602 research outputs found

    Muscle Synergies Facilitate Computational Prediction of Subject-Specific Walking Motions.

    Get PDF
    Researchers have explored a variety of neurorehabilitation approaches to restore normal walking function following a stroke. However, there is currently no objective means for prescribing and implementing treatments that are likely to maximize recovery of walking function for any particular patient. As a first step toward optimizing neurorehabilitation effectiveness, this study develops and evaluates a patient-specific synergy-controlled neuromusculoskeletal simulation framework that can predict walking motions for an individual post-stroke. The main question we addressed was whether driving a subject-specific neuromusculoskeletal model with muscle synergy controls (5 per leg) facilitates generation of accurate walking predictions compared to a model driven by muscle activation controls (35 per leg) or joint torque controls (5 per leg). To explore this question, we developed a subject-specific neuromusculoskeletal model of a single high-functioning hemiparetic subject using instrumented treadmill walking data collected at the subject's self-selected speed of 0.5 m/s. The model included subject-specific representations of lower-body kinematic structure, foot-ground contact behavior, electromyography-driven muscle force generation, and neural control limitations and remaining capabilities. Using direct collocation optimal control and the subject-specific model, we evaluated the ability of the three control approaches to predict the subject's walking kinematics and kinetics at two speeds (0.5 and 0.8 m/s) for which experimental data were available from the subject. We also evaluated whether synergy controls could predict a physically realistic gait period at one speed (1.1 m/s) for which no experimental data were available. All three control approaches predicted the subject's walking kinematics and kinetics (including ground reaction forces) well for the model calibration speed of 0.5 m/s. However, only activation and synergy controls could predict the subject's walking kinematics and kinetics well for the faster non-calibration speed of 0.8 m/s, with synergy controls predicting the new gait period the most accurately. When used to predict how the subject would walk at 1.1 m/s, synergy controls predicted a gait period close to that estimated from the linear relationship between gait speed and stride length. These findings suggest that our neuromusculoskeletal simulation framework may be able to bridge the gap between patient-specific muscle synergy information and resulting functional capabilities and limitations

    Musculoskeletal Modeling Analysis of Knee Joint Loading During Uphill and Downhill Waling In Patients with Total Knee Replacement

    Get PDF
    The purposes of these studies were to determine differences in total (TCF), medial (MCF) and lateral (LCF) tibiofemoral compartment compressive forces and related muscle forces between limbs (replaced, non-replaced, and control), and different slopes during uphill [0° (level), 5°, 10°], and downhill [0° (level), 5° 10°] using statistical parametric mapping (SPM). Static optimization was used to determine muscle and compressive forces for 9 patients with total knee arthroplasty (TKA) and 9 control participants during walking trials. Total , loading-response, and push-off TCF impulse were calculated. A 3×3 [Limb (replaced, non-replaced, control] × Slope (0°, 10°, 15°)] SPM[F] repeated measures ANOVA was conducted independently for both uphill and downhill walking. Independent 3×3 (Limb × Slope]) mixed-model ANOVA were used to detect differences for TCF impulse for both up- and downhill walking. For study one, significant between-limb differences were observed for MCF during 23-30% stance between replaced and control limbs. Significant differences between slopes were observed for all variables, except knee flexor muscle force. TCF impulse indicates that joint load is greater for all limbs as slope increases. A small sample size of patients with TKA who utilize different gait strategies may have rendered difference between limbs non-significant. For study two, significant differences were found for TCF, MCF, and knee flexor muscle forces between replaced and control limbs during early loading-response (1‑5% stance). No significant differences were found between limbs for MCF or LCF, suggesting that TKA may have been successful in correcting errant frontal plane alignment. Loading-response TCF impulse increased with increasing slope yet push-off TCF impulse decreased with increasing decline slope suggesting decreased knee joint loading during push-off while not having to overcome gravity. Uphill walking may be an effective exercise for high intensity early and long-term rehabilitation programs with increased muscular demand and quadriceps strengthening as slope increases while promoting the reacquisition of normal gait patterns following TKA. Downhill walking facilitates increased muscular demand and quadriceps strengthening via eccentric contractions while regaining normal gait patterns following TKA. Downhill walking, therefore, may be an effective exercise for high intensity early and long-term rehabilitation

