How Many Muscles? Optimal Muscles Set Search for Optimizing Myocontrol Performance

Abstract

In myo-control, for computational and setup constraints, the measurement of a high number of muscles is not always possible: the choice of the muscle set to use in a myo-control strategy depends on the desired application scope and a search for a reduced muscle set, tailored to the application, has never been performed. The identification of such set would involve finding the minimum set of muscles whose difference in terms of intention detection performance is not statistically significant when compared to the original set. Also, given the intrinsic sensitivity of muscle synergies to variations of EMG signals matrix, the reduced set should not alter synergies that come from the initial input, since they provide physiological information on motor coordination. The advantages of such reduced set, in a rehabilitation context, would be the reduction of the inputs processing time, the reduction of the setup bulk and a higher sensitivity to synergy changes after training, which can eventually lead to modifications of the ongoing therapy. In this work, the existence of a minimum muscle set, called optimal set, for an upper-limb myoelectric application, that preserves performance of motor activity prediction and the physiological meaning of synergies, has been investigated. Analyzing isometric contractions during planar reaching tasks, two types of optimal muscle sets were examined: a subject-specific one and a global one. The former relies on the subject-specific movement strategy, the latter is composed by the most recurrent muscles among subjects specific optimal sets and shared by all the subjects. Results confirmed that the muscle set can be reduced to achieve comparable hand force estimation performances. Moreover, two types of muscle synergies namely “Pose-Shared” (extracted from a single multi-arm-poses dataset) and “Pose-Related” (clustering pose-specific synergies), extracted from the global optimal muscle set, have shown a significant similarity with full-set related ones meaning a high consistency of the motor primitives. Pearson correlation coefficients assessed the similarity of each synergy. The discovering of dominant muscles by means of the optimization of both muscle set size and force estimation error may reveal a clue on the link between synergistic patterns and the force task.

Muscle synergies in joystick manipulation

“…In joystick isometric dual degree-of-freedom torque tasks, the torque history affects coordination patterns, and the motor system controls different orthogonal combinations of torque oscillations and constant torques employing a single oscillating muscle synergy (Ettema et al, 2005b). In joystick isometric force feedback tasks (Camardella et al, 2021), divided muscle synergies into groups with specific motor strategies and the same global groups for all subjects, confirming that muscle sets can be reduced to achieve comparable hand force estimation performances. For isotonic contraction tasks, the literature shows that the CNS can perceive the relationship between stiffness level and the size of the endpoint deviation (Gribble et al, 2003;Osu et al, 2004) and alter the mechanical impedance of the limb through the simultaneous activation of antagonist muscle groups (Feldman and Levin, 1995;Burdet et al, 2001), revealing the critical role of co-contraction in arm movement performance.…”

Editorial: Biological and Robotic Inter-Limb Coordination

“…As noted above, one level of control, allowing consistency and also adaptability in inter-limb coordination; is the muscular system. Camardella et al (2021) visit the cutting edge technique of myo-control: a type of brain-machine interface in which recorded electromyographic (EMG) signals are utilized in a computed control signal that drives robots or machines (e.g., limb prostheses control). For such applications, there is much interest in characterizing the minimum muscle set, termed an optimal set, that preserves performance and demonstrates a high consistency of motor activity.…”

Multifunctional Evaluation Technology for Diagnosing Malfunctions of Regional Pelvic Floor Muscles Based on Stretchable Electrode Array Probe

“…It has multiple electrode arrays specifically arranged according to the muscle distribution. These allow the multiple electrodes to make tight contact with muscles for accurate MC-sEMG signal acquisition, and subsequent comprehensive assessment and diagnosis of functions of regional PFM [ 23 , 24 ], provided a new method and strategy for diagnosis and treatment of PFD diseases.…”