TY - JOUR A1 - Lepke, Dietrich A1 - Lillie, Dirk A1 - Peterson, Leif Arne A1 - Hempe, Thomas T1 - Liegedauer von Holzschwellen in Tunneln der Hamburger Hochbahn AG JF - EI - Der Eisenbahningenieur N2 - Die Hamburger Hochbahn AG benötigte im Rahmen der Überarbeitung einer langfristigen Instandhaltungs- und Erneuerungsstrategie für ihre U-Bahn-Infrastruktur eine belastbare Aussage über die Restlebensdauer der Holzschwellen im Tunnel. Aus diesem Grunde beauftragte sie das Institut für Verkehrswesen, Eisenbahnbau und -betrieb (IVE) der Universität Hannover mit der Erstellung eines entsprechenden Gutachtens. Das Ergebnis führte zu der gesicherten Aussage einer erheblich längeren Restlebensdauer der Tunnelschwellen gegenüber den bisherigen, geschätzten Annahmen. Y1 - 2006 SN - 0013-2810 IS - 2 SP - 46 EP - 50 PB - DVV Media Group CY - Hamburg ER - TY - THES A1 - Peterson, Leif Arne T1 - Zum Tragverhalten nachgiebig verbundener Biegeträger aus Holz N2 - In der vorliegenden Dissertation werden zunächst die linear elastischen Bemessungsmöglichkeiten für nachgiebig verbundene Biegeträger unter statischer und dynamischer Beanspruchung diskutiert. Zum Vergleich wurden praktische Untersuchungen an zweiteiligen Kantholzbiegeträgem mit mechanischen Verbindungsmitteln unterschiedlicher Verformungscharakteristika durchgeführt, ebenso wie umfangreiche Materialprüfungen an den zusammengefügten Einzelquerschnitten. Hierdurch werden die Unterschiede zum realen, nicht elastischen, statischen Tragverhalten aufgezeigt. Der für das dynamische Verhalten maßgebende Systemparameter der Eigenfrequenz wird für mehrteilige Biegeträger theoretisch hinterfragt und an den nachgiebig verbundenen Kantholzbiegeträgem gemessen. Begleitet von weiteren praktischen Untersuchungen an einzelnen Verbindungsmitteln unter Blockscherbeanspruchung wird die rechnerische Berücksichtigung des plastischen Verbindungsmittelverhaltens auf zwei theoretischen Wegen erforscht. Auf Grundlage der Untersuchungen wird ein neues, semianalytisches y-Verfahren entwickelt. Gegenüber den Berechnungen mit finiten Volumen- und Kontakt-Elementen erweist sich das neue Verfahren auf Basis der, um die schubweichen Fugen erweiterten, Balkentheorie als leistungsfähiger. Der Einfluss des plastischen Verbindungsmittelverhaltens wird durch vergleichende Parameterstudien mit diesem neuen Verfahren als vom anerkannten Stand der Technik ausreichend berücksichtigt identifiziert. Für die linear elastische Dimensionierung werden optimierte Verbindungsmittelanordnungen hergeleitet, die durch übersichtliche Ergänzungen zum existierenden Bemessungskonzept des y-Verfahrens eine exaktere Berechnung ermöglichen. Y1 - 2008 SN - 9783816775973 N1 - Berichte des Instituts für Bauphysik, Band 1 PB - Fraunhofer IRB Verlag CY - Stuttgart ER - TY - JOUR A1 - Nabil, F. A1 - Peterson, Leif Arne A1 - Schmidt, A. A1 - Geerdes, D. T1 - Die Holzkuppel des Neuen Palais in Potsdam JF - Bauingenieur Y1 - 2010 SN - 0005-6650 VL - 85 IS - 8 SP - 324 EP - 330 PB - Springer-VDI-Verlag CY - Düsseldorf ER - TY - BOOK A1 - Nebgen, Nikolaus A1 - Peterson, Leif Arne T1 - Holzbau kompakt nach Eurocode 5 N2 - "Holzbau kompakt" wurde sowohl für Studierende als auch Praktiker konzipiert und beschränkt sich nicht auf reine Holzbauaufgaben, sondern setzt sich ggf. auch mit der Tragwerkslehre auseinander. Die Neuauflage basiert auf dem Eurocode 5 und berücksichtigt zahlreiche neue Erkenntnisse aus Forschung und praxisnaher Entwicklung. Neben den Grundlagen der Bemessung, der Baustoffe, der Dauerhaftigkeit und des Brandschutzes konzentriert sich das Grundlagenwerk besonders auf das Konstruieren mit Holz und Holzwerkstoffen, anschaulich dargestellt an sehr ausführlichen Beispielen für Wohnhaus und Hallentragwerk. Y1 - 2015 SN - 978-3-410-25455-3 PB - Beuth CY - Berlin ET - 5. Auflage ER - TY - BOOK A1 - Holschemacher, Klaus A1 - Peters, Klaus A1 - Peterson, Leif Arne A1 - Schneider, Klaus-Jürgen A1 - Thiele, Ralf T1 - Konstruktiver Ingenieurbau kompakt: Formelsammlung und Bemessungshilfen nach Eurocode für die Bereiche: Lastannahmen, Holzbau, Mauerwerksbau, Stahlbau, Stahlbetonbau, Geotechnik, statische Hinweise N2 - Das kompakte Nachschlagewerk für den konstruktiven Ingenieurbau wurde für den täglichen Gebrauch auf der Baustelle konzipiert und stellt alle für die rechnerische Nachweisführung und Konstruktion von Bauteilen wichtigsten Angaben in Form einer Formelsammlung mit Nachweishilfen zur Verfügung. Der Inhalt wurde auf Basis der neuen Eurocodes komplett aktualisiert und erweitert. Die 4. Auflage