    Muscle force contributions to knee joint loading

    Get PDF
    Anterior cruciate ligament (ACL) injuries are one of the most common knee injuries suffered by athletic populations. ACL injuries are particularly burdensome due to potential surgical requirements, extensive rehabilitation time and associated financial costs for the individual and the community. Additionally, ACL injuries are associated with increased risk of early onset knee osteoarthritis. As such, ACL injury preventative and rehabilitative strategies are of paramount importance. ACL injuries typically occur during non-contact dynamic tasks, such as unanticipated sidestep cutting. At the time of injury, the knee joint experiences relatively large degrees of knee valgus and rotation (either internal or external) and high mechanical loads. These loading patterns, along with the anterior shear force, are known to increase loads on the ACL, especially in combination with each other. Muscles produce forces that can cause and oppose these knee joint loads, and therefore play a critical role in dictating the size and the nature of the loads experienced by the ACL. Prior research has investigated the role of muscle force in ACL load development, and has indicated that the hamstrings are most capable of reducing ACL loads. Subsequently, any pathology that may influence hamstring function may increase the risk of ACL injury. Some studies have shown that participants with a history of hamstring strain injury (HSI) have lower knee flexor strength and hamstring muscle activation compared to healthy legs. Consequently, a relationship between prior HSI and ACL injury could exist. However, establishing this relationship is difficult due to the relatively low incidence of ACL injury. Subsequently, prospective studies aiming to investigate this relationship would be very costly, due to the requirement of very large sample sizes and long follow-up periods. Additionally, such a relationship would depend on the functional role of the hamstring muscle group during potentially ACL-injurious manoeuvres such as sidestep cutting, which has not been fully elucidated. Furthermore, given the multi-planar demands of tasks that place the ACL at risk of injury, better understanding the contribution of the individual hamstring muscles to knee joint loading relative to the other lower-limb muscles is imperative. Musculoskeletal simulation offers the ability to analyse cause-effect relationships between muscle force development and joint loading whilst accounting for whole body kinematics. This analysis could not only reveal the true potential of the hamstring muscles in protecting the ACL, but could also elucidate the role of other muscles which have been less studied. The purpose of this doctoral thesis was to explore the relationship between muscle forces in the development of knee joint loading during potentially injurious manoeuvres, as this knowledge may be used to inform interventions that aim to reduce ACL injury risk. Given recent hypotheses suggesting a possible association between prior injury to the hamstrings and an increased risk of ACL injury and based on the current literature, which indicates that the hamstrings are one of the most important muscle groups for unloading the ACL, the focus of the first study (Chapter 4) was to determine the impact of HSI on hamstring function. Specifically, a systematic review and meta-analysis was used to compare knee flexor strength and flexibility in previously injured legs to the uninjured contralateral leg. It was found that deficits in concentric and eccentric strength (and associated hamstring to quadriceps strength ratios) were present at and after return to play. Isometric strength deficits were also present after HSI, but these recovered within 20-30 days. Hamstring flexibility deficits were also found after HSI, but these recovered within 40-50 days post injury. A secondary aim of this study was to document the totality of measures reported in the literature that have been taken in previously injured hamstrings. The review revealed that knee flexor and extensor strength were the most commonly assessed variables in participants with previously injured hamstrings and that there are few studies which examine the function of other lower-limb muscles. Furthermore, there was limited information examining multi-planar movements. The findings of the review highlighted the need to better understand how the hamstrings contribute to knee joint loading, relative to the contribution of other lower-limb muscles, to better guide future work examining the link between prior HSI and future ACL injury. The conclusions obtained from Chapter 4 informed the direction of the three subsequent chapters. The focus of the second study (Chapter 5) was to investigate the contribution of the hamstrings to ACL loading during the weight acceptance phase of an unanticipated sidestep cut relative to other lower-limb muscles. A musculoskeletal modelling approach was