Darryl G. Thelen - US grants

DESCRIPTION (provided by applicant): The overall objective of this research is to establish a scientific understanding of the biomechanical factors that govern walking performance in the elderly. Walking speed is a common clinical measure of gait performance. Slow walking speed has been associated with falls, can contribute to physical disability and is one of the primary criteria used to describe the syndrome of frailty. Two factors that may contribute to slow walking are reduced muscle strength and decreased flexibility. Intervention studies have shown that elderly adults can often achieve remarkable gains in strength and flexibility through exercise. However, such gains have often not translated into faster walking speeds. These inconsistent outcomes may stem, in part, from a limited understanding of the specific factors that constrain elderly gait performance. This study will use forward dynamic simulations of subject-specific walking patterns to describe the causal relationship between muscle excitations and movement. Analysis of simulations of elderly adult gait will be used to rigorously investigate biomechanical factors that may limit gait speed. Aim 1 will examine the contributions of passive hip flexor stiffness to the multi-joint movements seen in gait. The hypothesis to be tested is that compared to young adults, elderly adults will exhibit a greater reliance on hip flexor tightness to assist swing leg movement as gait speed is increased. Aim 2 will determine whether gait speed is limited by ankle plantarflexor power capacity. The hypothesis is that healthy elderly adults will not demonstrate limitations in ankle power during walking. However as gait speed is increased, it is hypothesized that elderly adults will exhibit an increased dependence on hip muscles to compensate for functional limitations of the ankle plantarflexors to generate forward acceleration. Completion of these aims is an important step toward characterizing the limiting factors to gait among impaired elderly and developing targeted interventions for improving gait performance.

[unreadable] DESCRIPTION (provided by applicant): Muscle strain injuries are one of the most common conditions seen in sports medicine clinics. However, methods of treatment are variable and re-injury rates tend to be high which, in part, reflects a lack of fundamental understanding of the factors that influence injury risk. The prevailing theory is that injury occurs as a result of excessive strain of active muscle fibers. The goal of this study is to develop novel biocomputational tools to predict and analyze the strain distributions within skeletal muscles during movements associated with injury. Model predictions will be compared with strain measures obtained using state-of-the-art dynamic magnetic resonance imaging experiments. Once validated, we will use the biocomputational tools to investigate how morphology and coordination influence hamstring injury risk during running. Following are the specific aims. Aim 1 will use a dynamic magnetic resonance imaging technique to measure the strain distributions within the individual hamstring muscles during lengthening contractions, a loading condition commonly associated with injury. Comparisons between muscles will provide new insights into the propensity for hamstring injury to occur in the biceps femoris long head. Aim 2 will build a biocomputational framework to predict muscle strain distributions during movement. The framework will couple finite-element simulations of muscle tissue behavior with dynamic simulations of whole body movement. The methods will be validated by comparing strain predictions with those determined from the dynamic images in Aim 1. We will then use the framework to investigate the relationship between muscle excitations, hamstring tissue strains and skeletal movement during running. Aim 3 will evaluate whether computational models predict re-injury prevention strategies. We will build and validate models of subjects who exhibit residual changes in tissue structures as a result of a previous hamstring injury. We will then use the software framework to identify how movement coordination can be adapted to accommodate injury-induced changes in morphology. This research will establish a biocomputational framework that reveals the complex relationship between muscle morphology, coordination and injury risk, thus providing a new paradigm for identifying rehabilitation and injury prevention strategies. Muscle strain injuries are one of the most common conditions seen in sports medicine clinics. However, methods of treating muscle injuries are variable and re-injury rates tend to be high. This proposal couples novel biocomputational tools and imaging techniques to establish a scientific basis for preventing and rehabilitating hamstring muscle injuries. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): The objective of this research is to measure and simulate the function of biarticular muscles during human walking. The clinical treatment of locomotor impairments often includes targeted surgical and rehabilitative interventions performed on biarticular muscles. However, it can be extremely challenging to predict a priori how different treatments will alter an individual's gait. Computational models of the musculoskeletal system provide a systematic way of predicting how muscles actuate movement. It has previously been shown that model predictions are often non-intuitive, and sometimes inconsistent with assumptions that underlie current treatment strategies. However, the accuracy of the model predictions has not been established, which limits the impact of the models on treatment. The investigators in this study use electrical stimulation experiments to directly measure how two biarticular muscles, the rectus femoris and hamstrings, biomechanically function during walking. Abnormal activation of these muscles is often implicated as a cause of gait abnormalities that are characterized by diminished knee flexion during the swing phase of walking, and/or excessive knee flexion during the stance phase. In the experiments, subjects walk at a constant speed on an instrumented, split-belt treadmill. At select phases of a random gait cycle, electrical muscle stimulation is then used to alter the normal activation of the rectus femoris or hamstrings. The resulting perturbations to walking kinematics are recorded using a motion analysis system. Comparison of un-perturbed and perturbed walking provides a basis of assessing the movement induced by the individual muscles. The data are used to test the hypotheses that over-activation of the rectus femoris during stance induces a more extended limb during swing, while over-activation of the hamstrings during swing induces a more flexed limb during stance. Measurements are compared to computational model predictions, so as to rigorously evaluate the accuracy of assumptions regarding musculoskeletal geometry and muscle force transmission paths. The anticipated outcomes of this study are an enhanced understanding of biarticular muscle function during walking, and improved confidence in the use of computational models to evaluate surgical and rehabilitative treatments of locomotor impairments. PUBLIC HEALTH RELEVANCE: Locomotion impairments are common among individuals with neurological disorders such as cerebral palsy. Abnormal movement patterns can greatly increase the metabolic cost of walking and contribute to long-term joint degeneration and physical disability. For this reason, surgical and/or rehabilitative treatments are often used to try to correct abnormal gait patterns. However, it can be challenging to predict how different treatment options will affect a patient's gait. This study uses experimental and computational techniques to assess how muscles function normally during walking, so as to contribute to a scientific basis for establishing effective interventions.

