Understanding possible variations in muscle activation patterns and its functional implications to movement control is crucial for rehabilitation. Inter-/intra-subject variability is often observed in muscle activity used for performing the same task in both healthy and impaired individuals. However, the extent to which muscle activation patterns can vary under specific neuromuscular conditions and differ in function are still not well understood. Current musculoskeletal modeling approaches using optimization techniques to identify a unique solution cannot adequately address such questions. Here I developed a novel computational framework using detailed musculoskeletal model to reveal the latitude the nervous system has in selecting muscle activation patterns for a given task regarding neuromechanical constraints. I focused on isometric hindlimb endpoint force generation task relevant to balance behavior in cats. By identifying the explicit bounds on activation of individual muscles defined by biomechanical constraints, I demonstrate ample range of feasible activation patterns that account for experimental variability. By investigating the possible neuromechanical bases of using the same muscle activation pattern across tasks, I demonstrate that demand for generalization can affect the selection of muscle activation pattern. By characterizing the landscape of the solution space with respect to multiple functional properties, I demonstrate a possible trade-off between effort and stability. This framework is a useful tool for understanding principles underlying functional or impaired movements. We may gain valuable insights to developing effective rehabilitation strategies and biologically-inspired control principles for robots.

Dans les domaines de la réhabilitation, des sciences du sport et de l'ergonomie, l'évaluation des capacités de génération de force (CGF) peut aider à mieux comprendre les capacités motrices humaines. Le but de cette thèse a été d'évaluer les CGF du membre supérieur prédites au moyen de deux types de formalismes. Le premier provient du domaine de la robotique et a été utilisé pour déterminer l'ellipsoïde de force normalisé (EFN) et biomécanique (EFB), le polytope de force normalisé (PFN) et biomécanique (PFB). Pour une posture, ils sont calculés à partir d’un modèle polyarticulé du membre supérieur et de données sur les couples articulaires isométriques maximaux. Le second type fait appel à un modèle musculosquelettique afin de modéliser les CGF sous la forme d’un polytope de forces (PFMS). Tous ces modèles ont été comparés à un polytope de forces mesurées (PFM). Pour le construire, les forces maximales isométriques exercées par le membre supérieur au niveau de la main ont été évaluées dans vingt-six directions différentes. Enfin, le PFMS a été appliqué dans le cadre de la propulsion en fauteuil roulant afin de caractériser l'application des forces lors de cette tâche et un nouvel indice d’évaluation de la performance postural (IPP) a été proposé. / In fields like rehabilitation, sports sciences and ergonomics, the evaluation of the force feasible set (FFS) of the human limbs may help to better understand the human motor abilities. The aim of this thesis was to compare the upper-limb force capacity at the hand predicted by two different kinds of FFS formalism. The first one originating from the robotics field was used to compute the force ellipsoid (FE), scaled force ellipsoid (SFE), force polytope (FP) and scaled force polytope (SFP). For one posture, they are computed from the upper-limb model and hypotheses and data on maximum isometric joint torques. The second one permitted to compute the FFS modeled as a force polytope from a musculoskeletal model (MSFP). All the previously mentioned models were compared with a measured force polytope (MFP). To construct it, the maximum isometric forces exerted at the hand were assessed in twenty-six directions of the Cartesian space. Then, the MSFP was applied to the manual wheelchair propulsion in order to characterize the forces applied on the handrim during this task and a new evaluation index of postural performance (IPP) was also introduced.

To understand control strategies employed by the central nervous system (CNS) control movement or force generation in a limb, a seven degree of freedom cat hindlimb was modeled. In this study, the biomechanical constraints affecting force generation for balance and postural control were investigated. Due to the redundancies at the muscular and joint levels in the musculoskeletal system, even the muscle coordination pattern to statically produce a certain amount of force/torque at the ground is not straightforward. A 3D musculoskeletal model of the cat hindlimb was created from cat cadaver measurements using Software for Interactive Musculoskeletal Systems (SIMM, Musculographics, Inc.). Six kinematic degrees of freedom and 31 individual hindlimb muscles were modeled. The moment arms of the muscles were extracted from the software model to be used in a linear transformation between muscle activation, and end effector force and moment. The Jacobian matrix that establishes the relationship between joint torques and end effector wrench was calculated. Maximal muscle forces were estimated from the literature. A feasible set of forces that can be generated at the toe was constructed using combination of maximally activated muscle excitations. Because the endpoint torque is typically small in a cat, an optimization algorithm was also performed to maximize the force generation at the end effector while constraining the magnitude of the endpoint torque. The results are compared with the measured force magnitude and direction data from an acute cat hindlimb preparation for different postures. This static model is applicable for understanding muscle coordination during postural responses to small balance perturbations.

