[Resilience and General Self-Efficacy are Related to Perception of COVID-19 Symptomatology, Mental Health, and Coping with Acute COVID-19 Infection]. / Resilienz und Selbstwirksamkeitserwartung hängen mit der Wahrnehmung der COVID-19-Symptomatik, der psychischen Gesundheit und dem Umgang mit einer akuten COVID-19-Infektion zusammen.

OBJECTIVE: The COVID-19 pandemic may be associated with massive impacts on mental health. For example, people with pre-existing mental illness were particularly vulnerable to mental health deterioration. It is known that resilience and general self-efficacy can be protective factors for mental health in the face of stress and challenge such as the COVID-19 pandemic. This study is the first to examine the associations of resilience and general self-efficacy on mental health coping with acute COVID-19 infection in home isolation. METHODS: This study is a cross-sectional online survey of people with acute, PCR-diagnosed COVID-19 infection during their home isolation. Recruitment was conducted by telephone via the Freudenstadt health department (Germany). After informed consent, study participants received a link for an online questionnaire. The questionnaire assessed sociodemographic aspects, resilience, general self-efficacy, COVID-19 somatic health, psychological burden (depressiveness, anxiety, somatic symptom disorder), stress experience, and coping strategies. Descriptive statistics, correlational analyses, and multiple linear regressions with resilience and general self-efficacy as independent variables were performed. RESULTS: A total of 224 home-isolated people with acute COVID-19 infection were included in the study. Lower resilience and lower general self-efficacy were each related with more intense perception of COVID-19 somatic symptoms, higher psychological burden, increased stress perception, lower coping skills, and lower experienced support. DISCUSSION: Resilience and general self-efficacy are essential for mental health as well as for coping with acute COVID-19 infection. They not only protect against negative effects on mental health but also enhance positive effects. Resilience is positively related to the perception and evaluation of somatic COVID-19 symptoms. More resilient people with COVID-19 infection feel physically healthier. CONCLUSION: Home-isolated people with acute COVID-19 infection should be screened for support needs using standardized brief questionnaires to avoid negative psychological and somatic consequences. Demand-driven, low-threshold, digital, and individualized intervention programs should also be developed and established for the home isolation setting.

A method for the estimation of a motor unit innervation zone center position evaluated with a computational sEMG model.

Motion predictions for limbs can be performed using commonly called Hill-based muscle models. For this type of models, a surface electromyogram (sEMG) of the muscle serves as an input signal for the activation of the muscle model. However, the Hill model needs additional information about the mechanical system state of the muscle (current length, velocity, etc.) for a reliable prediction of the muscle force generation and, hence, the prediction of the joint motion. One feature that contains potential information about the state of the muscle is the position of the center of the innervation zone. This feature can be further extracted from the sEMG. To find the center, a wavelet-based algorithm is proposed that localizes motor unit potentials in the individual channels of a single-column sEMG array and then identifies innervation point candidates. In the final step, these innervation point candidates are clustered in a density-based manner. The center of the largest cluster is the estimated center of the innervation zone. The algorithm has been tested in a simulation. For this purpose, an sEMG simulator was developed and implemented that can compute large motor units (1,000's of muscle fibers) quickly (within seconds on a standard PC).

Direction-of-arrival estimation for acoustic signals based on direction-dependent parameter tuning of a bioinspired binaural coupling system.

Bioinspired methods for sound source localization offer opportunities for resource reduction as well as concurrent performance improvement in contrast to conventional techniques. Usually, sound source localization requires a large number of microphones arranged in irregular geometries, and thus has high resource requirements in terms of space and data processing. Motivated by biology and using digital signal processing methods, an approach that adapts the coupled hearing system of the flyOrmia ochraceawith a minimally distant two-microphone array is presented. Despite its physiology, the fly is able to overcome physical limitations in localizing low-frequency sound sources. By exploiting the filtering effect of the coupling system, the direction-of-arrival of the sound is determined with two microphones at an intermediate distance of 0.06 m. For conventional beamforming algorithms, these physical limitations would result in degraded localization performance. In this work, the bioinspired coupling system is analyzed and subsequently parameterized direction-sensitive for different directions of incidence of the sound. For the parameterization, an optimization method is presented which can be adopted for excitation with plane as well as spherical sound wave propagation. Finally, the method was assessed using simulated and measured data. For 90% of the simulated scenarios, the correct direction of incidence could be determined with an accuracy of less than 1∘despite the use of a minimal distant two-microphone array. The experiments with measured data also resulted in a correct determination of the direction of incidence, which qualifies the bioinspired method for practical use in digital hardware systems.

sEMG-based prediction of human forearm movements utilizing a biomechanical model based on individual anatomical/ physiological measures and a reduced set of optimization parameters.