PI: Thelen, Darryl G., Negrut, Dan, and Dhaher, Yasin
Proposal Number: 0966535 & 0966742

Individuals who experience knee ligament injuries are at high risk for early onset osteoarthritis, which can result in chronic pain and loss of function. It is believed that biomechanical factors may contribute to such long term problems, with abnormal cartilage loading inducing secondary micro-trauma and joint degeneration processes. The goal of this study is to establish a validated computational framework that would be used to investigate how injury (e.g. partial or full ligament tears), surgical (e.g. ligament reattachment sites, soft tissue tensioning) and rehabilitative (e.g. stretching, muscle re-training) factors can alter tissue loading during movement. Two research aims focus technical effort to meet the stated goal.

The first aim involves the construction of subject-specific, finite element (FE) knee models from high resolution medical images. The FE models include continuum descriptions of connective tissues, and uniquely account for interactions between the tibio-femoral and patella-femoral joints. The second aim investigates a computational approach for predicting knee kinematics, ligament strains and cartilage loading during movement. A co-simulation framework is proposed in which finite element models are solved simultaneously with multi-body and musculo-tendon dynamics, thereby accounting for inherent interactions that exist between knee mechanics and movement dynamics. Bayesian analysis techniques will be used to both statistically calibrate and validate the computational models by comparing model predictions to in vivo measures obtained using dynamic magnetic resonance imaging.

The outreach objectives are to: 1) educate medical practitioners about the inherent coupling between movement and internal joint mechanics that arise naturally during functional tasks, 2) engage minority high school students from Wisconsin and Illinois in Computational Science related activities. The research/education integration plan involves the development of case studies for the physiatry residency program at the Rehabilitation Institute of Chicago (RIC). By relying on the predictive simulation capability developed under this project, these studies will illustrate the importance of considering biomechanical factors when planning clinical interventions that address musculoskeletal injury and diseases. The high school outreach effort will involve a two tier approach that each year will (a) start by organizing seminars that popularize computational science, and (b) follow up by a one week residential summer program at the University of Wisconsin-Madison. The program, ?Promoting the Computational Science Initiative? (ProCSI), is aimed at under-represented high-school students.

The intellectual merit of this study stems from combining advanced computational science, biomechanical modeling and statistical analysis techniques to establish a new computational framework for simulating musculoskeletal function. Broader impact will be achieved by promoting the use of biomechanical modeling to scientifically evaluate the clinical treatment of musculoskeletal injuries, and also by providing under-represented students an opportunity to use computational tools to address meaningful medical problems.