used to determine how different lower-limb muscles contribute to the key markers of ACL loading, namely the anteroposterior tibiofemoral shear force, and the valgus and rotation reaction moments. It was found that the hamstrings and gluteal muscles play a dominant role in protecting the ACL, by opposing the anterior shear force and valgus reaction moment, respectively. These same muscle groups were found to oppose each other in the transverse plane, thus limiting knee rotation loading. The focus of the third study (Chapter 6) was to determine the contribution of the hamstrings to the medial and lateral tibiofemoral compartment contact force during unanticipated sidestep cutting relative to other lower-limb muscles. This was because ACL injuries rarely occur in isolation, and are associated with long-term degeneration of articular knee cartilage. A custom musculoskeletal model was created with a modified knee joint mechanism, which permitted the computation of tibiofemoral compartment contact forces via a dynamic equilibrium approach. It was found that medial tibiofemoral contact loading was primarily produced by the vasti, gluteus medius and gluteus maximus and the medial gastrocnemius, whilst lateral tibiofemoral loading was produced primarily by the vasti, soleus, and the medial and lateral gastrocnemius. The medial hamstrings tended to load both compartments, whilst the biceps femoris long head loaded the lateral compartment and induced a relatively small decompression impulse in the medial compartment. Additionally, it was found that most muscles tended to compress both compartments, whilst other muscles had the ability to compress one compartment and decompress the other. The focus of the fourth study (Chapter 7) was to determine how the hamstrings contribute to coordinating the stance phase of an unanticipated sidestep cut. A musculoskeletal modelling approach was used to estimate lower-limb muscle forces, and a ground reaction force (GRF) decomposition method was used to determine how muscles contributed to the GRFs. It was found that bodyweight support is primarily modulated by the vasti, gluteus maximus, soleus, and gastrocnemius. These same muscles, along with the hamstrings, were also the primary modulators of anteroposterior progression. By contributing to the medial GRF, the vasti, gluteus maximus and gluteus medius were primarily responsible for redirecting the centre-of-mass toward the cutting direction. This program of research has identified the contribution of the hamstrings, as well as other lower-limb muscles, to knee joint loading and performance during a change-of-direction task. The first study synthesised the retrospective evidence base investigating hamstring strength and flexibility in participants with a history of HSI. This study also identified that assessments of function post HSI tend to focus mostly on the hamstrings during isolated strength assessments, neglecting other lower-limbs muscles. This highlighted the need to better understand the hamstrings role in potentially ACL injurious tasks, relative to other lower-limb muscles. In these investigations the hamstrings were found to be an important muscle group to oppose anterior shear forces during unanticipated sidestep cutting, whilst other non-knee-spanning muscles were found to have a substantial role in developing and opposing other surrogate markers of ACL loading. Similarly, both knee-spanning and non-knee-spanning muscles were found to play a substantial role in compressive loading of the medial and lateral tibiofemoral compartments. Additionally this program of research developed a greater understanding of the contribution of the hamstrings, and other lower-limb muscles, to the coordination of a sidestep cut. The hamstrings played a key role in maintaining anterior propulsion during early stance, although the majority of the demands of sidestep cutting (bodyweight support, propulsion and redirection) were provided by the vasti, gluteus maximus, soleus and gastrocnemius. The data from this program of research will inform ACL injury rehabilitation and injury prevention practices which should consider not only targeting the hamstrings but also other non-knee-spanning muscles for loading and unloading the knee during sidestep cutting. Additionally, this thesis provides data that may inform strategies aiming to modulate muscle forces to alter tibiofemoral compressive forces, which may be involved in ACL injury and concomitant meniscal and articular cartilage injury. Finally, this thesis provides further data informing how these muscles contribute to the performance of sidestep cut, in order to achieve optimal balance between performance and injury risk considerations. The findings from this thesis also dictates that future investigations that aim to examine the link between prior HSI and increased knee joint loading need to broaden the scope of such work to consider the influence of other lower-limb muscles as well as multi-planar movements

