Generating Optimal Control Simulations of Musculoskeletal Movement using OpenSim and MATLAB

Computer modeling, simulation and optimization are powerful tools that have seen increased use in biomechanics research. Dynamic optimizations can be categorized as either data-tracking or predictive problems. The data-tracking approach has been used extensively to address human movement problems of clinical relevance. The predictive approach also holds great promise, but has seen limited use in clinical applications. Enhanced software tools would facilitate the application of predictive musculoskeletal simulations to clinically-relevant research. The open-source software OpenSim provides tools for generating tracking simulations but not predictive simulations. However, OpenSim includes an extensive application programming interface that permits extending its capabilities with scripting languages such as MATLAB. In the work presented here, we combine the computational tools provided by MATLAB with the musculoskeletal modeling capabilities of OpenSim to create a framework for generating predictive simulations of musculoskeletal movement based on direct collocation optimal control techniques. In many cases, the direct collocation approach can be used to solve optimal control problems considerably faster than traditional shooting methods. Cyclical and discrete movement problems were solved using a simple 1 degree of freedom musculoskeletal model and a model of the human lower limb, respectively. The problems could be solved in reasonable amounts of time (several seconds to 1–2 hours) using the open-source IPOPT solver. The problems could also be solved using the fmincon solver that is included with MATLAB, but the computation times were excessively long for all but the smallest of problems. The performance advantage for IPOPT was derived primarily by exploiting sparsity in the constraints Jacobian. The framework presented here provides a powerful and flexible approach for generating optimal control simulations of musculoskeletal movement using OpenSim and MATLAB. This should allow researchers to more readily use predictive simulation as a tool to address clinical conditions that limit human mobility

OPTIMALITY CRITERIA FOR HUMAN RUNNING INVESTIGATED BY FORWARD DYNAMICS SIMULATIONS

There are currently no generally accepted optimality criteria for human running. The purpose of the study was to test a set of potential criteria by generating performance based forward dynamics simulations. Simulation results were compared to measurements from human runners. Minimizing muscle activation generated the simulation that most accurately matched the experimental kinematic and metabolic data. The results suggest that minimizing activation, which avoids fatiguing any one muscle, is an important control policy for human running

Adaptive Remodeling of Achilles Tendon: A Multi-scale Computational Model

While it is known that musculotendon units adapt to their load environments, there is only a limited understanding of tendon adaptation in vivo. Here we develop a computational model of tendon remodeling based on the premise that mechanical damage and tenocyte-mediated tendon damage and repair processes modify the distribution of its collagen fiber lengths. We explain how these processes enable the tendon to geometrically adapt to its load conditions. Based on known biological processes, mechanical and strain-dependent proteolytic fiber damage are incorporated into our tendon model. Using a stochastic model of fiber repair, it is assumed that mechanically damaged fibers are repaired longer, whereas proteolytically damaged fibers are repaired shorter, relative to their pre-damage length. To study adaptation of tendon properties to applied load, our model musculotendon unit is a simplified three-component Hill-type model of the human Achilles-soleus unit. Our model results demonstrate that the geometric equilibrium state of the Achilles tendon can coincide with minimization of the total metabolic cost of muscle activation. The proposed tendon model independently predicts rates of collagen fiber turnover that are in general agreement with in vivo experimental measurements. While the computational model here only represents a first step in a new approach to understanding the complex process of tendon remodeling in vivo, given these findings, it appears likely that the proposed framework may itself provide a useful theoretical foundation for developing valuable qualitative and quantitative insights into tendon physiology and pathology

A model‐based motion capture marker location refinement approach using inverse kinematics from dynamic trials

Marker‐based motion capture techniques are commonly used to measure human body kinematics. These techniques require an accurate mapping from physical marker position to model marker position. Traditional methods utilize a manual process to achieve marker positions that result in accurate tracking. In this work, we present an optimization algorithm for model marker placement to minimize marker tracking error during inverse kinematics analysis of dynamic human motion. The algorithm sequentially adjusts model marker locations in 3‐D relative to the underlying rigid segment. Inverse kinematics is performed for a dynamic motion capture trial to calculate the tracking error each time a marker position is changed. The increase or decrease of the tracking error determines the search direction and number of increments for each marker coordinate. A final marker placement for the model is reached when the total search interval size for every coordinate falls below a user‐defined threshold. Individual marker coordinates can be locked in place to prevent the algorithm from overcorrecting for data artifacts such as soft tissue artifact. This approach was used to refine model marker placements for eight able‐bodied subjects performing walking trials at three stride frequencies. Across all subjects and stride frequencies, root mean square (RMS) tracking error decreased by 38.4% and RMS tracking error variance decreased by 53.7% on average. The resulting joint kinematics were in agreement with expected values from the literature. This approach results in realistic kinematics with marker tracking errors well below accepted thresholds while removing variance in the model‐building procedure introduced by individual human tendencies.A new approach for refining human musculoskeletal models algorithmically adjusts motion capture marker locations based on inverse kinematics solutions of dynamic trials. The approach was applied to gait trials from eight able‐bodied subjects and was demonstrated to (a) reduce inverse kinematics marker tracking error overall, (b) reduce inter‐subject tracking error variability, and (c) produce normal walking kinematics for able‐bodied persons.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153769/1/cnm3283_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153769/2/cnm3283.pd