DESCRIPTION (provided by applicant): Anterior cruciate ligament (ACL) tears are an extremely common and debilitating injury. ACL reconstruction surgery is successful at improving short-term function. However, long-term outcomes remain sub-optimal with a large majority of patients developing osteoarthritis (OA) at 10-15 year follow-up, which can result in extended periods of pain and disability before joint replacement becomes a feasible option. Thus, there is an urgent need to develop improved treatment options for patients with ACL reconstruction to halt the progression of joint degeneration and thereby improve long-term outcomes. This study will investigate whether altered cartilage contact patterns persist following ACL reconstructive surgery, and then contribute to the pathogenesis of early cartilage degeneration. The first Aim will establish a new dynamic magnetic resonance (MR) imaging approach for rapidly acquiring three-dimensional (3D) image volumes during knee flexion-extension motion. High resolution models of bone and cartilage morphology will be optimally registered with these dynamic images, allowing for simultaneous analysis of joint motion and inter-segmental cartilage contact. The second Aim will assess whether abnormal cartilage contact patterns are evident during loaded movement in ACL reconstructed knees. Eighteen patients who underwent ACL reconstructive surgery between 1 and 2 years prior will be bilaterally imaged while performing a knee flexion-extension task within the bore of a 3.0T MR scanner. The data will be used to test the hypothesis that relatively small changes in knee motion can significantly shift the cartilage contact to regions that are less accustomed to compressive loading. The final Aim will investigate the relationship between cartilage contact and MR parameters of early cartilage degeneration. The 18 subjects with ACL reconstruction in Aim 2 will undergo high resolution morphological and physiological imaging to identify regional changes in cartilage composition and thickness. Cartilage T1-rho and T2 relaxation time and cartilage thickness maps will be compared to cartilage contact maps in the reconstructed and contralateral knees. These data will be used to test the hypothesis that areas of cartilage which are loaded in the reconstructed knee but not the contralateral knee will show the greatest changes in MR biomarkers of cartilage physiology and morphology. Successful completion of this exploratory proposal will establish the MR technology needed to further investigate the pathogenesis of OA in patients with ACL reconstruction while also considering the influence of other potential risk factors including meniscal tears and osteochondral injuries. The innovative approach could also be used to assess the efficacy of alternative surgical treatment options for patients with ACL injury which may better restore joint kinematics and thereby prevent the development of early OA.

DESCRIPTION (provided by applicant): Anterior cruciate ligament (ACL) reconstructive surgeries are often successful at improving joint stability, but patients have a highly elevated rik for developing early onset osteoarthritis (OA). It is not well understood why OA develops in these patients, or how one can best plan a treatment strategy to mitigate the risk for OA. This is a very challenging question to answer empirically, since prospective studies require large subject numbers and many years to decipher. Current computational models in biomechanics are ill-suited to solve this problem because they decouple behavior that occurs at the macro (whole body) and micro (tissue mechanics) scales. Hence, a new multi-scale computational construct is being formulated to examine the inherent coupling that exists between musculoskeletal dynamics and soft tissue mechanics during gait. This construct is used to gain insights into the key surgical factors that can affect cartilage contact stresses after ACL reconstruction, which are believed to predicate osteoarthritic changes to the joint. The three aims of the study are to: 1) Assess effects of ACL graft stiffness, pre-tension and tunnel architecture on intra-operative assessments of knee laxity, 2) Investigate the coupled influence of surgical factors and muscle forces on in vivo knee mechanics as measured using dynamic MRI, 3) Investigate the multi-scale biomechanical behavior of reconstructed knees during human locomotion. These aims are used to test the hypothesis that articular cartilage contact stress magnitudes and location vary significantly with active muscle loading, and are also highly sensitive to the position and orientation of the tunnels used to reconstruct the ACL. The results of these studies are important for informing clinical approaches that can best mitigate the risk fo OA following ligament injury and surgical repair.

