Universität Stuttgart
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Item Open Access Influence of layer separation on the determination of stomach smooth muscle properties(2021) Borsdorf, Mischa; Böl, Markus; Siebert, TobiasUniaxial tensile experiments are a standard method to determine the contractile properties of smooth muscles. Smooth muscle strips from organs of the urogenital and gastrointestinal tract contain multiple muscle layers with different muscle fiber orientations, which are frequently not separated for the experiments. During strip activation, these muscle fibers contract in deviant orientations from the force-measuring axis, affecting the biomechanical characteristics of the tissue strips. This study aimed to investigate the influence of muscle layer separation on the determination of smooth muscle properties. Smooth muscle strips, consisting of longitudinal and circumferential muscle layers (whole-muscle strips [WMS]), and smooth muscle strips, consisting of only the circumferential muscle layer (separated layer strips [SLS]), have been prepared from the fundus of the porcine stomach. Strips were mounted with muscle fibers of the circumferential layer inline with the force-measuring axis of the uniaxial testing setup. The force–length (FLR) and force–velocity relationships (FVR) were determined through a series of isometric and isotonic contractions, respectively. Muscle layer separation revealed no changes in the FLR. However, the SLS exhibited a higher maximal shortening velocity and a lower curvature factor than WMS. During WMS activation, the transversally oriented muscle fibers of the longitudinal layer shortened, resulting in a narrowing of this layer. Expecting volume constancy of muscle tissue, this narrowing leads to a lengthening of the longitudinal layer, which counteracted the shortening of the circumferential layer during isotonic contractions. Consequently, the shortening velocities of the WMS were decreased significantly. This effect was stronger at high shortening velocities.Item Open Access Editorial - the stretch-shortening cycle of active muscle and muscle-tendon complex : what, why and how it increases muscle performance?(2021) Seiberl, Wolfgang; Hahn, Daniel; Power, Geoffrey A.; Fletcher, Jared R.; Siebert, TobiasItem Open Access Role of rotated head postures on volunteer kinematics and muscle activity in braking scenarios performed on a driving simulator(2022) Kempter, Fabian; Lantella, Lorena; Stutzig, Norman; Fehr, Jörg; Siebert, TobiasOccupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.Item Open Access Reference measures of lower-limb joint range of motion, muscle strength, and selective voluntary motor control of typically developing children aged 5-17 years(2024) Scherff, Emily; Schnell, Sabrina Elisabeth; Siebert, Tobias; D’Souza, SoniaBackground: Joint range of motion based on the neutral null method, muscle strength based on manual muscle testing, and selective voluntary motor control based on selective control assessment of the lower extremity are standard parameters of a pediatric three-dimensional clinical gait analysis. Lower-limb reference data of children are necessary to identify and quantify abnormalities, but these are limited and when present restricted to specific joints or muscles. Methods: This is the first study that encompasses the aforementioned parameters from a single group of 34 typically developing children aged 5–17 years. Left and right values were averaged for each participant, and then the mean and standard deviation calculated for the entire sample. The data set was tested for statistical significance ( p < 0.05). Results: Joint angle reference values are mostly consistent with previously published standards, although there is a large variability in the existing literature. All muscle strength distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 5. The mean number of repetitions of heel-rise test is 12 ± 5. Selective voluntary motor control shows that all distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 2. Conclusion: Since typically developing children do not match expectations and reference values from the available literature and clinical use, this study emphasizes the importance of normative data. Excessively high expectations lead to typically developing children being falsely underestimated and affected children being rated too low. This is of great relevance for therapists and clinicians. Level of evidence: 3.Item 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, TobiasAfter 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.Item Open Access 3D ultrasound-based determination of skeletal muscle fascicle orientations(2024) Sahrmann, Annika S.; Vosse, Lukas; Siebert, Tobias; Handsfield, Geoffrey G.; Röhrle, OliverArchitectural parameters of skeletal muscle such as pennation angle provide valuable information on muscle function, since they can be related to the muscle force generating capacity, fiber packing, and contraction velocity. In this paper, we introduce a 3D ultrasound-based workflow for determining 3D fascicle orientations of skeletal muscles. We used a custom-designed automated motor driven 3D ultrasound scanning system for obtaining 3D ultrasound images. From these, we applied a custom-developed multiscale-vessel enhancement filter-based fascicle detection algorithm and determined muscle volume and pennation angle. We conducted trials on a phantom and on the human tibialis anterior (TA) muscle of 10 healthy subjects in plantarflexion (157 ± 7 ∘), neutral position (109 ± 7 ∘, corresponding to neutral standing), and one resting position in between (145 ± 6 ∘). The results of the phantom trials showed a high accuracy with a mean absolute error of 0.92 ± 0.59 ∘. TA pennation angles were significantly different between all positions for the deep muscle compartment; for the superficial compartment, angles are significantly increased for neutral position compared to plantarflexion and resting position. Pennation angles were also significantly different between superficial and deep compartment. The results of constant muscle volumes across the 3 ankle joint angles indicate the suitability of the method for capturing 3D muscle geometry. Absolute pennation angles in our study were slightly lower than recent literature. Decreased pennation angles during plantarflexion are consistent with previous studies. The presented method demonstrates the possibility of determining 3D fascicle orientations of the TA muscle in vivo.