@article{BelavyAlbrachtBruggemannetal.2016,
  author    = {Belavy, Daniel L. and Albracht, Kirsten and Bruggemann, Gert-Peter and Vergroesen, Pieter-Paul A. and Dieen, Jaap H. van},
  title     = {Can exercise positively influence the intervertebral disc?},
  series = {Sports Medicine},
  volume    = {46},
  journal   = {Sports Medicine},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1179-2035},
  doi       = {10.1007/s40279-015-0444-2},
  pages     = {473 -- 485},
  year      = {2016},
  abstract  = {To better understand what kinds of sports and exercise could be beneficial for the intervertebral disc (IVD), we performed a review to synthesise the literature on IVD adaptation with loading and exercise. The state of the literature did not permit a systematic review; therefore, we performed a narrative review. The majority of the available data come from cell or whole-disc loading models and animal exercise models. However, some studies have examined the impact of specific sports on IVD degeneration in humans and acute exercise on disc size. Based on the data available in the literature, loading types that are likely beneficial to the IVD are dynamic, axial, at slow to moderate movement speeds, and of a magnitude experienced in walking and jogging. Static loading, torsional loading, flexion with compression, rapid loading, high-impact loading and explosive tasks are likely detrimental for the IVD. Reduced physical activity and disuse appear to be detrimental for the IVD. We also consider the impact of genetics and the likelihood of a 'critical period' for the effect of exercise in IVD development. The current review summarises the literature to increase awareness amongst exercise, rehabilitation and ergonomic professionals regarding IVD health and provides recommendations on future directions in research.},
  language  = {en}
}
@article{YangKriechbaumerAlbrachtetal.2015,
  author    = {Yang, Peng-Fei and Kriechbaumer, Andreas and Albracht, Kirsten and Sanno, Maximilian and Ganse, Bergita and Koy, Timmo and Shang, Peng and Br{\"u}ggemann, Gert-Peter and M{\"u}ller, Lars Peter and Rittweger, J{\"o}rn},
  title     = {On the relationship between tibia torsional deformation and regional muscle contractions in habitual human exercises in vivo},
  series = {Journal of Biomechanics},
  volume    = {48},
  journal   = {Journal of Biomechanics},
  number    = {3},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0021-9290},
  doi       = {10.1016/j.jbiomech.2014.12.031},
  pages     = {456 -- 464},
  year      = {2015},
  language  = {en}
}
@article{SeynnesBojsenMollerAlbrachtetal.2015,
  author    = {Seynnes, O. R. and Bojsen-Moller, J. and Albracht, Kirsten and Arndt, A. and Cronin, N. J. and Finni, T. and Magnusson, S. P.},
  title     = {Ultrasound-based testing of tendon mechanical properties: a critical evaluation},
  series = {Journal of Applied Physiology},
  volume    = {118},
  journal   = {Journal of Applied Physiology},
  number    = {2},
  issn      = {8750-7587},
  doi       = {10.1152/japplphysiol.00849.2014},
  pages     = {133 -- 141},
  year      = {2015},
  language  = {en}
}
@article{AlbrachtArampatzis2013,
  author    = {Albracht, Kirsten and Arampatzis, Adamantios},
  title     = {Exercise-induced changes in triceps surae tendon stiffness and muscle strength affect running economy in humans},
  series = {European Journal of Applied Physiology},
  volume    = {113},
  journal   = {European Journal of Applied Physiology},
  number    = {6},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1439-6327},
  doi       = {10.1007/s00421-012-2585-4},
  pages     = {1605 -- 1615},
  year      = {2013},
  language  = {en}
}
@article{KaramanidisAlbrachtBraunsteinetal.2011,
  author    = {Karamanidis, Kiros and Albracht, Kirsten and Braunstein, Bjoern and Catala, Maria Moreno and Goldmann, Jan-Peter and Br{\"u}ggemann, Gert-Peter},
  title     = {Lower leg musculoskeletal geometry and sprint performance},
  series = {Gait and Posture},
  volume    = {34},
  journal   = {Gait and Posture},
  number    = {1},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0966-6362},
  doi       = {10.1016/j.gaitpost.2011.03.009},
  pages     = {138 -- 141},
  year      = {2011},
  abstract  = {The purpose of this study was to investigate whether sprint performance is related to lower leg musculoskeletal geometry within a homogeneous group of highly trained 100-m sprinters. Using a cluster analysis, eighteen male sprinters were divided into two groups based on their personal best (fast: N = 11, 10.30 ± 0.07 s; slow: N = 7, 10.70 ± 0.08 s). Calf muscular fascicle arrangement and Achilles tendon moment arms (calculated by the gradient of tendon excursion versus ankle joint angle) were analyzed for each athlete using ultrasonography. Achilles tendon moment arm, foot and ankle skeletal geometry, fascicle arrangement as well as the ratio of fascicle length to Achilles tendon moment arm showed no significant (p > 0.05) correlation with sprint performance, nor were there any differences in the analyzed musculoskeletal parameters between the fast and slow sprinter group. Our findings provide evidence that differences in sprint ability in world-class athletes are not a result of differences in the geometrical design of the lower leg even when considering both skeletal and muscular components.},
  language  = {en}
}
@article{ArampatzisKaramanidisMademlietal.2009,
  author    = {Arampatzis, Adamantios and Karamanidis, Kiros and Mademli, Lida and Albracht, Kirsten},
  title     = {Plasticity of the human tendon to short and long-term mechanical loading},
  series = {Exercise and Sport Sciences Reviews},
  volume    = {37},
  journal   = {Exercise and Sport Sciences Reviews},
  number    = {2},
  issn      = {1538-3008},
  doi       = {10.1097/JES.0b013e31819c2e1d},
  pages     = {66 -- 72},
  year      = {2009},
  language  = {en}
}
@article{AlbrachtArampatzisBaltzopoulos2008,
  author    = {Albracht, Kirsten and Arampatzis, A. and Baltzopoulos, V.},
  title     = {Assessment of muscle volume and physiological cross-sectional area of the human triceps surae muscle in vivo},
  series = {Journal of Biomechanics},
  volume    = {41},
  journal   = {Journal of Biomechanics},
  issn      = {0021-9290},
  doi       = {10.1016/j.jbiomech.2008.04.020},
  pages     = {2211 -- 2218},
  year      = {2008},
  language  = {en}
}
@article{ArampatzisKaramanidisAlbracht2007,
  author    = {Arampatzis, Adamantios and Karamanidis, Kiros and Albracht, Kirsten},
  title     = {Adaptational responses of the human Achilles tendon by modulation of the applied cyclic strain magnitude},
  series = {Journal of Experimental Biology},
  volume    = {210},
  journal   = {Journal of Experimental Biology},
  number    = {15},
  issn      = {0022-0949},
  doi       = {10.1242/jeb.003814},
  pages     = {2743 -- 2753},
  year      = {2007},
  language  = {en}
}
@article{AlbrachtArampatzis2006,
  author    = {Albracht, Kirsten and Arampatzis, Adamantios},
  title     = {Influence of the mechanical properties of the muscle-tendon unit on force generation in runners with different running economy},
  series = {Biological Cybernetics},
  volume    = {95},
  journal   = {Biological Cybernetics},
  number    = {1},
  issn      = {1432-0770},
  doi       = {10.1007/s00422-006-0070-z},
  pages     = {87 -- 96},
  year      = {2006},
  language  = {en}
}
@incollection{AbelBoninAlbrachtetal.2015,
  author    = {Abel, Thomas and Bonin, Dominik and Albracht, Kirsten and Zeller, Sebastian and Burkett, Brendan},
  title     = {Kinematische Untersuchung der Kurbelbewegung im Handcycling: Entwicklung einer sportartspezifischen Methode},
  series = {Behindertensport 1951-2011 : Historische und aktuelle Aspekte im nationalen und internationalen Dialog},
  booktitle = {Behindertensport 1951-2011 : Historische und aktuelle Aspekte im nationalen und internationalen Dialog},
  publisher = {Meyer \& Meyer},
  address   = {Aachen},
  isbn      = {9783898997249},
  pages     = {82 -- 91},
  year      = {2015},
  language  = {de}
}
@inproceedings{KolditzAlbinAlbrachtetal.2016,
  author    = {Kolditz, Melanie and Albin, Thivaharan and Albracht, Kirsten and Br{\"u}ggemann, Gert-Peter and Abel, Dirk},
  title     = {Isokinematic leg extension training with an industrial robot},
  series = {6th IEEE RAS/EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob) June 26-29, 2016. UTown, Singapore},
  booktitle = {6th IEEE RAS/EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob) June 26-29, 2016. UTown, Singapore},
  doi       = {10.1109/BIOROB.2016.7523750},
  pages     = {950 -- 955},
  year      = {2016},
  language  = {de}
}
@inproceedings{GoldmannBraunsteinHeinrichetal.2015,
  author    = {Goldmann, Jan-Peter and Braunstein, Bjoern and Heinrich, Kai and Sanno, Maximilian and St{\"a}udle, Benjamin and Ritzdorf, Wolfgang and Br{\"u}ggemann, Gert-Peter and Albracht, Kirsten},
  title     = {Joint work of the take-off leg during elite high jump},