enthält in bewährter Manier eine umfangreiche Formelsammlung, Querschnittswerte und Bemessungshilfen zu den Bereichen Lastannahmen, Holzbau, Mauerwerksbau, Stahlbau, Stahlbetonbau, Geotechnik sowie statische Hinweise. Farbiges Papier erleichtert den zielgerichteten Zugriff auf die einzelnen Fachgebiete. Y1 - 2013 SN - 978-3-410-22775-5 PB - Beuth CY - Berlin ET - 4., vollständig überarbeitete Auflage ER - TY - CHAP A1 - Frühwald, Katja A1 - Peterson, Leif Arne A1 - Hasenstab, Andreas ED - Fouad, Nabil A. T1 - Prüfverfahren zur Begutachtung der Materialeigenschaften von Holztragwerken T2 - Bauphysik‐Kalender 2012: Schwerpunkt: Gebäudediagnostik N2 - Dieses Kapitel beinhaltet: - Einleitung - Ausgewählte typische Schäden an Holzbauwerken - Das Material Holz und seine Besonderheiten - Bestandserfassung - Labormethoden - Begutachtungsbeispiele - Zusammenfassung und Schlussfolgerungen - Literatur Y1 - 2012 SN - 9783433029862 (Print) SN - 9783433601235 (Online) U6 - https://doi.org/10.1002/9783433601235.ch4 SP - 103 EP - 155 PB - Ernst & Sohn CY - Berlin ER - TY - JOUR A1 - Ketelhut, Maike A1 - Brügge, G. M. A1 - Göll, Fabian A1 - Braunstein, Bjoern A1 - Albracht, Kirsten A1 - Abel, Dirk T1 - Adaptive iterative learning control of an industrial robot during neuromuscular training JF - IFAC PapersOnLine N2 - To prevent the reduction of muscle mass and loss of strength coming along with the human aging process, regular training with e.g. a leg press is suitable. However, the risk of training-induced injuries requires the continuous monitoring and controlling of the forces applied to the musculoskeletal system as well as the velocity along the motion trajectory and the range of motion. In this paper, an adaptive norm-optimal iterative learning control algorithm to minimize the knee joint loadings during the leg extension training with an industrial robot is proposed. The response of the algorithm is tested in simulation for patients with varus, normal and valgus alignment of the knee and compared to the results of a higher-order iterative learning control algorithm, a robust iterative learning control and a recently proposed conventional norm-optimal iterative learning control algorithm. Although significant improvements in performance are made compared to the conventional norm-optimal iterative learning control algorithm with a small learning factor, for the developed approach as well as the robust iterative learning control algorithm small steady state errors occur. KW - Iterative learning control KW - Robotic rehabilitation KW - Adaptive control Y1 - 2020 U6 - https://doi.org/10.1016/j.ifacol.2020.12.741 SN - 2405-8963 VL - 53 IS - 2 SP - 16468 EP - 16475 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ketelhut, Maike A1 - Kolditz, Melanie A1 - Göll, Fabian A1 - Braunstein, Bjoern A1 - Albracht, Kirsten A1 - Abel, Dirk T1 - Admittance control of an industrial robot during resistance training JF - IFAC-PapersOnLine N2 - Neuromuscular strength training of the leg extensor muscles plays an important role in the rehabilitation and prevention of age and wealth related diseases. In this paper, we focus on the design and implementation of a Cartesian admittance control scheme for isotonic training, i.e. leg extension and flexion against a predefined weight. For preliminary testing and validation of the designed algorithm an experimental research and development platform consisting of an industrial robot and a force plate mounted at its end-effector has been used. Linear, diagonal and arbitrary two-dimensional motion trajectories with different weights for the leg extension and flexion part are applied. The proposed algorithm is easily adaptable to trajectories consisting of arbitrary six-dimensional poses and allows the implementation of individualized trajectories. KW - Assistive technology KW - Rehabilitation engineering KW - Human-Computer interaction KW - Automatic control Y1 - 2019 U6 - https://doi.org/10.1016/j.ifacol.2019.12.102 SN - 2405-8963 N1 - 14th IFAC Symposium on Analysis, Design, and Evaluation of Human Machine Systems HMS 2019 Tallinn, Estonia, 16–91 September 2019 VL - 52 IS - 19 SP - 223 EP - 228 PB - Elsevier CY - Amsterdam ER - TY - CHAP A1 - Ketelhut, Maike A1 - Göll, Fabian A1 - Braunstein, Bjoern A1 - Albracht, Kirsten A1 - Abel, Dirk T1 - Iterative learning control of an industrial robot for neuromuscular training T2 - 2019 IEEE Conference on Control Technology and Applications N2 - Effective training requires high muscle forces potentially leading to