The high demands of manual wheelchair propulsion put users at risk of additional pain and injury that can lead to further reductions in independence and quality of life. Seat position is an adjustable parameter that has been shown to influence propulsion biomechanics. As a result, a number of studies have attempted to optimize this position. However, due to complexities in quantifying upper extremity demand, seat position guidelines are often based on studies aimed at reducing indirect quantities (e.g., cadence, handrim forces, joint ranges of motion and muscle excitation levels) rather than more direct measures of demand (e.g., muscle stress and metabolic cost). Forward dynamics simulations provide an alternative approach to systematically investigate the influence of seat position on more direct measures of upper extremity demand. The objective of this study was to generate and analyze a set of forward dynamics simulations of wheelchair propulsion across the range of attainable seat positions to identify the optimal seat position that minimizes upper extremity demand (i.e., muscle stress, metabolic cost and muscle antagonism). The optimization results showed both metabolic cost and muscle stresses were near minimal values at superior/inferior positions corresponding to top dead center elbow angles between 110 and 120 degrees while at an anterior/posterior position with a hub-shoulder angle between 10 and 2.5 degrees. These minimal values coincided with a reduction in the level of antagonistic muscle activity, primarily at the glenohumeral joint. Seat positions that deviated from these minimal values increased the level of co-contraction required to maintain a stable, smooth propulsive stroke, and consequentially increased upper extremity demand. These results can provide guidelines for positioning the seat to help reduce upper extremity overuse injuries and pain, and thus improve the overall quality of life for wheelchair users. / text

The ability to stand still in one place is important in a variety of activities of daily living. For persons with motion disorders, orthopaedic treatment, which changes geometric or biomechanical properties, can improve the individual'sposture and walking ability. Decisions on such treatment require insight in how posture and walking ability are aected, however, despite expectations based on experience, it is never a-priori known how a patient will react to a treatment. As this is very challenging to observe by the naked eye, engineering tools are increasingly employed to support clinical diagnostics and treatment planning. The development of predictive simulations allows for the evaluation of the eect of changed biomechanical parameters on the human biological system behavior and could become a valuable tool in future clinical decision making. In the first paper, we evaluated the use of the Zero Moment Point as a computationally inexpensive tool to obtain the ground reaction forces (GRFs) for normal human gait. The method was applied on ten healthy subjects walking in a motion analysis laboratory and predicted GRFs are evaluated against the simultaneously measured force plate data. Apart from the antero-posterior forces, GRFs are well-predicted and errors fall within the error ranges from other published methods. The computationally inexpensive method evaluated in this study can reasonably well predict the GRFs for normal human gait without using prior knowledge of common gait kinetics. The second manuscript addresses the complications in the creation and analysis of a posture prediction framework. The fmincon optimization function in MATLAB was used in conjunction with a musculoskeletal model in OpenSim. One clear local minimum was found in the form of a symmetric standing posture but perturbation analyses revealed the presence of many other postural congurations, each representing its own unique local minimum in the feasible parameter space. For human postural stance, this can translate to there being many different ways of standing without actually noticing a difference in the efforts required for these poses. / <p>This work was financially supported by the Swedish Scientic Council(Vetenskapsrådet) grant no. 2010-9401-79187-68, the ProMobilia handicapfoundation (ref. 13093), Sunnerdahls Handicap foundation (ansökan nr 11/14),and Norrbacka-Eugenia foundation (ansökan nr 218/15).</p><p></p><p></p>

No description available.