  series = {Proceedings of the 33th International Conference on Biomechanics in Sports (ISBS)},
  booktitle = {Proceedings of the 33th International Conference on Biomechanics in Sports (ISBS)},
  pages     = {3 S.},
  year      = {2015},
  language  = {en}
}
@inproceedings{DroszezSannoGoldmannetal.2016,
  author    = {Droszez, Anna and Sanno, Maximilian and Goldmann, Jan-Peter and Albracht, Kirsten and Br{\"u}ggemann, Gerd-Peter and Braunstein, Bjoern},
  title     = {Differences between take-off behavior during vertical jumps and two artistic elements},
  series = {34th International Conference of Biomechanics in Sport, Tsukuba, Japan, July 18-22, 2016},
  booktitle = {34th International Conference of Biomechanics in Sport, Tsukuba, Japan, July 18-22, 2016},
  issn      = {1999-4168},
  pages     = {577 -- 580},
  year      = {2016},
  language  = {en}
}
@inproceedings{AbelBoninAlbrachtetal.2010,
  author    = {Abel, Thomas and Bonin, Dominik and Albracht, Kirsten and Zeller, Sebastian and Br{\"u}ggemann, Gert-Peter and Burkett, Brendan and Str{\"u}der, Heiko K.},
  title     = {Kinematic profile of the elite handcyclist},
  series = {28th International Conference on Biomechanics in Sports, Marquette, Michigan, USA, July 19 - 23, 2010},
  booktitle = {28th International Conference on Biomechanics in Sports, Marquette, Michigan, USA, July 19 - 23, 2010},
  issn      = {1999-4168},
  pages     = {140 -- 141},
  year      = {2010},
  language  = {en}
}
@inproceedings{BraunsteinGoldmannAlbrachtetal.2013,
  author    = {Braunstein, Bjoern and Goldmann, Jan-Peter and Albracht, Kirsten and Sanno, Maximilian and Willwacher, Steffen and Heinrich, Kai and Herrmann, Volker and Br{\"u}ggemann, Gert-Peter},
  title     = {Joint specific contribution of mechanical power and work during acceleration and top speed in elite sprinters},
  series = {31 International Conference on Biomechanics in Sports, Taipei, Taiwan, July 07 - July 22, 2013},
  booktitle = {31 International Conference on Biomechanics in Sports, Taipei, Taiwan, July 07 - July 22, 2013},
  issn      = {1999-4168},
  year      = {2013},
  language  = {en}
}
@phdthesis{Albracht2010,
  author    = {Albracht, Kirsten},
  title     = {Influence of mechanical properties of the leg extensor muscletendon units on running economy},
  publisher = {Deutsche Sporthochschule K{\"o}ln},
  address   = {K{\"o}ln},
  pages     = {X, 1221 Bl. : graph. Darst.},
  year      = {2010},
  language  = {en}
}
@article{KolditzAlbinBrueggemannetal.2016,
  author    = {Kolditz, Melanie and Albin, Thivaharan and Br{\"u}ggemann, Gert-Peter and Abel, Dirk and Albracht, Kirsten},
  title     = {Robotergest{\"u}tztes System f{\"u}r ein verbessertes neuromuskul{\"a}res Aufbautraining der Beinstrecker},
  series = {at - Automatisierungstechnik},
  volume    = {64},
  journal   = {at - Automatisierungstechnik},
  number    = {11},
  publisher = {De Gruyter},
  address   = {Berlin},
  issn      = {2196-677X},
  doi       = {10.1515/auto-2016-0044},
  pages     = {905 -- 914},
  year      = {2016},
  abstract  = {Neuromuskul{\"a}res Aufbautraining der Beinstrecker ist ein wichtiger Bestandteil in der Rehabilitation und Pr{\"a}vention von Muskel-Skelett-Erkrankungen. Effektives Training erfordert hohe Muskelkr{\"a}fte, die gleichzeitig hohe Belastungen von bereits gesch{\"a}digten Strukturen bedeuten. Um trainingsinduzierte Sch{\"a}digungen zu vermeiden, m{\"u}ssen diese Kr{\"a}fte kontrolliert werden. Mit heutigen Trainingsger{\"a}ten k{\"o}nnen diese Ziele allerdings nicht erreicht werden. F{\"u}r ein sicheres und effektives Training sollen durch den Einsatz der Robotik, Sensorik, eines Regelkreises sowie Muskel-Skelett-Modellen Belastungen am Zielgewebe direkt berechnet und kontrolliert werden. Auf Basis zweier Vorstudien zu m{\"o}glichen Stellgr{\"o}ßen wird der Aufbau eines robotischen Systems vorgestellt, das sowohl f{\"u}r Forschungszwecke als auch zur Entwicklung neuartiger Trainingsger{\"a}te verwendet werden kann.},
  language  = {de}
}
@inproceedings{KolditzAlbrachtFasseetal.2015,
  author    = {Kolditz, Melanie and Albracht, Kirsten and Fasse, Alessandro and Albin, Thivaharan and Br{\"u}ggemann, Gert-Peter and Abel, Dirk},
  title     = {Evaluation of an industrial robot as a leg press training device},
  series = {XV International Symposium on Computer Simulation in Biomechanics July 9th - 11th 2015, Edinburgh, UK},
  booktitle = {XV International Symposium on Computer Simulation in Biomechanics July 9th - 11th 2015, Edinburgh, UK},
  pages     = {41 -- 42},
  year      = {2015},
  language  = {en}
}
@inproceedings{KolditzAlbinFasseetal.2015,
  author    = {Kolditz, Melanie and Albin, Thivaharan and Fasse, Alessandro and Br{\"u}ggemann, Gert-Peter and Abel, Dirk and Albracht, Kirsten},
  title     = {Simulative Analysis of Joint Loading During Leg Press Exercise for Control Applications},
  series = {IFAC-PapersOnLine},
  volume    = {48},
  booktitle = {IFAC-PapersOnLine},
  number    = {20},
  doi       = {10.1016/j.ifacol.2015.10.179},
  pages     = {435 -- 440},
  year      = {2015},
  language  = {en}
}
@article{ZangeSchopenAlbrachtetal.2017,
  author    = {Zange, Jochen and Schopen, Kathrin and Albracht, Kirsten and Gerlach, Darius A. and Frings-Meuthen, Petra and Maffiuletti, Nicola A. and Bloch, Wilhelm and Rittweger, J{\"o}rn},
  title     = {Using the Hephaistos orthotic device to study countermeasure effectiveness of neuromuscular electrical stimulation and dietary lupin protein supplementation, a randomised controlled trial},
  series = {Plos one},
  volume    = {12},
  journal   = {Plos one},
  number    = {2},
  doi       = {10.1371/journal.pone.0171562},
  year      = {2017},
  language  = {en}
}
@article{WerkhausenAlbrachtCroninetal.2017,
  author    = {Werkhausen, Amelie and Albracht, Kirsten and Cronin, Neil J. and Meier, Rahel and Mojsen-Moeller, Jens and Seynnes, Olivier R.},
  title     = {Modulation of muscle-tendon interaction in the human triceps surae during an energy dissipation task},
  series = {Journal of Experimental Biology},
  volume    = {220},
  journal   = {Journal of Experimental Biology},
  number    = {22},
  issn      = {0022-0949},
  doi       = {10.1242/jeb.164111},
  pages     = {4141 -- 4149},
  year      = {2017},
  language  = {en}
}
@article{RittwegerAlbrachtFluecketal.2018,
  author    = {Rittweger, J{\"o}rn and Albracht, Kirsten and Fl{\"u}ck, Martin and Ruoss, Severin and Brocca, Lorenza and Longa, Emanuela and Moriggi, Manuela and Seynnes, Olivier and Di Giulio, Irene and Tenori, Leonardo and Vignoli, Alessia and Capri, Miriam and Gelfi, Cecilia and Luchinat, Claudio and Franceschi, Claudio and Bottinelli, Roberto and Cerretelli, Paolo and Narici, Marco},
  title     = {Sarcolab pilot study into skeletal muscle's adaptation to longterm spaceflight},
  series = {npj Microgravity},
  volume    = {4},
  journal   = {npj Microgravity},
  number    = {1},
  publisher = {Nature Portfolio},
  issn      = {2373-8065},
  doi       = {10.1038/s41526-018-0052-1},
  pages     = {1 -- 9},
  year      = {2018},
  language  = {en}
}
@inproceedings{RichterBraunsteinStaeudleetal.2018,
  author    = {Richter, Charlotte and Braunstein, Bjoern and St{\"a}udle, Benjamin and Attias, Julia and Suess, Alexander and Weber, T. and Rittweger, Joern and Green, David A. and Albracht, Kirsten},
  title     = {In vivo fascicle length of the gastrocnemius muscle during walking in simulated martian gravity using two different body weight support devices},
  series = {23rd Annual Congress of the European College of Sport Science, Dublin, Irland},
  booktitle = {23rd Annual Congress of the European College of Sport Science, Dublin, Irland},
  year      = {2018},
  language  = {en}
}
@article{HeinkeKnickerAlbracht2018,
  author    = {Heinke, Lars N. and Knicker, Axel J. and Albracht, Kirsten},
  title     = {Evaluation of passively induced shoulder stretch reflex using an isokinetic dynamometer in male overhead athletes},
  series = {Isokinetics and Exercise Science},
  volume    = {26},
  journal   = {Isokinetics and Exercise Science},
  number    = {4},
  publisher = {IOS Press},
  address   = {Amsterdam},
  issn      = {1878-5913},
  doi       = {10.3233/IES-184111},
  pages     = {265 -- 274},
  year      = {2018},
  abstract  = {BACKGROUND: Muscle stretch reflexes are widely considered to beneficially influence joint stability and power generation in the lower limbs. While in the upper limbs and especially in the muscles surrounding the shoulder joint such evidence is lacking. OBJECTIVE: To quantify the electromyographical response in the muscles crossing the shoulder of specifically trained overhead athletes to an anterior perturbation force. METHODS: Twenty healthy male participants performed six sets of different external shoulder rotation stretches on an isokinetic dynamometer over a range of amplitudes and muscle pre-activation moment levels. All stretches were applied with a dynamometer acceleration of 10,000∘/s2 and a velocity of 150∘/s. Electromyographical response was measured via sEMG. RESULTS: Consistent reflexes were not observed in all experimental conditions. The reflex latencies revealed a significant muscle main effect (F (2,228) = 99.31, p< 0.001; η2= 0.466; f= 0.934) and a pre-activation main effect (F (1,228) = 142.21, p< 0.001; η2= 0.384; f= 1.418). The stretch reflex amplitude yielded a significant pre-activation main effect (F (1,222) = 470.373, p< 0.001; η2= 0.679; f= 1.454). CONCLUSION: Short latency muscle reflexes showed a tendency to an anterior to posterior muscle recruitment whereby the main internal rotator muscles of the shoulder revealed the most consistent results.},
