However, our previous work shows that postural responses in cats can be robustly reproduced by the activation of a few muscle synergies. We now investigate whether a similar neural strategy is used for human postural control. We hypothesized that a few muscle synergies could account for the intertrial variability in automatic postural responses from different perturbation directions, as well as different postural strategies. Postural responses to multidirectional support-surface translations in 16 muscles of the lower back and leg were analyzed in nine healthy subjects. Six or fewer muscle synergies were required to reproduce the postural responses of each subject. The composition and temporal activation of several muscle synergies identified across all subjects were consistent with the previously identified "ankle" and "hip" strategies in human postural responses. Moreover, intertrial variability in muscle activation patterns was successfully reproduced by modulating the activity of the various muscle synergies. This suggests that trial-to-trial variations in the activation of individual muscles are correlated and, moreover, represent variations in the amplitude of descending neural commands that activate individual muscle synergies. Finally, composition and temporal activation of most of the muscle synergies were similar across subjects. These results suggest that muscle synergies represent a general neural strategy underlying muscle coordination in postural tasks.
Force estimation based on electromyography (EMG) has been proven to be useful for deriving proportional control for myoelectric devices. Muscle synergies seem to be relevant for force estimation since they are patterns of co-activation of muscles during actions. This study investigates the use of muscle synergies extracted from targeted surface EMG for estimating force during multiple - degree-of-freedom (DoF) contractions involving the wrist and hand. For this purpose, muscle synergies were extracted from twelve forearm muscles from eight able-bodied subjects. The constrained isotonic force produced by the wrist and the hand during these contractions was recorded along multiple axes, each responsible for one DoF. The derived neural inputs were then input into an artificial neural network (ANN) to estimate the force. The results were evaluated by comparing them with those obtained using mean absolute values (MAVs) for force estimation. The results obtained using muscle synergies were significantly better (p<0.05) than those obtained using MAVs in the estimation of force when training with both 1-and 2-DoF contractions (p=0.02) and also when training with only 1-DoF contractions (p=0.001). The latter case was important, as a training protocol that includes all desired 2 DoF contractions is very difficult for amputee users. For this case, the results obtained using muscle synergies were significantly improved compared to those obtained using MAVs. In addition, the robustness of muscle synergies was examined across different force levels. The results indicate that muscle synergies are robust and reliable for the force estimation of multiple - DoF tasks, and are thus a promising approach for the proportional control of prostheses.
Objective
Incomplete spinal cord injury (iSCI) disrupts motor control and limits the ability to coordinate muscles for overground walking. Inappropriate muscle activity has been proposed as a source of clinically observed walking deficits after iSCI. We hypothesized that persons with iSCI exhibit lower locomotor complexity compared to able-body (AB) controls as reflected by fewer motor modules, as well as, altered module composition and activation.
Methods
Eight persons with iSCI and eight age-matched AB controls walked overground at prescribed cadences. Electromyograms of fourteen single leg muscles were recorded. Non-negative matrix factorization was used to identify the composition and activation of motor modules, which represent groups of consistently co-activated muscles that accounted for 90% of variability in muscle activity.
Results
Motor module number, composition, and activation were significantly altered in persons with iSCI as compared to AB controls during overground walking at self-selected cadences. However, there was no significant difference in module number between persons with iSCI and AB controls when cadence and assistive device were matched.
Conclusions
Muscle coordination during overground walking is impaired after chronic iSCI.
Significance
Our results are indicative of neuromuscular constraints on muscle coordination after iSCI. Altered muscle coordination contributes to person-specific gait deficits during overground walking.