training-induced injuries. Thus, continuous monitoring and controlling of the loadings applied to the musculoskeletal system along the motion trajectory is required. In this paper, a norm-optimal iterative learning control algorithm for the robot-assisted training is developed. The algorithm aims at minimizing the external knee joint moment, which is commonly used to quantify the loading of the medial compartment. To estimate the external knee joint moment, a musculoskeletal lower extremity model is implemented in OpenSim and coupled with a model of an industrial robot and a force plate mounted at its end-effector. The algorithm is tested in simulation for patients with varus, normal and valgus alignment of the knee. The results show that the algorithm is able to minimize the external knee joint moment in all three cases and converges after less than seven iterations. KW - Knee KW - Training KW - Load modeling KW - Force KW - Iterative learning control Y1 - 2019 SN - 978-1-7281-2767-5 (ePub) SN - 978-1-7281-2766-8 (USB) SN - 978-1-7281-2768-2 (PoD) U6 - https://doi.org/10.1109/CCTA.2019.8920659 N1 - 2019 IEEE Conference on Control Technology and Applications (CCTA) Hong Kong, China, August 19-21, 2019 PB - IEEE CY - New York ER - TY - GEN A1 - Blottner, Dieter A1 - Hastermann, Maria A1 - Muckelt, Paul A1 - Albracht, Kirsten A1 - Schoenrock, Britt A1 - Salanova, Michele A1 - Warner, Martin A1 - Gunga, Hans-Christian A1 - Stokes, Maria T1 - MYOTONES - Inflight muscle health status monitoring during long-duration space missions onboard the International Space Station: a single case study T2 - IAC Papers Archive N2 - The MYOTONES experiment is the first to monitor changes in the basic biomechanical properties (tone, elasticity and stiffness) of the resting human myofascial system due to microgravity with a oninvasive, portable device on board the ISS. The MyotonPRO device applies several brief mechanical stimuli to the surface of the skin, and the natural oscillation signals of the tissue beneath are detected and computed by the MyotonPRO. Thus, an objective, quick and easy determination of the state of the underlying tissue is possible. Two preflight, four inflight and four post flight measurements were performed on a male astronaut using the same 10 measurement points (MP) for each session. MPs were located on the plantar fascia, Achilles tendon, M. soleus, M. gastrocnemius, M. multifidus, M. splenius capitis, M. deltoideus anterior, M. rectus femoris, infrapatellar tendon, M. tibialis anterior. Subcutaneous tissues thickness above the MPs was measured using ultrasound imaging. Magnetic resonance images (MRI) of lower limb muscles and functional tests were also performed pre- and postflight. Our first measurements on board the ISS confirmed increased tone and stiffness of the lumbar multifidus muscle, an important trunk stabilizer, dysfunction of which is known to be associated with back pain. Furthermore, reduced tone and stiffness of Achilles tendon and plantar fascia were observed inflight vs. preflight, confirming previous findings from terrestrial analog studies and parabolic flights. Unexpectedly, the deltoid showed negative inflight changes in tone and stiffness, and increased elasticity, suggesting a potential risk of muscle atrophy in longer spaceflight that should be addressed by adequate inflight countermeasure protocols. Most values from limb and back MPS showed deflected patterns (in either directions) from inflight shortly after the re-entry phase on the landing day and one week later. Most parameter values then normalized to baseline after 3 weeks likely due to 1G re-adaptation and possible outcome of the reconditioning protocol. No major changes in subcutaneous tissues thickness above the MPs were found inflight vs preflight, suggesting no bias (i.e., fluid shift, extreme tissue thickening or loss). Pre- and postflight MRI and functional tests showed negligible changes in calf muscle size, power and force, which is likely due to training effects from current inflight exercise protocols. The MYOTONES experiment is currently ongoing to collect data from further crew members. The potential impact of this research is to better understand the effects of microgravity and countermeasures over the time course of an ISS mission cycle. This will enable exercise countermeasures to be tailored Y1 - 2019 SN - 00741795 N1 - International Astronautical Congress: space: the power of the past, the promise of the future - Washington DC, USA/Vereinigte Staaten von Amerika Dauer: 