Determining tendon tension in the finger is essential to understanding forces that may be detrimental to hand function. Direct measurement is not feasible, making biomechanical modelling the best way to estimate these forces. In this study, the intrinsic muscles and extensor mechanism were added to an existing model of the index finger, and as such, it has been named the Intrinsic model. The Intrinsic model of the index finger has 4 degrees of freedom and 7 muscles (with 14 components). Muscle properties and paths for all extrinsic and intrinsic muscles were derived from the literature. Two models were evaluated, the Intrinsic model and the model it was adapted from (identified in this thesis as the Extrinsic-only model). To complement the model, multiple static optimization solution methods were also developed that allowed for EMG-constrained solutions and applied objective functions to promote co-contraction. To test the models and solution methods, 10 participants performed 9 static pressing tasks at 3 force levels, and 5 free motion dynamic tasks at 2 speeds. Kinematics, contact forces, and EMG (from the extrinsic muscles and first dorsal interosseous) were collected. For all solution methods, muscle activity predicted using the Intrinsic model was compared to activity from the model currently available through open-source software (OpenSim). Just by using the Intrinsic model, co-contraction increased by 16% during static palmar pressing tasks. The EMG-constrained solution methods gave a smaller difference between predicted and experimental activity compared to the optimization-only approach (p < 0.03). The model and solution methods developed in this thesis improve co-contraction and tendon tension estimates in the finger. As such, this work contributes to our understanding of the control of the hand and the forces that may be detrimental to hand function. / Thesis / Master of Science (MSc)

