Adam Kłodowski

Effect of innervation zones in estimating biceps brachii force–EMG relationship during isometric contraction

Measuring muscle forces in vivo is invasive and consequently indirect methods e.g., electromyography (EMG) are used in estimating muscular force production. The aim of the present paper was to examine what kind of effect the disruption of the physiological signal caused by the innervation zone has in predicting the force/torque output from surface EMG. Twelve men (age 26 (SD ±3)years; height 179 (±6)cm; body mass 73 (±6)kg) volunteered as subjects. They were asked to perform maximal voluntary isometric contraction (MVC) in elbow flexion, and submaximal contractions at 10%, 20%, 30%, 40%, 50% and 75% of the recorded MVC. EMG was measured from biceps brachii muscle with an electrode grid of 5 columns×13 rows. Force-EMG relationships were determined from individual channels and as the global mean value. The relationship was deemed inconsistent if EMG value did not increase in successive force levels. Root mean squared errors were calculated for 3rd order polynomial fits. All subjects had at least one (4-52) inconsistent channel. Two subjects had inconsistent relationship calculated from the global mean. The mean root mean squared error calculated using leave one out method for the fits of the individual channels (0.33±0.17) was higher (P<0.001) than the error for the global mean fit (0.16±0.08). It seems that the disruption of the physiological signal caused by the innervation zone affects the consistency of the force-EMG relationship on single bipolar channel level. Multichannel EMG recordings used for predicting force overcame this disruption.

Importance of Patella, Quadriceps Forces, and Depthwise Cartilage Structure on Knee Joint Motion and Cartilage Response During Gait

In finite-element (FE) models of the knee joint, patella is often omitted. We investigated the importance of patella and quadriceps forces on the knee joint motion by creating an FE model of the subjects knee. In addition, depthwise strains and stresses in patellar cartilage with different tissue properties were determined. An FE model was created from subjects magnetic resonance images. Knee rotations, moments, and translational forces during gait were recorded in a motion laboratory and used as an input for the model. Three material models were implemented into the patellar cartilage: (1) homogeneous model, (2) inhomogeneous (arcadelike fibrils), and (3) random fibrils at the superficial zone, mimicking early stages of osteoarthritis (OA). Implementation of patella and quadriceps forces into the model substantially reduced the internal-external femoral rotations (versus without patella). The simulated rotations in the model with the patella matched the measured rotations at its best. In the inhomogeneous model, maximum principal stresses increased substantially in the middle zone of the cartilage. The early OA model showed increased compressive strains in the superficial and middle zones of the cartilage and decreased stresses and fibril strains especially in the middle zone. The results suggest that patella and quadriceps forces should be included in moment- and force-driven FE knee joint models. The results indicate that the middle zone has a major role in resisting shear forces in the patellar cartilage. Also, early degenerative changes in the collagen network substantially affect the cartilage depthwise response in the patella during walking.

A full body musculoskeletal model based on flexible multibody simulation approach utilised in bone strain analysis during human locomotion

Load-induced strains applied to bone can stimulate its development and adaptation. In order to quantify the incident strains within the skeleton, in vivo implementation of strain gauges on the surfaces of bone is typically used. However, in vivo strain measurements require invasive methodology that is challenging and limited to certain regions of superficial bones only such as the anterior surface of the tibia. Based on our previous study [Al Nazer et al. (2008) J Biomech. 41:1036–1043], an alternative numerical approach to analyse in vivo strains based on the flexible multibody simulation approach was proposed. The purpose of this study was to extend the idea of using the flexible multibody approach in the analysis of bone strains during physical activity through integrating the magnetic resonance imaging (MRI) technique within the framework. In order to investigate the reliability and validity of the proposed approach, a three-dimensional full body musculoskeletal model with a flexible tibia was used as a demonstration example. The model was used in a forward dynamics simulation in order to predict the tibial strains during walking on a level exercise. The flexible tibial model was developed using the actual geometry of human tibia, which was obtained from three-dimensional reconstruction of MRI. Motion capture data obtained from walking at constant velocity were used to drive the model during the inverse dynamics simulation in order to teach the muscles to reproduce the motion in the forward dynamics simulation. Based on the agreement between the literature-based in vivo strain measurements and the simulated strain results, it can be concluded that the flexible multibody approach enables reasonable predictions of bone strain in response to dynamic loading. The information obtained from the present approach can be useful in clinical applications including devising exercises to prevent bone fragility or to accelerate fracture healing.