21.10.2019 → 25.10.2019 PB - Pergamon CY - Oxford ER - TY - JOUR A1 - Bruksle, Ieva A1 - Chwallek, Constanze A1 - Krastina, Anzelika T1 - Strengthening sustainability in entrepreneurship education - implications for shifting entrepreneurial thinking towards sustainability at universities JF - ACTA PROSPERITATIS N2 - By developing innovative solutions to social and environmental problems, sustainable ventures carry greatpotential. Entrepreneurship which focuses especially on new venture creation can be developed through education anduniversities, in particular, are called upon to provide an impetus for social change. But social innovations are associatedwith certain hurdles, which are related to the multi-dimensionality, i.e. the tension between creating social,environmental and economic value and dealing with a multiplicity of stakeholders. The already complex field ofentrepreneurship education has to face these challenges. This paper, therefore, aims to identify starting points for theintegration of sustainability into entrepreneurship education. To pursue this goal experiences from three differentproject initiatives between the partner universities: Lapland University of Applied Sciences, FH Aachen University ofApplied Sciences and Turiba University are reflected and findings are systematically condensed into recommendationsfor education on sustainable entrepreneurship. KW - climate change KW - entrepreneurship education KW - Finland KW - Germany KW - Latvia Y1 - 2023 U6 - https://doi.org/10.37804/1691-6077-2023-14-37-48 SN - 1691-6077 VL - 14 IS - 1 SP - 37 EP - 48 PB - Sciendo ER - TY - JOUR A1 - Werkhausen, Amelie A1 - Cronin, Neil J. A1 - Albracht, Kirsten A1 - Paulsen, Gøran A1 - Larsen, Askild V. A1 - Bojsen-Møller, Jens A1 - Seynnes, Olivier R. T1 - Training-induced increase in Achilles tendon stiffness affects tendon strain pattern during running JF - PeerJ N2 - Background During the stance phase of running, the elasticity of the Achilles tendon enables the utilisation of elastic energy and allows beneficial contractile conditions for the triceps surae muscles. However, the effect of changes in tendon mechanical properties induced by chronic loading is still poorly understood. We tested the hypothesis that a training-induced increase in Achilles tendon stiffness would result in reduced tendon strain during the stance phase of running, which would reduce fascicle strains in the triceps surae muscles, particularly in the mono-articular soleus. Methods Eleven subjects were assigned to a training group performing isometric singleleg plantarflexion contractions three times per week for ten weeks, and another ten subjects formed a control group. Before and after the training period, Achilles tendon stiffness was estimated, and muscle-tendon mechanics were assessed during running at preferred speed using ultrasonography, kinematics and kinetics. Results Achilles tendon stiffness increased by 18% (P <0:01) in the training group, but the associated reduction in strain seen during isometric contractions was not statistically significant. Tendon elongation during the stance phase of running was similar after training, but tendon recoil was reduced by 30% (P <0:01), while estimated tendon force remained unchanged. Neither gastrocnemius medialis nor soleus fascicle shortening during stance was affected by training. Discussion These results show that a training-induced increase in Achilles tendon stiffness altered tendon behaviour during running. Despite training-induced changes in tendon mechanical properties and recoil behaviour, the data suggest that fascicle shortening patterns were preserved for the running speed that we examined. The asymmetrical changes in tendon strain patterns supports the notion that simple inseries models do not fully explain the mechanical output of the muscle-tendon unit during a complex task like running. KW - Achilles tendon KW - Stiffness KW - Running KW - Tendon properties KW - Architectural gear ratio Y1 - 2019 U6 - https://doi.org/10.7717/peerj.6764 SN - 21678359 PB - Peer CY - London ER - TY - JOUR A1 - Ketelhut, Maike A1 - Göll, Fabian A1 - Braunstein, Björn A1 - Albracht, Kirsten A1 - Abel, Dirk T1 - Comparison of different training algorithms for the leg extension training with an industrial robot JF - Current Directions in Biomedical Engineering N2 - In the past, different training scenarios have been developed and implemented on robotic research platforms, but no systematic analysis and comparison have been done so far. This paper deals with