{"d4c6f9a31ee0320fc3be6307a85d6c4einspo5":{"DOI":"10.1007/s00424-023-02794-z","ISBN":"","ISSN":"1432-2013","URL":"","abstract":"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.","annote":"","author":[{"family":"Tomalka","given":"André"}],"citation-label":"tomalka2023eccentric","collection-editor":[],"collection-title":"","container-author":[],"container-title":"Pflügers Archiv","documents":[],"edition":"","editor":[],"event-date":{"date-parts":[["2023"]],"literal":"2023"},"event-place":"","id":"d4c6f9a31ee0320fc3be6307a85d6c4einspo5","interhash":"c1587910394340ebda12596b663f7b66","intrahash":"d4c6f9a31ee0320fc3be6307a85d6c4e","issue":"","issued":{"date-parts":[["2023"]],"literal":"2023"},"keyword":"Titin Simtech muscle Contractile Stretch physiology Muscle behaviour Sarcomere Skeletal","misc":{"issn":"1432-2013","language":"eng","doi":"10.1007/s00424-023-02794-z"},"note":"","number":"","number-of-pages":"14","page":"421-435","page-first":"421","publisher":"Springer","publisher-place":"","status":"","title":"Eccentric muscle contractions : from single muscle fibre to whole muscle mechanics","type":"article-journal","username":"inspo5","version":"","volume":"475"},"13d1c527b422f0c2fbfb26d98885b1f6inspo5":{"DOI":"10.1242/jeb.247377","ISBN":"","ISSN":"1477-9145","URL":"http://dx.doi.org/10.1242/jeb.247377","abstract":"Stretch-shortening cycles (SSCs) involve muscle lengthening (eccentric contractions) instantly followed by shortening (concentric contractions). This combination enhances force, work, and power output compared to pure shortening (SHO), which is known as SSC-effect. Recent evidence indicates both cross-bridge-based (XB) and non-cross-bridge-based (non-XB, e.g., titin) structures contribute to this effect. This study analyzed force re-development following SSCs and SHO 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%, 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. Results showed SSCs led to significantly greater (1.02±.15 vs. 0.68±.09 [ΔF/Δt]; t(62)=8.61, p<.001, d=2.79) and faster (75 ms vs. 205 [ms]; t(62) = -6.37, p<.001, d=-1.48) force re-development compared to SHO in the control treatment. In the blebbistatin treatment, SSCs still resulted in greater (.11±.03 vs. .06±.01 [ΔF/Δt]; t(62) = 8.00, p<.001, d=2.24) and faster (3010±1631 vs. 7916±3230 [ms]; t(62) = -8.00, p<.001, d=-1.92) force re-development compared to SHO. These findings deepen our understanding of the SSC-effect, underscoring the involvement of non-XB structures like titin in modulating force production. This modulation likely involves complex mechanosensory coupling from stretch to signal transmission during muscle contraction.","annote":"","author":[{"family":"Tomalka","given":"André"},{"family":"Weidner","given":"Sven"},{"family":"Hahn","given":"Daniel"},{"family":"Seiberl","given":"Wolfgang"},{"family":"Siebert","given":"Tobias"}],"citation-label":"Tomalka_2024","collection-editor":[{"family":"Siebert","given":"Tobias"}],"collection-title":"","container-author":[{"family":"Siebert","given":"Tobias"}],"container-title":"Journal of Experimental Biology","documents":[],"edition":"","editor":[{"family":"Siebert","given":"Tobias"}],"event-date":{"date-parts":[["2024","08"]],"literal":"2024"},"event-place":"","id":"13d1c527b422f0c2fbfb26d98885b1f6inspo5","interhash":"1a1ddb22b3fc4a98ff638b17f957aa71","intrahash":"13d1c527b422f0c2fbfb26d98885b1f6","issue":"","issued":{"date-parts":[["2024","08"]],"literal":"2024"},"keyword":"Blebbistatin damping Cross-bridge Mechanosensing Signaling Mechanical Contractile power Muscle behaviour block Sarcomere","misc":{"issn":"1477-9145","doi":"10.1242/jeb.247377"},"note":"","number":"","page":"","page-first":"","publisher":"The Company of Biologists","publisher-place":"","status":"","title":"Force re-development after shortening reveals a role for titin in stretch-shortening performance enhancement in skinned muscle fibres","type":"article-journal","username":"inspo5","version":"","volume":""},"99b830ed1c9a63a531065abdca43aebcinspo5":{"DOI":"10.1038/s41598-023-45821-w","ISBN":"","ISSN":"2045-2322","URL":"https://doi.org/10.1038/s41598-023-45821-w","abstract":"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.","annote":"","author":[{"family":"Christensen","given":"Kasper B."