Cooperation of mono- and bi-articular muscles: human lower limb.

OBJECTIVES: The aim of this study was to create and analyze a Pareto-optimal problem that would describe cooperation between mono- and bi-articulate lower limb muscles in sagittal plane. METHODS: Equations describing the problem were derived and analyzed, additional constrains were introduced and experimental verification based on gait video analysis was performed. RESULTS: Uncertainty of Pareto-optimal solution is shown for the muscular-skeletal system. An explanation of this situation is presented and discussed. Moreover, this theoretical observation is compared with a lack of gait reproducibility. Small but noticeable differences in gait cycles are shown and explained. CONCLUSIONS: A muscular system redundancy is shown and explained by the meaning of Pareto problem. Theoretical considerations were confirmed through a gait analysis. This leads to the conclusion, that during muscle cooperation each movement cycle can be different from the previous one, however due to physiological restrictions only a narrow equivalence class of the possible solutions exists.

Modeling and Strength Calculations of Parts Made Using 3D Printing Technology and Mounted in a Custom-Made Lower Limb Exoskeleton.

This study is focused on the application of 3D-printed elements and conventional elements to create a prototype of a custom-made exoskeleton for lower limb rehabilitation. The 3D-printed elements were produced by using Fused Deposition Modeling technology and acrylonitrile butadiene styrene (ABS) material. The scope of this work involved the design and construction of an exoskeleton, experimental testing of the ABS material and numerical research by using the finite element method. On the basis of the obtained results, it was possible to deduce whether the load-bearing 3D-printed elements can be used in the proposed mechanical construction. The work contains full data of the material models used in FEM modeling, taking into account the orthotropic properties of the ABS material. Various types of finite elements were used in the presented FE models. The work is a comprehensive combination of material testing issues with the possibility of implementing the obtained results in numerical strength models of machine parts.

Timed rolling and rising tests in Duchenne muscular dystrophy ambulant boys: a feasibility study.

BACKGROUND: Functional activities are extensively used in motor assessments of patients with Duchenne muscular dystrophy. The role of timed items has been reported as an early prognostic factor for disease progression. However, there are two functional activities that are not widely assessed in clinical practice among Duchenne muscular dystrophy patients: rolling and bed rising. This study aimed to investigate whether the 360-degree roll (roll) and supine to sit-to-edge (bed rise) measurements are feasible tools reflecting the functional status of ambulatory DMD children by establishing possible correlations between validated measures: the Vignos Scale (VS), timed rise from floor and the 6-Minute Walk Test (6MWT). METHODS: A total of 32 ambulant boys with DMD were assessed using timed items, the 6MWT and VS. RESULTS: The roll and bed rise are correlated with each other. The 6MWT, the floor rise and VS are correlated with the roll and with the bed rise. CONCLUSIONS: Findings offer preliminary empirical evidence addressing feasibility and safety of roll and bed rise measurements. There is a potential clinical utility of these tests in assessing functional status of DMD ambulant patients.

Fluid structure interaction study of non-Newtonian Casson fluid in a bifurcated channel having stenosis with elastic walls.

Fluid-structure interaction (FSI) gained a huge attention of scientists and researchers due to its applications in biomedical and mechanical engineering. One of the most important applications of FSI is to study the elastic wall behavior of stenotic arteries. Blood is the suspension of various cells characterized by shear thinning, yield stress, and viscoelastic qualities that can be assessed by using non-Newtonian models. In this study we explored non-Newtonian, incompressible Casson fluid flow in a bifurcated artery with a stenosis. The two-dimensional Casson model is used to study the hemodynamics of the flow. The walls of the artery are supposed to be elastic and the stenosis region is constructed in both walls. Suitable scales are used to transform the nonlinear differential equations into a dimensionless form. The problem is formulated and discretized using Arbitrary Lagrangian-Eulerian (ALE) approach. The finite element method (FEM) technique is used to solve the system of equations, together with appropriate boundary conditions. The analysis is carried out for the Bingham number, Hartmann number, and Reynolds number. The graphical results of pressure field, velocity profile, and load on the walls are assessed and used to study the influence of hemodynamic effects on stenotic arteries, bifurcation region, and elastic walls. This study shows that there is an increase in wall shear stresses (WSS) with increasing values of Bingham number and Hartmann number. Also, for different values of the Bingham number, the load on the upper wall is computed against the Hartmann number. The result indicate that load at the walls increases as the values of Bingham number and Hartmann number increase.

