11/13/2023 0 Comments Muscle synergy upper lowerConversely, evidence for muscle synergies due to purely mechanical constraints arises from computer simulations of the upper arm movement on a single plane (Inouye and Valero-Cuevas 2016) and cadaveric studies (Kutch and Valero-Cuevas 2012). 2018), and in the presence of CNS damage after stroke (Cheung et al. 2015), for postural control (Weiss and Flanders 2004), when extracted from the frequency domain (Frere 2017), irrespective of muscle fatigue (Ortega-Auriol et al. Similarly, human experiments are consistent with a neural source of muscle synergies during natural movements (d’Avella and Bizzi 2005 Safavynia and Ting 2012), affecting learning rates (Berger et al. 2009) models support a neural origin for muscle synergies. 2008 Hart and Giszter 2013) and computational (Neptune et al. Animal studies using electrical stimulation (Tresch and Bizzi 1999 Bizzi et al. Second, if muscle synergies arise from a control strategy, which neural structures are responsible for their emergence and modulation?Įvidence exists on both sides of the debate on whether synergies arise from neural structures. 2015) or are they merely an artefact of the task requirements and mathematical derivation (Kutch and Valero-Cuevas 2012). First, do muscle synergies represent a deliberate neurophysiological control strategy (Bizzi and Cheung 2013 McMorland et al. There are two ongoing debates relating to muscle synergies that we will address in this study. These low-dimensional networks can explain the behaviour of the complete set of muscles measured. Dimensionality reduction applied to EMG signals from multiple muscles shows the presence of lower dimensional networks, which we call muscle synergies. The musculoskeletal system is highly redundant, meaning many possible muscle activations can achieve the same single purposeful action. Our findings suggest cortical modulation of some of the synergies and the consequential existence of shared input between muscles within cortically modulated synergies. The presence of a shared input onto synergistic muscles within a synergy supports the idea of neurally derived muscle synergies that build human movement. In contrast, no significant CMC was found between the motor cortex area and synergy muscles. Interestingly, CSC alpha band was also significantly higher across muscles with higher weights within a synergy. Moreover, IMC alpha band was higher between muscles with higher weights within a synergy. A significant alpha band IMC was consistently present in all extracted synergies. Overall, we were able to identify four different synergies from the multidirectional task. A subsequent coherence task, consisting of generating forces isometrically in the synergy PDs, was used to assess the functional connectivity properties of synergies. A preliminary multidirectional task was used to identify synergy-preferred directions (PDs). Using non-negative matrix factorisation (NMF), we calculated muscle synergies from two different tasks. Cortical activity was recorded using 32-channel electroencephalography (EEG) and muscle activity using 16-channel electromyography (EMG). Fourteen healthy participants executed an isometric upper limb task in synergy-tuned directions. To elucidate the underlying physiological mechanisms of muscle synergies, we investigated long-range functional connectivity by cortico-muscular (CMC), intermuscular (IMC) and cortico-synergy (CSC) coherence.
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