  language  = {en}
}
@article{CapriMorsianiSantoroetal.2019,
  author    = {Capri, Miriam and Morsiani, Cristina and Santoro, Aurelia and Moriggi, Manuela and Conte, Maria and Martucci, Morena and Bellavista, Elena and Fabbri, Cristina and Giampieri, Enrico and Albracht, Kirsten and Fl{\"u}ck, Martin and Ruoss, Severin and Brocca, Lorenza and Canepari, Monica and Longa, Emanuela and Giulio, Irene Di and Bottinelli, Roberto and Cerretelli, Paolo and Salvioli, Stefano and Gelfi, Cecilia and Franceschi, Claudio and Narici, Marco and Rittweger, J{\"o}rn},
  title     = {Recovery from 6-month spaceflight at the International Space Station: muscle-related stress into a proinflammatory setting},
  series = {The FASEB journal : official publication of the Federation of American Societies for Experimental Biology},
  volume    = {33},
  journal   = {The FASEB journal : official publication of the Federation of American Societies for Experimental Biology},
  number    = {4},
  doi       = {10.1096/fj.201801625R},
  pages     = {5168 -- 5180},
  year      = {2019},
  language  = {en}
}
@article{QuittmannAbelAlbrachtetal.2019,
  author    = {Quittmann, Oliver J. and Abel, Thomas and Albracht, Kirsten and Str{\"u}der, Heiko K.},
  title     = {Reliability of muscular activation patterns and their alterations during incremental handcycling in able-bodied participants},
  series = {Sports Biomechanics},
  journal   = {Sports Biomechanics},
  number    = {Article in press},
  publisher = {Taylor \& Francis},
  address   = {London},
  issn      = {1752-6116},
  doi       = {10.1080/14763141.2019.1593496},
  year      = {2019},
  language  = {en}
}
@article{HeinkeKnickerAlbracht2020,
  author    = {Heinke, Lars N. and Knicker, Axel J. and Albracht, Kirsten},
  title     = {Increased shoulder muscle stretch reflex elicitability in supine subject posture},
  series = {Isokinetics and Exercise Science},
  volume    = {28},
  journal   = {Isokinetics and Exercise Science},
  number    = {2},
  publisher = {IOS Press},
  address   = {Amsterdam},
  issn      = {1878-5913},
  doi       = {10.3233/IES-192219},
  pages     = {139 -- 146},
  year      = {2020},
  abstract  = {BACKGROUND: Muscle stretch reflexes are widely used to examine neural muscle function. The knowledge of reflex response in muscles crossing the shoulder is limited. OBJECTIVE: To quantify reflex modulation according to various subject postures and different procedures of muscle pre-activation steering. METHODS: Thirteen healthy male participants performed two sets of external shoulder rotation stretches in various positions and with different procedures of muscle pre-activation steering on an isokinetic dynamometer over a range of two different pre-activation levels. All stretches were applied with a dynamometer acceleration of 104∘/s2 and a velocity of 150∘/s. Electromyographical response was measured via sEMG. RESULTS: Consistent reflexive response was observed in all tested muscles in all experimental conditions. The reflex elicitation rate revealed a significant muscle main effect (F (5,288) = 2.358, ρ= 0.040; η2= 0.039; f= 0.637) and a significant test condition main effect (F (1,288) = 5.884, ρ= 0.016; η2= 0.020; f= 0.143). Reflex latency revealed a significant muscle pre-activation level main effect (F (1,274) = 5.008, ρ= 0.026; η2= 0.018; f= 0.469). CONCLUSION: Muscular reflexive response was more consistent in the primary internal rotators of the shoulder. Supine posture in combination with visual feedback of muscle pre-activation level enhanced the reflex elicitation rate.},
  language  = {en}
}
@article{HeinkeKnickerAlbracht2021,
  author    = {Heinke, Lars N. and Knicker, Axel J. and Albracht, Kirsten},
  title     = {Test-retest reliability of the internal shoulder rotator muscles' stretch reflex in healthy men},
  series = {Journal of Electromyography and Kinesiology},
  volume    = {62},
  journal   = {Journal of Electromyography and Kinesiology},
  number    = {Article 102611},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1050-6411},
  doi       = {10.1016/j.jelekin.2021.102611},
  year      = {2021},
  abstract  = {Until now the reproducibility of the short latency stretch reflex of the internal rotator muscles of the glenohumeral joint has not been identified. Twenty-three healthy male participants performed three sets of external shoulder rotation stretches with various pre-activation levels on two different dates of measurement to assess test-retest reliability. All stretches were applied with a dynamometer acceleration of 104°/s2 and a velocity of 150°/s. Electromyographical response was measured via surface EMG. Reflex latencies showed a pre-activation effect (ƞ2 = 0,355). ICC ranged from 0,735 to 0,909 indicating an overall "good" relative reliability. SRD 95\% lay between ±7,0 to ±12,3 ms.. The reflex gain showed overall poor test-retest reproducibility. The chosen methodological approach presented a suitable test protocol for shoulder muscles stretch reflex latency evaluation. A proof-of-concept study to validate the presented methodical approach in shoulder involvement including subjects with clinically relevant conditions is recommended.},
  language  = {en}
}
@article{LiphardtFernandezGonzaloAlbrachtetal.2023,
  author    = {Liphardt, Anna-Maria and Fernandez-Gonzalo, Rodrigo and Albracht, Kirsten and Rittweger, J{\"o}rn and Vico, Laurence},
  title     = {Musculoskeletal research in human space flight - unmet needs for the success of crewed deep space exploration},
  series = {npj Microgravity},
  volume    = {9},
  journal   = {npj Microgravity},
  number    = {Article number: 9},
  publisher = {Springer Nature},
  issn      = {2373-8065},
  doi       = {10.1038/s41526-023-00258-3},
  pages     = {1 -- 9},
  year      = {2023},
  abstract  = {Based on the European Space Agency (ESA) Science in Space Environment (SciSpacE) community White Paper "Human Physiology - Musculoskeletal system", this perspective highlights unmet needs and suggests new avenues for future studies in musculoskeletal research to enable crewed exploration missions. The musculoskeletal system is essential for sustaining physical function and energy metabolism, and the maintenance of health during exploration missions, and consequently mission success, will be tightly linked to musculoskeletal function. Data collection from current space missions from pre-, during-, and post-flight periods would provide important information to understand and ultimately offset musculoskeletal alterations during long-term spaceflight. In addition, understanding the kinetics of the different components of the musculoskeletal system in parallel with a detailed description of the molecular mechanisms driving these alterations appears to be the best approach to address potential musculoskeletal problems that future exploratory-mission crew will face. These research efforts should be accompanied by technical advances in molecular and phenotypic monitoring tools to provide in-flight real-time feedback.},
  language  = {en}
}
@article{SchoenrockMuckeltHastermannetal.2024,
  author    = {Schoenrock, Britt and Muckelt, Paul E. and Hastermann, Maria and Albracht, Kirsten and MacGregor, Robert and Martin, David and Gunga, Hans-Christian and Salanova, Michele and Stokes, Maria J. and Warner, Martin B. and Blottner, Dieter},
  title     = {Muscle stiffness indicating mission crew health in space},
  series = {Scientific Reports},
  volume    = {14},
  journal   = {Scientific Reports},
  number    = {Article number: 4196},
  publisher = {Springer Nature},
  address   = {London},
  issn      = {2045-2322},
  doi       = {10.1038/s41598-024-54759-6},
  pages     = {13 Seiten},
  year      = {2024},