For assistive devices such as active orthoses, exoskeletons or other close-to-body robotic-systems, the immediate prediction of biological limb movements based on biosignals in the respective control system can be used to enable intuitive operation also by untrained users e.g. in healthcare, rehabilitation or industrial scenarios. Surface electromyography (sEMG) signals from the muscles that drive the limbs can be measured before the actual movement occurs and, hence, can be used as source for predicting limb movements. The aim of this work was to create a model that can be adapted to a new user or movement scenario with little measurement and computing effort. Therefore, a biomechanical model is presented that predicts limb movements of the human forearm based on easy to measure sEMG signals of the main muscles involved in forearm actuation (lateral and long head of triceps and short and long head of biceps). The model has 42 internal parameters of which 37 were attributed to 8 individually measured physiological measures (location of acromion at the shoulder, medial/lateral epicondyles as well as olecranon at the elbow, and styloid processes of radius/ulna at the wrist; maximum muscle forces of biceps and triceps). The remaining 5 parameters are adapted to specific movement conditions in an optimization process. The model was tested in an experimental study with 31 subjects in which the prediction quality of the model was assessed. The quality of the movement prediction was evaluated by using the normalized mean absolute error (nMAE) for two arm postures (lower, upper), two load conditions (2 kg, 4 kg) and two movement velocities (slow, fast). For the resulting 8 experimental combinations the nMAE varied between nMAE = 0.16 and nMAE = 0.21 (lower numbers better). An additional quality score (QS) was introduced that allows direct comparison between different movements. This score ranged from QS = 0.25 to QS = 0.40 (higher numbers better) for the experimental combinations. The above formulated aim was achieved with good prediction quality by using only 8 individual measurements (easy to collect body dimensions) and the subsequent optimization of only 5 parameters. At the same time, just easily accessible sEMG measurement locations are used to enable simple integration, e.g. in exoskeletons. This biomechanical model does not compete with models that measure all sEMG signals of the muscle heads involved in order to achieve the highest possible prediction quality.

Approach to the management of slipped capital femoral epiphysis and primary hyperparathyroidism.

CONTEXT: Worldwide, only nine cases of slipped capital femoral epiphysis (SCFE) associated with primary hyperparathyroidism (PHP) have been reported. CASE ILLUSTRATION: This is a report on adolescent subjects with SCFE associated with PHP exhibiting the leading pathogenesis and clinical course. METHODS: Here, we reviewed all known cases and developed an effective approach to the management of SCFE and PHP. RESULTS: In cases of emergency, SCFE fixation is primarily done regardless of any preexistent hypercalcemia due to PHP and is followed by parathyroidectomy as soon as possible. In cases of mild and moderate hypercalcemia, whether SCFE fixation is followed by parathyroidectomy and vice versa or resolved during a single operating session depends on the side effects of hypercalcemia. Severely hypercalcemic patients should undergo urgent parathyroidectomy followed by immediate orthopedic surgery or even as a simultaneous procedure. This is to avoid onset of hypercalcemic side effects or worsening of preexisting side manifestations resulting from hypercalcemia. CONCLUSION: Our report demonstrates that SCFE patients presenting with hypercalcemia, signs of low bone density, or with non-typical age of onset deserve further workup for secondary causes. In addition, the newly developed systematic approach toward achieving an effective, efficient management should help in improving the patients' long-term outcome.

Approach to the management of slipped capital femoral epiphysis and primary hyperparathyroidism.