    Neural and Electromyographic Correlates of Wrist Posture Control

    Get PDF
    In identical experiments in and out of a MR scanner, we recorded functional magnetic resonance imaging and electromyographic correlates of wrist stabilization against constant and time-varying mechanical perturbations. Positioning errors were greatest while stabilizing random torques. Wrist muscle activity lagged changes in joint angular velocity at latencies suggesting trans-cortical reflex action. Drift in stabilized hand positions gave rise to frequent, accurately directed, corrective movements, suggesting that the brain maintains separate representations of desired wrist angle for feedback control of posture and the generation of discrete corrections. Two patterns of neural activity were evident in the blood-oxygenation-level-dependent (BOLD) time series obtained during stabilization. A cerebello-thalamo-cortical network showed significant activity whenever position errors were present. Here, changes in activation correlated with moment-by-moment changes in position errors (not force), implicating this network in the feedback control of hand position. A second network, showing elevated activity during stabilization whether errors were present or not, included prefrontal cortex, rostral dorsal premotor and supplementary motor area cortices, and inferior aspects of parietal cortex. BOLD activation in some of these regions correlated with positioning errors integrated over a longer time-frame consistent with optimization of feedback performance via adjustment of the behavioral goal (feedback setpoint) and the planning and execution of internally generated motor actions. The finding that nonoverlapping networks demonstrate differential sensitivity to kinematic performance errors over different time scales supports the hypothesis that in stabilizing the hand, the brain recruits distinct neural systems for feedback control of limb position and for evaluation/adjustment of controller parameters in response to persistent errors

    Model-Based Estimation of Muscle Forces Exerted During Movements

    Get PDF
    Estimation of individual muscle forces during human movement can provide insight into neural control and tissue loading and can thus contribute to improved diagnosis and management of both neurological and orthopaedic conditions. Direct measurement of muscle forces is generally not feasible in a clinical setting, and non-invasive methods based on musculoskeletal modeling should therefore be considered. The current state of the art in clinical movement analysis is that resultant joint torques can be reliably estimated from motion data and external forces (inverse dynamic analysis). Static optimization methods to transform joint torques into estimates of individual muscle forces using musculoskeletal models, have been known for several decades. To date however, none of these methods have been successfully translated into clinical practice. The main obstacles are the lack of studies reporting successful validation of muscle force estimates, and the lack of user-friendly and efficient computer software. Recent advances in forward dynamics methods have opened up new opportunities. Forward dynamic optimization can be performed such that solutions are less dependent on measured kinematics and ground reaction forces, and are consistent with additional knowledge, such as the force–length–velocity–activation relationships of the muscles, and with observed electromyography signals during movement. We conclude that clinical applications of current research should be encouraged, supported by further development of computational tools and research into new algorithms for muscle force estimation and their validation

    Remembering Forward: Neural Correlates of Memory and Prediction in Human Motor Adaptation

    Get PDF
    We used functional MR imaging (FMRI), a robotic manipulandum and systems identification techniques to examine neural correlates of predictive compensation for spring-like loads during goal-directed wrist movements in neurologically-intact humans. Although load changed unpredictably from one trial to the next, subjects nevertheless used sensorimotor memories from recent movements to predict and compensate upcoming loads. Prediction enabled subjects to adapt performance so that the task was accomplished with minimum effort. Population analyses of functional images revealed a distributed, bilateral network of cortical and subcortical activity supporting predictive load compensation during visual target capture. Cortical regions – including prefrontal, parietal and hippocampal cortices – exhibited trial-by-trial fluctuations in BOLD signal consistent with the storage and recall of sensorimotor memories or “states” important for spatial working memory. Bilateral activations in associative regions of the striatum demonstrated temporal correlation with the magnitude of kinematic performance error (a signal that could drive reward-optimizing reinforcement learning and the prospective scaling of previously learned motor programs). BOLD signal correlations with load prediction were observed in the cerebellar cortex and red nuclei (consistent with the idea that these structures generate adaptive fusimotor signals facilitating cancelation of expected proprioceptive feedback, as required for conditional feedback adjustments to ongoing motor commands and feedback error learning). Analysis of single subject images revealed that predictive activity was at least as likely to be observed in more than one of these neural systems as in just one. We conclude therefore that motor adaptation is mediated by predictive compensations supported by multiple, distributed, cortical and subcortical structures

    Cervical spine injuries: A whole-body musculoskeletal model for the analysis of spinal loading