  abstract  = {Muscle function is compromised by gravitational unloading in space affecting overall musculoskeletal health. Astronauts perform daily exercise programmes to mitigate these effects but knowing which muscles to target would optimise effectiveness. Accurate inflight assessment to inform exercise programmes is critical due to lack of technologies suitable for spaceflight. Changes in mechanical properties indicate muscle health status and can be measured rapidly and non-invasively using novel technology. A hand-held MyotonPRO device enabled monitoring of muscle health for the first time in spaceflight (> 180 days). Greater/maintained stiffness indicated countermeasures were effective. Tissue stiffness was preserved in the majority of muscles (neck, shoulder, back, thigh) but Tibialis Anterior (foot lever muscle) stiffness decreased inflight vs. preflight (p < 0.0001; mean difference 149 N/m) in all 12 crewmembers. The calf muscles showed opposing effects, Gastrocnemius increasing in stiffness Soleus decreasing. Selective stiffness decrements indicate lack of preservation despite daily inflight countermeasures. This calls for more targeted exercises for lower leg muscles with vital roles as ankle joint stabilizers and in gait. Muscle stiffness is a digital biomarker for risk monitoring during future planetary explorations (Moon, Mars), for healthcare management in challenging environments or clinical disorders in people on Earth, to enable effective tailored exercise programmes.},
  language  = {en}
}
@article{QuittmannMeskemperAlbrachtetal.2020,
  author    = {Quittmann, Oliver J. and Meskemper, Joshua and Albracht, Kirsten and Abel, Thomas and Foitschik, Tina and Str{\"u}der, Heiko K.},
  title     = {Normalising surface EMG of ten upper-extremity muscles in handcycling: Manual resistance vs. sport-specific MVICs},
  series = {Journal of Electromyography and Kinesiology},
  volume    = {51},
  journal   = {Journal of Electromyography and Kinesiology},
  number    = {Article 102402},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1050-6411},
  doi       = {10.1016/j.jelekin.2020.102402},
  year      = {2020},
  abstract  = {Muscular activity in terms of surface electromyography (sEMG) is usually normalised to maximal voluntary isometric contractions (MVICs). This study aims to compare two different MVIC-modes in handcycling and examine the effect of moving average window-size. Twelve able-bodied male competitive triathletes performed ten MVICs against manual resistance and four sport-specific trials against fixed cranks. sEMG of ten muscles [M. trapezius (TD); M. pectoralis major (PM); M. deltoideus, Pars clavicularis (DA); M. deltoideus, Pars spinalis (DP); M. biceps brachii (BB); M. triceps brachii (TB); forearm flexors (FC); forearm extensors (EC); M. latissimus dorsi (LD) and M. rectus abdominis (RA)] was recorded and filtered using moving average window-sizes of 150, 200, 250 and 300 ms. Sport-specific MVICs were higher compared to manual resistance for TB, DA, DP and LD, whereas FC, TD, BB and RA demonstrated lower values. PM and EC demonstrated no significant difference between MVIC-modes. Moving average window-size had no effect on MVIC outcomes. MVIC-mode should be taken into account when normalised sEMG data are illustrated in handcycling. Sport-specific MVICs seem to be suitable for some muscles (TB, DA, DP and LD), but should be augmented by MVICs against manual/mechanical resistance for FC, TD, BB and RA.},
  language  = {en}
}
@article{QuittmannMeskemperAbeletal.2018,
  author    = {Quittmann, Oliver J. and Meskemper, Joshua and Abel, Thomas and Albracht, Kirsten and Foitschik, Tina and Rojas-Vega, Sandra and Str{\"u}der, Heiko K.},
  title     = {Kinematics and kinetics of handcycling propulsion at increasing workloads in able-bodied subjects},
  series = {Sports Engineereing},
  volume    = {21},
  journal   = {Sports Engineereing},
  number    = {21},
  publisher = {Springer Nature},
  address   = {Cham},
  issn      = {1460-2687},
  doi       = {10.1007/s12283-018-0269-y},
  pages     = {283 -- 294},
  year      = {2018},
  abstract  = {In Paralympic sports, biomechanical optimisation of movements and equipment seems to be promising for improving performance. In handcycling, information about the biomechanics of this sport is mainly provided by case studies. The aim of the current study was (1) to examine changes in handcycling propulsion kinematics and kinetics due to increasing workloads and (2) identify parameters that are associated with peak aerobic performance. Twelve non-disabled male competitive triathletes without handcycling experience voluntarily participated in the study. They performed an initial familiarisation protocol and incremental step test until exhaustion in a recumbent racing handcycle that was attached to an ergometer. During the incremental test, tangential crank kinetics, 3D joint kinematics, blood lactate and ratings of perceived exertion (local and global) were identified. As a performance criterion, the maximal power output during the step test (Pmax) was calculated and correlated with biomechanical parameters. For higher workloads, an increase in crank torque was observed that was even more pronounced in the pull phase than in the push phase. Furthermore, participants showed an increase in shoulder internal rotation and abduction and a decrease in elbow flexion and retroversion. These changes were negatively correlated with performance. At high workloads, it seems that power output is more limited by the transition from pull to push phase than at low workloads. It is suggested that successful athletes demonstrate small alterations of their kinematic profile due to increasing workloads. Future studies should replicate and expand the test spectrum (sprint and continuous loads) as well as use methods like surface electromyography (sEMG) with elite handcyclists.},
  language  = {de}
}
@article{QuittmannAbelAlbrachtetal.2020,
  author    = {Quittmann, Oliver J. and Abel, Thomas and Albracht, Kirsten and Meskemper, Joshua and Foitschik, Tina and Str{\"u}der, Heiko K.},
  title     = {Biomechanics of handcycling propulsion in a 30-min continuous load test at lactate threshold: Kinetics, kinematics, and muscular activity in able-bodied participants},
  series = {European Journal of Applied Physiology},
  journal   = {European Journal of Applied Physiology},
  number    = {120},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1439-6327},
  doi       = {10.1007/s00421-020-04373-x},
  pages     = {1403 -- 1415},
  year      = {2020},
  abstract  = {Purpose This study aims to investigate the biomechanics of handcycling during a continuous load trial (CLT) to assess the mechanisms underlying fatigue in upper body exercise. Methods Twelve able-bodied triathletes performed a 30-min CLT at a power output corresponding to lactate threshold in a racing recumbent handcycle mounted on a stationary ergometer. During the CLT, ratings of perceived exertion (RPE), tangential crank kinetics, 3D joint kinematics, and muscular activity of ten muscles of the upper extremity and trunk were examined using motion capturing and surface electromyography. Results During the CLT, spontaneously chosen cadence and RPE increased, whereas crank torque decreased. Rotational work was higher during the pull phase. Peripheral RPE was higher compared to central RPE. Joint range of motion decreased for elbow-flexion and radial-duction. Integrated EMG (iEMG) increased in the forearm flexors, forearm extensors, and M. deltoideus (Pars spinalis). An earlier onset of activation was found for M. deltoideus (Pars clavicularis), M. pectoralis major, M. rectus abdominis, M. biceps brachii, and the forearm flexors. Conclusion Fatigue-related alterations seem to apply analogously in handcycling and cycling. The most distal muscles are responsible for force transmission on the cranks and might thus suffer most from neuromuscular fatigue. The findings indicate that peripheral fatigue (at similar lactate values) is higher in handcycling compared to leg cycling, at least for inexperienced participants. An increase in cadence might delay peripheral fatigue by a reduced vascular occlusion. We assume that the gap between peripheral and central fatigue can be reduced by sport-specific endurance training.},
  language  = {en}
}
@inproceedings{PohleFroehlichDalitzRichteretal.2020,
  author    = {Pohle-Fr{\"o}hlich, Regina and Dalitz, Christoph and Richter, Charlotte and Hahnen, Tobias and St{\"a}udle, Benjamin and Albracht, Kirsten},
  title     = {Estimation of muscle fascicle orientation in ultrasonic images},
  series = {VISIGRAPP 2020 - Proceedings of the 15th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications, 5},
  booktitle = {VISIGRAPP 2020 - Proceedings of the 15th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications, 5},
  pages     = {79 -- 86},
  year      = {2020},
  language  = {en}
}
@article{WerkhausenCroninAlbrachtetal.2019,
  author    = {Werkhausen, Amelie and Cronin, Neil J. and Albracht, Kirsten and Bojsen-M{\o}ller, Jens and Seynnes, Olivier R.},
  title     = {Distinct muscle-tendon interaction during running at different speeds and in different loading conditions},
  series = {Journal of Applied Physiology},
  volume    = {127},
  journal   = {Journal of Applied Physiology},
  number    = {1},
  issn      = {1522-1601},
  doi       = {10.1152/japplphysiol.00710.2018},
  pages     = {246 -- 253},
  year      = {2019},
  language  = {en}
}
@article{WaldvogelRitzmannFreyleretal.2021,
  author    = {Waldvogel, Janice and Ritzmann, Ramona and Freyler, Kathrin and Helm, Michael and Monti, Elena and Albracht, Kirsten and St{\"a}udle, Benjamin and Gollhofer, Albert and Narici, Marco},
