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Background and Aims: The sensory experience of wine aroma is challenging to study. Given the presence of numerous and trace level volatiles, the subtle aroma nuances involved, as well as the complexity of human odour processing, the contribution of individual compounds and mixtures can be difficult to determine. In white wines, the volatile compounds eliciting stone fruit aromas are not well understood. Methods and Results: Factorial designs were used with odorants added to model wine and assessed using sensory quantitative descriptive analysis. In model Viognier‐like wines, several monoterpenes were confirmed to convey stone fruit attributes Apricot and Peach, which were strongly suppressed by aldehydes which imparted Cardboard‐like odours. Importantly, lactones increased Apricot aroma when combined with the monoterpenes. For model unoaked Australian Chardonnay wine, sensory‐directed screening followed by factorial studies showed that aliphatic ethyl esters, in particular ethyl octanoate, directed Peach aroma. Fatty acids were strong suppressors of the Peach attribute and gave Cheesy odours. Conclusions: Apricot and peach aromas in Viognier and Chardonnay, although perceptually similar, were caused by different chemical compound families: grape‐derived monoterpenes with lactones and yeast‐derived fatty acid ethyl esters, respectively. Significance of the Study: Having confirmed the compounds responsible for apricot and peach white wine aromas, there is potential to modify their concentration through established viticultural and winemaking practices. [ABSTRACT FROM AUTHOR]

The aim of the present study was to compare the H-reflex evoked at rest and at 20% maximal voluntary contraction ( MVC) prior to and after fatiguing the lateral gastrocnemius ( LG). The maximal H-reflex and M-wave were recorded in the LG, and soleus ( SOL). Electrical evoked potentials were delivered to the posterior tibial nerve when muscles were inactivated and at 20% MVC. After fatigue, the Hmax/Mmax ratio of the fatigued LG was increased for both contraction levels (rest and 20% MVC) and remained unaltered for non-fatigued SOL. Before fatigue, the Hmax/Mmax ratio of SOL was enhanced at rest compared with the Hmax/Mmax ratio at 20% MVC. No differences were observed for LG. Fatigue of a single muscle leads to increased spinal reflex activity of the homonymous muscle. Contrary to previous recommendations in the literature, there appears to be no benefit with regard to the H-reflex amplitude in evoking electrical potentials during constant voluntary contractions at 20% MVC compared with inactivated muscles. The observed difference in SOL prior to fatigue was most likely due to hyperpolarization of the muscle fiber membrane. [ABSTRACT FROM AUTHOR]

The author discusses the influence of lifestyle factors on semen. The implications of a study which indicated a significant relationship between modifiable lifestyle factors, such as coffee consumption and body mass index (BMI), and semen parameters are described. The significance of a healthy lifestyle in couples who are trying to conceive is also emphasized.

The article describes a case of spine cord injury (SCI) and infertility in a 43-year-old paraplegic man. The patient and his wife presented to the clinic with primary infertility of five years. Several intra-cytoplasmic sperm injections were performed and antagonist protocol was used for ovarian stimulation before they were able to achieve a single pregnancy.

The article describes a case of anabolic steroid-induced hypogonadism and infertility in a 42-year-old man. The patient had a history of chronic anabolic steroid abuse and hypogonadotrophic hypogonadism, and he also admitted consuming other drugs such as cocaine and ecstasy. The link between infertility and anabolic-androgenic steroid (AAS) abuse is discussed.

During muscle contraction, not only are the fascicles shortening but also the pennation angle changes, which leads to a faster contraction of the muscle than of its fascicles. This phenomenon is called muscle gearing, and it has a direct influence on the force output of the muscle. There are few studies showing pennation angle changes during isometric and concentric contractions for different contraction intensities and muscle lengths. Therefore, the aim was to determine these influences over a wide range of contraction intensities and ankle joint angles for human triceps surae. Additionally, the influence of contraction intensity and ankle joint angle on muscle gearing was evaluated. Ten sport students performed concentric and isometric contractions with intensities between 0 and 90% of the maximum voluntary contraction and ankle joint angles from 50° to 120°. During these contractions, the m. gastrocnemius medialis and lateralis and the m. soleus were recorded via ultrasound imaging. A nonlinear relationship between fascicle length and pennation angle was discovered, which can be described with a quadratic fit for each of the muscles during isometric contraction. A nearly identical relationship was detected during dynamic contraction. The muscle gearing increased almost linearly with contraction intensity and ankle joint angle., (© 2024. The Author(s).)