Lateral forces determine dimensional accuracy of the narrow-kerf sawing of wood.

The shrinking global forest area limits the supply of industrially usable raw resources. This, in combination with the ever-increasing consumption of timber due to population growth can lead to the lack of a positive balance between the annual volumetric growth and consumption of wood. An important innovation toward increasing environmental and economic sustainability of timber production is to reduce the volume of wood residues by minimizing the sawing kerf. It results in higher material yield but may impact the dimensional accuracy of derived products. Therefore, the cutting tool geometry as well as the sawing process as a whole must be carefully optimized to assure optimal use of resources. The goal of this study is to better understand the causes of machining errors that occur when sawing wood with saws of varying thickness of kerf, with a special focus on re-sawing thin lamellae performed on the gang saw. Numerical simulations were tested against experimental results, considering influence of diverse components of cutting forces, in addition to the initial and operating stiffness coefficients of the saw blade. It has been demonstrated that asymmetric loads from the cutting process for the scraper saw blade can cause sawing inaccuracies. The simulation methodology developed in this research can be straightforwardly extended towards determination of optimal geometry of other cutting tools, particularly with the reduced sawing kerf. This may lead to more sustainable use of natural resources as well as an increase in economic gain for the wood processing industries.

The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait.

Asymmetrical external loading acting on the musculoskeletal system is generally considered unhealthy. Despite this knowledge, carrying loads in an asymmetrical manner like carrying on one shoulder, with one hand, or on the strap across the torso is a common practice. This study is aimed at presenting the effects of the mentioned load carrying methods on muscle activity assessed by using thermal field and ground reaction forces. Infrared thermography and pedobarographic force platform (ground reaction force/pressure measurement) were used in this study. Experimental results point out an increased load-dependent asymmetry of temperature distribution on the chosen areas of torso and the influence of external loading on ground reaction forces. Results point out that wearing an asymmetrical load should be avoided and are showing which type of carrying the external load is potentially less and the most harmful.

Perceptual and Motor Effects of Muscle Co-activation in a Force Production Task.

We tested several predictions of the theory of motor control with spatial referent coordinates related to effects of muscle coactivation on force production and perception. In particular, we predicted that subjects would produce unintentional force increase by finger flexors and be unaware of this force increase. Healthy subjects performed steady force production task in isometric conditions with visual feedback on the force level. They coactivated muscles of the arm trying to keep the force constant in the absence of visual feedback. This led to a consistent force increase not perceived by the subjects as reflected by their verbal reports. In contrast, when asked to match the force with the contralateral hand, adequate force matching was observed. Using the "inverse piano" apparatus confirmed no change in the referent coordinate of the fingers and an increase in its apparent stiffness. The results confirm the earlier hypothesis on the reciprocal command being hierarchically higher than the coactivation command. The observations suggest that verbal reports and force matching use different neural mechanisms of force perception; the former are dominated by sense of effort, which reflects primarily the magnitude of the reciprocal command. There were only minor differences between the dominant and non-dominant hands, likely reflecting the faster unintentional drifts of control variables in the dominant hand.

Application of muscle model to the musculoskeletal modeling.

The purpose of this paper is to investigate new fusiform muscle models. Each of these models treats a muscle as a system composed of parts characterized by different mechanical properties. These models explain the influence of differences in the stiffness of lateral parts and the degree of muscle model discretization. Each muscle model is described by a system of differential equations and a single integro-differential equation. Responses of fifty-four muscle model forms are examined using a complex exertion composed of three types: eccentric-concentric exertion, isokinetic-isometric exertion and step exertion.

Analysis of muscles' behaviour. Part II. The computational model of muscles' group acting on the elbow joint.

The purpose of this paper is to present the computational model of muscles' group describing the movements of flexion/extension at the elbow joint in the sagittal plane of the body when the forearm is being kept in the fixed state of supination/pronation. The method of evaluating the muscle forces is discussed in detail. This method is the basis for the quantitative and qualitative verification of the proposed computational model of muscles' group. Applying this computational model, the forces of real muscles belonging to the muscles' group can be evaluated without using any optimization technique.

Analysis of muscles behaviour. Part I. The computational model of muscle.

The purpose of this paper is to present the computational model of skeletal muscle, which was treated as the structure of different mechanical properties. The method of identification of those properties is described in detail. In addition, the method of quantitative and qualitative verification of this model is proposed. Applying this computational model, the forces of real muscles can be evaluated without using any optimization technique. Such an approach will be described in the part II of the paper.