  title     = {The Anticipation of Gravity in Human Ballistic Movement},
  series = {Frontiers in Physiology},
  journal   = {Frontiers in Physiology},
  publisher = {Frontiers},
  address   = {Lausanne},
  issn      = {1664-042X},
  doi       = {10.3389/fphys.2021.614060},
  year      = {2021},
  abstract  = {Stretch-shortening type actions are characterized by lengthening of the pre-activated muscle-tendon unit (MTU) in the eccentric phase immediately followed by muscle shortening. Under 1 g, pre-activity before and muscle activity after ground contact, scale muscle stiffness, which is crucial for the recoil properties of the MTU in the subsequent push-off. This study aimed to examine the neuro-mechanical coupling of the stretch-shortening cycle in response to gravity levels ranging from 0.1 to 2 g. During parabolic flights, 17 subjects performed drop jumps while electromyography (EMG) of the lower limb muscles was combined with ultrasound images of the gastrocnemius medialis, 2D kinematics and kinetics to depict changes in energy management and performance. Neuro-mechanical coupling in 1 g was characterized by high magnitudes of pre-activity and eccentric muscle activity allowing an isometric muscle behavior during ground contact. EMG during pre-activity and the concentric phase systematically increased from 0.1 to 1 g. Below 1 g the EMG in the eccentric phase was diminished, leading to muscle lengthening and reduced MTU stretches. Kinetic energy at take-off and performance were decreased compared to 1 g. Above 1 g, reduced EMG in the eccentric phase was accompanied by large MTU and muscle stretch, increased joint flexion amplitudes, energy loss and reduced performance. The energy outcome function established by linear mixed model reveals that the central nervous system regulates the extensor muscles phase- and load-specifically. In conclusion, neuro-mechanical coupling appears to be optimized in 1 g. Below 1 g, the energy outcome is compromised by reduced muscle stiffness. Above 1 g, loading progressively induces muscle lengthening, thus facilitating energy dissipation.},
  language  = {en}
}
@article{MoratFaudeHanssenetal.2020,
  author    = {Morat, Mareike and Faude, Oliver and Hanssen, Henner and Ludyga, Sebastian and Zacher, Jonas and Eibl, Angi and Albracht, Kirsten and Donath, Lars},
  title     = {Agility Training to Integratively Promote Neuromuscular, Cognitive, Cardiovascular and Psychosocial Function in Healthy Older Adults: A Study Protocol of a One-Year Randomized-Controlled Trial},
  series = {International Journal of Environmental Research and Public Health},
  volume    = {17},
  journal   = {International Journal of Environmental Research and Public Health},
  number    = {6},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {1660-4601},
  doi       = {10.3390/ijerph17061853},
  pages     = {1 -- 14},
  year      = {2020},
  abstract  = {Exercise training effectively mitigates aging-induced health and fitness impairments. Traditional training recommendations for the elderly focus separately on relevant physiological fitness domains, such as balance, flexibility, strength and endurance. Thus, a more holistic and functional training framework is needed. The proposed agility training concept integratively tackles spatial orientation, stop and go, balance and strength. The presented protocol aims at introducing a two-armed, one-year randomized controlled trial, evaluating the effects of this concept on neuromuscular, cardiovascular, cognitive and psychosocial health outcomes in healthy older adults. Eighty-five participants were enrolled in this ongoing trial. Seventy-nine participants completed baseline testing and were block-randomized to the agility training group or the inactive control group. All participants undergo pre- and post-testing with interim assessment after six months. The intervention group currently receives supervised, group-based agility training twice a week over one year, with progressively demanding perceptual, cognitive and physical exercises. Knee extension strength, reactive balance, dual task gait speed and the Agility Challenge for the Elderly (ACE) serve as primary endpoints and neuromuscular, cognitive, cardiovascular, and psychosocial meassures serve as surrogate secondary outcomes. Our protocol promotes a comprehensive exercise training concept for older adults, that might facilitate stakeholders in health and exercise to stimulate relevant health outcomes without relying on excessively time-consuming physical activity recommendations.},
  language  = {en}
}
@article{RichterBraunsteinStaeudleetal.2021,
  author    = {Richter, Charlotte and Braunstein, Bjoern and Staeudle, Benjamin and Attias, Julia and Suess, Alexander and Weber, Tobias and Mileva, Katya N. and Rittweger, Joern and Green, David A. and Albracht, Kirsten},
  title     = {Contractile behavior of the gastrocnemius medialis muscle during running in simulated hypogravity},
  series = {npj Microgravity},
  volume    = {7},
  journal   = {npj Microgravity},
  number    = {Article number: 32},
  publisher = {Springer Nature},
  address   = {New York},
  issn      = {2373-8065},
  doi       = {10.1038/s41526-021-00155-7},
  pages     = {7 Seiten},
  year      = {2021},
  abstract  = {Vigorous exercise countermeasures in microgravity can largely attenuate muscular degeneration, albeit the extent of applied loading is key for the extent of muscle wasting. Running on the International Space Station is usually performed with maximum loads of 70\% body weight (0.7 g). However, it has not been investigated how the reduced musculoskeletal loading affects muscle and series elastic element dynamics, and thereby force and power generation. Therefore, this study examined the effects of running on the vertical treadmill facility, a ground-based analog, at simulated 0.7 g on gastrocnemius medialis contractile behavior. The results reveal that fascicle-series elastic element behavior differs between simulated hypogravity and 1 g running. Whilst shorter peak series elastic element lengths at simulated 0.7 g appear to be the result of lower muscular and gravitational forces acting on it, increased fascicle lengths and decreased velocities could not be anticipated, but may inform the development of optimized running training in hypogravity. However, whether the alterations in contractile behavior precipitate musculoskeletal degeneration warrants further study.},
  language  = {en}
}
@misc{BlottnerHastermannMuckeltetal.2019,
  author    = {Blottner, Dieter and Hastermann, Maria and Muckelt, Paul and Albracht, Kirsten and Schoenrock, Britt and Salanova, Michele and Warner, Martin and Gunga, Hans-Christian and Stokes, Maria},
  title     = {MYOTONES - Inflight muscle health status monitoring during long-duration space missions onboard the International Space Station: a single case study},
  series = {IAC Papers Archive},
  journal   = {IAC Papers Archive},
  publisher = {Pergamon},
  address   = {Oxford},
  issn      = {00741795},
  pages     = {2 Seiten},
  year      = {2019},
  abstract  = {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},
  language  = {en}
}
@article{WerkhausenCroninAlbrachtetal.2019,
  author    = {Werkhausen, Amelie and Cronin, Neil J. and Albracht, Kirsten and Paulsen, G{\o}ran and Larsen, Askild V. and Bojsen-M{\o}ller, Jens and Seynnes, Olivier R.},
  title     = {Training-induced increase in Achilles tendon stiffness affects tendon strain pattern during running},
  series = {PeerJ},
  journal   = {PeerJ},
  publisher = {Peer},
  address   = {London},
  issn      = {21678359},
  doi       = {10.7717/peerj.6764},
  pages     = {18 Seiten},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{KetelhutGoellBraunsteinetal.2018,
  author    = {Ketelhut, Maike and G{\"o}ll, Fabian and Braunstein, Bj{\"o}rn and Albracht, Kirsten and Abel, Dirk},
  title     = {Comparison of different training algorithms for the leg extension training with an industrial robot},
  series = {Current Directions in Biomedical Engineering},
  volume    = {4},
  journal   = {Current Directions in Biomedical Engineering},
  number    = {1},
  publisher = {De Gruyter},
  address   = {Berlin},
  issn      = {2364-5504},
  doi       = {10.1515/cdbme-2018-0005},
  pages     = {17 -- 20},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{WerkhausenAlbrachtCroninetal.2018,
  author    = {Werkhausen, Amelie and Albracht, Kirsten and Cronin, Neil J and Paulsen, G{\o}ran and Bojsen-M{\o}ller, Jens and Seynnes, Olivier R},
  title     = {Effect of training-induced changes in achilles tendon stiffness on muscle-tendon behavior during landing},
  series = {Frontiers in physiology},
  journal   = {Frontiers in physiology},
  number    = {9},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-042X},
  doi       = {10.3389/fphys.2018.00794},
  pages     = {11 Seiten},
  year      = {2018},