the comparison of an isokinematic (motion with constant velocity) and an isotonic (motion against constant weight) training algorithm. Both algorithms are designed for a robotic research platform consisting of a 3D force plate and a high payload industrial robot, which allows leg extension training with arbitrary six-dimensional motion trajectories. In the isokinematic as well as the isotonic training algorithm, individual paths are defined i n C artesian s pace by sufficient s upport p oses. I n t he i sotonic t raining s cenario, the trajectory is adapted to the measured force as the robot should only move along the trajectory as long as the force applied by the user exceeds a minimum threshold. In the isotonic training scenario however, the robot’s acceleration is a function of the force applied by the user. To validate these findings, a simulative experiment with a simple linear trajectory is performed. For this purpose, the same force path is applied in both training scenarios. The results illustrate that the algorithms differ in the force dependent trajectory adaption. KW - Rehabilitation Technology and Prosthetics KW - Surgical Navigation and Robotics Y1 - 2018 U6 - https://doi.org/10.1515/cdbme-2018-0005 SN - 2364-5504 VL - 4 IS - 1 SP - 17 EP - 20 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Stäudle, Benjamin A1 - Seynnes, Olivier A1 - Laps, Guido A1 - Brüggemann, Gert-Peter A1 - Albracht, Kirsten T1 - Altered gastrocnemius contractile behavior in former achilles tendon rupture patients during walking JF - Frontiers in Physiology N2 - Achilles tendon rupture (ATR) remains associated with functional limitations years after injury. Architectural remodeling of the gastrocnemius medialis (GM) muscle is typically observed in the affected leg and may compensate force deficits caused by a longer tendon. Yet patients seem to retain functional limitations during—low-force—walking gait. To explore the potential limits imposed by the remodeled GM muscle-tendon unit (MTU) on walking gait, we examined the contractile behavior of muscle fascicles during the stance phase. In a cross-sectional design, we studied nine former patients (males; age: 45 ± 9 years; height: 180 ± 7 cm; weight: 83 ± 6 kg) with a history of complete unilateral ATR, approximately 4 years post-surgery. Using ultrasonography, GM tendon morphology, muscle architecture at rest, and fascicular behavior were assessed during walking at 1.5 m⋅s–1 on a treadmill. Walking patterns were recorded with a motion capture system. The unaffected leg served as control. Lower limbs kinematics were largely similar between legs during walking. Typical features of ATR-related MTU remodeling were observed during the stance sub-phases corresponding to series elastic element (SEE) lengthening (energy storage) and SEE shortening (energy release), with shorter GM fascicles (36 and 36%, respectively) and greater pennation angles (8° and 12°, respectively). However, relative to the optimal fascicle length for force production, fascicles operated at comparable length in both legs. Similarly, when expressed relative to optimal fascicle length, fascicle contraction velocity was not different between sides, except at the time-point of peak series elastic element (SEE) length, where it was 39 ± 49% lower in the affected leg. Concomitantly, fascicles rotation during contraction was greater in the affected leg during the whole stance-phase, and architectural gear ratios (AGR) was larger during SEE lengthening. Under the present testing conditions, former ATR patients had recovered a relatively symmetrical walking gait pattern. Differences in seen AGR seem to accommodate the profound changes in MTU architecture, limiting the required fascicle shortening velocity. Overall, the contractile behavior of the GM fascicles does not restrict length- or velocity-dependent force potentials during this locomotor task. KW - tendon rupture KW - muscle fascicle behavior KW - walking gait KW - force generation KW - ultrasound imaging Y1 - 2022 U6 - https://doi.org/10.3389/fphys.2022.792576 SN - 1664-042X VL - 13 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Quittmann, Oliver J. A1 - Abel, Thomas A1 - Albracht, Kirsten A1 - Strüder, Heiko K. T1 - Biomechanics of all-out handcycling exercise: kinetics, kinematics and muscular activity of a 15-s sprint test in able-bodied participants JF - Sports Biomechanics N2 - This study aims to quantify the kinematics, kinetics and muscular activity of all-out handcycling exercise and examine their alterations