Heiko Stark

• Dr. rer. nat.
• PostDoc Position at Friedrich Schiller University Jena

A muscle's architecture, described by geometric variables such as fascicle pennation angles or lengths, plays a crucial role in its functionality. Usually, single parameters are used to estimate force vectors or lengthening rates, thereby assuming that they represent the architecture properly and are constant during contraction. To describe muscle...

An interesting problem in hemorheology is to calculate that volume fraction of erythrocytes (hematocrit) that is optimal for transporting a maximum amount of oxygen. If the hematocrit is too low, too few erythrocytes are present to transport oxygen. If it is too high, the blood is very viscous and cannot flow quickly, so that oxygen supply to the t...

Many training concepts take muscle properties such as contraction speed or muscle topography into account to achieve an optimal training outcome. Thus far, the internal architecture of muscles has largely been neglected, although it is well known that parameters such as pennation angles or the lengths of fascicles but also the proportions of fleshy...

Aging research is a very popular field of research in which the deterioration or decline of various physiological features is studied. Here we consider the molecular level, which can also have effects on the macroscopic level. The proteinogenic amino acids differ in their susceptibilities to non-enzymatic modification. Some of these modifications c...

This study aimed to measure human connective tissue distribution and characterise material properties. We used, therefore, the existing data sets of a male and female body donor from the Visible Human Project (VHP). In the first step, collagen-containing structures were segmented and reconstructed using digital image processing. In addition, severa...

To understand how small animals cope with complex, unstructured, and unpredictable substrates, we analyzed the kinetics of rats (n = 10) moving at a fast and at a moderate trot over an unperturbed substrate and a substrate subjected to active horizontal perturbations. Perturbations were active single forwards or backwards displacements of an instru...

Collagens are structural proteins that are predominantly found in the extracellular matrix of multicellular animals, where they are mainly responsible for the stability and structural integrity of various tissues. All collagens contain polypeptide strands (α-chains). There are several types of collagens, some of which differ significantly in form,...

In humans and higher animals, a trade-off between a sufficiently high concentration of erythrocytes (hematocrit), to bind oxygen and sufficiently low blood viscosity to allow rapid blood flow has been achieved during evolution. The optimal value lies between the extreme cases of pure blood plasma, which cannot practically transport any oxygen, and...

A medically important feature of several types of tumors is their ability to “decide” between staying at a primary site in the body or leaving it and forming metastases. The present theoretical study aims to provide a better understanding of the ultimate reasons for this so-called “go-or-grow” dichotomy. To that end, we use game theory, which has p...

Collagens are structural proteins that are predominantly found in the extracellular matrix, where they are mainly responsible for the stability and structural integrity of various tissues. There are several different types of collagens, some of which differ significantly in form, function, and tissue specificity. Subdivisions into so-called collage...

Cover Caption: Strepsiptera is a small taxon of holometabolous insects comprising around 600 extant species. All life stages of Strepsiptera are highly specialized in life style and morphology, i.e., the immatures are either highly mobile infesting primary larva or endoparasitic trophic stages. In this issue of the Journal of Morphology, Tröger and...

The morphology of the adult free-living females of Mengenilla moldrzyki and Eoxenos laboulbenei (Strepsiptera, Mengenillidae) was documented with µCT-based 3D reconstructions and histological serial sections. External and internal features of both species are characterized by far-reaching specialization and structural simplification. The well-devel...

Based on our existing musculoskeletal models of the dog (Beagle & German Shepard) we have developed two additional ones. We have chosen the Dachshund and the Great Dane because they represent extreme body size values along dog breads. Models for the French Bulldog, the Whippet, and Malinois will follow. We are confident that our models will advance...

Small cursorial birds display remarkable walking skills and can negotiate complex and unstructured terrains with ease. The neuromechanical control strategies necessary to adapt to these challenging terrains are still not well understood. Here, we analyzed the 2D- and 3D pelvic and leg kinematic strategies employed by the common quail to negotiate v...