Test methodology for virtual commissioning based on behaviour simulation of production systems

Todays highly increasing product diversity and decreasing product life cycles, also in the automotive industry lead to fast changing production systems with a high ratio of mechatronic components and (control) software. That again leads to ever increasing use of Virtual Commissioning during the development process of automated manufacturing plants. Paired with the still increasing request towards better control program quality, this leads to the need of improved and more efficient virtual plants with more effortless set ups. The common techniques of simulating the plant within the Virtual Commissioning do no longer fulfil these needs, new approaches have to be developed. At the same time, requests towards higher efficiency and higher test coverage during Virtual Commissioning are rising, which leads to the need of developments of easier testing processes. The presented work is concerned with this further developments, especially the test methodology for virtual commissioning based on appropriate behaviour simulation of automated production systems within the automotive industry. Therefore the state of the art is analysed and existing spheres of activity are identified. Afterwards, new approach and solutions for this fields, namely the appropriate behaviour simulation as well as the automatization of testing, are elaborated. An extensive example implementation evaluates the presented results regarding feasibility and eligible performance. Thus, the elaborated outstanding improvements of Virtual Commissioning are not only presented but the corresponding proof of concept is also adduced.

Leakage-proof nozzle design for RepRap community 3D printer

The RepRap 3D printer development project is a fast growing, open-hardware initiative relying on the input of hobbyist designers. One of its key components is the printer nozzle. The performance and reliability deficiencies of currently available nozzle designs are common topics in the RepRap community, and our own experience with a RepRap 3D printer has identified a need for improvement in a few particular areas. We set out to eliminate melt leakage, improve thermal isolation, and develop a more effective method of nozzle assembly attachment. Here, we review the issues, describe design efforts, and report results.

Estimating Lower Limb Skeletal Loading

Osteoporosis, accidents and subsequent bone fractures cause suffering on an individual level, as well as an economical burden to the society (Ortiz-Luna et al., 2009; Stevens & Olson, 2000). It has been estimated that, in Finland alone, between 30,000 to 40,000 osteoporosis-related fractures occur annually and that 400,000 Finnish people have osteoporosis (Duodecim, 2008). There are a few potential ways of preventing bone fracture, i.e. strengthening bones and/or preventing falls (Ortiz-Luna et al., 2009; Stevens & Olson, 2000). In order to withstand prevalent loading without breaking; while remaining relatively light in weight to allow for locomotion, bones have the ability to adapt their structure to functional loading (Frost, 2000; 2003; Sievanen, 2005). It has been demonstrated that physical activity affects the weight bearing skeleton more than the non-weight bearing one (Mikkola et al., 2008), and it may therefore be argued that, the skeleton is loaded mainly by locomotory actions that impart strains on bones. Bones are loaded in daily activities by muscles accelerating and decelerating body segments and resisting the pull of gravity (Burr et al., 1996). Since falling is the single most significant bone fracture risk factor (Jarvinen et al., 2008) and up to 90% of fractures are caused by falls (Cummings & Melton, 2002; Stevens & Olson, 2000; Wagner et al., 2009), exercise can be viewed as a potential intervention for fracture prevention. Exercise seemingly has a potential of both reducing the fall rate and also increasing bone strength. In agreement, exercise interventions have been shown to successfully decrease the fall rate (Kemmler et al., 2010; Korpelainen et al., 2006), to strengthen the bones and to decrease the fracture rate (Korpelainen et al., 2006; Sinaki et al., 2002). It is quite obvious, that in some cases even the strongest bone could not withstand the loading associated with falling. Therefore, it is reasonable to question whether strengthening bones makes a significant contribution in preventing fractures. A prospective study has shown that people with higher calcaneal bone mineral density had lower fracture rate even while the fall rates between the groups were relatively similar (Cheng et al., 1997). The differences between the groups in bone mineral density were relatively large (~10%). In agreement, prospective studies have shown that increasing the amount of bone mineral with drugs by about 10% is effective in decreasing fracture rates (Cummings et al., 2009). On the other hand, the increments in bone mineral amount associated with year long exercise interventions are relatively modest, i.e. in the order of 1 2% (Nikander et al., 2010). There are examples of fractures for which this kind of relatively modest bone strength increase does play an important role. One of the most convincing examples is vertebral fractures. It has been shown in a prospective study that vertebral bone mineral density (represents 11