during the course of a 15-s sprint test. Twelve able-bodied competitive triathletes performed a 15-s all-out sprint test in a recumbent racing handcycle that was attached to an ergometer. During the sprint test, tangential crank kinetics, 3D joint kinematics and muscular activity of 10 muscles of the upper extremity and trunk were examined using a power metre, motion capturing and surface electromyography (sEMG), respectively. Parameters were compared between revolution one (R1), revolution two (R2), the average of revolution 3 to 13 (R3) and the average of the remaining revolutions (R4). Shoulder abduction and internal-rotation increased, whereas maximal shoulder retroversion decreased during the sprint. Except for the wrist angles, angular velocity increased for every joint of the upper extremity. Several muscles demonstrated an increase in muscular activation, an earlier onset of muscular activation in crank cycle and an increased range of activation. During the course of a 15-s all-out sprint test in handcycling, the shoulder muscles and the muscles associated to the push phase demonstrate indications for short-duration fatigue. These findings are helpful to prevent injuries and improve performance in all-out handcycling. KW - Handbike KW - sEMG KW - Paralympic sport KW - performance testing KW - high-intensity exercise Y1 - 2022 U6 - https://doi.org/10.1080/14763141.2020.1745266 SN - 1752-6116 (Onlineausgabe) SN - 1476-3141 (Druckausgabe) VL - 21 IS - 10 SP - 1200 EP - 1223 PB - Taylor & Francis CY - London ER - TY - JOUR A1 - Werkhausen, Amelie A1 - Willwacher, Steffen A1 - Albracht, Kirsten T1 - Medial gastrocnemius muscle fascicles shorten throughout stance during sprint acceleration JF - Scandinavian Journal of Medicine & Science in Sports N2 - The compliant nature of distal limb muscle-tendon units is traditionally considered suboptimal in explosive movements when positive joint work is required. However, during accelerative running, ankle joint net mechanical work is positive. Therefore, this study aims to investigate how plantar flexor muscle-tendon behavior is modulated during fast accelerations. Eleven female sprinters performed maximum sprint accelerations from starting blocks, while gastrocnemius muscle fascicle lengths were estimated using ultrasonography. We combined motion analysis and ground reaction force measurements to assess lower limb joint kinematics and kinetics, and to estimate gastrocnemius muscle-tendon unit length during the first two acceleration steps. Outcome variables were resampled to the stance phase and averaged across three to five trials. Relevant scalars were extracted and analyzed using one-sample and two-sample t-tests, and vector trajectories were compared using statistical parametric mapping. We found that an uncoupling of muscle fascicle behavior from muscle-tendon unit behavior is effectively used to produce net positive mechanical work at the joint during maximum sprint acceleration. Muscle fascicles shortened throughout the first and second steps, while shortening occurred earlier during the first step, where negative joint work was lower compared with the second step. Elastic strain energy may be stored during dorsiflexion after touchdown since fascicles did not lengthen at the same time to dissipate energy. Thus, net positive work generation is accommodated by the reuse of elastic strain energy along with positive gastrocnemius fascicle work. Our results show a mechanism of how muscles with high in-series compliance can contribute to net positive joint work. KW - locomotion KW - muscle mechanics KW - running KW - sprint start KW - ultrasonography Y1 - 2021 U6 - https://doi.org/10.1111/sms.13956 SN - 0905-7188 (Druckausgabe) SN - 1600-0838 (Onlineausgabe) VL - 31 IS - 7 SP - 1471 EP - 1480 PB - Wiley-Blackwell CY - Oxford ER - TY - JOUR A1 - Monti, Elena A1 - Waldvogel, Janice A1 - Ritzmann, Ramona A1 - Freyler, Kathrin A1 - Albracht, Kirsten A1 - Helm, Michael A1 - De Cesare, Niccolò A1 - Pavan, Piero A1 - Reggiani, Carlo A1 - Gollhofer, Albert A1 - Narici, Marco Vincenzo T1 - Muscle in variable gravity: “I do not know where I am, but I know what to do” JF - Frontiers in Physiology N2 - Performing tasks, such as running and jumping, requires activation of the agonist and antagonist muscles before (motor unit pre-activation) and during movement performance (Santello and Mcdonagh, 1998). A well-timed and regulated muscle activation elicits a stretch-shortening cycle (SSC) response, naturally occurring in bouncing movements (Ishikawa