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Vielemeyer J, Schreff L, Hochstein S, Müller R. Virtual pivot point: Always experimentally observed in human walking? PLoS One 2023; 18:e0292874. [PMID: 37831656 PMCID: PMC10575527 DOI: 10.1371/journal.pone.0292874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 10/01/2023] [Indexed: 10/15/2023] Open
Abstract
A main challenge in human walking is maintaining stability. One strategy to balance the whole body dynamically is to direct the ground reaction forces toward a point above the center of mass, called virtual pivot point (VPP). This strategy could be observed in various experimental studies for human and animal gait. A VPP was also observed when VPP input variables like center of mass or ground reaction forces were perturbed. In this study, the kinetic and kinematic consequences of a center of pressure manipulation and the influence on the VPP are investigated. Thus, eleven participants walked with manipulated center of pressure (i.e. barefoot, backwards, with a rigid sole, with stilts, and in handstand compared to shoe walking). In all conditions a VPP could be observed, only one participant showed no VPP in handstand walking. The vertical VPP position only differs between shoe walking and rigid sole walking, there are no significant differences between the conditions in the horizontal VPP position and the spread around the VPP. However, it is conceivable that for more severe gait changes, walking without VPP could be observed. To further analyze this issue, the authors provide a VPP calculation tool for testing data regarding the existence of the VPP.
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Affiliation(s)
- Johanna Vielemeyer
- Institute of Sport Sciences, Friedrich-Schiller-University Jena, Jena, Germany
- GaitLab, Klinikum Bayreuth GmbH, Bayreuth, Germany
| | - Lucas Schreff
- GaitLab, Klinikum Bayreuth GmbH, Bayreuth, Germany
- Bayreuth Center of Sport Science, University of Bayreuth, Bayreuth, Germany
| | - Stefan Hochstein
- Institute of Sport Sciences, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Roy Müller
- GaitLab, Klinikum Bayreuth GmbH, Bayreuth, Germany
- Bayreuth Center of Sport Science, University of Bayreuth, Bayreuth, Germany
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Vielemeyer J, Staufenberg NS, Schreff L, Rixen D, Müller R. Walking like a robot: do the ground reaction forces still intersect near one point when humans imitate a humanoid robot? R Soc Open Sci 2023; 10:221473. [PMID: 37266041 PMCID: PMC10230186 DOI: 10.1098/rsos.221473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Accepted: 05/04/2023] [Indexed: 06/03/2023]
Abstract
Bipedal walking while keeping the upper body upright is a complex task. One strategy to cope with this task is to direct the ground reaction forces toward a point above the centre of mass of the whole body, called virtual pivot point (VPP). This behaviour could be observed in various experimental studies for human and animal walking, but not for the humanoid robot LOLA. The question arose whether humans still show a VPP when walking like LOLA. For this purpose, ten participants imitated LOLA in speed, posture, and mass distribution (LOLA-like walking). It could be found that humans do not differ from LOLA in spatio-temporal parameters for the LOLA-like walking, in contrast to upright walking with preferred speed. Eight of the participants show a VPP in all conditions (R2 > 0.90 ± 0.09), while two participants had no VPP for LOLA-like walking (R2 < 0.52). In the latter case, the horizontal ground reaction forces are not balanced around zero in the single support phase, which is presumably the key variable for the absence of the VPP.