Each human lower-limb contains over 50 muscles that are coordinated during locomotion. It has been hypothesized that the nervous system simplifies muscle control through modularity, using neural patterns to activate muscles in groups called synergies. Here we investigate how simple modular controllers based on invariant neural primitives (synergies or patterns) might generate muscle activity observed during multidirectional locomotion. We extracted neural primitives from unilateral electromyographic recordings of 25 lower-limb muscles during five locomotor tasks, walking forwards, backwards, leftwards, rightwards and stepping in place. A subset of subjects also performed five variations of forward (unidirectional) walking: self-selected cadence, fast cadence, slow cadence, tiptoe and uphill (20% incline). We assessed the results in the context of dimensionality reduction, defined here as the number of neural signals needing to be controlled. For individual tasks we found that modular architectures could theoretically reduce dimensionality compared to independent muscle control, but we also observed trade-offs for each strategy. Specifically, we found that modular strategies relying on neural primitives shared across different tasks were limited in their ability to account for muscle activations during multi- and uni-directional locomotion. The utility of shared primitives may thus depend on if they can be adapted for specific task demands, for instance, by means of sensory feedback or by being embedded within a more complex sensorimotor controller. Our findings indicate the need for more sophisticated formulations of modular control or alternative motor control hypotheses in order to understand muscle coordination during locomotion.
Objective:
Individual muscle activation patterns may be controlled by motor modules constructed by the central nervous system to simplify motor control. This study compared modular control of gait between persons with Parkinson's disease (PD) and neurologically-healthy older adults (HOA) and investigated relationships between modular organization and gait parameters in persons with PD.
Methods:
Fifteen persons with idiopathic PD and fourteen HOA participated. Electromyographic recordings were made from eight leg muscles bilaterally while participants walked at their preferred walking speed for 10 min on an instrumented treadmill. Non-negative matrix factorization techniques decomposed the electromyographic signals, identifying the number and nature of modules accounting for 95% of variability in muscle activations during treadmill walking.
Results:
Generally, fewer modules were required to reconstruct muscle activation patterns during treadmill walking in PD compared to HOA (p < .05). Control of knee flexor and ankle plantar flexor musculature was simplified in PD. Activation timing was altered in PD while muscle weightings were unaffected. Simplified neuromuscular control was related to decreased walking speed in PD.
Conclusion:
Neuromuscular control of gait is simplified in PD and may contribute to gait deficits in this population.
Significance:
Future studies of locomotor rehabilitation in PD should consider neuromuscular complexity to maximize intervention effectiveness.
To determine which trunk inclination directions most accurately predict multidirectional-seated limits of stability among individuals with spinal cord injury (SCI).
Predictive study using cross-sectional data.
Pathokinesiology Laboratory.
Twenty-one individuals with complete or incomplete sensorimotor SCI affecting various vertebral levels participated in this study.
Participants were instructed to lean their trunk as far as possible in eight directions, separated by 45° intervals, while seated on an instrumented chair with their feet positioned on force plates. Outcomes measures: Eight direction-specific stability indices (DSIs) were used to define an overall stability index (OSI) (limits of stability).
All DSIs significantly correlated with the OSI (r = 0.816-0.925). A protocol that only tests the anterior, left postero-lateral, and right lateral trunk inclinations accurately predicts multidirectional-seated postural stability (r(2) = 0.98; P < 0.001).
Multidirectional-seated postural stability can be predicted almost perfectly by evaluating trunk inclinations performed toward the anterior, left postero-lateral, and right lateral directions.