CONTEXT: Worldwide, only nine cases of revealing slipped capital femoral epiphysis (SCFE) associated with primary hyperparathyroidism (PHP) have been reported. CASE ILLUSTRATION: This study included adolescent subjects with the described association, the clinical course, and exhibiting the leading pathogeneses. METHODS: Here, we reviewed all known cases and developed an effective approach to the management of SCFE and PHP. RESULTS: In cases of emergency, SCFE fixation is primarily done regardless of any preexistent hypercalcemia due to PHP and followed by parathyroidectomy as soon as possible. In cases of mild and moderate hypercalcemia, whether SCFE fixation is followed by parathyroidectomy and vice versa or resolved during a single operating session depends on manifest side effects due to hyercalcemia. Patients with severe hypercalcema should undergo urgent parathyroidectomy, followed by immediate orthopedic surgery, even as a simultaneous procedure. This is to avoid onset of hypercalcemic side effects or worsening of preexisting side manifestations resulting from hypercalcemia. CONCLUSION: Our report demonstrates that SCFE presenting with hypercalcemia, with signs of low bone density, or in atypical age deserves further workup for secondary causes. In addition, the newly developed systematic approach toward achieving an effective, efficient management should help to improve the patients' long-term outcome.

Manual and semi-automatic determination of elbow angle-independent parameters for a model of the biceps brachii distal tendon based on ultrasonic imaging.

Tendons consist of passive soft tissue with non linear material properties. They play a key role in force transmission from muscle to skeletal structure. The properties of tendons have been extensively examined in vitro. In this work, a non linear model of the distal biceps brachii tendon was parameterized based on measurements of myotendinous junction displacements in vivo at different load forces and elbow angles. The myotendinous junction displacement was extracted from ultrasound B-mode images within an experimental setup which also allowed for the retrieval of the exerted load forces as well as the elbow joint angles. To quantify the myotendinous junction movement based on visual features from ultrasound images, a manual and an automatic method were developed. The performance of both methods was compared. By means of exemplary data from three subjects, reliable fits of the tendon model were achieved. Further, different aspects of the non linear tendon model generated in this way could be reconciled with individual experiments from literature.

How to Motivate SARS-CoV-2 Convalescents to Receive a Booster Vaccination? Influence on Vaccination Willingness.

(1) Background: Booster vaccinations for SARS-CoV-2 convalescents are essential for achieving herd immunity. For the first time, this study examined the influencing factors of vaccination willingness among SARS-CoV-2 infected individuals and identified vaccination-hesitant subgroups. (2) Methods: Individuals with positive SARS-CoV-2 PCR results were recruited by telephone. They completed an online questionnaire during their home isolation in Germany. This questionnaire assessed the vaccination willingness and its influencing factors. (3) Results: 224 home-isolated individuals with acute SARS-CoV-2 infection were included in the study. Vaccination willingness of home-isolated SARS-CoV-2 infected individuals with asymptomatic or moderate course was 54%. The following factors were associated with significantly lower vaccination willingness: younger age, foreign nationality, low income, low trust in vaccination effectiveness, fear of negative vaccination effects, low trust in the governmental pandemic management, low subjective informativeness about SARS-CoV-2, support of conspiracy theories. (4) Conclusions: The vaccination willingness of home-isolated SARS-CoV-2 infected individuals with asymptomatic or moderate symptomatic course was low. Motivational vaccination campaigns should be adapted to individuals with acute SARS-CoV-2 infection and consider the vaccination-hesitant groups. Vaccination education should be demand-driven, low-threshold, begin during the acute infection phase, and be guided for example by the established 5C model ("confidence, complacency, constraints, calculation, collective responsibility").

SARS-CoV-2 Positive and Isolated at Home: Stress and Coping Depending on Psychological Burden.

Objective: The SARS-CoV-2 pandemic has led to pronounced health changes, especially for those infected and psychologically burdened. This cross-sectional study examined the stress experience and coping strategies during home isolation of SARS-CoV-2 infected individuals and analyzed differences regarding psychological burden. Methods: SARS-CoV-2 infected respondents were recruited by telephone and completed an online survey during their home isolation. This questionnaire assessed sociodemographic aspects, somatic factors, psychological burden (depressive symptoms, anxiety, and somatic symptom disorder), perceived stress and coping behavior during the home isolation. Results: Out of 838 SARS-CoV-2 infected individuals during the study period, 648 were contacted and 224 home-isolated respondents were included in the study. Disgrace, social restrictions, job fear, health concerns, and infectiousness could be explored as stressors during the home isolation. Fifty-four percent experienced psychological burden. SARS-CoV-2 infected and home-isolated individuals with psychological burden perceived significant stressors more strongly (p < 0.001, r = 0.5) and coped significantly less (p < 0.001, r = 0.3) with their infection and home isolation compared to SARS-CoV-2 infected individuals without psychological burden. Conclusion: SARS-CoV-2 infected individuals with psychological burden experienced higher stressors and were unable to cope adaptively with home isolation. Therefore, a general and standardized screening procedure for psychological burden should be established. SARS-CoV-2 infected individuals with psychological burden should receive targeted support with professional help in the areas of stress experience and coping skills during their home isolation and beyond to avoid long-term consequences.