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Affiliation(s)
- Johanna Vielemeyer
- Institute of Sport Sciences, Friedrich-Schiller-University Jena, 07737 Jena, Germany
- GaitLab, Klinikum Bayreuth GmbH, 95445 Bayreuth, Germany
| | - Nora-Sophie Staufenberg
- Munich Institute of Robotics and Machine Intelligence, Technical University Munich, 85748 Garching, Germany
| | - Lucas Schreff
- GaitLab, Klinikum Bayreuth GmbH, 95445 Bayreuth, Germany
- Bayreuth Center of Sport Science, University of Bayreuth, 95447 Bayreuth, Germany
| | - Daniel Rixen
- Munich Institute of Robotics and Machine Intelligence, Technical University Munich, 85748 Garching, Germany
| | - Roy Müller
- GaitLab, Klinikum Bayreuth GmbH, 95445 Bayreuth, Germany
- Bayreuth Center of Sport Science, University of Bayreuth, 95447 Bayreuth, Germany
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Schreff L, Haeufle DFB, Badri-Spröwitz A, Vielemeyer J, Müller R. 'Virtual pivot point' in human walking: Always experimentally observed but simulations suggest it may not be necessary for stability. J Biomech 2023; 153:111605. [PMID: 37148700 DOI: 10.1016/j.jbiomech.2023.111605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Revised: 04/21/2023] [Accepted: 04/25/2023] [Indexed: 05/08/2023]
Abstract
The intersection of ground reaction forces near a point above the center of mass has been observed in computer simulation models and human walking experiments. Observed so ubiquitously, the intersection point (IP) is commonly assumed to provide postural stability for bipedal walking. In this study, we challenge this assumption by questioning if walking without an IP is possible. Deriving gaits with a neuromuscular reflex model through multi-stage optimization, we found stable walking patterns that show no signs of the IP-typical intersection of ground reaction forces. The non-IP gaits found are stable and successfully rejected step-down perturbations, which indicates that an IP is not necessary for locomotion robustness or postural stability. A collision-based analysis shows that non-IP gaits feature center of mass (CoM) dynamics with vectors of the CoM velocity and ground reaction force increasingly opposing each other, indicating an increased mechanical cost of transport. Although our computer simulation results have yet to be confirmed through experimental studies, they already indicate that the role of the IP in postural stability should be further investigated. Moreover, our observations on the CoM dynamics and gait efficiency suggest that the IP may have an alternative or additional function that should be considered.
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Affiliation(s)
- Lucas Schreff
- Department of Neurology/Department of Orthopedic Surgery, Klinikum Bayreuth GmbH, Bayreuth, Germany; Bayreuth Center of Sport Science, University of Bayreuth, Bayreuth, Germany.
| | - Daniel F B Haeufle
- Hertie Institute for Clinical Brain Research and Center for Integrative Neuroscience, Tübingen, Germany; Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Germany
| | - Alexander Badri-Spröwitz
- Dynamic Locomotion Group, Max Planck Institute for Intelligent Systems, Stuttgart, Germany; Department of Mechanical Engineering, KU Leuven, Belgium
| | - Johanna Vielemeyer
- Department of Neurology/Department of Orthopedic Surgery, Klinikum Bayreuth GmbH, Bayreuth, Germany; Institute of Sport Sciences, Friedrich Schiller University Jena, Jena, Germany
| | - Roy Müller
- Department of Neurology/Department of Orthopedic Surgery, Klinikum Bayreuth GmbH, Bayreuth, Germany; Bayreuth Center of Sport Science, University of Bayreuth, Bayreuth, Germany
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Vielemeyer J, Müller R, Staufenberg NS, Renjewski D, Abel R. Ground reaction forces intersect above the center of mass in single support, but not in double support of human walking. J Biomech 2021; 120:110387. [PMID: 33798969 DOI: 10.1016/j.jbiomech.2021.110387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 03/05/2021] [Accepted: 03/09/2021] [Indexed: 10/21/2022]
Abstract
There are various simplifying models that describe balance strategies of human walking. In one model it is assumed that ground reaction forces are directed to a point (virtual pivot point) above the center of mass during the whole stride. This was observed in several experimental investigations, but only for the single support phase. It has not yet been concretely considered whether humans use the same stabilization strategy during the double support phase. For analyzing this, nine volunteers walked at self-selected speed while kinetic and kinematic data were measured. We found that in contrast to the single support phase, where the virtual pivot point was significantly above the center of mass, in the double support phase of human walking the ground reaction forces point around the center of mass with a small spread (R2=92.5%). The different heights of the virtual pivot point in the different support phases could be caused by the vertical movement of the center of mass, which has a lower amplitude in the double support phase. This is also reflected in the ground reaction forces, whereby the ratio of the horizontal and vertical ground reaction forces can explain the height of the virtual pivot point. In the double support phase the ratio is shifted in favor of the horizontal component compared to the single support phase, because of a shorter contact time and a delayed braking impulse. Thus, the whole body seems to rotate around the center of mass, which presumably minimizes required energy.