DESCRIPTION (provided by applicant): Children with Cerebral Palsy (CP) often exhibit crouch gait, which is characterized by excessive knee flexion during stance. This form of walking is extremely fatiguing and tends to progress until eventually walking ability ceases. A newly revived surgical procedure, distal femoral extension osteotomy (DFEO) and patellar tendon advancement (PTA), simultaneously addresses both knee flexion contractures and patella alta (superiorly displaced patella) that often co-exist in those with crouch. Initial outcoe studies demonstrate greater improvements in gait than conventional surgical treatments. However, complication rates remain high and some patients exhibit little to no improvement in gait after surgery. The first aim of this study is to investigate the effects of patella position, crouch and surgical parameters on functional knee mechanics. Computational knee models will be created that include detailed representations of ligament and articular cartilage geometry within the tibiofemoral and patellofemoral joints. Patella alta and knee flexion contractures will be introduced, and surgical simulations will be performed virtually. The computational models will then be used to simulate knee mechanics when walking in normal, and mild, moderate, and severe crouch gait postures. Probabilistic simulations will then be used to investigate how variability in physical characteristics and surgical factors can contribute to variable outcomes. The effects of surgery and crouch gait on cartilage pressure patterns will also be determined, which is relevant for understanding subsequent skeletal growth and long-term cartilage health. The second aim investigates whether a combination of quantitative measures of physical characteristics and surgical parameters can retrospectively classify post-surgical gait performance. Pre- and post-surgical x- rays will be used to quantitatively measure the Koshino index (metric of patella alta/baja), the magnitude and location of the DFEO, and the PTA advancement distance in patients who previously underwent DFEO+PTA. Pre-surgical measures of knee flexion contracture and spasticity will also be obtained. Pre- and post-operative gait analysis data will be used to assess changes in gait mechanics, while functional surveys will assess changes in performance on activities of daily living. The random forest algorithm will then be used to identify decision trees and associate predictor variables that can classify those patients whose gait and overall function improved after surgery. These results will be interpreted in the context of modeling results from Aim 1, thereby providing a potential mechanistic explanation for clinical observations. The research will impact innumerable CP patients as the DFEO+PTA surgical procedures are adopted around the world, and will also set the groundwork for more rigorous scientific study of other procedures used to treat gait disorders.

? DESCRIPTION (provided by applicant): A reduction in plantarflexor power during the push-off phase of walking leads to the slowing of preferred walking speed with age, which in turn negatively affects old adults' health and independence. Although commonly implicated, sarcopenia and muscle weakness alone cannot fully explain the reduction in plantarflexor power or accompanying changes in coordination. We postulate that this disconnect arises from age-related changes in Achilles tendon behavior that alter muscle-tendon dynamics during movement. This study tightly integrates novel in vivo imaging, computational modeling, and motion analysis to investigate tendon deformations associated with physiological loading and movement to an unprecedented level of detail. Our overarching hypothesis is that age-related changes in tendon elasticity and inter-fascicle adhesions have a substantial effect on the ability for muscles to generate sufficient plantarflexor power during movement. This study has three aims. The first aim is to determine how advancing age affects the in vivo behavior of the plantarflexor muscles and Achilles tendon during prescribed ankle flexion movements under physiological loading. We will combine high-resolution static MRI, dynamic MRI, and shear wave elastography to test the hypothesis that advancing age brings altered spatial patterns of Achilles tendon tissue elasticity that predict measured muscle tissue deformation patterns. The second aim is to predict the functional implications of age- related changes in Achilles tendon tissue mechanics on plantarflexor performance during movement. We will link measurements of human movement with a unique computational framework that includes detailed structural representations of the 3D morphology of the plantarflexor muscle-tendons and their dynamic interactions. We will test the primary hypothesis that simulating age-related changes in Achilles tendon elasticity and inter-fascicle adhesions will diminish power production and increase localized tissue strains. The third aim is to investigate age-related changes in Achilles tendon behavior during walking and its relevance to functional motor performance and response to gait interventions. We will measure in vivo Achilles tendon deformations, plantarflexor fascicle behavior, and plantarflexor power during walking. We will couple these measurements with biofeedback designed to elicit prescribed increases in plantarflexor power output. We will use these data to test the hypotheses that: 1) more uniform tendon deformations during walking with aging, which would reflect a reduction in sliding between tendon fascicles, will predict reduced ankle joint kinetics and altered plantarflexor muscle fascicle kinematics, and 2) with aging, different coordination strategies will be used to increase plantarflexor power, adaptations that will be consistent with Aim 2 model predictions. Combined, these aims will reveal the influence of age-related changes in Achilles tendon mechanics on plantarflexor muscle behavior during movement, insights critical for developing informed interventions to maintain or restore mobility while mitigating risk for muscle-tendon tissue damage.