Motion parallax for object localization in electric fields.

Parallax, as a visual effect, is used for depth perception of objects. But is there also the effect of parallax in the context of electric field imagery? In this work, the example of weakly electric fish is used to investigate how the self-generated electric field that these fish utilize for orientation and communication alike, may be used as a template to define electric parallax. The skin of the electric fish possesses a vast amount of electroreceptors that detect the self-emitted dipole-like electric field. In this work, the weakly electric fish is abstracted as an electric dipole with a sensor line in between the two emitters. With an analytical description of the object distortion for a uniform electric field, the distortion in a dipole-like field is simplified and simulated. On the basis of this simulation, the parallax effect could be demonstrated in electric field images i.e. by closer inspection of voltage profiles on the sensor line. Therefore, electric parallax can be defined as the relative movement of a signal feature of the voltage profile (here, the maximum or peak of the voltage profile) that travels along the sensor line peak trace (PT). The PT width correlates with the object's vertical distance to the sensor line, as close objects create a large PT and distant objects a small PT, comparable with the effect of visual motion parallax.

Resource-efficient bio-inspired visual processing on the hexapod walking robot HECTOR.

Emulating the highly resource-efficient processing of visual motion information in the brain of flying insects, a bio-inspired controller for collision avoidance and navigation was implemented on a novel, integrated System-on-Chip-based hardware module. The hardware module is used to control visually-guided navigation behavior of the stick insect-like hexapod robot HECTOR. By leveraging highly parallelized bio-inspired algorithms to extract nearness information from visual motion in dynamically reconfigurable logic, HECTOR is able to navigate to predefined goal positions without colliding with obstacles. The system drastically outperforms CPU- and graphics card-based implementations in terms of speed and resource efficiency, making it suitable to be also placed on fast moving robots, such as flying drones.

Integrative Biomimetics of Autonomous Hexapedal Locomotion.

Despite substantial advances in many different fields of neurorobotics in general, and biomimetic robots in particular, a key challenge is the integration of concepts: to collate and combine research on disparate and conceptually disjunct research areas in the neurosciences and engineering sciences. We claim that the development of suitable robotic integration platforms is of particular relevance to make such integration of concepts work in practice. Here, we provide an example for a hexapod robotic integration platform for autonomous locomotion. In a sequence of six focus sections dealing with aspects of intelligent, embodied motor control in insects and multipedal robots-ranging from compliant actuation, distributed proprioception and control of multiple legs, the formation of internal representations to the use of an internal body model-we introduce the walking robot HECTOR as a research platform for integrative biomimetics of hexapedal locomotion. Owing to its 18 highly sensorized, compliant actuators, light-weight exoskeleton, distributed and expandable hardware architecture, and an appropriate dynamic simulation framework, HECTOR offers many opportunities to integrate research effort across biomimetics research on actuation, sensory-motor feedback, inter-leg coordination, and cognitive abilities such as motion planning and learning of its own body size.

Application of reduced sensor movement sequences as a precursor for search area partitioning and a selection of discrete EEV contour-ring fragments for active electrolocation.

In addition to their visual sense, weakly electric fish use active electrolocation to detect and analyse objects in their nearby environment. Their ability to generate and sense electric fields combined with scanning-like swimming movements are intended to extract further parameters like the size, shape and material properties of objects. Inspired by this biological example, this work introduces an application for active electrolocation based on reduced sensor movement sequences as presented in Wolf-Homeyer et al (2016 Bioinspir. Biomim. 11 055002). Initially, the application is conducted with a simulated receptor-system consisting of an emitter-dipole and an orthogonally arranged pair of sensor-electrodes. Close inspection of a minimal set of scanning movements allows the exclusion of sectors of the general search area early in the proposed localization algorithm (search area partitioning). Furthermore, the proposed algorithm is based on an analytical representation of the electric field and of the so-called EEV (ensemble of electrosensory viewpoints) (Solberg et al 2008 Int. J. Robot. Res. 27 529-48) rather than using computationally expensive FEM simulations, rendering it suitable for embedded computer systems. Two-dimensional discrete EEV contour-ring points (CRPs) of desired accuracy are extracted. In the core of the localization algorithm, fragments of the EEV are selected from valid sectors of the search area, which generates sets of CRPs, one for each sensor-emitter position/orientation. These sets are investigated by means of a nearness metric to find points in different sets which correspond to each other in order to estimate the object position. Two resultant scanning strategies/localization algorithms are introduced.