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Affiliation(s)
- Johanna Vielemeyer
- GaitLab, Klinikum Bayreuth GmbH, Hohe Warte 8, 95445 Bayreuth, Germany; Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany.
| | - Roy Müller
- GaitLab, Klinikum Bayreuth GmbH, Hohe Warte 8, 95445 Bayreuth, Germany; Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany
| | - Nora-Sophie Staufenberg
- Institute of Applied Mechanics, Technical University of Munich, Boltzmannstr. 15, 85748 Garching, Germany
| | - Daniel Renjewski
- Institute of Applied Mechanics, Technical University of Munich, Boltzmannstr. 15, 85748 Garching, Germany
| | - Rainer Abel
- Department of Ortopedic Surgery, Klinikum Bayreuth GmbH, Hohe Warte 8, 95445 Bayreuth, Germany
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Drama Ö, Vielemeyer J, Badri-Spröwitz A, Müller R. Postural stability in human running with step-down perturbations: an experimental and numerical study. R Soc Open Sci 2020; 7:200570. [PMID: 33391782 PMCID: PMC7735328 DOI: 10.1098/rsos.200570] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 10/23/2020] [Indexed: 05/23/2023]
Abstract
Postural stability is one of the most crucial elements in bipedal locomotion. Bipeds are dynamically unstable and need to maintain their trunk upright against the rotations induced by the ground reaction forces (GRFs), especially when running. Gait studies report that the GRF vectors focus around a virtual point above the centre of mass (VPA), while the trunk moves forward in pitch axis during the stance phase of human running. However, a recent simulation study suggests that a virtual point below the centre of mass (VPB) might be present in human running, because a VPA yields backward trunk rotation during the stance phase. In this work, we perform a gait analysis to investigate the existence and location of the VP in human running at 5 m s-1, and support our findings numerically using the spring-loaded inverted pendulum model with a trunk. We extend our analysis to include perturbations in terrain height (visible and camouflaged), and investigate the response of the VP mechanism to step-down perturbations both experimentally and numerically. Our experimental results show that the human running gait displays a VPB of ≈-30 cm and a forward trunk motion during the stance phase. The camouflaged step-down perturbations affect the location of the VPB. Our simulation results suggest that the VPB is able to encounter the step-down perturbations and bring the system back to its initial equilibrium state.
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Affiliation(s)
- Özge Drama
- Dynamic Locomotion Group, Max Planck Institute for Intelligent Systems, Stuttgart, Germany
| | - Johanna Vielemeyer
- Department of Neurology/Orthopedic Surgery, Klinikum Bayreuth GmbH, Germany
- Department of Motion Science, Friedrich Schiller University-Jena, Jena, Germany
| | | | - Roy Müller
- Department of Neurology/Orthopedic Surgery, Klinikum Bayreuth GmbH, Germany
- Department of Motion Science, Friedrich Schiller University-Jena, Jena, Germany
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AminiAghdam S, Vielemeyer J, Abel R, Müller R. Reactive gait and postural adjustments following the first exposures to (un)expected stepdown. J Biomech 2019; 94:130-137. [PMID: 31399205 DOI: 10.1016/j.jbiomech.2019.07.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/04/2019] [Accepted: 07/21/2019] [Indexed: 10/26/2022]
Abstract
This study evaluated the reactive biomechanical strategies associated with both upper- and lower-body (lead and trail limbs) following the first exposures to (un)expected stepdown at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Eleven healthy adults completed 34 trails per walking velocity over an 8-m, custom-built track with two forceplates embedded in its center. For the expected stepdown, the track was lowered by 0-, -10- and -20-cm from the site of the second forceplate, whereas the unexpected stepdown was created by camouflaging the second forceplate (-10-cm). Two-way repeated-measurement ANOVAs detected no velocity-related effects of stepdown on kinematic and kinetic parameters during lead limb stance-phase, and on the trail limb stepping kinematics. However, analyses of significant interactions revealed greater peak flexion angles across the trunk and the trail limb joints (hip, knee and ankle) in unexpected versus expected stepdown conditions at a faster walking velocity. The -10-cm unexpected stepdown (main effect) had a greater influence on locomotor behavior compared to expected conditions due mainly to the absence of predictive adjustments, reflected by a significant decrease in peak knee flexion, contact time and vertical impulse during stance-phase. Walking faster (main effect) was associated with an increase in hip peak flexion and net anteroposterior impulse, and a decrease in contact time and vertical impulse during stepdown. The trail limb, in response, swung forward faster, generating a larger and faster recovery step. However, such reactive stepping following unexpected stepdown was yet a sparse compensation for an unstable body configuration, assessed by significantly smaller step width and anteroposterior margin-of-stability at foot-contact in the first-recovery-step compared with expected conditions. These findings depict the impact of the expectedness of stepdown onset on modulation of global dynamic postural control for a successful accommodation of (un)expected surface elevation changes in young, healthy adults.