Skeletal muscle is responsible for voluntary force generation across animals, and muscle architecture largely determines the parameters of mechanical output. The ability to analyze muscle performance through muscle architecture is thus a key step towards better understanding the ecology and evolution of movements and morphologies. In pennate skelet...

Small cursorial birds display remarkable walking skills and can negotiate complex and unstructured terrains with ease. The neuromechanical control strategies necessary to adapt to these challenging terrains are still not well understood. Here, we analyzed the 2D- and 3D pelvic and leg kinematic strategies employed by the common quail to negotiate v...

The domestic dog is interesting to investigate because of the wide range of body size, body mass, and physique in the many breeds. In the last several years, the number of clinical and biomechanical studies on dog locomotion has increased. However, the relationship between body structure and joint load during locomotion, as well as between joint lo...

In humans and higher animals, a trade-off between sufficiently high erythrocyte concentrations to bind oxygen and sufficiently low blood viscosity to allow rapid blood flow has been achieved during evolution. Optimal hematocrit theory has been successful in predicting hematocrit (HCT) values of about 0.3–0.5, in very good agreement with the normal...

Understanding the process of aging is still an important challenge to enable healthy aging and to prevent age-related diseases. Most studies in age research investigate the decline in organ functionality and gene activity with age. The focus on decline can even be considered a paradigm in that field. However, there are certain aspects that remain s...

Dogs are an interesting object of investigation because of the wide range of body size, body mass, and physique. In the last several years, the number of clinical and biomechanical studies on dog locomotion has increased. However, the relationship between body structure and joint load during locomotion, as well as between joint load and degenerativ...

In humans and higher animals, a trade-off between sufficiently high erythrocyte concentrations to bind oxygen and sufficiently low blood viscosity to allow rapid blood flow has been achieved during evolution. Optimal hematocrit theory has been successful in predicting hematocrit values of about 0.3 - 0.5, in very good agreement with the normal valu...

Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and s...

Aging research is a very popular field of research in which the gradual transformation of functional states into dysfunctional states are studied. Here we only consider the molecular level, which can also have effects on the macroscopic level. It is known that the proteinogenic amino acids differ in their modification susceptibilities and this can...

Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and s...

In individuals of similar body mass representing closely related species with different lifestyles, muscle architectural properties can be assumed to reflect adaptation to differing, lifestyle-related functional demands. We here employ a fibre recognition algorithm on contrast-enhanced micro-computed tomography (µCT) scans of one specimen each of a...

Protein damage (partly followed by protein aggregation) plays a significant role in ageing, cancer and in neurodegenerative and other diseases. It is known that the proteinogenic amino acids differ in their susceptibility to non-enzymatic modification, such as hydroxylation, peroxidation, chlorination etc. In a novel bioinformatics approach, we int...

The fascicular architecture of skeletal muscle dictates functional parameters such as force production and contractile velocity. Muscle microarchitecture is typically determined by means of manual dissection, a technique that is inherently destructive to specimens. Furthermore, fascicle lengths and pennation angles are commonly assessed at only a l...

For producing ATP, tumour cells rely on glycolysis leading to lactate to about the same extent as on respiration. Thus, the ATP synthesis flux from glycolysis is considerably higher than in the corresponding healthy cells. This is known as the Warburg effect (named after German biochemist Otto H. Warburg) and also applies to striated muscle cells,...

In this review, we revisit the metabolic shift from respiration to glycolysis in lymphocytes upon activation, which is known as the Warburg effect in tumour cells. We compare the situation in lymphocytes with those in several other cell types, such as muscle cells, Kupffer cells, microglia cells, astrocytes, stem cells, tumour cells and various uni...

Skeletal muscle models are used to investigate motion and force generation in both biological and bioengineering research. Yet, they often lack a realistic representation of the muscle's internal architecture which is primarily composed of muscle fibre bundles, known as fascicles. Recently, it has been shown that fascicles can be resolved with micr...