Fluid therapy and outcome: a prospective observational study in 65 German intensive care units between 2010 and 2011.

BACKGROUND: Outcome data on fluid therapy in critically ill patients from randomised controlled trials may be different from data obtained by observational studies under "real-life" conditions. We conducted this prospective, observational study to investigate current practice of fluid therapy (crystalloids and colloids) and associated outcomes in 65 German intensive care units (ICUs). In total, 4545 adult patients who underwent intravenous fluid therapy were included. The main outcome measures were 90-day mortality, ICU mortality and acute kidney injury (AKI). Data were analysed using logistic and Cox regression models, as appropriate. RESULTS: In the predominantly post-operative overall cohort, unadjusted 90-day mortality was 20.1%. Patients who also received colloids (54.6%) had a higher median Simplified Acute Physiology Score II [25 (interquartile range 11; 41) vs. 17 (7; 31)] and incidence of severe sepsis (10.2 vs. 7.4%) on admission compared to patients who received exclusively crystalloids (45.4%). 6% hydroxyethyl starch (HES 130/0.4) was the most common colloid (57.0%). Crude rates of 90-day mortality were higher for patients who received colloids (OR 1.845 [1.560; 2.181]). After adjustment for baseline variables, the HR was 1.666 [1.405; 1.976] and further decreased to indicate no associated risk (HR 1.003 [0.980; 1.027]) when it was adjusted for vasopressor use, severity of disease and transfusions. Similarly, the crude risk of AKI was higher in the colloid group (crude OR 3.056 [2.528; 3.694]), after adjustment for baseline variables OR 1.941 [1.573; 2.397], and after full adjustment OR 0.696 [0.629; 0.770]), the risk of AKI turned out to be reduced. The same was true for the subgroup of patients treated with 6% HES 130/0.4 (crude OR 1.931 [1.541; 2.419], adjusted for baseline variables OR 2.260 [1.730; 2.953] and fully adjusted OR 0.800 [0.704; 0.910]) as compared to crystalloids only. CONCLUSIONS: The present analysis of mostly post-operative patients in routine clinical care did not reveal an independent negative effect of colloids (mostly 6% HES 130/0.4) on renal function or survival after multivariable adjustment. Signals towards a reduced risk in subgroup analyses deserve further study. Trial registration ClinicalTrials.gov Identifier: NCT01122277, registered May 11th, 2010.

Electrolocation of objects in fluids by means of active sensor movements based on discrete EEVs.

Weakly electric fish use self-generated electric fields for communication and for active electrolocation. The sensor part of the biological system consists of a vast amount of electroreceptors which are distributed across the skin of the electric fish. Fish utilise changes of their position and body geometry to aid in the extraction of sensory information. Inspired by the biological model, this study looks for a fixed, minimal scanning strategy compiled of active receptor-system movements that allows unique identification of the positions of objects in the vicinity. The localisation method is based on the superposition of numerical extracted contour-rings of rotated and/or linearly shifted EEVs (Solberg et al 2008 Int. J. Rob. Res. 27 529-48), simulated by means of FEM. For the evaluation of a movement sequence, matrices of unique intersection points and respective contrast functions are introduced. The resultant optimal scanning strategy consists of a combination of a linear shift and a rotation of the original EEV.

Reduced Microvascular Density in Omental Biopsies of Children with Chronic Kidney Disease.