  abstract  = {During rapid deceleration of the body, tendons buffer part of the elongation of the muscle-tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle-tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarflexion force, peak Achilles tendon strain and stiffness were measured during isometric contractions, using a combination of dynamometry, ultrasound and kinematics data. Additionally, testing included a step-landing task, during which joint mechanics and lengths of gastrocnemius and soleus fascicles, Achilles tendon, and MTU were determined using synchronized ultrasound, kinematics and kinetics data collection. After training, plantarflexion strength and Achilles tendon stiffness increased (15 and 18\%, respectively), and tendon strain during landing remained similar. Likewise, lengthening and negative work produced by the gastrocnemius MTU did not change detectably. However, in the training group, gastrocnemius fascicle length was offset (8\%) to a longer length at touch down and, surprisingly, fascicle lengthening and velocity were reduced by 27 and 21\%, respectively. These changes were not observed for soleus fascicles when accounting for variation in task execution between tests. These results indicate that a training-induced increase in tendon stiffness does not noticeably affect the buffering action of the tendon when the MTU is rapidly stretched. Reductions in gastrocnemius fascicle lengthening and lengthening velocity during landing occurred independently from tendon strain. Future studies are required to provide insight into the mechanisms underpinning these observations and their influence on energy dissipation.},
  language  = {en}
}
@article{YangKriechbaumerAlbrachtetal.2014,
  author    = {Yang, Peng-Fei and Kriechbaumer, Andreas and Albracht, Kirsten and Sanno, Maximilian and Ganse, Bergita and Koy, Timmo and Shang, Peng and br{\"u}ggemann, Gert-Peter and M{\"u}ller, Lars Peter and Rittweger, J{\"o}rn},
  title     = {A novel optical approach for assessing in vivo bone segment deformation and its application in muscle-bone relationship studies in humans},
  series = {Journal of Orthopaedic Translation},
  volume    = {2},
  journal   = {Journal of Orthopaedic Translation},
  number    = {4},
  publisher = {Elsevier},
  address   = {Singapore},
  issn      = {2214-0328},
  doi       = {10.1016/j.jot.2014.07.078},
  pages     = {238 -- 238},
  year      = {2014},
  language  = {en}
}
@techreport{AlbrachtRitzmannKrameretal.2017,
  author    = {Albracht, Kirsten and Ritzmann, Ramona and Kramer, Andreas and Meskemper, Joshua and St{\"a}udle, Benjamin and K{\"u}mmel, Jacob and Freyler, Katrin and Felsenberg, Dieter and Gruber, Marksu and Gollhofer, Albert and Belavy, Daniel},
  title     = {Vorhaben: Muskelkraftgenerierungsf{\"a}higkeit in Mikrogravitation},
  publisher = {Deutsche Sporthochschule K{\"o}ln},
  address   = {Kl{\"o}n},
  doi       = {10.2314/KXP:1670327353},
  pages     = {23 Seiten},
  year      = {2017},
  language  = {de}
}
@article{StaeudleSeynnesLapsetal.2022,
  author    = {St{\"a}udle, Benjamin and Seynnes, Olivier and Laps, Guido and Br{\"u}ggemann, Gert-Peter and Albracht, Kirsten},
  title     = {Altered gastrocnemius contractile behavior in former achilles tendon rupture patients during walking},
  series = {Frontiers in Physiology},
  volume    = {13},
  journal   = {Frontiers in Physiology},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-042X},
  doi       = {10.3389/fphys.2022.792576},
  pages     = {12 Seiten},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{RichterBraunsteinStaeudleetal.2021,
  author    = {Richter, Charlotte and Braunstein, Bjoern and St{\"a}udle, Benjamin and Attias, Julia and Suess, Alexander and Weber, Tobias and Mileva, Katja N. and Rittweger, Joern and Green, David A. and Albracht, Kirsten},
  title     = {Gastrocnemius medialis contractile behavior is preserved during 30\% body weight supported gait training},
  series = {Frontiers in Sports and Active Living},
  volume    = {2021},
  journal   = {Frontiers in Sports and Active Living},
  number    = {2},
  publisher = {Frontiers},
  address   = {Lausanne},
  issn      = {2624-9367},
  doi       = {10.3389/fspor.2020.614559},
  pages     = {Artikel 614559},
  year      = {2021},
  abstract  = {Rehabilitative body weight supported gait training aims at restoring walking function as a key element in activities of daily living. Studies demonstrated reductions in muscle and joint forces, while kinematic gait patterns appear to be preserved with up to 30\% weight support. However, the influence of body weight support on muscle architecture, with respect to fascicle and series elastic element behavior is unknown, despite this having potential clinical implications for gait retraining. Eight males (31.9 ± 4.7 years) walked at 75\% of the speed at which they typically transition to running, with 0\% and 30\% body weight support on a lower-body positive pressure treadmill. Gastrocnemius medialis fascicle lengths and pennation angles were measured via ultrasonography. Additionally, joint kinematics were analyzed to determine gastrocnemius medialis muscle-tendon unit lengths, consisting of the muscle's contractile and series elastic elements. Series elastic element length was assessed using a muscle-tendon unit model. Depending on whether data were normally distributed, a paired t-test or Wilcoxon signed rank test was performed to determine if body weight supported walking had any effects on joint kinematics and fascicle-series elastic element behavior. Walking with 30\% body weight support had no statistically significant effect on joint kinematics and peak series elastic element length. Furthermore, at the time when peak series elastic element length was achieved, and on average across the entire stance phase, muscle-tendon unit length, fascicle length, pennation angle, and fascicle velocity were unchanged with respect to body weight support. In accordance with unchanged gait kinematics, preservation of fascicle-series elastic element behavior was observed during walking with 30\% body weight support, which suggests transferability of gait patterns to subsequent unsupported walking.},
  language  = {en}
}
@article{QuittmannAbelAlbrachtetal.2022,
  author    = {Quittmann, Oliver J. and Abel, Thomas and Albracht, Kirsten and Str{\"u}der, Heiko K.},
  title     = {Biomechanics of all-out handcycling exercise: kinetics, kinematics and muscular activity of a 15-s sprint test in able-bodied participants},
  series = {Sports Biomechanics},
  volume    = {21},
  journal   = {Sports Biomechanics},
  number    = {10},
  publisher = {Taylor \& Francis},
  address   = {London},
  issn      = {1752-6116 (Onlineausgabe)},
  doi       = {10.1080/14763141.2020.1745266},
  pages     = {1200 -- 1223},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{RichterBraunsteinStaeudleetal.2021,
  author    = {Richter, Charlotte and Braunstein, Bj{\"o}rn and St{\"a}udle, Benjamin and Attias, Julia and S{\"u}ss, Alexander and Weber, Tobias and Mileva, Katya N. and Rittweger, J{\"o}rn and Green, David A. and Albracht, Kirsten},
  title     = {Gastrocnemius medialis contractile behavior during running differs between simulated Lunar and Martian gravities},
  series = {Scientific reports},
  volume    = {11},
  journal   = {Scientific reports},
  number    = {Article number: 22555},
  publisher = {Springer Nature},
  address   = {London},
  issn      = {2045-2322},
  doi       = {10.1038/s41598-021-00527-9},
  pages     = {13 Seiten},
  year      = {2021},
  abstract  = {The international partnership of space agencies has agreed to proceed forward to the Moon sustainably. Activities on the Lunar surface (0.16 g) will allow crewmembers to advance the exploration skills needed when expanding human presence to Mars (0.38 g). Whilst data from actual hypogravity activities are limited to the Apollo missions, simulation studies have indicated that ground reaction forces, mechanical work, muscle activation, and joint angles decrease with declining gravity level. However, these alterations in locomotion biomechanics do not necessarily scale to the gravity level, the reduction in gastrocnemius medialis activation even appears to level off around 0.2 g, while muscle activation pattern remains similar. Thus, it is difficult to predict whether gastrocnemius medialis contractile behavior during running on Moon will basically be the same as on Mars. Therefore, this study investigated lower limb joint kinematics and gastrocnemius medialis behavior during running at 1 g, simulated Martian gravity, and simulated Lunar gravity on the vertical treadmill facility. The results indicate that hypogravity-induced alterations in joint kinematics and contractile behavior still persist between simulated running on the Moon and Mars. This contrasts with the concept of a ceiling effect and should be carefully considered when evaluating exercise prescriptions and the transferability of locomotion practiced in Lunar gravity to Martian gravity.},