From the mechanical point of view the spinal system is highly complex, containing a multitude of components, passive and active. In fact, even if the active components (the muscles) were exchanged by passive springs, the total number of elements considerably exceeds the minimum needed to maintain static equilibrium. In other words, the system is statically highly indeterminate. The particular role of the active components at static equilibrium is to enable a virtually arbitrary choice of posture, independent of the distribution and magnitude of the outer load albeit within physiological limits. Simultaneously this implies that ordinary procedures known from the analysis of mechanical systems with passive components cannot be applied. Hence the distribution of the forces over the different elements is not uniquely determined. Consequently nervous control of the force distribution over the muscles is needed, but little is known about how this achieved. This lack of knowledge implies great difficulties at numerical simulation of equilibrium states of the spinal system. These difficulties remain even if considerable reductions are made, such as the assumption that the thoracic cage behaves like a rigid body. A particularly useful point of view about the main principles of the force distributions appears to be the distinction between a local and a global system of muscles engaged in the equilibrium of the lumbar spine. The local system consists of muscles with insertion or origin (or both) at lumbar vertebrae, whereas the global system consists of muscles with origin on the pelvis and insertions on the thoracic cage. Given the posture of the lumbar spine, the force distribution over the local system appears to be essentially independent of the outer load of the body (though the force magnitudes are, of course, dependent on the magnitude of this load). Instead different distributions of the outer load on the body are met by different distributions of the forces in the global system. Thus, roughly speaking, the global system appears to take care of different distributions of outer forces on the body, whereas the local system performs an action, which is essentially locally determined (i.e. by the posture of the lumbar spine). The present work focuses on the upright standing posture with different degree of lumbar lordosis. The outer load is assumed to consist of weights carried on the shoulders. By reduction of the number of unknown forces, which is done by using a few different principles, a unique determination of the total force distributions at static equilibrium is obtained.(ABSTRACT TRUNCATED AT 400 WORDS)
The development of new patterns of postural control in patients with a complete thoracic spinal cord injury (SCI) during their active clinical rehabilitation was studied. Especially the role of non-postural muscles, like the latissimus dorsi (LD) and the trapezius pars ascendens (TPA), in maintaining and restoring sitting balance during standardized bimanual task performance was investigated. Twelve patients, diagnosed with an acute complete thoracic SCI between spinal cord level T2 and T12, participated in a longitudinal experimental study. Changes in the centre of pressure (CP) and electromyographic activity of the erector spinae (ES) at level L3, T9 and T3, the LD, the TPA, the pectoralis major (PM), the serratus anterior and the oblique abdominal muscles were investigated at several moments in the rehabilitation process. Results show a gradual development of specific muscle activation patterns for both high and low thoracic SCI patients. These patterns seem to be related to a combination of restoration of function of the ES-L3 and ES-T9 in the low thoracic SCI subjects and increased compensatory muscle use of the LD, TPA and PM in high SCI patients. The range in which low thoracic SCI patients can actively vary their CP increased slightly during rehabilitation.
To compensate for postural muscle function loss spinal cord injured (SCI) people have to use parts of the sensorimotor system which are still intact. In this study, postural control was investigated in high and low thoracic SCI people and in able-bodied controls, using a bimanual forward-reaching task. Muscle activity was recorded bilaterally from the erector spinae (ES) at level L3, T9 and T3, latissimus dorsi (LD), ascending part of the trapezius muscle (TPA), serratus anterior (SA), sternocostal head of the pectoralis major (PM) and the oblique abdominal muscles (OA) by means of surface electromyography. Sitting balance was monitored by measuring the changes in the location of the centre of pressure (CP) using a force platform. Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement. SCI people make alternative use of non-postural muscles like the LD and TPA to maintain their sitting balance.
Dr. Nakazawa worked at the National Rehabilitation Center for Persons with Disabilities (NRCD) Research Institute in Tokorozawa, Japan. From 1997-1998, he worked in Prof. Dietz's Lab at University Hospital Balgrist in Zurich
Kimitaka Nakazawa was born in 1962 in Nagano,
Japan. From 1991-2009, Dr. Nakazawa worked at the
National Rehabilitation Center for Persons with Disabilities (NRCD) Research Institute in Tokorozawa,
Japan. From 1997-1998, he worked in Prof. Dietz's Lab
at University Hospital Balgrist in Zurich, Switzerland.
Since 2009, Dr. Nakazawa has been working at the
Department of Life Sciences, Graduate School of Arts
and Sciences, The University of Tokyo, Japan.
Milner Award for outstanding contributions in the area of Assistive Technologies from the Health Technology Exchange. Also, in 2013, together with Drs
- Lehn Prodic
- Mr Huerta-Olivares
- Dr Tarulli
Milner Award for outstanding contributions in the area of Assistive Technologies
from the Health Technology Exchange. Also, in 2013, together with Drs. Prodic,
Lehn, and Huerta-Olivares, and Mr. Tarulli, Dr. Popovic received the University of
Toronto Inventor of the Year Award. In 2015, Dr. Popovic received the 2014