},{"family":"Guenther","given":"Michael"},{"family":"Schmitt","given":"Syn"},{"family":"Siebert","given":"Tobias"}],"citation-label":"Christensen2023","collection-editor":[],"collection-title":"","container-author":[],"container-title":"Scientific Reports","documents":[],"edition":"","editor":[],"event-date":{"date-parts":[["2023","11","09"]],"literal":"2023"},"event-place":"","id":"99b830ed1c9a63a531065abdca43aebcinspo5","interhash":"ecb747b2d59e56c22f32a2e77661295e","intrahash":"99b830ed1c9a63a531065abdca43aebc","issue":"1","issued":{"date-parts":[["2023","11","09"]],"literal":"2023"},"keyword":"Biomechanics Animal models behaviour Musculoskeletal","misc":{"language":"English","issn":"2045-2322","doi":"10.1038/s41598-023-45821-w"},"note":"","number":"1","page":"19575","page-first":"19575","publisher":"","publisher-place":"","status":"","title":"Muscle wobbling mass dynamics: eigenfrequency dependencies on activity, impact strength, and ground material","type":"article-journal","username":"inspo5","version":"","volume":"13"},"1c85bdf11cbecb538cd5edf98a8597ddinspo5":{"DOI":"10.1038/s41598-021-02819-6","ISBN":"","ISSN":"2045-2322","URL":"https://doi.org/10.1038/s41598-021-02819-6","abstract":"Legged locomotion has evolved as the most common form of terrestrial locomotion. When the leg makes contact with a solid surface, muscles absorb some of the shock-wave accelerations (impacts) that propagate through the body. We built a custom-made frame to which we fixated a rat (Rattus norvegicus, Wistar) muscle (m. gastrocnemius medialis and lateralis: GAS) for emulating an impact. We found that the fibre material of the muscle dissipates between 3.5 and \\$\\$23\\backslash,\\backslashupmu \\backslashhbox \\J\\\\$\\$ranging from fresh, fully active to passive muscle material, respectively. Accordingly, the corresponding dissipated energy in a half-sarcomere ranges between 10.4 and \\$\\$68\\backslash,z\\backslashhbox \\J\\\\$\\$, respectively. At maximum activity, a single cross-bridge would, thus, dissipate 0.6\\% of the mechanical work available per ATP split per impact, and up to 16\\% energy in common, submaximal, activities. We also found the cross-bridge stiffness as low as \\$\\$2.2\\backslash,\\backslashhbox \\pN\\\\backslash,\\backslashhbox \\nm\\^\\-1\\\\$\\$, which can be explained by the Coulomb-actuating cross-bridge part dominating the sarcomere stiffness. Results of the study provide a deeper understanding of contractile dynamics during early ground contact in bouncy gait.","annote":"","author":[{"family":"Christensen","given":"Kasper B."},{"family":"Günther","given":"Michael"},{"family":"Schmitt","given":"Syn"},{"family":"Siebert","given":"Tobias"}],"citation-label":"Christensen2021","collection-editor":[{"family":"Siebert","given":"Tobias"}],"collection-title":"","container-author":[{"family":"Siebert","given":"Tobias"}],"container-title":"Scientific Reports","documents":[],"edition":"","editor":[{"family":"Siebert","given":"Tobias"}],"event-date":{"date-parts":[["2021","12","08"]],"literal":"2021"},"event-place":"","id":"1c85bdf11cbecb538cd5edf98a8597ddinspo5","interhash":"043bc2c5e9b044a62a58167156c7fcb0","intrahash":"1c85bdf11cbecb538cd5edf98a8597dd","issue":"1","issued":{"date-parts":[["2021","12","08"]],"literal":"2021"},"keyword":"Biomechanics Nonlinear Animal dynamics Bioenergetics behaviour","misc":{"issn":"2045-2322","doi":"10.1038/s41598-021-02819-6"},"note":"","number":"1","page":"23638","page-first":"23638","publisher":"","publisher-place":"","status":"","title":"Cross-bridge mechanics estimated from skeletal muscles' work-loop responses to impacts in legged locomotion","type":"article-journal","username":"inspo5","version":"","volume":"11"}}