Assuming a neural origin of muscle synergies, neural pathologies might alter the modular organization of the neuromuscular system. In MSP, the pathology-related degeneration of the neuromuscular system and the resulting deficits in the motor control efficiency can be considered as perturbations generated from internal, physiological sources ( Van Hooren et al., 2018). Earlier studies that investigated the modular organization of motor control during walking and running in the presence of perturbations showed that a common strategy of the human system is to increase control robustness (i.e., ability to cope with perturbations) ( Rabinovich and Abarbanel, 1998 Santuz et al., 2018a) to ensure safe locomotion ( Santuz et al., 2018a, 2020a). ![]() ![]() As a commonly accepted hypothesis, the CNS may manage to overcome the complexity of motor control by activating functionally related muscles in common patterns called muscle synergies ( Bernstein, 1967 Bizzi et al., 2008). ![]() Walking requires muscle coordination that controls the activation level and timing of multiple muscles ( Bernstein, 1967 Winter and Yack, 1987). In middle-aged MSP, persons with mobility impairments who do not use an assistive device have the highest risk of multiple falls ( Coote et al., 2014). More than 45% of falls in MSP have been attributed to external perturbations, such as slipping or tripping ( Matsuda et al., 2011). Compared with healthy age-matched controls, females with MS have three times higher risk of falls ( Cameron et al., 2011). Correspondingly, it is reported that more than 50% of MSP fall within an observation period of 6 months ( Cattaneo et al., 2002) or 1 year ( Finlayson and Peterson, 2010). In the MS disability spectrum, gait is perceived as the most important bodily function ( Heesen et al., 2008), and up to 85% of MSP report mobility impairments ( LaRocca, 2011). These include lower cadence and shorter step length resulting in a reduced walking speed ( Benedetti et al., 1999 Cameron and Wagner, 2011 Comber et al., 2017). About 75% of multiple sclerosis patients (MSP) experience clinically relevant walking disturbances ( Hobart et al., 2001 Kasser and Jacobs, 2014). The heterogeneous pathological and clinical presentation of MS typically includes deficits in the sensory ( Fling et al., 2014), motor ( Lambert et al., 2001 Thoumie et al., 2005 Kalron et al., 2011), and cognitive functions ( Wingerchuk et al., 2001). The chronic degenerative neurological disease of multiple sclerosis (MS) is inflammatory-mediated and results in the demyelination of the central nervous system (CNS) ( Bo et al., 2006 Popescu and Lucchinetti, 2012). This further increased the overlap of temporally-adjacent muscle synergies to provide sufficient robustness in motor control to accomplish the more demanding motor task while coping with pathology-related motor deficits during walking. Moreover, inclined walking revealed a demand-specific adjustment in the modular organization in MSP, resulting in an extra synergy compared with HP. ![]() Compared with HP, MSP demonstrated a widening in the time-dependent coefficients (motor primitives), as well as altered relative muscle contribution (motor modules), in certain synergies during level and inclined walking. We analyzed temporal gait parameters and muscle synergies from myoelectric signals of 13 ipsilateral leg muscles using non-negative matrix factorization. We hypothesized a widening of the time-dependent activation patterns (motor primitives) in MSP to increase the overlap of temporally-adjacent muscle synergies, especially during inclined walking, as a strategy to increase the robustness of motor control, thus compensating pathology-related deficits. Using the concept of muscle synergies, this study investigated the modular organization of motor control during level and inclined walking in MS patients (MSP) compared with healthy participants (HP) to identify the potential demand-specific adjustments in motor control in MSP. 2Berlin School of Movement Science, Humboldt-Universität zu Berlin, Berlin, Germanyįor patients with multiple sclerosis (MS), deficits in gait significantly reduce the quality of life.1Department of Training and Movement Sciences, Humboldt-Universität zu Berlin, Berlin, Germany.Lars Janshen 1 *, Alessandro Santuz 1,2 and Adamantios Arampatzis 1,2
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