    Get PDF
    This is the final version of the article. Available from Public Library of Science via the DOI in this record.Cervical spine trauma from sport or traffic collisions can have devastating consequences for individuals and a high societal cost. The precise mechanisms of such injuries are still unknown as investigation is hampered by the difficulty in experimentally replicating the conditions under which these injuries occur. We harness the benefits of computer simulation to report on the creation and validation of i) a generic musculoskeletal model (MASI) for the analyses of cervical spine loading in healthy subjects, and ii) a population-specific version of the model (Rugby Model), for investigating cervical spine injury mechanisms during rugby activities. The musculoskeletal models were created in OpenSim, and validated against in vivo data of a healthy subject and a rugby player performing neck and upper limb movements. The novel aspects of the Rugby Model comprise i) population-specific inertial properties and muscle parameters representing rugby forward players, and ii) a custom scapula-clavicular joint that allows the application of multiple external loads. We confirm the utility of the developed generic and population-specific models via verification steps and validation of kinematics, joint moments and neuromuscular activations during rugby scrummaging and neck functional movements, which achieve results comparable with in vivoand in vitrodata. The Rugby Model was validated and used for the first time to provide insight into anatomical loading and cervical spine injury mechanisms related to rugby, whilst the MASI introduces a new computational tool to allow investigation of spinal injuries arising from other sporting activities, transport, and ergonomic applications. The models used in this study are freely available at simtk.org and allow to integrate in silico analyses with experimental approaches in injury prevention.Funding: This project is funded by the Rugby Football Union (RFU) Injured Players Foundation. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

    Quantification of knee extensor muscle forces: a multimodality approach

    Get PDF
    Given the growing interest of using musculoskeletal (MSK) models in a large number of clinical applications for quantifying the internal loading of the human MSK system, verification and validation of the model’s predictions, especially at the knee joint, have remained as one of the biggest challenges in the use of the models as clinical tools. This thesis proposes a methodology for more accurate quantification of knee extensor forces by exploring different experimental and modelling techniques that can be used to enhance the process of verification and validation of the knee joint model within the MSK models for transforming the models to a viable clinical tool. In this methodology, an experimental protocol was developed for simultaneous measurement of the knee joint motion, torques, external forces and muscular activation during an isolated knee extension exercise. This experimental protocol was tested on a cohort of 11 male subjects and the measurements were used to quantify knee extensor forces using two different MSK models representing a simplified model of the knee extensor mechanism and a previously-developed three-dimensional MSK model of the lower limb. The quantified knee extensor forces from the MSK models were then compared to evaluate the performance of the models for quantifying knee extensor forces. The MSK models were also used to investigate the sensitivity of the calculated knee extensor forces to key modelling parameters of the knee including the method of quantifying the knee centre of rotation and the effect of joint translation during motion. In addition, the feasibility of an emerging ultrasound-based imaging technique (shear wave elastography) for direct quantification of the physiologically-relevant musculotendon forces was investigated. The results in this thesis showed that a simplified model of the knee can be reliably used during a controlled planar activity as a computationally-fast and effective tool for hierarchical verification of the knee joint model in optimisation-based large-scale MSK models to provide more confidence in the outputs of the models. Furthermore, the calculation of knee extensor muscle forces has been found to be sensitive to knee joint translation (moving centre of rotation of the knee), highlighting the importance of this modelling parameter for quantifying physiologically-realistic knee muscle forces in the MSK models. It was also demonstrated how the movement of the knee axis of rotation during motion can be used as an intuitive tool for understanding the functional anatomy of the knee joint. Moreover, the findings in this thesis indicated that the shear wave elastography technique can be potentially used as a novel method for direct quantification of the physiologically-relevant musculotendon forces for independent validation of the predictions of musculotendon forces from the MSK models.Open Acces