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Affiliation(s)
- Soran AminiAghdam
- Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Department of Neurology, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Sport and Exercise Science Research Centre, School of Applied Sciences, London South Bank University, London, United Kingdom.
| | - Johanna Vielemeyer
- Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Department of Neurology, Bayreuth Hospital, Bayreuth, Bavaria, Germany
| | - Rainer Abel
- Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany
| | - Roy Müller
- Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany; Department of Neurology, Bayreuth Hospital, Bayreuth, Bavaria, Germany
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AminiAghdam S, Griessbach E, Vielemeyer J, Müller R. Dynamic postural control during (in)visible curb descent at fast versus comfortable walking velocity. Gait Posture 2019; 71:38-43. [PMID: 31005853 DOI: 10.1016/j.gaitpost.2019.04.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 03/27/2019] [Accepted: 04/11/2019] [Indexed: 02/02/2023]
Abstract
BACKGROUND The unexpectedness of ground-contact onset in stepping down due, e.g., to a camouflaged curb during ongoing gait may impose potential postural control challenges, which might be deteriorated when walking faster. RESEARCH QUESTION Does traversing camouflaged versus visible curbs, at a fast walking velocity, induce more unstable body configurations, assessed by a smaller anteroposterior "margin of stability" (MoS)? METHODS For twelve healthy participants, we investigated MoS at foot touchdown in descent and in the first recovery step from 0- and 10-cm visible and camouflaged curbs at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Three-way (velocity, elevation, visibility) and two-way (velocity, visibility) repeated-measurement ANOVAs were performed to determine their interactions on MoS, and its determining parameters, during curb negotiation and recovery step, respectively. RESULTS No greater postural instability when traversing a camouflaged versus visible curb at a faster walking velocity during curb descent, indicated by no three-way interaction effects on MoS. However, an elevation-by-visibility interaction showed a dramatic decrease of MoS when descending a 10-cm camouflaged versus visible curb. This was because of a farther anterior displacement of center-of-mass with a larger velocity. Furthermore, the walking velocity was independently associated with a smaller MoS and a more anteriorly-shifted center-of-mass with a higher velocity. In the recovery step, participants demonstrated a reduced stability of the body configuration when walking faster or recovering from a camouflaged than from a visible curb. The mentioned result implies that the potential to increase the base-of-support to compensate for an increased center-of-mass velocity, induced by an increased walking velocity, is limited. SIGNIFICANCE Despite a significant independent main effect of walking velocity, a more unstable postural control observed during traversing of camouflaged versus visible curbs was found not to be walking velocity-related in young individuals. Further research, including elderly may shed more light on these results.