Abstract The long-term goal of this research is to use in vivo muscle-tendon force measurements to enhance the clinical treatment of gait disorders in individuals with cerebral palsy (CP). We have recently shown that the frequency at which a tendon vibrates is dependent on the applied stress. This phenomenon is similar to the tension-dependent vibration seen in guitar strings. Vibration frequency reflects the speed at which transverse, or shear, waves propagate. Hence, it may be feasible to monitor shear wave speed in tendon as a proxy for tissue loading. This study will investigate the potential to measure and interpret shear wave speeds in human tendons. The initial two aims are designed to investigate the validity and robustness of the relationship between shear wave speed and tendon loading. Skin-mounted tensiometers will be designed that induce and track propagating shear waves of micron-scale amplitude. Cadaveric ankle-foot specimens will be tested in aim 1. A robotic gait simulator will drive external foot and internal tendon loading to emulate human walking. Tendon tensions and wave speeds will be simultaneously monitored. Human subjects will be tested in Aim 2. Tensiometers positioned over superficial knee and ankle tendons will monitor wave speeds while subjects perform isometric and isokinetic exertions. Data from aims 1 and 2 will be used to investigate how subject- and tendon-specific geometry can modulate the relationship between tendon wave speed and load. The final two aims will use tensiometers to measure shear wave speeds in the superficial leg tendons during walking. Typically developing children will be tested in Aim 3 to establish a normative database of wave speed patterns over a gait cycle. Individuals with CP who exhibit either equinus (toe-walking) or crouch (flexed knee) will be tested in Aim 4. Tendon wave speed measures will be obtained while subjects are undergoing a standard clinical gait analysis. We will explore clinical utility by performing direct comparisons between shear wave speed data, joint kinetics, EMG signals and clinical interpretations based on traditional gait analysis. The anticipated outcome of this study is a ground-breaking approach to assess in vivo muscle-tendon loads during both normal and pathological gait. Successful completion of the aims could lead to enhanced diagnosis and outcomes assessment of gait disorders.

Abstract The goal of this research is to establish an intraoperative tool for measuring ligament tension during total knee arthroplasty (TKA). This technology would enable surgeons to identify and correct individual structures that may be improperly tensioned, which could mitigate post-operative pain, stiffness, and instability. We have recently shown that the speed at which shear waves propagate in tendons and ligaments can be measured and used to infer the tension in the structure. In this project, we will construct and test a handheld device suitable for intraoperative measurements of shear wave speed in ligaments. The device, termed a shear wave tensiometer, will induce and track propagating shear waves of micron- scale amplitude. In Aim 1, we will measure shear wave speeds in isolated superficial medial and lateral collateral ligaments (sMCL and LCL) and patellar ligaments (PL) undergoing axial loading. These experiments will be used to investigate the effects of ligament cross-sectional geometry on the shear wave speed-tension relationship. In Aim 2, we will measure shear wave speeds in the sMCL and LCL following incremental ligament releases, which are performed intraoperatively to reduce the tension in an overly-tight ligament. These experiments will be used to assess the sensitivity with which ligament shear wave speed data can be used to objectively guide incremental releases. In Aim 3, TKA will be performed on cadaveric knees. Three-dimensionally printed femoral, tibial, and patellar components will be used to simulate subtle adjustments in component alignment that would represent those made clinically. We will perform standard clinical assessments of knee laxity and range-of-motion while ligament shear wave speeds, externally applied loads, and joint kinematics are simultaneously measured. These experiments will be used to assess the sensitivity with which ligament shear wave speed data can be used to guide subtle adjustments in component alignment. The outcome of this study will be a novel intraoperative approach needed by surgeons to objectively plan, execute, and evaluate TKAs, which should improve patient satisfaction and reduce the need for revision procedures. Beyond TKA, the fundamental technology has broader relevance for objectively assessing ligament behavior following injury, during healing, and due to diseases such as osteoarthritis.

Advances in exosuit technologies are enabling the use of powered assistance to enhance walking performance in healthy individuals and assist individuals who exhibit gait pathologies, e.g. individuals with stroke. Unlike rigid exoskeletons, exosuits are lightweight and use soft materials that provide a comfortable and unobtrusive fit with the body. A pack worn at the waist uses battery-powered motors to generate forces that are transmitted to the ankle and hip. In spite of demonstrated success in decreasing the energy needed to walk, it remains challenging to tune exosuit assistance patterns for individual users. Thus, the long-term goal of this work is to enable individualized assistance that can adapt in real time to a user?s unique gait patterns and to the environment. To do this, novel sensors, termed shear wave tensiometers, will be used to track adaptations in knee and ankle muscle loading that arise when assistance is provided by a powered ankle exosuit. Studies will be performed to determine how different exosuit assistance control patterns modulate internal muscle loading under varied walking conditions, including with and without exosuit assistance, with and without carrying a load (backpack) and walking in an outdoor/real-world environment (declines, inclines and variable walking speeds.) Theses studies will enhance the fundamental understanding of neuromuscular responses to exosuit assistance and thus enable human-in-the-loop implementations that adapt assistance based on the needs of an individual. Educational and outreach impact will be achieved by using fundamentals underlying the robotic, biomechanics and sensor technologies developed in this project as a platform for engaging K-12 students in STEM. Simplified versions of the exosuits and sensors will be incorporated into the annual engineering outreach event at the University of Wisconsin-Madison which reaches thousands of K-12 students and their teachers every year. Also, the Soft Robotics Toolkit hosted by Harvard will be used to create engaging content that describes human-machine interaction, biomechanics, physiology and gait.