    Description of motor control using inverse models

    Get PDF
    Humans can perform complicated movements like writing or running without giving them much thought. The scientific understanding of principles guiding the generation of these movements is incomplete. How the nervous system ensures stability or compensates for injury and constraints – are among the unanswered questions today. Furthermore, only through movement can a human impose their will and interact with the world around them. Damage to a part of the motor control system can lower a person’s quality of life. Understanding how the central nervous system (CNS) forms control signals and executes them helps with the construction of devices and rehabilitation techniques. This allows the user, at least in part, to bypass the damaged area or replace its function, thereby improving their quality of life. CNS forms motor commands, for example a locomotor velocity or another movement task. These commands are thought to be processed through an internal model of the body to produce patterns of motor unit activity. An example of one such network in the spinal cord is a central pattern generator (CPG) that controls the rhythmic activation of synergistic muscle groups for overground locomotion. The descending drive from the brainstem and sensory feedback pathways initiate and modify the activity of the CPG. The interactions between its inputs and internal dynamics are still under debate in experimental and modelling studies. Even more complex neuromechanical mechanisms are responsible for some non-periodic voluntary movements. Most of the complexity stems from internalization of the body musculoskeletal (MS) system, which is comprised of hundreds of joints and muscles wrapping around each other in a sophisticated manner. Understanding their control signals requires a deep understanding of their dynamics and principles, both of which remain open problems. This dissertation is organized into three research chapters with a bottom-up investigation of motor control, plus an introduction and a discussion chapter. Each of the three research chapters are organized as stand-alone articles either published or in preparation for submission to peer-reviewed journals. Chapter two introduces a description of the MS kinematic variables of a human hand. In an effort to simulate human hand motor control, an algorithm was defined that approximated the moment arms and lengths of 33 musculotendon actuators spanning 18 degrees of freedom. The resulting model could be evaluated within 10 microseconds and required less than 100 KB of memory. The structure of the approximating functions embedded anatomical and functional features of the modelled muscles, providing a meaningful description of the system. The third chapter used the developments in musculotendon modelling to obtain muscle activity profiles controlling hand movements and postures. The agonist-antagonist coactivation mechanism was responsible for producing joint stability for most degrees of freedom, similar to experimental observations. Computed muscle excitations were used in an offline control of a myoelectric prosthesis for a single subject. To investigate the higher-order generation of control signals, the fourth chapter describes an analytical model of CPG. Its parameter space was investigated to produce forward locomotion when controlled with a desired speed. The model parameters were varied to produce asymmetric locomotion, and several control strategies were identified. Throughout the dissertation the balance between analytical, simulation, and phenomenological modelling for the description of simple and complex behavior is a recurrent theme of discussion

    Achieving Practical Functional Electrical Stimulation-driven Reaching Motions In An Individual With Tetraplegia

    Get PDF
    Functional electrical stimulation (FES) is a promising technique for restoring the ability to complete reaching motions to individuals with tetraplegia due to a spinal cord injury (SCI). FES has proven to be a successful technique for controlling many functional tasks such as grasping, standing, and even limited walking. However, translating these successes to reaching motions has proven difficult due to the complexity of the arm and the goaldirected nature of reaching motions. The state-of-the-art systems either use robots to assist the FES-driven reaching motions or control the arm of healthy subjects to complete planar motions. These controllers do not directly translate to controlling the full-arm of an individual with tetraplegia because the muscle capabilities of individuals with spinal cord injuries are unique and often limited due to muscle atrophy and the loss of function caused by lower motor neuron damage. This dissertation aims to develop a full-arm FES-driven reaching controller that is capable of achieving 3D reaching motions in an individual with a spinal cord injury. Aim 1 was to develop a complete-arm FES-driven reaching controller that can hold static hand positions for an individual with high tetraplegia due to SCI. We developed a combined feedforward-feedback controller which used the subject-specific model to automatically determine the muscle stimulation commands necessary to hold a desired static hand position. Aim 2 was to develop a subject-specific model-based control strategy to use FES to drive the arm of an individual with high tetraplegia due to SCI along a desired path in the subject’s workspace. We used trajectory optimization to find feasible trajectories which explicitly account for the unique muscle characteristics and the simulated arm dynamics of our subject with tetraplegia. We then developed a model predictive control controller to iii control the arm along the desired trajectory. The controller developed in this dissertation is a significant step towards restoring full arm reaching function to individuals with spinal cord injuries
    • …
    corecore