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, v max , 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 v max , 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., (© 2024. The Author(s).)

In their physiological condition, muscles are surrounded by connective tissue, other muscles and bone. These tissues exert transverse forces that change the three-dimensional shape of the muscle compared to its isolated condition, in which all surrounding tissues are removed. A change in shape affects the architecture of a muscle and therefore its mechanical properties. The rabbit M. plantaris is a multi-pennate calf muscle consisting of two compartments. A smaller, bi-pennate inner muscle compartment is embedded in a larger, uni-pennate outer compartment (Böl et al., 2015). As part of the calf, the plantaris is tightly packed between other muscles. It is unclear how packing affects the shape and architecture of the plantaris. Therefore, we examined the isolated and packed plantaris of the contralateral legs of three rabbits to determine the influence of the surrounding muscles on its shape and architectural properties using photogrammetric reconstruction and manual digitization, respectively. In the packed condition, the plantaris showed a 27% increase in fascicle pennation and a 54% increase in fascicle curvature compared to the isolated condition. Fascicle length was not affected by muscle packing. The change in muscle architecture occurred mainly in the outer compartment of the plantaris. Furthermore, the isolated plantaris showed a more circular shape and a reduced width of its muscle belly. It can be concluded that the packed plantaris is flattened by the forces exerted by the surrounding muscles, causing a complex architectural change. The data provided improve our understanding of muscle packages in general and can be used to develop and validate realistic three-dimensional muscle models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Digital human body models are used to simulate injuries that occur as a result of vehicle collisions, vibration, sports, and falls. Given enough time the body's musculature can generate force, affect the body's movements, and change the risk of some injuries. The finite-element code LS-DYNA is often used to simulate the movements and injuries sustained by the digital human body models as a result of an accident. In this work, we evaluate the accuracy of the three muscle models in LS-DYNA (MAT_156, EHTM, and the VEXAT) when simulating a range of experiments performed on isolated muscle: force-length-velocity experiments on maximally and sub-maximally stimulated muscle, active-lengthening experiments, and vibration experiments. The force-length-velocity experiments are included because these conditions are typical of the muscle activity that precedes an accident, while the active-lengthening and vibration experiments mimic conditions that can cause injury. The three models perform similarly during the maximally and sub-maximally activated force-length-velocity experiments, but noticeably differ in response to the active-lengthening and vibration experiments. The VEXAT model is able to generate the enhanced forces of biological muscle during active lengthening, while both the MAT_156 and EHTM produce too little force. In response to vibration, the stiffness and damping of the VEXAT model closely follows the experimental data while the MAT_156 and EHTM models differ substantially. The accuracy of the VEXAT model comes from two additional mechanical structures that are missing in the MAT_156 and EHTM models: viscoelastic cross-bridges, and an active titin filament. To help others build on our work we have made our simulation code publicly available., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: none, (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Stretch-shortening cycles (SSCs) involve muscle lengthening (eccentric contractions) instantly followed by shortening (concentric contractions). This combination enhances force, work and power output compared with pure shortening contractions, which is known as the SSC effect. Recent evidence indicates both cross-bridge (XB)-based and non-XB-based (e.g. titin) structures contribute to this effect. This study analysed force re-development following SSCs and pure shortening contractions to gain further insight into the roles of XB and non-XB structures regarding the SSC effect. Experiments were conducted on rat soleus muscle fibres (n=16) with different SSC velocities (30%, 60% and 85% of maximum shortening velocity) and constant stretch-shortening magnitudes (18% of optimum length). The XB inhibitor blebbistatin was used to distinguish between XB and non-XB contributions to force generation. The results showed SSCs led to significantly greater [mean±s.d. 1.02±0.15 versus 0.68±0.09 (ΔF/Δt); t62=8.61, P<0.001, d=2.79) and faster (75 ms versus 205 ms; t62=-6.37, P<0.001, d=-1.48) force re-development compared with pure shortening contractions in the control treatment. In the blebbistatin treatment, SSCs still resulted in greater [0.11±0.03 versus 0.06±0.01 (ΔF/Δt); t62=8.00, P<0.001, d=2.24) and faster (3010±1631 versus 7916±3230 ms; t62=-8.00, P<0.001, d=-1.92) force re-development compared with pure shortening contractions. These findings deepen our understanding of the SSC effect, underscoring the involvement of non-XB structures such as titin in modulating force production. This modulation is likely to involve complex mechanosensory coupling from stretch to signal transmission during muscle contraction., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Purpose: This study aimed to better understand the coping strategy of the neuromuscular system under perturbed afferent feedback. To this end, the neuromechanical effects of transient blood flow restriction (BFR) compared to atmospheric pressure were investigated in an antagonistic muscle pair., Methods: Perceived discomfort and neuromechanical parameters (torque and high-density electromyography) were recorded during submaximal isometric ankle dorsiflexion before, during and after BFR. The tibialis anterior and gastrocnemius lateralis muscles were studied in 14 healthy young adults., Results: Discomfort increased during BFR and decreased to baseline level afterwards. The exerted torque and the co-activation index remained constant, whereas the EMG signal energy increased significantly during BFR. Coherence analysis of the delta band remained constant, whereas the alpha band shows an increase during BFR. Median frequency and muscle fibre conduction velocity showed a positive trend during the first minutes of BFR before significantly decreasing. Both parameters exceeded baseline values after cuff deflation., Conclusion: Perturbed afferent feedback leads to altered neuromechanical parameters. We assume that increased central drive is required to maintain force output, resulting in changed muscle fibre activity. Glycolytic fast-switch fibres are only active for a short time due to oxygen deprivation and hyperacidity, but fatigue effects predominate in the long term., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Stretch-shortening cycles (SSCs) outperform shortening contractions preceded by isometric contractions in terms of enhanced force/torque, work, and power production during shortening. This so-called SSC effect is presumably related to the active muscle stretch before shortening in SSCs. However, it remains unclear whether the effects of stretch-induced higher preload level or stretch-induced history dependence maximize the SSC effect. Therefore, we analyzed fascicle behavior, muscle-tendon unit (MTU) shortening work, and torque/force ( n = 12 participants) via ultrasound and dynamometry during electrically stimulated submaximal plantar flexion contractions from 10° plantarflexion to 15° dorsiflexion. To elucidate the effects of preload level and preload modality (i.e., contraction type) on shortening performance, muscle-tendon unit shortening was preceded by fixed-end (SHO), active stretch (SSC), and preload-matched fixed-end (MATCHED) contractions. Before shortening, MATCHED and SCC had the same preload level (1% torque difference), similar joint position, and muscle fascicle lengths. Compared with SHO, shortening work was significantly ( P < 0.001, partial η 2 = 0.749) increased by 85% and 55% for SSC and MATCHED, respectively, with SSC shortening work being significantly higher than MATCHED ( P = 0.016). This indicates that preload contributes by 65% to the overall SSC effect so that 35% needs to be referred to stretched-induced history-dependent mechanisms. In addition, SSC showed larger fascicle forces at the end of shortening ( P < 0.001) and 20% less depressed isometric torque following shortening compared with MATCHED ( P < 0.001). As potential decoupling effects by the series elastic element were controlled by matching the preload levels, we conclude that the difference between SSC and MATCHED is related to stretch-induced long-lasting history-dependent effects. NEW & NOTEWORTHY Using a torque-matched preload protocol, we found that 2/3 of the performance enhancement in muscle-tendon unit stretch-shortening cycles (SSCs) is caused by the increased preload level. The remaining 1/3 is owed to the long-lasting history-dependent effects triggered during the stretch in SSCs. This increased performance output is attributed to passive elastic structures within the contractile element that do not require additional muscle activation, therefore contributing to the higher efficiency of the neuromuscular system in SSCs.