and Komi, 2004; Taube et al., 2012). By definition, the SSC describes the stretching of a pre-activated muscle-tendon complex immediately followed by a muscle shortening in the concentric push-off phase (Komi, 1984). Given the importance of SSC actions for human movement, it is not surprising that many studies investigated the biomechanics of this phenomenon; in particular, drop jumps (DJs) represent a good paradigm to study muscle fascicle and tendon behavior in ballistic movements involving the SSC. Within a DJ, three main phases [pre-activation, braking, and push-off (PO; Komi, 2000)] have been recognized and extensively studied in common and challenging conditions, such as changes in load, falling height, or simulated hypo-gravity (Avela et al., 1994; Arampatzis et al., 2001; Fukashiro et al., 2005; Ishikawa et al., 2005; Sousa et al., 2007; Ritzmann et al., 2016; Helm et al., 2020). These studies show that the timing and amount of triceps-surae muscle-tendon unit pre-activation in DJs are differentially regulated based on the load applied to the muscle, being optimal in normal “Earth” gravity conditions (Avela et al., 1994), but decreased in simulated hypo-gravity, hyper-gravity (Avela et al., 1994; Ritzmann et al., 2016), or unknown conditions (i.e., unknown falling heights; Helm et al., 2020). Some authors indicated that, when falling from heights different from the optimal one [defined as the drop height giving a maximum DJ performance indicated as peak ground reaction force (GRF) or jump high], electromyographic (EMG) activity of the plantar flexors increases from lower than optimal to higher than optimal heights (Ishikawa and Komi, 2004; Sousa et al., 2007). These findings highlight the ability of the central nervous system to regulate the timing and amount of pre-activation according to different jumping conditions, thus regulating muscle fascicle length, tendon and joint stiffness as well as position, in order to safely land on the ground and quickly re-bounce. Similarly, to pre-activation, also in the braking phase, the plantar flexors are differentially regulated. In optimal height (i.e., load) jumping conditions, gastrocnemius medialis (GM) fascicles shorten at early ground contact (possibly due to the intervention of the stretch reflex; Gollhofer et al., 1992) and behave quasi-isometrically in the late braking phase, enabling tendon elongation, and storage of elastic energy (Gollhofer et al., 1992; Fukashiro et al., 2005; Sousa et al., 2007). When increasing the falling height (augmenting the impact GRF), the quasi-isometric behavior of fascicles disappears, and fast fascicle lengthening occurs (Ishikawa et al., 2005; Sousa et al., 2007). In the third and last PO phase, fascicles shorten and the tendon releases the elastic energy previously stored. Bobbert et al. (1987) reported no influence of jumping height on the work done and on the net vertical impulse assessed during PO; this observation suggests that, despite an optimal DJ performance might be achieved only in specific conditions (falling heights, loads), the central nervous system seems to be able to regulate muscle behavior in order to effectively perform the required task also in challenging situations. Although the regulation of triceps-surae muscle-tendon unit in DJs has been extensively investigated, very few studies focused on sarcomeres behavior during the performance of this SSC movement (Kurokawa et al., 2003; Fukashiro et al., 2005, 2006). Sarcomeres represent muscle contractile units and are known to express different amounts of force depending on their length (Gordon et al., 1966; Walker and Schrodt, 1974); thus, understanding the time course of their responses during DJs is fundamental to gain further insights into muscle force-generating capacity. In vivo measurement of sarcomere length in humans has been so far been performed only in static positions and under highly controlled experimental conditions (Llewellyn et al., 2008; Sanchez et al., 2015). Instead, human sarcomere length estimation (achieved by dividing GM measured fascicle length for a fixed sarcomere number) in dynamic contractions provided an indirect measure of sarcomere operating range during squat jump, countermovement jump, and DJ (Fukashiro et al., 2005, 2006; Kurokawa et al., 2003). The results of these studies showed that sarcomeres operate in the ascending limb of their length-tension (L-T) relationship in all types of jumps, and particularly so in DJ. However, most of the available observations on sarcomere and muscle fascicle behavior were made in condition of constant gravity. Thus, in order to understand how sarcomere and muscle fascicle length are regulated in variable gravity conditions, we performed experiments in a parabolic flight, involving variable gravity levels, ranging from about zero-g to about double the Earth’s gravity (1 g; Waldvogel et al., 2021). Specifically, the aims of the present study were as follows: 1. To investigate the ability of the neuromuscular system in regulating fascicle length in response to conditions of variable gravity. 