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A methodology to facilitate analysis of dynamic subject-specific patellofemoral function is presented. An enhanced understanding of patellofemoral biomechanics will enable orthopaedic surgeons to identify the mechanisms responsible for imbalances in the joint stabilisers, while also providing objective information on which to base treatment methods. Dynamic patellofemoral function of three volunteers was simulated with a musculoskeletal computational model. The individuals underwent scans from which three-dimensional models of their patellofemoral joints were constructed. Skeletal muscles and soft tissue stabilisers were added to the skeletal models, after which subject-specific motion was simulated. After trochlear engagement, the patellae of the volunteers followed a lateral path, whereas patella tilt was subject-specific. Comparison of the predicted tilt and mediolateral position values at 30 degrees knee flexion to in-vivo MRI values showed a mean accuracy of 62.1 % and 96.9 % respectively. The patellofemoral contact load . quadriceps tendon load ratio varied between 0.7 and 1.3, whereas the mediolateral load component . resultant load ratio ranged between 0 and 0.4. Both parameters. values were similar to previous findings. The medial patellofemoral ligament tension decreased with knee flexion, while the patellar tendon-quadriceps tendon ratio followed a similar trend to that of previous findings (varied between 0.4 and 1.2). After induction of a tubercle osteotomy in the coronal plane, Volunteer One.s patella engaged the trochlear groove at an earlier knee flexion angle, while the patella of Volunteer Two only underwent a small medial displacement. Finite element analyses were employed to investigate the influence of the osteotomy on the patellofemoral pressure distribution. The mean pressure in Volunteer One.s patellofemoral joint was alleviated (17 % smaller) at all angles of flexion with the exception of 60 degrees (12 % greater). Pressure in Volunteer Two.s joint was alleviated at 30 and 45 degrees knee flexion (6 % smaller), while it was elevated (9.1 % greater) at other angles of flexion. Two commercial patellofemoral prostheses were tested on the three Volunteers. joints in the virtual environment. Prosthesis Two delivered patella shift and tilt patterns similar to the baseline values. Patellar tendon tension was slightly greater after resurfacing, with the tensions elevated most with Prosthesis Two. Medial patellofemoral ligament tension was reduced most with Prosthesis Two, while lateral retinaculum tension was increased slightly. Prosthesis Two was the best candidate to reproduce patella kinematics, while the patellofemoral kinetics was largely independent from the type of prosthesis used. The prostheses performed worse for Volunteer Three, supporting the need for the development of patient-specific prostheses. Three validated subject-specific musculoskeletal models facilitated the analysis of the individuals. patellofemoral biomechanics. The technique can potentially be employed by orthopaedic surgeons to visualise the change that an osteotomy or patellofemoral arthroplasty might induce on an individual.s patellofemoral joint. This technique might aid in the development of a tool to assist biomedical engineers in the development of new patellofemoral prostheses. Most importantly, the outcome of surgical intervention may be predicted beforehand, and a treatment procedure may be tailored to optimally fit the patellofemoral biomechanics of that individual. / AFRIKAANSE OPSOMMING: 'n Ondersoekmetode van die dinamiese gedrag van pasiënt-spesifieke patellofemorale gewrigte word beskryf. Indien die patellofemorale biomeganika beter verstaan word, kan ortopediese chirurge die meganismes wat verantwoordelik is vir oneffektiewe stabiliseerders identifiseer en behandeling op objektiewe bevindinge baseer. Die dinamiese patellofemorale funksie van drie vrywilligers is gesimuleer m.b.v. `n spier-skelet rekenaarmodel. Drie-dimensionele modelle van die individue se patellofemorale gewrig is gekonstrueer m.b.v. skanderings. Die skeletspiere en sagte ondersteuningsweefsel is tot die model toegevoeg, voordat vrywilliger-spesifieke beweging gesimuleer is. Die knieskywe van die vrywilligers het `n laterale pad gevolg nadat dit die groef binnegetree het, met die tiltwaardes uniek vir elke vrywilliger. Vergelyking van die beraamde knieskyf mediolaterale tilt en posisies by 30 grade fleksie met in-vivo magnetiese resonansieskandering waardes het `n akkuraatheid van 62.1 % en 96.9 % respektiewelik getoon. Die patellofemorale kontaklas-kwadriseps seningspanning verhouding het gewissel tussen 0.7 en 1.3; asook die mediale komponent – resultante komponent patellofemorale kontaklas wat gewissel het tussen 0 en 0.4. Beide parameters se waardes was soortgelyk aan voorheen-gepubliseerde data. Die mediale patellofemorale ligamentspanning het afgeneem met fleksie. Die patella sening-kwadriseps seningspanning verhouding was soortgelyk aan vorige gepubliseerde waardes en het gewissel tussen 0.4 en 1.2. Nadat 'n tuberkel-osteotomie in die koronale vlak aangebring is, het Vrywilliger Een se patella die femorale groef vroeër binnegetree. Vrywilliger Twee se patella het slegs `n mediale verskuiwing ondergaan. Eindige element analises is ingespan om die effek van die osteotomie op die spanningsverspreiding in die patellofemorale gewrig te ondersoek. Die gemiddelde spanning in Vrywilliger Een se gewrig was minder by alle hoeke van fleksie (17 % minder), met uitsondering van die spanning by 60 grade (12 % meer). Die spanning in Vrywilliger Twee se gewrig was minder by 30 en 45 grade (6 % minder), maar hoër by ander hoeke (9.1 % meer). Twee kommersiële patellofemorale prosteses is getoets op die drie Vrywilligers d.m.v. die model. Prostese Twee het die knieskyf-kinematika die beste nageboots. Die patella-seningspanning was effens groter na die vervanging. Prostese Twee het gesorg vir die grootste toename. Die mediale patellofemorale ligamentspanning was die kleinste toe Prostese Twee gebruik is, maar dit het gesorg vir effense hoër laterale retinakulumlaste. Die analises het getoon dat Prostese Twee die beste kandidaat is om die korrekte kinematika te herbewerkstellig. Die kinetika daarteenoor was onafhanklik van die tipe prostese wat gebruik is. Geeneen van die twee prosteses was geskik vir Vrywilliger Drie nie, wat as motivering vir die ontwikkeling van pasiënt-spesifieke prosteses dien. Drie bekragtigde vrywilliger-spesifieke spier-skelet modelle het die analise van patellofemorale biomeganika bewerkstellig. Die tegniek het die potensiaal om ortopediste in staat te stel om die effek van `n osteotomie of patellofemorale vervanging te visualiseer. Die tegniek kan verder gebruik word deur biomediese ingenieurs in die vervaardiging van nuwe patellofemorale prosteses. Meer belangrik is die feit dat die resultaat van chirurgiese ingryping voorspel kan word en optimale behandelingsprosedures beplan kan word vir die patellofemorale biomeganika van `n individu.

