Browsing by Author "Eskofier, Bjoern"
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- ItemOpen AccessLayer-wise Relevance Propagation and its Applications in Running Biomechanics(2022-07) Hoitz, Fabian Christoph; Nigg, Benno; Kuo, Arthur; Edwards, William Brent; Eskofier, Bjoern; Boyd, Steven; Jacob, Christian; Schollhorn, WolfgangBiomechanics has entered an era of ’big data’, where human locomotion data is generated rapidly and in large quantities. This poses new challenges because conventional analysis methods are ineffective in the presence of the myriad of interacting variables that describe human locomotion in contemporary datasets. Consequently, there is a need for novel, more appropriate analysis methods that can help direct attention towards the ’right’ variables. The purpose of this thesis was to apply layer-wise relevance propagation, a novel analysis method, within the context of human locomotion to isolate variables from large datasets that describe highly relevant movement characteristics that may inspire and direct future biomechanics research. Specifically, the challenges of separating unique / generic movement characteristics of runners, and forming functional groups based on runner-specific movement adaptations (induced by footwear interventions) were addressed. It was shown that (1) unique locomotion characteristics of novice runners were best described by variables belonging to the movement trajectories of the coronal and transverse plane during early stance within a dataset of lower extremity kinematics and ground reaction forces. Further, (2) kinematic variables that describe unique locomotion characteristics of highly trained runners were associated with movements of the spine and lower extremities during mid-stance and mid-swing, while generic locomotion characteristics were associated with sagittal plane movements of the spine during early and late stance within a dataset of full body kinematics. Finally, (3) groups of runners who adopt similar kinematic movement responses to a given footwear intervention were identified by clustering relevance patterns of subject-specific artificial neural network models. Based on the presented findings it was concluded that layer-wise relevance propagation is a promising analysis method that can help direct a researcher’s focus towards those variables that are most relevant for black-box machine learning models such as artificial neural networks. It, therefore, addresses many of the emerging challenges that biomechanics research faces during the contemporary era of ’big data’.
- ItemOpen AccessTask-Dependent Intermuscular Motor Unit Synchronization between Medial and Lateral Vastii Muscles during Dynamic and Isometric Squats(PLoS ONE, 2015-11-03) Mohr, Maurice; Nann, Marius; von Tschamer, Vinzenz; Eskofier, Bjoern; Nigg, Benno MaurusPurpose Motor unit activity is coordinated between many synergistic muscle pairs but the functional role of this coordination for the motor output is unclear. The purpose of this study was to investigate the short-term modality of coordinated motor unit activity–the synchronized discharge of individual motor units across muscles within time intervals of 5ms–for the Vastus Medialis (VM) and Lateralis (VL). Furthermore, we studied the task-dependency of intermuscular motor unit synchronization between VM and VL during static and dynamic squatting tasks to provide insight into its functional role. Methods Sixteen healthy male and female participants completed four tasks: Bipedal squats, single-leg squats, an isometric squat, and single-leg balance. Monopolar surface electromyography (EMG) was used to record motor unit activity of VM and VL. For each task, intermuscular motor unit synchronization was determined using a coherence analysis between the raw EMG signals of VM and VL and compared to a reference coherence calculated from two desynchronized EMG signals. The time shift between VM and VL EMG signals was estimated according to the slope of the coherence phase angle spectrum. Results For all tasks, except for singe-leg balance, coherence between 15–80Hz significantly exceeded the reference. The corresponding time shift between VM and VL was estimated as 4ms. Coherence between 30–60Hz was highest for the bipedal squat, followed by the single-leg squat and the isometric squat. Conclusion There is substantial short-term motor unit synchronization between VM and VL. Intermuscular motor unit synchronization is enhanced for contractions during dynamic activities, possibly to facilitate a more accurate control of the joint torque, and reduced during single-leg tasks that require balance control and thus, a more independent muscle function. It is proposed that the central nervous system scales the degree of intermuscular motor unit synchronization according to the requirements of the movement task at hand.