Craig-Bampton Modal Reduction Applied to Human Tibia Tradeoff Between Accuracy and Speed

Human bones adapt to external loading through bone growth and resorption processes (1) . Strains within specific range induced by physical loading can lead to strengthening of affected bones. On the other hand, when external forces are too high, it can lead to bone fracture (2) or cause significant loads in the joints, which in turn can be damaging for the cartilage surfaces (3) and ligaments. Optimization of the gym equipment as well as the techniques of exercising is necessary to achieve bone growth stimulation without overloading the bones or the joints. This issue has been recently addressed with the use of flexible multibody simulations supported by modal reduction techniques. Although the strain output of the simulations is sound (4) , it is necessary to understand the tradeoffs between accuracy and speed of the modal reduction methods. This paper presents a comparison of the tibial strains, stresses and global displacements obtained from modal representation of the bone and results obtained from the initial finite element model. Strains are obtained at the same nodes in both models during various static case loadings. Efficiency of both methods is compared by correlating computation times. Accuracy of modal representation is verified by using bending, torsion, tension and compression tests, which represent the possible physical loading conditions of tibia. Influence of the material models as well as discretization level has also been taken into account. Finally conclusions are drawn from the results providing guidelines for future work.Copyright

Design and control of system for elbow rehabilitation: Preliminary findings

BACKGROUND The use of an exoskeleton elbow is considered an effective treatment in several pathologies, including post-stroke complications, traumatic brain injury (TBI) and spinal cord injury (SCI), as well as in patients with neurodegenerative disorders. The effectiveness of rehabilitation is closely linked to a suitably chosen therapy. The treatment can be performed only by specialized personnel, significantly supported by the use of automated devices. OBJECTIVES The aim of this study was to present a novel exoskeleton for elbow rehabilitation without a complicated control system. MATERIAL AND METHODS Single-degree-of-freedom (SDOF) solution in constructing the prototype of an elbow exoskeleton for rehabilitation purposes has been applied. The simplicity of the actuation mechanism was set as one of the priorities in the design; thus, a single-axis stepper motor with a controller was found to be adequate for providing a reliable and precise source of motion for the exoskeleton. RESULTS Technological development may provide novel solutions, such as an exoskeleton - a wearable, external structure which supports or (in selected applications) even replaces the muscle actuation in the patient. The reported advantages of the proposed exoskeleton reflect current state-of-the-art. The proposed control strategy relies on closed-loop position control, performance, low manufacturing cost, and predicted performance in a rehabilitation scenario. All these factors play an important role in establishing the directions for further research, e.g., an integrated force sensor in the device, measurements of torque interactions on the elbow joint, and assessment and response to an overload of articulation. CONCLUSIONS This study suggests not only the clinical but also the possible economic and logistical advantages offered by the portability of the system, and its effective support for therapists applying an elbow exoskeleton.