Most manual wheelchair users will experience upper extremity injury and pain during their lifetime, which can be partly attributed to the high load requirements, repetitive motions and extreme joint postures required during wheelchair propulsion. Recent efforts have attempted to determine how different propulsion techniques influence upper extremity demand using broad measures of demand (e.g., metabolic cost). However studies using more specific measures (e.g., muscle stress), have greater potential to determine how altering propulsion technique influences demand. The goal of this research was to use a musculoskeletal model with forward dynamics simulations of wheelchair propulsion to determine how altering propulsion technique influences muscle demand. Three studies were performed to achieve this goal. In the first study, a wheelchair propulsion simulation was used with a segment power analysis to identify muscle functional roles. The analysis showed that muscles contributed to either the push (i.e. delivering handrim power) or recovery (i.e. repositioning the hand) subtasks, with the transition period between the subtasks requiring high muscle co-contraction. The high co-contraction suggests that future studies focused on altering transition period biomechanics may have the greatest potential to reduce upper extremity demand. The second study investigated how changing the fraction effective force (i.e. the ratio of the tangential to total handrim force, FEF) influenced muscle demand. Simulations maximizing and minimizing FEF both had higher muscle work and stress relative to the nominal simulation. Therefore, the optimal FEF value appears to balance increasing FEF with minimizing upper extremity demand and care should be taken when using FEF to reduce demand. In the third study, simulations of biofeedback trials were used to determine the influence of cadence, push angle and peak handrim force on muscle demand. Although minimizing peak force had the lowest total muscle stress, individual stresses of many muscles were >20% and the simulation had the highest cadence, suggesting that this variable may not reduce demand. Instead minimizing cadence may be most effective, which had the lowest total muscle work and slowest cadence. These results have important implications for designing effective rehabilitation strategies that can reduce upper extremity injury and pain among manual wheelchair users. / text

Although people can typically maintain balance on moving trains, or press the appropriate button on an elevator with little conscious effort, the apparent ease of these sensorimotor tasks is courtesy of neural mechanisms that continuously interpret many sensory input signals to activate muscles throughout the body. The overall hypothesis of this work is that motor behaviors emerge from the interacting constraints and features of the nervous and musculoskeletal systems. The nervous system may simplify the control problem by recruiting muscles in groups called muscle synergies rather than individually. Because muscles cannot be recruited individually, muscle synergies may represent a neural constraint on behavior. However, the constraints of the musculoskeletal system and environment may also contribute to determining motor behaviors, and so must be considered in order to identify and interpret muscle synergies. Here, I integrated techniques from musculoskeletal modeling, control systems engineering, and data analysis to identify neural and biomechanical constraints that determine the muscle activity and ground reaction forces during the automatic postural response (APR) in cats. First, I quantified the musculoskeletal constraints on force production during postural tasks in a detailed, 3D musculoskeletal model of the cat hindlimb. I demonstrated that biomechanical constraints on force production in the isolated hindlimb do not uniquely determine the characteristic patterns of force activity observed during the APR. However, when I constrained the muscles in the model to activate in a few muscle synergies based on experimental data, the force production capability drastically changed, exhibiting a characteristic rotation with the limb axis as the limb posture was varied that closely matched experimental data. Finally, after extending the musculoskeletal model to be quadrupedal, I simulated the optimal feedforward control of individual muscles or muscle synergies to regulate the center of mass (CoM) during the postural task. I demonstrated that both muscle synergy control and optimal muscle control reproduced the characteristic force patterns observed during postural tasks. These results are consistent with the hypothesis that the nervous system may use a low-dimension control scheme based on muscle synergies to approximate the optimal motor solution for the postural task given the constraints of the musculoskeletal system. One primary contribution of this work was to demonstrate that the influences of biomechanical mechanisms in determining motor behaviors may be unclear in reduced models, a factor that may need to be considered in other studies of motor control. The biomechanical constraints on force production in the isolated hindlimb did not predict the stereotypical forces observed during the APR unless a muscle synergy organization was imposed, suggesting that neural constraints were critical in resolving musculoskeletal redundancy during the postural task. However, when the model was extended to represent the quadrupedal system in the context of the task, the optimal control of the musculoskeletal system predicted experimental force patterns in the absence of neural constraints. A second primary contribution of this work was to test predictions concerning muscle synergies developed in theoretical neuromechanical models in the context of a natural behavior, suggesting that these concepts may be generally useful for understanding motor control. It has previously been shown in abstract neuromechanical models that low-dimension motor solutions such as muscle synergies can emerge from the optimal control of individual muscles. This work demonstrates for the first time that low-dimension motor solutions can emerge from optimal muscle control in the context of a natural behavior and a realistic musculoskeletal model. This work also represents the first explicit comparison of muscle synergy control and optimal muscle control during a natural behavior. It demonstrates that an explicit low-dimension control scheme based on muscle synergies is competent for performance of the postural task across biomechanical conditions, and in fact, may approximate the motor solution predicted by optimal muscle control. This work advances our understanding how the constraints and features of the nervous and musculoskeletal systems interact to produce motor behaviors. In the future, this understanding may inform improved clinical interventions, prosthetic applications, and the general design of distributed, hierarchal systems.