![]() Maximum voluntary contraction (MVC) is the most commonly used method for EMG normalization ( Hsu et al., 2006). Therefore, raw EMG signals need to be normalized for quantitative comparisons between different muscles and experimental sessions within and between subjects ( Burden, 2010). However, surface EMG relies on measurements of the electric activity of muscles through the skin, making it vulnerable to intrinsic and extrinsic factors such as motor unit properties, skin condition, and the placement of the electrode ( Hsu et al., 2006 Gaudet et al., 2016). To measure EMG signals in a non-invasive way, surface EMG is measured by attaching electrodes on the skin. The EMG analysis is widely applied to monitor and evaluate the motor performance of neurotypical individuals ( Brueckner et al., 2018 Singh et al., 2018) and the motor function and physiological condition of individuals with neurological deficits ( Cheung et al., 2012 Singh et al., 2018 Pan et al., 2021). The proposed rotating task can, therefore, be used in future motor learning, clinical diagnosis, and neurorehabilitation studies.Įlectromyography (EMG) describes muscle activation by measuring the electrical activity of muscles ( Wu et al., 2013). ![]() In addition, the extraction of synergies was as reliable and more stable than with the multidirection reaching task. Compared with normalization with MVC, joint torque normalization allowed reliable EMG normalization at low force levels. We assessed the reliability of joint torque normalization and synergy extraction in the rotating task in young neurotypical individuals. To obtain a reference EMG value for normalization without requiring maximal effort, we estimated a linear relationship between joint torques and muscle activations. To relax constraints on motor control precision, the target is widened and blurred. ![]() In this task, participants maintain a cursor controlled by the arm end-point force on a target that rotates at a constant angular velocity at a designated force level. In this study, we proposed a new isometric rotating task that does not require precise motor control or large forces. However, some participants with motor impairments cannot perform this task because it requires precise motor control. Second, synergy extraction in the upper limb is typically performed with a multidirection reaching task. In addition, the MVC is known to be highly unreliable, with widely different forces produced in repeated measures. However, some individuals with motor impairments have difficulties producing maximal effort in the MVC task. ![]() First, the necessary normalization of EMG signals is performed via maximum voluntary contraction (MVC), which requires maximal isometric force production in each muscle. However, current methods to extract muscle synergies in the upper limb suffer from two major issues. Muscle synergy analysis via surface electromyography (EMG) is useful to study muscle coordination in motor learning, clinical diagnosis, and neurorehabilitation.
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