Architectural 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., (© 2024. The Author(s).)

Muscles and muscle fibers are volume-constant constructs that deform when contracted and develop internal pressures. However, muscles embedded in hydrostatic skeletons are also exposed to external pressures generated by their activity. For two examples, the pressure generation in spiders and in annelids, we used simplified biomechanical models to demonstrate that high intracellular pressures diminishing the resulting tensile stress of the muscle fibers are avoided in the hydrostatic skeleton. The findings are relevant for a better understanding of the design and functionality of biological hydrostatic skeletons., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Purpose: In this paper, we introduce a novel method for determining 3D deformations of the human tibialis anterior (TA) muscle during dynamic movements using 3D ultrasound., Materials and Methods: An existing automated 3D ultrasound system is used for data acquisition, which consists of three moveable axes, along which the probe can move. While the subjects perform continuous plantar- and dorsiflexion movements in two different controlled velocities, the ultrasound probe sweeps cyclically from the ankle to the knee along the anterior shin. The ankle joint angle can be determined using reflective motion capture markers. Since we considered the movement direction of the foot, i.e., active or passive TA, four conditions occur: slow active, slow passive, fast active, fast passive. By employing an algorithm which defines ankle joint angle intervals, i.e., intervals of range of motion (ROM), 3D images of the volumes during movement can be reconstructed., Results: We found constant muscle volumes between different muscle lengths, i.e., ROM intervals. The results show an increase in mean cross-sectional area (CSA) for TA muscle shortening. Furthermore, a shift in maximum CSA towards the proximal side of the muscle could be observed for muscle shortening. We found significantly different maximum CSA values between the fast active and all other conditions, which might be caused by higher muscle activation due to the faster velocity., Conclusion: In summary, we present a method for determining muscle volume deformation during dynamic contraction using ultrasound, which will enable future empirical studies and 3D computational models of skeletal muscles., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Sahrmann, Vosse, Siebert, Handsfield and Röhrle.)

