Electromyography and ultrasound investigation of upper-arm muscles

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My research program is oriented toward the study of upper limb muscles activation. Focus is on the multifunctional biceps brachii because physiologically, its motor units are activated in different regions of the muscle depending on the arm position, and anatomically because of up to 6 individually innervated compartments can be observed on its inner surface. Our objective is to find how those compartments could voluntarily be contracted and thus behave as “muscles” within a muscle. This fundamental aspect has a practical impact for upper limb amputees who use modern prostheses requiring many electromyographic (EMG) control signals to fully benefit from their ability to produce many movements. In our lab, EMG recordings were done with 10 surface electrode pairs positioned across the biceps of 10 normal subjects who experimented different upper limb and hand positions while their biceps was contracted. To those surface signals, will be associated the presence of electric dipoles within the biceps tissue. Location of those dipoles will be done with an inverse problem solving method applied on a finite element upper arm model. This model will be established with information obtained on upper arm magnetic resonance images. To include the presence of compartments within this model, high resolution magnetic images obtained from human biceps will be segmented to identify location and size of the compartments all along the length of their biceps. As our hand posture changes, tissues under the skin are subjected to deformations which can be imaged with an ultrasound (US) equipment. On the obtained images a semi-automatic segmentation algorithm will be used to identify the short and long head of the biceps, the top of the humerus bone and the cephalic and basilic veins. Between those identified structures, distance and angular position will be measured and area of the short and long heads of the biceps measured. Those under the skin changes will be used in the analysis of surface EMG signals. Within a contracted biceps, zones of high stiffness stress will be identified with US elastography, Obtained in condition similar to those of EMG recording, high stiffness zones are expected to overlap the electric dipole positions. Recently, extraction of muscular synergies from many surface EMG signals proved to be useful to control a prosthesis. We found that muscle synergy could also be extracted from a single muscle such as the biceps. As a proof of concept, muscle synergies of 5 signals of the biceps will be used to have a small humanoid robot to on-line duplicate arm movements produced by normal subjects. Fusion of several modalities, exploration of muscle compartments and muscular synergy could lead to an easier control of myoelectric prostheses.