Sloths are morphologically specialized in upside-down quadrupedal suspensory locomotion. The evolution of this locomotor mode lead to a loss of asymmetrical gaits and thus a reduced necessity of powerful extension of the spine in the sagittal plane. It is here tested whether this aberrant locomotor mode is reflected in the three-dimensional (3D) in...

1) The main part of optimal hematocrit theory as we reviewed it in our paper (8) does not consider the diameters of blood vessels. Some calculations do consider this effect, such as those by Pries et al. (6), as we had mentioned. Of course, the theory can be extended and refined in various directions. However, to make the main point, that is, to ex...

The structure of a skeletal muscle is dominated by its hierarchical architecture in which thousands of muscle fibres are arranged within a connective tissue network. The single muscle fibre consists of many force-producing cells, known as sarcomeres, which contribute to the contraction of the whole muscle. There are a lot of questions concerning th...

Erratum to: Arch Appl Mech (2010) 80:557–567 DOI 10.1007/s00419-009-0378-y By a mistake, not all authors have been listed. The complete list of authors is as follows: Markus Böl (Institute of Solid Mechanics, Department of Mechanical Engineering, Technische Universität Carolo-Wilhelmina) (as corresponding author), NadjaSchilling(InstituteofSystemat...

Verschiedene Trainingskonzepte in der medizinischen Vorsorge und Rehabilita- tion berücksichtigen Muskeleigenschaften, wie die Kontraktionsgeschwindigkeit (schnell vs. langsam) oder die Topographie der Muskulatur (ein- oder zweige- lenkig), um ein optimales Trainingsergebnis zu erzielen. Bisher wurde dabei die innere Architektur der Muskeln weitgeh...

Basierend auf Voruntersuchungen am M. soleus der Ratte zeigte sich, dass ein senkrecht aufgehängter Muskel eine Volumenverschiebung in Richtung der Gravitation aufwies. Ziel dieser Arbeit war es zu untersuchen, inwieweit der Fiederungswinkel einen Einfluss auf die Volumenverschiebung hat. Dazu wurden Simulationen an einem künstlichen Muskel durchge...

This work deals with the development and implementation of a new fatigue model for simulating fatigue effects in skeletal muscles. Basic idea of this modelling strategy is an approach that divides the fibres of a muscle into three groups: fibres in the active state, those that are already fatigued and fibres in the resting state. All fibres are abl...

Trainingsprogramme für das muskuläre System wie beispielsweise zur Prävention von negativen Auswirkungen arbeitsbedingter Belastungen oder auch im rehabilitativen Training sollten die Muskulatur entsprechend ihrer Funktionsweise trainieren. Die meisten Trainingsprogramme beziehen dabei beispielsweise die Kontraktionseigenschaften der zu trainierend...

Biomechanical models describing muscle characteristics are very complex and different techniques like forward kinematics, inverse kinematics and finite element method were used in the past. None of them take all influential 3D features into account, such as the fibre type distribution or the geometrical arrangement of the muscle fascicles. In parti...

Biomechanische Muskelmodelle zur Beschreibung von Muskeleigenschaften sind in ihrer Modellierung sehr komplex und nutzen verschiedene Techniken, wie die Forward Kinematik, die Inverse Kinematik und die Finite-Element-Methode (FEM). Allen gemeinsam ist jedoch die fehlende Beschreibung der wichtigen Feinstrukturen wie der Fasertypenverteilung oder di...

Biomechanical models describing muscle characteristics are very complex and different techniques like forward kinematics, inverse kinematics and finite element method were used in the past. None of them take all influential 3D features into account, such as the fibre type distribution or the geometrical arrangement of the muscle fascicles. In parti...

Biomechanische Muskelmodelle sind heutzutage im Aufbau sehr komplex und nutzen verschiedene Techniken wie inverse Kinematik und Finite-Element-Methode (FEM). Jedoch beschreiben sie nicht alle wichtigen Feinstrukturen. Eine Reihe von Autoren [Zuurbier CJ, 1993; van Donkelaar CC, 1999; Gorb SN, 2000; Schilling N, 2003 & 2004] haben darauf hingewiesen...