The goal of this project is to use novel tissue load sensors, termed shear wave tensiometers, to investigate biomechanical adaptations to exosuit assistance within and beyond the laboratory environment. Though current exosuit technologies have been shown to lower the metabolic cost of walking in healthy subjects and improve propulsion, ground clearance, and symmetry in stroke survivors, the extent of these benefits varies widely across subjects. The project builds on a new collaboration between the lab that invented the tensiometer method to directly gauge tendon loading by measuring the propagation speed of shear waves along the tendon?s axis (University of Wisconsin-Madison) and a lab that is recognized for leadership in developing the next generation of soft exosuits (Harvard.) The Research Plan is organized under three aims, with each aim being evaluated in 10 human subjects. The FIRST Aim is to develop and incorporate a wearable shear wave tensiometer into an ankle exosuit to continuously monitor Achilles tendon loading during prolonged treadmill walking trials. Ankle joint torque determined from tensiometer measurements will be compared to measurements based on motion capture. The result of this aim will be a validated wearable sensor for quantifying changes in tendon tissue loading induced by exosuit assistance. The SECOND Aim is to evaluate relationship between ankle exosuit assistance magnitude and change in muscle-tendon loading during walking with and without added mass. Results of this aim will provide novel insights into the relationship between exosuit assistance and biological soft tissue loads, with expectations that the tested variables (exosuit force, exosuit timing, and added mass) will have various effects on the user?s muscle-tendon load. The THIRD Aim is to evaluate the effect of ankle exosuit assistance on muscle-tendon loading while walking in an outdoor circuit that includes inclines, declines, comfortable speed and fast walking. Measurements include tendon loading with the mobile tensiometer, muscle kinematics with ultrasound, and biomechanics and suit data with suit IMUs and load cells. Results of this aim are expected to demonstrate that, similar to how a motion capture and force plate setup in a lab environment allows for estimating joint moments, the suit sensors and tensiometer will allow for evaluating joint kinematics and tendon kinetics in outdoor environments. Success of the project is expected to lead to a new design of exosuits with integrated tensiometer sensors, produce new understanding of biomechanics with exosuits, and potentially inform optimization of personalized wearable exoskeletons for clinical and/or aged populations.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Project Summary The goal of this project is to commercialize a wireless, wearable system to estimate the tension in superficial tendons throughout the limbs during dynamic movements. Tendon tension provides an estimate of muscle force, which is important information for understanding biomechanical behavior in all types of movement. Understanding muscle-tendon function inside the body is especially important for rehabilitation from musculoskeletal injuries: this information can elucidate the effectiveness of therapy, provide biofeedback to improve this effectiveness, and evaluate the level of impairment and recovery as a person progresses through recovery. Yet, muscle-tendon function has previously been difficult to measure. Tendon tensiometry uses skin- mounted accelerometers to track the propagation of shear waves along a tendon, after the waves are induced by a light mechanical tap on the tendon. The speed of wave propagation depends on the tension in the tendon, so measuring wave speed provides a measurement of tendon tension. The proposed project will build and test a wearable system to make these tendon tension measurements during free movement. These measurements promise to enable new methods of injury assessment, rehabilitation, and treatment of musculoskeletal disorders. This will refine current prototype tensiometry technology into a commercial product to allow convenient outdoor wearable data collections of muscle-tendon mechanics. It will refine the skin-mounted sensor and mounting sleeves for different joints and tendons. It will integrate drive and data logging electronics into a convenient, wearable multi-channel controller. It will create efficient programs to process the signals for real-time data streaming, and user interfaces for clinical monitoring of tendon tensiometry in common movements. The project will also develop means of convenient subject-specific calibration. Human subjects testing will be performed to establish a database of tendon loading profiles in healthy young and older adults. Finally, the research will develop methods to fuse tendon tension data with wearable movement sensor data to improve the quality of biomechanical insight available from real- world testing. The Specific Aims of this project are: 1. Establish a wearable shear wave tensiometer that is usable on multiple tendons by non-experts. 2. Build a software system for real-time wireless transmission and display of tensiometer metrics. 3. Integrate wearable tensiometers and inertial sensors to enable motion analysis in the real world.