2. To estimate sarcomere operative length in the different DJ phases, in order to calculate its theoretical force production and its possible modulation in conditions of variable gravity. We hypothesized that muscle fascicles would be differentially regulated in different gravity conditions compared to 1 g, particularly in anticipation of landing and re-bouncing in unknown gravity levels. In addition, we hypothesized that sarcomeres would operate in the upper part of the ascending limb of their L-T relationship, possibly lengthening during the braking phase (especially in hyper-gravity) while operating quasi-isometrically in 1 g. KW - parabolic flight KW - drop jump KW - hypo-gravity KW - hyper-gravity KW - sarcomere operating length Y1 - 2021 U6 - https://doi.org/10.3389/fphys.2021.714655 SN - 1664-042X VL - 12 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Stäudle, Benjamin A1 - Seynnes, Olivier A1 - Laps, Guido A1 - Göll, Fabian A1 - Brüggemann, Gert-Peter A1 - Albracht, Kirsten T1 - Recovery from achilles tendon repair: a combination of Postsurgery Outcomes and Insufficient remodeling of muscle and tendon JF - Medicine & Science in Sports & Exercise N2 - Achilles tendon rupture (ATR) patients have persistent functional deficits in the triceps surae muscle–tendon unit (MTU). The complex remodeling of the MTU accompanying these deficits remains poorly understood. The purpose of the present study was to associate in vivo and in silico data to investigate the relations between changes inMTU properties and strength deficits inATR patients. Methods: Elevenmale subjects who had undergone surgical repair of complete unilateral ATR were examined 4.6 ± 2.0 (mean ± SD) yr after rupture. Gastrocnemius medialis (GM) tendon stiffness, morphology, and muscle architecture were determined using ultrasonography. The force–length relation of the plantar flexor muscles was assessed at five ankle joint angles. In addition, simulations (OpenSim) of the GM MTU force–length properties were performed with various iterations of MTU properties found between the unaffected and the affected side. Results: The affected side of the patients displayed a longer, larger, and stiffer GM tendon (13% ± 10%, 105% ± 28%, and 54% ± 24%, respectively) compared with the unaffected side. The GM muscle fascicles of the affected side were shorter (32% ± 12%) and with greater pennation angles (31% ± 26%). A mean deficit in plantarflexion moment of 31% ± 10% was measured. Simulations indicate that pairing an intact muscle with a longer tendon shifts the optimal angular range of peak force outside physiological angular ranges, whereas the shorter muscle fascicles and tendon stiffening seen in the affected side decrease this shift, albeit incompletely. Conclusions: These results suggest that the substantial changes in MTU properties found in ATR patients may partly result from compensatory remodeling, although this process appears insufficient to fully restore muscle function. KW - Tendon Rupture KW - Stiffness KW - Simulation KW - Muscle Force KW - Muscle Fascicle Y1 - 2021 U6 - https://doi.org/10.1249/MSS.0000000000002592 SN - 1530-0315 VL - 53 IS - 7 SP - 1356 EP - 1366 PB - American College of Sports Medicine CY - Philadelphia, Pa. ER - TY - CHAP A1 - Dreschers, Martin ED - Mönning, Rolf-Dieter T1 - §25 Arbeitsrechtliche Probleme im Rahmen der Betriebsfortführung T2 - Betriebsfortführung in Restrukturierung und Insolvenz Y1 - 2023 SN - 978-3-8145-2012-4 (print) SN - 978-3-8145-5888-2 (e-book) U6 - https://doi.org/https://doi.org/10.15375/9783814558882-028 SP - 947 EP - 988 PB - RWS Verlag CY - Köln ER - TY - CHAP A1 - Dreschers, Martin ED - Kübler, Bruno M. ED - Bork, Reinhard ED - Prütting, Hanns T1 - §18 Grenzüberschreitende Eigenverwaltung T2 - HRI II - Handbuch Restrukturierung in der Insolvenz Y1 - 2023 SN - 978-3-8145-2010-0 (print) SN - 978-3-8145-5871-4 (e-book) U6 - https://doi.org/10.15375/9783814558714-028 SP - 524 EP - 556 PB - RWS Verlag CY - Köln ER -