  language  = {en}
}
@article{WerkhausenWillwacherAlbracht2021,
  author    = {Werkhausen, Amelie and Willwacher, Steffen and Albracht, Kirsten},
  title     = {Medial gastrocnemius muscle fascicles shorten throughout stance during sprint acceleration},
  series = {Scandinavian Journal of Medicine \& Science in Sports},
  volume    = {31},
  journal   = {Scandinavian Journal of Medicine \& Science in Sports},
  number    = {7},
  publisher = {Wiley-Blackwell},
  address   = {Oxford},
  issn      = {0905-7188 (Druckausgabe)},
  doi       = {10.1111/sms.13956},
  pages     = {1471 -- 1480},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@article{MontiWaldvogelRitzmannetal.2021,
  author    = {Monti, Elena and Waldvogel, Janice and Ritzmann, Ramona and Freyler, Kathrin and Albracht, Kirsten and Helm, Michael and De Cesare, Niccol{\`o} and Pavan, Piero and Reggiani, Carlo and Gollhofer, Albert and Narici, Marco Vincenzo},
  title     = {Muscle in variable gravity: "I do not know where I am, but I know what to do"},
  series = {Frontiers in Physiology},
  volume    = {12},
  journal   = {Frontiers in Physiology},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-042X},
  doi       = {10.3389/fphys.2021.714655},
  pages     = {19 Seiten},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@article{StaeudleSeynnesLapsetal.2021,
  author    = {St{\"a}udle, Benjamin and Seynnes, Olivier and Laps, Guido and G{\"o}ll, Fabian and Br{\"u}ggemann, Gert-Peter and Albracht, Kirsten},
  title     = {Recovery from achilles tendon repair: a combination of Postsurgery Outcomes and Insufficient remodeling of muscle and tendon},
  series = {Medicine \& Science in Sports \& Exercise},
  volume    = {53},
  journal   = {Medicine \& Science in Sports \& Exercise},
  number    = {7},
  publisher = {American College of Sports Medicine},
  address   = {Philadelphia, Pa.},
  issn      = {1530-0315},
  doi       = {10.1249/MSS.0000000000002592},
  pages     = {1356 -- 1366},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@article{KetelhutBrueggeGoelletal.2020,
  author    = {Ketelhut, Maike and Br{\"u}gge, G. M. and G{\"o}ll, Fabian and Braunstein, Bjoern and Albracht, Kirsten and Abel, Dirk},
  title     = {Adaptive iterative learning control of an industrial robot during neuromuscular training},
  series = {IFAC PapersOnLine},
  volume    = {53},
  journal   = {IFAC PapersOnLine},
  number    = {2},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2405-8963},
  doi       = {10.1016/j.ifacol.2020.12.741},
  pages     = {16468 -- 16475},
  year      = {2020},
  abstract  = {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.},
  language  = {en}
}
@article{KetelhutKolditzGoelletal.2019,
  author    = {Ketelhut, Maike and Kolditz, Melanie and G{\"o}ll, Fabian and Braunstein, Bjoern and Albracht, Kirsten and Abel, Dirk},
  title     = {Admittance control of an industrial robot during resistance training},
  series = {IFAC-PapersOnLine},
  volume    = {52},
  journal   = {IFAC-PapersOnLine},
  number    = {19},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2405-8963},
  doi       = {10.1016/j.ifacol.2019.12.102},
  pages     = {223 -- 228},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@inproceedings{KetelhutGoellBraunsteinetal.2019,
  author    = {Ketelhut, Maike and G{\"o}ll, Fabian and Braunstein, Bjoern and Albracht, Kirsten and Abel, Dirk},
  title     = {Iterative learning control of an industrial robot for neuromuscular training},
  series = {2019 IEEE Conference on Control Technology and Applications},
  booktitle = {2019 IEEE Conference on Control Technology and Applications},
  publisher = {IEEE},
  address   = {New York},
  isbn      = {978-1-7281-2767-5 (ePub)},
  doi       = {10.1109/CCTA.2019.8920659},
  pages     = {7 Seiten},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{HeieisBoeckerD'Angeloetal.2023,
  author    = {Heieis, Jule and B{\"o}cker, Jonas and D'Angelo, Olfa and Mittag, Uwe and Albracht, Kirsten and Sch{\"o}nau, Eckhard and Meyer, Andreas and Voigtmann, Thomas and Rittweger, J{\"o}rn},
  title     = {Curvature of gastrocnemius muscle fascicles as function of muscle-tendon complex length and contraction in humans},
  series = {Physiological Reports},
  volume    = {11},
  journal   = {Physiological Reports},
  number    = {11},
  publisher = {Wiley},
  issn      = {2051-817X},
  doi       = {10.14814/phy2.15739},
  pages     = {e15739, Seite 1-11},
  year      = {2023},
  abstract  = {It has been shown that muscle fascicle curvature increases with increasing contraction level and decreasing muscle-tendon complex length. The analyses were done with limited examination windows concerning contraction level, muscle-tendon complex length, and/or intramuscular position of ultrasound imaging. With this study we aimed to investigate the correlation between fascicle arching and contraction, muscle-tendon complex length and their associated architectural parameters in gastrocnemius muscles to develop hypotheses concerning the fundamental mechanism of fascicle curving. Twelve participants were tested in five different positions (90°/105°*, 90°/90°*, 135°/90°*, 170°/90°*, and 170°/75°*; *knee/ankle angle). They performed isometric contractions at four different contraction levels (5\%, 25\%, 50\%, and 75\% of maximum voluntary contraction) in each position. Panoramic ultrasound images of gastrocnemius muscles were collected at rest and during constant contraction. Aponeuroses and fascicles were tracked in all ultrasound images and the parameters fascicle curvature, muscle-tendon complex strain, contraction level, pennation angle, fascicle length, fascicle strain, intramuscular position, sex and age group were analyzed by linear mixed effect models. Mean fascicle curvature of the medial gastrocnemius increased with contraction level (+5 m-1 from 0\% to 100\%; p = 0.006). Muscle-tendon complex length had no significant impact on mean fascicle curvature. Mean pennation angle (2.2 m-1 per 10°; p < 0.001), inverse mean fascicle length (20 m-1 per cm-1; p = 0.003), and mean fascicle strain (-0.07 m-1 per +10\%; p = 0.004) correlated with mean fascicle curvature. Evidence has also been found for intermuscular, intramuscular, and sex-specific intramuscular differences of fascicle curving. Pennation angle and the inverse fascicle length show the highest predictive capacities for fascicle curving. Due to the strong correlations between pennation angle and fascicle curvature and the intramuscular pattern of curving we suggest for future studies to examine correlations between fascicle curvature and intramuscular fluid pressure.},
  language  = {en}
}
@article{WaldvogelFreylerHelmetal.2023,
  author    = {Waldvogel, Janice and Freyler, Kathrin and Helm, Michael and Monti, Elena and St{\"a}udle, Benjamin and Gollhofer, Albert and Narici, Marco V. and Ritzmann, Ramona and Albracht, Kirsten},
  title     = {Changes in gravity affect neuromuscular control, biomechanics, and muscle-tendon mechanics in energy storage and dissipation tasks},
  series = {Journal of Applied Physiology},
  volume    = {134},
  journal   = {Journal of Applied Physiology},
  number    = {1},
  publisher = {American Physiological Society},
  address   = {Bethesda, Md.},
  issn      = {1522-1601 (Onlineausgabe)},
  doi       = {10.1152/japplphysiol.00279.2022},
  pages     = {190 -- 202},
  year      = {2023},
  abstract  = {This study evaluates neuromechanical control and muscle-tendon interaction during energy storage and dissipation tasks in hypergravity. During parabolic flights, while 17 subjects performed drop jumps (DJs) and drop landings (DLs), electromyography (EMG) of the lower limb muscles was combined with in vivo fascicle dynamics of the gastrocnemius medialis, two-dimensional (2D) kinematics, and kinetics to measure and analyze changes in energy management. Comparisons were made between movement modalities executed in hypergravity (1.8 G) and gravity on ground (1 G). In 1.8 G, ankle dorsiflexion, knee joint flexion, and vertical center of mass (COM) displacement are lower in DJs than in DLs; within each movement modality, joint flexion amplitudes and COM displacement demonstrate higher values in 1.8 G than in 1 G. Concomitantly, negative peak ankle joint power, vertical ground reaction forces, and leg stiffness are similar between both movement modalities (1.8 G). In DJs, EMG activity in 1.8 G is lower during the COM deceleration phase than in 1 G, thus impairing quasi-isometric fascicle behavior. In DLs, EMG activity before and during the COM deceleration phase is higher, and fascicles are stretched less in 1.8 G than in 1 G. Compared with the situation in 1 G, highly task-specific neuromuscular activity is diminished in 1.8 G, resulting in fascicle lengthening in both movement modalities. Specifically, in DJs, a high magnitude of neuromuscular activity is impaired, resulting in altered energy storage. In contrast, in DLs, linear stiffening of the system due to higher neuromuscular activity combined with lower fascicle stretch enhances the buffering function of the tendon, and thus the capacity to safely dissipate energy.},
