Browsing by Author "Tomalka, André"

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Open Access
Determination of biomechanical and architectural muscle properties : from single muscle fibre to whole muscle mechanics
(2018) Tomalka, André; Siebert, Tobias (Prof. Dr.)
The work presented in this thesis aims to provide a more detailed insight in the complex physiology of certain muscle tissue types. This thesis builds upon the results of in vitro contractile and ex vivo architectural experiments with muscle tissue preparations from rats (Rattus norvegicus), rabbits (Oryctolagus cuniculus) and pigs (Sus scrofa domesticus) - investigated by experimental and modelling approaches. During the course of this work the chapters are intended to determine, describe and interprete the distinct properties of muscle tissue samples of striated skeletal and smooth musculature. These species-specific properties have not been observed before, but are needed for modelling approaches and a better understanding of contractile mechanics and muscle growth. Despite the numerous studies on skeletal and smooth muscle tissue, there are still fundamental questions about the physiology and force generation of the muscle. Hence, the determination of specific biomechanical and architectural muscle properties allows a quantitative understanding of the mechanisms involved in force development. Moreover, this is a crucial step towards reliable, realistic muscle models and thus also to increased predictive quality of muscle-driven multi-body models.
Open Access
Eccentric muscle contractions : from single muscle fibre to whole muscle mechanics
(2023) Tomalka, André
Eccentric muscle loading encompasses several unique features compared to other types of contractions. These features include increased force, work, and performance at decreased oxygen consumption, reduced metabolic cost, improved energy efficiency, as well as decreased muscle activity. This review summarises explanatory approaches to long-standing questions in terms of muscular contraction dynamics and molecular and cellular mechanisms underlying eccentric muscle loading. Moreover, this article intends to underscore the functional link between sarcomeric components, emphasising the fundamental role of titin in skeletal muscle. The giant filament titin reveals versatile functions ranging from sarcomere organisation and maintenance, providing passive tension and elasticity, and operates as a mechanosensory and signalling platform. Structurally, titin consists of a viscoelastic spring segment that allows activation-dependent coupling to actin. This titin-actin interaction can explain linear force increases in active lengthening experiments in biological systems. A three-filament model of skeletal muscle force production (mediated by titin) is supposed to overcome significant deviations between experimental observations and predictions by the classic sliding-filament and cross-bridge theories. Taken together, this review intends to contribute to a more detailed understanding of overall muscle behaviour and force generation - from a microscopic sarcomere level to a macroscopic multi-joint muscle level - impacting muscle modelling, the understanding of muscle function, and disease.
Open Access
Impact of lengthening velocity on the generation of eccentric force by slow-twitch muscle fibers in long stretches
(2024) Weidner, Sven; Tomalka, André; Rode, Christian; Siebert, Tobias
After an initial increase, isovelocity elongation of a muscle fiber can lead to diminishing (referred to as Give in the literature) and subsequently increasing force. How the stretch velocity affects this behavior in slow-twitch fibers remains largely unexplored. Here, we stretched fully activated individual rat soleus muscle fibers from 0.85 to 1.3 optimal fiber length at stretch velocities of 0.01, 0.1, and 1 maximum shortening velocity, vmax, and compared the results with those of rat EDL fast-twitch fibers obtained in similar experimental conditions. In soleus muscle fibers, Give was 7%, 18%, and 44% of maximum isometric force for 0.01, 0.1, and 1 vmax, respectively. As in EDL fibers, the force increased nearly linearly in the second half of the stretch, although the number of crossbridges decreased, and its slope increased with stretch velocity. Our findings are consistent with the concept of a forceful detachment and subsequent crossbridge reattachment in the stretch’s first phase and a strong viscoelastic titin contribution to fiber force in the second phase of the stretch. Interestingly, we found interaction effects of stretch velocity and fiber type on force parameters in both stretch phases, hinting at fiber type-specific differences in crossbridge and titin contributions to eccentric force. Whether fiber type-specific combined XB and non-XB models can explain these effects or if they hint at some not fully understood properties of muscle contraction remains to be shown. These results may stimulate new optimization perspectives in sports training and provide a better understanding of structure-function relations of muscle proteins.
Open Access
Power amplification increases with contraction velocity during stretch-shortening cycles of skinned muscle fibers
(2021) Tomalka, André; Weidner, Sven; Hahn, Daniel; Seiberl, Wolfgang; Siebert, Tobias
Muscle force, work, and power output during concentric contractions (active muscle shortening) are increased immediately following an eccentric contraction (active muscle lengthening). This increase in performance is known as the stretch-shortening cycle (SSC)-effect. Recent findings demonstrate that the SSC-effect is present in the sarcomere itself. More recently, it has been suggested that cross-bridge (XB) kinetics and non-cross-bridge (non-XB) structures (e.g., titin and nebulin) contribute to the SSC-effect. As XBs and non-XB structures are characterized by a velocity dependence, we investigated the impact of stretch-shortening velocity on the SSC-effect. Accordingly, we performed in vitro isovelocity ramp experiments with varying ramp velocities (30, 60, and 85% of maximum contraction velocity for both stretch and shortening) and constant stretch-shortening magnitudes (17% of the optimum sarcomere length) using single skinned fibers of rat soleus muscles. The different contributions of XB and non-XB structures to force production were identified using the XB-inhibitor Blebbistatin. We show that (i) the SSC-effect is velocity-dependent - since the power output increases with increasing SSC-velocity. (ii) The energy recovery (ratio of elastic energy storage and release in the SSC) is higher in the Blebbistatin condition compared with the control condition. The stored and released energy in the Blebbistatin condition can be explained by the viscoelastic properties of the non-XB structure titin. Consequently, our experimental findings suggest that the energy stored in titin during the eccentric phase contributes to the SSC-effect in a velocity-dependent manner.