A Robotic Ankle-Foot Prosthesis With Active Alignment

An ankle-foot prosthesis designed to mimic the missing physiological limb generates a large sagittal moment during push off which must be transferred to the residual limb through the socket connection. The large moment is correlated with high internal socket pressures that are often a source of discomfort for the person with amputation, limiting prosthesis use. In this paper, the concept of active alignment is developed. Active alignment realigns the affected residual limb toward the center of pressure (CoP) during stance. During gait, the prosthesis configuration changes to shorten the moment arm between the ground reaction force (GRF) and the residual limb. This reduces the peak moment transferred through the socket interface during late stance. A tethered robotic ankle prosthesis has been developed, and evaluation results are presented for active alignment during normal walking in a laboratory setting. Preliminary testing was performed with a subject without amputation walking with able-bodied adapters at a constant speed. The results show a 33% reduction in the peak resultant moment transferred at the socket limb interface

_

SUMMARY Musculoskeletal models have become important tools for studying a range of muscle-driven movements. However, most work has been in modern humans, with few applications in other species. Chimpanzees are facultative bipeds and our closest living relatives, and have provided numerous important insights into our own evolution. A chimpanzee musculoskeletal model would allow integration across a wide range of laboratory-based experimental data, providing new insights into the determinants of their locomotor performance capabilities, as well as the origins and evolution of human bipedalism. Here, we described a detailed three-dimensional (3D) musculoskeletal model of the chimpanzee pelvis and hind limb. The model includes geometric representations of bones and joints, as well as 35 muscle-tendon units that were represented using 44 Hill-type muscle models. Muscle architecture data, such as muscle masses, fascicle lengths and pennation angles, were drawn from literature sources. The model permits calculation of 3D muscle moment arms, muscle-tendon lengths and isometric muscle forces over a wide range of joint positions. Muscle-tendon moment arms predicted by the model were generally in good agreement with tendon-excursion estimates from cadaveric specimens. Sensitivity analyses provided information on the parameters that model predictions are most and least sensitive to, which offers important context for interpreting future results obtained with the model. Comparisons with a similar human musculoskeletal model indicate that chimpanzees are better suited for force production over a larger range of joint positions than humans. This study represents an important step in understanding the integrated function of the neuromusculoskeletal systems in chimpanzee locomotion

A case-series study to explore the efficacy of foot orthoses in treating first metatarsophalangeal joint pain

Background: First metatarsophalangeal (MTP) joint pain is a common foot complaint which is often considered to be a consequence of altered mechanics. Foot orthoses are often prescribed to reduce 1 stMTP joint pain with the aim of altering dorsiflexion at propulsion. This study explores changes in 1 stMTP joint pain and kinematics following the use of foot orthoses.Methods: The effect of modified, pre-fabricated foot orthoses (X-line ®) were evaluated in thirty-two patients with 1 stMTP joint pain of mechanical origin. The primary outcome was pain measured at baseline and 24 weeks using the pain subscale of the foot function index (FFI). In a small sub-group of patients (n = 9), the relationship between pain and kinematic variables was explored with and without their orthoses, using an electromagnetic motion tracking (EMT) system.Results: A significant reduction in pain was observed between baseline (median = 48 mm) and the 24 week endpoint (median = 14.50 mm, z = -4.88, p < 0.001). In the sub-group analysis, we found no relationship between pain reduction and 1 stMTP joint motion, and no significant differences were found between the 1 stMTP joint maximum dorsiflexion or ankle/subtalar complex maximum eversion, with and without the orthoses.Conclusions: This observational study demonstrated a significant decrease in 1 stMTP joint pain associated with the use of foot orthoses. Change in pain was not shown to be associated with 1 stMTP joint dorsiflexion nor with altered ankle/subtalar complex eversion. Further research into the effect of foot orthoses on foot function is indicated. © 2010 Welsh et al; licensee BioMed Central Ltd

Mobilising Opportunities for Water Security: Politics, Institutions and Participation in Water Governance

muscle energy consumption during locomotion, based on computational models and muscle blood flow measurements, demonstrate complex patterns of energy use across the gait cycle, which are further complicated when task demands change. A deeper understanding of muscle energetics in locomotion will benefit from efforts to more tightly integrate muscle-specific approaches with organismal measurements

Testing the planar assumption during ergometer cycling

Utilisation de la cinématographie pour étudier la cinématique du membre inférieur en cyclisme dans le cadre de modèles bi-dimensionnel