Background: 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., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2024.)

As part of the digestive system, the stomach plays a crucial role in the health and well-being of an organism. It produces acids and performs contractions that initiate the digestive process and begin the break-up of ingested food. Therefore, its mechanical properties are of interest. This study includes a detailed investigation of strains in the porcine stomach wall during passive organ filling. In addition, the observed strains were applied to tissue samples subjected to biaxial tensile tests. The results show inhomogeneous strains during filling, which tend to be higher in the circumferential direction (antrum: 13.2%, corpus: 22.0%, fundus: 67.8%), compared to the longitudinal direction (antrum: 4.8%, corpus: 24.7%, fundus: 50.0%) at a maximum filling of 3500 ml. Consequently, the fundus region experienced the greatest strain. In the biaxial tensile experiments, the corpus region appeared to be the stiffest, reaching nominal stress values above 400 kPa in the circumferential direction, whereas the other regions only reached stress levels of below 50 kPa in both directions for the investigated stretch range. Our findings gain new insight into stomach mechanics and provide valuable data for the development and validation of computational stomach models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Connective tissues can be recognized as an important structural support element in muscles. Recent studies have also highlighted its importance in active force generation and transmission between muscles, particularly through the epimysium. In the present study, we aimed to investigate the impact of the endomysium, the connective tissue surrounding muscle fibers, on both passive and active force production. Pairs of skeletal muscle fibers were extracted from the extensor digitorum longus muscles of rats and, after chemical skinning, their passive and active force-length relationships were measured under two conditions: (i) with the endomysium between muscle fibers intact, and (ii) after its dissection. We found that the dissection of the endomysium caused force to significantly decrease in both active (by 22.2 % when normalized to the maximum isometric force; p < 0.001) and passive conditions (by 25.9 % when normalized to the maximum isometric force; p = 0.034). These findings indicate that the absence of endomysium compromises muscle fiber's not only passive but also active force production. This effect may be attributed to increased heterogeneity in sarcomere lengths, enhanced lattice spacing between myofilaments, or a diminished role of trans-sarcolemmal proteins due to dissecting the endomysium. Future investigations into the underlying mechanisms and their implications for various extracellular matrix-related diseases are warranted., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: We aimed to evaluate the incidence of postoperative adhesion formation and adhesion-related consequences (eg, bowel obstruction) after placement of a sodium hyaluronate-carboxymethylcellulose adhesion barrier after laparoscopic abdominopelvic surgery., Methods: In this systematic review and meta-analysis, we searched the Medical Literature Analysis and Retrieval System Online and Embase via Ovid, Cochrane Central Register of Controlled Trials, ScienceDirect, BIOSIS Previews, Cumulative Index to Nursing and Allied Health Literature, and Clinical Trial Registries. A manual search (eg, Google Scholar and professional association websites) was also conducted to supplement the electronic database results. Two reviewers independently identified relevant studies based on inclusion and exclusion criteria and extracted data., Results: A total of 28 studies were included in the systematic qualitative review. Three of the 28 studies included had comparable outcome measures, interventions, and control groups, allowing the pooling of study data. A total of 938 patients (490 patients in the sodium hyaluronate-carboxymethylcellulose barrier group and 448 in the no adhesion barrier group) from these 3 studies were included in the meta-analyses, which found the incidence of bowel obstruction was significantly lower (65% risk reduction) in the sodium hyaluronate-carboxymethylcellulose barrier group compared with the control group (relative risk = 0.35; 95% confidence interval, 0.19-0.63; P = .005) with extremely low heterogeneity between studies (I 2  = 0; P = .41). The placement of sodium hyaluronate-carboxymethylcellulose barrier laparoscopically did not create new safety signals nor did it increase the incidence of adverse events., Conclusion: Our meta-analysis found that laparoscopic application of a sodium hyaluronate-carboxymethylcellulose barrier in abdominopelvic surgery reduces the risk of bowel obstruction where applied during the early postoperative phase., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The