BACKGROUND: Endothelial dysfunction is an early manifestation of cardiovascular disease (CVD) and consistently observed in patients with chronic kidney disease (CKD). We hypothesized that CKD is associated with systemic damage to the microcirculation, preceding macrovascular pathology. To assess the degree of "uremic microangiopathy", we have measured microvascular density in biopsies of the omentum of children with CKD. PATIENTS AND METHODS: Omental tissue was collected from 32 healthy children (0-18 years) undergoing elective abdominal surgery and from 23 age-matched cases with stage 5 CKD at the time of catheter insertion for initiation of peritoneal dialysis. Biopsies were analyzed by independent observers using either a manual or an automated imaging system for the assessment of microvascular density. Quantitative immunohistochemistry was performed for markers of autophagy and apoptosis, and for the abundance of the angiogenesis-regulating proteins VEGF-A, VEGF-R2, Angpt1 and Angpt2. RESULTS: Microvascular density was significantly reduced in uremic children compared to healthy controls, both by manual imaging with a digital microscope (median surface area 0.61% vs. 0.95%, p<0.0021 and by automated quantification (total microvascular surface area 0.89% vs. 1.17% p = 0.01). Density measured by manual imaging was significantly associated with age, height, weight and body surface area in CKD patients and healthy controls. In multivariate analysis, age and serum creatinine level were the only independent, significant predictors of microvascular density (r2 = 0.73). There was no immunohistochemical evidence for apoptosis or autophagy. Quantitative staining showed similar expression levels of the angiogenesis regulators VEGF-A, VEGF-receptor 2 and Angpt1 (p = 0.11), but Angpt2 was significantly lower in CKD children (p = 0.01). CONCLUSIONS: Microvascular density is profoundly reduced in omental biopsies of children with stage 5 CKD and associated with diminished Angpt2 signaling. Microvascular rarefaction could be an early systemic manifestation of CKD-induced cardiovascular disease.

A biologically inspired active compliant joint using local positive velocity feedback (LPVF).

Starting from studies which revealed that positive feedback is found in the control system for walking in arthropods, we have constructed a new positive feedback driven joint that can be used for solving compliant motion tasks. We propose two different joint constructions each of which shows passive compliance. Based on these joints we introduce three different local positive velocity feedback (LPVF) controllers and discuss their properties in the context of motion generation in closed kinematic chains. The third circuit named undelayed dLPVF is used for the control of a compliant planar manipulator which turns a crank. Our concept is of highly decentralized nature and follows the idea of embodiment. In our case this means that a process which is controlled by LPVF controllers reveals its nature when the controllers interact with this process.

A hexapod walker using a heterarchical architecture for action selection.

Moving in a cluttered environment with a six-legged walking machine that has additional body actuators, therefore controlling 22 DoFs, is not a trivial task. Already simple forward walking on a flat plane requires the system to select between different internal states. The orchestration of these states depends on walking velocity and on external disturbances. Such disturbances occur continuously, for example due to irregular up-and-down movements of the body or slipping of the legs, even on flat surfaces, in particular when negotiating tight curves. The number of possible states is further increased when the system is allowed to walk backward or when front legs are used as grippers and cannot contribute to walking. Further states are necessary for expansion that allow for navigation. Here we demonstrate a solution for the selection and sequencing of different (attractor) states required to control different behaviors as are forward walking at different speeds, backward walking, as well as negotiation of tight curves. This selection is made by a recurrent neural network (RNN) of motivation units, controlling a bank of decentralized memory elements in combination with the feedback through the environment. The underlying heterarchical architecture of the network allows to select various combinations of these elements. This modular approach representing an example of neural reuse of a limited number of procedures allows for adaptation to different internal and external conditions. A way is sketched as to how this approach may be expanded to form a cognitive system being able to plan ahead. This architecture is characterized by different types of modules being arranged in layers and columns, but the complete network can also be considered as a holistic system showing emergent properties which cannot be attributed to a specific module.

Novel bioinspired control approaches to increase the stiffness variability in multi-muscle driven joints.

Antagonistic muscle pairs pulling on a joint are in general able to modulate stiffness through co-activation. Closer analysis of the stiffness, however, shows that, depending on the muscle and joint parameters, domains might occur in joint angle space for which stiffness variation is limited (low stiffness variability) or even impossible (stiffness nodes). As a consequence, stiffness control utilizing pure co-activation might fail. This work presents novel strategies for simultaneous control of torque and stiffness in a hinge joint actuated by two antagonistic muscle pairs. One strategy handles stiffness nodes by shifting them away from the current joint position and thus regaining stiffness controllability. To prevent domains of low stiffness variation, an optimal muscle configuration is sought and finally defined which allows for a maximal stiffness variation across a wide joint angle range. Based on this optimal configuration, four additional control strategies are proposed and tested which deliver stiffnesses and torques comparable to those obtained in the optimal case. The strategies combine torque control and stiffness control by co-activation with novel ideas like activation overflow and an inverse model approach. All strategies are tested in simulation and the results are compared with those of the optimal setup.