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Affiliation(s)
- Soran AminiAghdam
- Department of Motion Science, Institute of Sport Science, Friedrich-Schiller-University Jena, Jena, Thuringia, Germany; Department of Neurology/Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany.
| | - Eric Griessbach
- Department for the Psychology of Human Movement and Sport, Institute of Sport Science, Friedrich-Schiller-University Jena, Thuringia, Germany
| | - Johanna Vielemeyer
- Department of Neurology/Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany
| | - Roy Müller
- Department of Motion Science, Institute of Sport Science, Friedrich-Schiller-University Jena, Jena, Thuringia, Germany; Department of Neurology/Department of Orthopedic Surgery, Bayreuth Hospital, Bayreuth, Bavaria, Germany
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Vielemeyer J, Grießbach E, Müller R. Ground reaction forces intersect above the center of mass even when walking down visible and camouflaged curbs. J Exp Biol 2019; 222:jeb.204305. [DOI: 10.1242/jeb.204305] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 06/24/2019] [Indexed: 11/20/2022]
Abstract
A main objective in bipedal walking is controlling the whole body to stay upright. One strategy that promotes this objective is to direct the ground reaction forces (GRF) to a point above the center of mass (COM). In humans such force patterns can be observed for unperturbed walking, but it is not known if the same strategy is used when humans walk across a change in walkway height. In this study, eleven volunteers stepped down off a visible (0, 10, and 20 cm) and a camouflaged (0 or 10 cm) curb while walking at two different speeds (1.2±0.1 m s−1 and 1.7±0.1 m s−1). The results showed that in all conditions the GRF pointed predominantly above the COM. Vectors directed from the center of pressure (COP) to the intersection point (IP) closely fitted the measured GRF direction not only in visible conditions (R2>97.5%), but also in camouflaged curb negotiation (R2>89.8%). Additional analysis of variables included in the calculation of the IP location showed considerable differences for the camouflaged curb negotiation: Compared to level walking, the COP shifted posterior relative to the COM and the vertical GRF were higher in the beginning and lower in later parts of the stance phase of the perturbed contact. The results suggest that IP behavior can be observed for both visible and camouflaged curb negotiation. For further regulation of the whole body angle the asymmetrical vertical GRF could counteract the effect of a posterior shifted step.
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Affiliation(s)
| | | | - Roy Müller
- Friedrich-Schiller-University Jena, Germany
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Müller R, Rode C, Aminiaghdam S, Vielemeyer J, Blickhan R. Force direction patterns promote whole body stability even in hip-flexed walking, but not upper body stability in human upright walking. Proc Math Phys Eng Sci 2017; 473:20170404. [PMID: 29225495 DOI: 10.1098/rspa.2017.0404] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 10/12/2017] [Indexed: 11/12/2022] Open
Abstract
Directing the ground reaction forces to a focal point above the centre of mass of the whole body promotes whole body stability in human and animal gaits similar to a physical pendulum. Here we show that this is the case in human hip-flexed walking as well. For all upper body orientations (upright, 25°, 50°, maximum), the focal point was well above the centre of mass of the whole body, suggesting its general relevance for walking. Deviations of the forces' lines of action from the focal point increased with upper body inclination from 25 to 43 mm root mean square deviation (RMSD). With respect to the upper body in upright gait, the resulting force also passed near a focal point (17 mm RMSD between the net forces' lines of action and focal point), but this point was 18 cm below its centre of mass. While this behaviour mimics an unstable inverted pendulum, it leads to resulting torques of alternating sign in accordance with periodic upper body motion and probably provides for low metabolic cost of upright gait by keeping hip torques small. Stabilization of the upper body is a consequence of other mechanisms, e.g. hip reflexes or muscle preflexes.
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Affiliation(s)
- Roy Müller
- Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07740 Jena, Germany.,Department of Neurology/Department of Orthopaedic Surgery, Klinikum Bayreuth GmbH, Hohe Warte 8, 95445 Bayreuth, Germany
| | - Christian Rode
- Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07740 Jena, Germany
| | - Soran Aminiaghdam
- Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07740 Jena, Germany
| | - Johanna Vielemeyer
- Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07740 Jena, Germany
| | - Reinhard Blickhan
- Motionscience, Institute of Sport Sciences, Friedrich Schiller University Jena, Seidelstraße 20, 07740 Jena, Germany
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