function of a muscle is highly dependent on its architecture, which is characterized by the length, pennation, and curvature of the fascicles, and the geometry of the aponeuroses. During in vivo function, muscles regularly undergo changes in length, thereby altering their architecture. During passive muscle lengthening, fascicle length (FL) generally increases and the angle of fascicle pennation (FP) and the fascicle curvature (FC) decrease, while the aponeuroses increase in length but decrease in width. Muscles are differently structured, making their change during muscle lengthening complex and multifaceted. To obtain comprehensive data on architectural changes in muscles during passive length, the present study determined the three-dimensional fascicle geometry of rabbit M. gastrocnemius medialis (GM), M. gastrocnemius lateralis (GL), and M. plantaris (PLA). For this purpose, the left and right legs of three rabbits were histologically fixed at targeted ankle joint angles of 95° (short muscle length [SML]) and 60° (long muscle length [LML]), respectively, and the fascicles were tracked by manual three-dimensional digitization. In a second set of experiments, the GM aponeurosis dimensions of ten legs from five rabbits were determined at varying muscle lengths via optical marker tracking. The GM consisted of a uni-pennated compartment, whereas the GL and PLA contained multiple compartments of differently pennated fascicles. In the LML compared to the SML, the GM, GL, and PLA had on average a 41%, 29%, and 41% increased fascicle length, and a 30%, 25%, and 33% decrease in fascicle pennation and a 32%, 11%, and 35% decrease in fascicle curvature, respectively. Architectural properties were also differentiated among the different compartments of the PLA and GL, allowing for a more detailed description of their fascicle structure and changes. It was shown that the compartments change differently with muscle length. It was also shown that for each degree of ankle joint angle reduction, the proximal GM aponeurosis length increased by 0.11%, the aponeurosis width decreased by 0.22%, and the area was decreased by 0.20%. The data provided improve our understanding of muscles and can be used to develop and validate muscle models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In legged locomotion, muscles undergo damped oscillations in response to the leg contacting the ground (an impact). How muscle oscillates varies depending on the impact situation. We used a custom-made frame in which we clamped an isolated rat muscle (M. gastrocnemius medialis and lateralis: GAS) and dropped it from three different heights and onto two different ground materials. In fully activated GAS, the dominant eigenfrequencies were 163 Hz, 265 Hz, and 399 Hz, which were signficantly higher (p < 0.05) compared to the dominant eigenfrequencies in passive GAS: 139 Hz, 215 Hz, and 286 Hz. In general, neither changing the falling height nor ground material led to any significant eigenfrequency changes in active nor passive GAS, respectively. To trace the eigenfrequency values back to GAS stiffness values, we developed a 3DoF model. The model-predicted GAS muscle eigenfrequencies matched well with the experimental values and deviated by - 3.8%, 9.0%, and 4.3% from the passive GAS eigenfrequencies and by - 1.8%, 13.3%, and - 1.5% from the active GAS eigenfrequencies. Differences between the frequencies found for active and passive muscle impact situations are dominantly due to the attachment of myosin heads to actin., (© 2023. The Author(s).)

In this work, a three-dimensional model was developed to describe the passive mechanical behaviour of anisotropic skeletal muscle tissue. To validate the model, orientation-dependent axial ([Formula: see text], [Formula: see text], [Formula: see text]) and semi-confined compression experiments (mode I, II, III) were performed on soleus muscle tissue from rabbits. In the latter experiments, specimen deformation is prescribed in the loading direction and prevented in an additional spatial direction, fibre compression at [Formula: see text] (mode I), fibre elongation at [Formula: see text] (mode II) and a neutral state of the fibres at [Formula: see text] where their length is kept constant (mode III). Overall, the model can adequately describe the mechanical behaviour with a relatively small number of model parameters. The stiffest tissue response during orientation-dependent axial compression ([Formula: see text] kPa) occurs when the fibres are oriented perpendicular to the loading direction ([Formula: see text]) and are thus stretched during loading. Semi-confined compression experiments yielded the stiffest tissue ([Formula: see text] kPa) in mode II when the muscle fibres are stretched. The extensive data set collected in this study allows to study the different error measures depending on the deformation state or the combination of deformation states., (© 2022. The Author(s).)