  language  = {en}
}
@techreport{GoellBraunsteinAlbracht2021,
  author    = {G{\"o}ll, Fabian and Braunstein, Bj{\"o}rn and Albracht, Kirsten},
  title     = {Lernende roboterassistierte Systeme f{\"u}r das neuromuskul{\"a}re Training - RoSylerNT; Teilvorhaben: Entwicklung eines neuromuskuloskelettalen Modells als Basis f{\"u}r die Interaktionsf{\"a}higkeiten autonomer Assistenzsysteme},
  publisher = {Deutsche Sporthochschule K{\"o}ln},
  address   = {K{\"o}ln},
  doi       = {10.2314/KXP:1855318741},
  pages     = {14 Seiten},
  year      = {2021},
  language  = {de}
}
@article{AggeloussisGiannakouAlbrachtetal.2010,
  author    = {Aggeloussis, Nickos and Giannakou, Erasmia and Albracht, Kirsten and Arampatzis, Adamantios},
  title     = {Reproducibility of fascicle length and pennation angle of gastrocnemius medialis in human gait in vivo},
  series = {Gait and Posture},
  volume    = {31},
  journal   = {Gait and Posture},
  number    = {1},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0966-6362},
  doi       = {10.1016/j.gaitpost.2009.08.249},
  pages     = {73 -- 77},
  year      = {2010},
  abstract  = {The purpose of the current study was to examine the reproducibility of fascicle length and pennation angle of gastrocnemius medialis while human walking. To the best of our knowledge, this is the first study of the reproducibility of fascicle length and pennation angle of gastrocnemius medialis in vivo during human gait. Twelve males performed 10 gait trials on a treadmill, in 2 separate days. B-mode ultrasonography, with the ultrasound probe firmly adjusted in the transverse and frontal planes using a special cast, was used to measure the fascicle length and the pennation angle of the gastrocnemius medialis (GM). A Vicon 624 system with three cameras operating at 120 Hz was also used to record the ankle and knee joint angles. The results showed that measurements of fascicle length and pennation angle showed high reproducibility during the gait cycle, both within the same day and between different days. Moreover, the root mean square differences between the repeated waveforms of both variables were very small, compared with their ranges (fascicle length: RMS = ∼3 mm, range: 38-63 mm; pennation angle: RMS = ∼1.5°, range: 22-32°). However, their reproducibility was lower compared to the joint angles. It was found that representative data have to be derived by a wide number of gait trials (fascicle length ∼six trials, pennation angle more than 10 trials), to assure the reliability of the fascicle length and pennation angle in human gait.},
  language  = {en}
}
@article{ArampatzisPeperBierbaumetal.2010,
  author    = {Arampatzis, Adamantios and Peper, Andreas and Bierbaum, Stefanie and Albracht, Kirsten},
  title     = {Plasticity of human Achilles tendon mechanical and morphological properties in response to cyclic strain},
  series = {Journal of Biomechanics},
  volume    = {43},
  journal   = {Journal of Biomechanics},
  number    = {16},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0021-9290},
  doi       = {10.1016/j.jbiomech.2010.08.014},
  pages     = {3073 -- 3079},
  year      = {2010},
  abstract  = {The purpose of the current study in combination with our previous published data (Arampatzis et al., 2007) was to examine the effects of a controlled modulation of strain magnitude and strain frequency applied to the Achilles tendon on the plasticity of tendon mechanical and morphological properties. Eleven male adults (23.9±2.2 yr) participated in the study. The participants exercised one leg at low magnitude tendon strain (2.97±0.47\%), and the other leg at high tendon strain magnitude (4.72±1.08\%) of similar frequency (0.5 Hz, 1 s loading, 1 s relaxation) and exercise volume (integral of the plantar flexion moment over time) for 14 weeks, 4 days per week, 5 sets per session. The exercise volume was similar to the intervention of our earlier study (0.17 Hz frequency; 3 s loading, 3 s relaxation) allowing a direct comparison of the results. Before and after the intervention ankle joint moment has been measured by a dynamometer, tendon-aponeurosis elongation by ultrasound and cross-sectional area of the Achilles tendon by magnet resonance images (MRI). We found a decrease in strain at a given tendon force, an increase in tendon-aponeurosis stiffness and tendon elastic modulus of the Achilles tendon only in the leg exercised at high strain magnitude. The cross-sectional area (CSA) of the Achilles tendon did not show any statistically significant (P>0.05) differences to the pre-exercise values in both legs. The results indicate a superior improvement in tendon properties (stiffness, elastic modulus and CSA) at the low frequency (0.17 Hz) compared to the high strain frequency (0.5 Hz) protocol. These findings provide evidence that the strain magnitude applied to the Achilles tendon should exceed the value, which occurs during habitual activities to trigger adaptational effects and that higher tendon strain duration per contraction leads to superior tendon adaptational responses.},
  language  = {en}
}
@article{HerssensCowburnAlbrachtetal.2022,
  author    = {Herssens, Nolan and Cowburn, James and Albracht, Kirsten and Braunstein, Bjoern and Cazzola, Dario and Colyer, Steffi and Minetti, Alberto E. and Pavei, Gaspare and Rittweger, J{\"o}rn and Weber, Tobias and Green, David A.},
  title     = {Movement in low gravity environments (MoLo) programme - the MoLo-L.O.O.P. study protocol},
  series = {PLOS ONE / Public Library of Science},
  volume    = {17},
  journal   = {PLOS ONE / Public Library of Science},
  number    = {11},
  editor    = {Cattaneo, Luigi},
  publisher = {Plos},
  address   = {San Francisco},
  issn      = {1932-6203},
  doi       = {10.1371/journal.pone.0278051},
  pages     = {e0278051},
  year      = {2022},
  abstract  = {Exposure to prolonged periods in microgravity is associated with deconditioning of the musculoskeletal system due to chronic changes in mechanical stimulation. Given astronauts will operate on the Lunar surface for extended periods of time, it is critical to quantify both external (e.g., ground reaction forces) and internal (e.g., joint reaction forces) loads of relevant movements performed during Lunar missions. Such knowledge is key to predict musculoskeletal deconditioning and determine appropriate exercise countermeasures associated with extended exposure to hypogravity.},
  language  = {en}
}
@article{KolditzAlbinAbeletal.2016,
  author    = {Kolditz, Melanie and Albin, Thivaharan and Abel, Dirk and Fasse, Alessandro and Br{\"u}ggemann, Gert-Peter and Albracht, Kirsten},
  title     = {Evaluation of foot position and orientation as manipulated variables to control external knee adduction moments in leg extension training},
  series = {Computer methods and programs in biomedicine},
  volume    = {171},
  journal   = {Computer methods and programs in biomedicine},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0169-2607},
  doi       = {10.1016/j.cmpb.2016.09.005},
  pages     = {81 -- 86},
  year      = {2016},
  abstract  = {Background and Objective Effective leg extension training at a leg press requires high forces, which need to be controlled to avoid training-induced damage. In order to avoid high external knee adduction moments, which are one reason for unphysiological loadings on knee joint structures, both training movements and the whole reaction force vector need to be observed. In this study, the applicability of lateral and medial changes in foot orientation and position as possible manipulated variables to control external knee adduction moments is investigated. As secondary parameters both the medio-lateral position of the center of pressure and the frontal-plane orientation of the reaction force vector are analyzed. Methods Knee adduction moments are estimated using a dynamic model of the musculoskeletal system together with the measured reaction force vector and the motion of the subject by solving the inverse kinematic and dynamic problem. Six different foot conditions with varying positions and orientations of the foot in a static leg press are evaluated and compared to a neutral foot position. Results Both lateral and medial wedges under the foot and medial and lateral shifts of the foot can influence external knee adduction moments in the presented study with six healthy subjects. Different effects are observed with the varying conditions: the pose of the leg is changed and the direction and center of pressure of the reaction force vector is influenced. Each effect results in a different direction or center of pressure of the reaction force vector. Conclusions The results allow the conclusion that foot position and orientation can be used as manipulated variables in a control loop to actively control knee adduction moments in leg extension training.},
  language  = {en}
}