Upon a change of electrical potential, typically induced through nerve or pacemaker cells, muscles have the ability to contract and generate force. The change of electrical state induces an electrical field within the tissue that can be measured. In case of the heart, the electrocardiogram (ECG) depicts measurement of the electrical field induced by the heart contraction. One can measure the electrical activity of skeletal muscles using a technique called electromyography (EMG). Much like the heart, one can infer from such EMG data information about muscle activity/recruitment. High-density electromyography (HD-EMG) measures many signals in a relatively compact and confined space with specialised electrodes. This technique has become popular over the years for its advantages compared against traditional needle-based and the modern surface acquisition techniques.
HD-EMG can be used to investigate the heterogeneities in the spatial activation of a muscle, which provide useful insights on the anatomy and physiology of the muscle tissue, and the way it is controlled by the central nervous system. Exploiting the redundancy of information, it is even possible to decode the contribution of individual motor neurons in the spinal cord, and investigate the descending drive of the central nervous system. Changes over time of the motor units recruitment are correlated with diseases, chronic pain, fatigue and the outcomes of training.
However, this method is still confined to laboratory settings as more portable and user-friendly versions are missing. Moreover, ccommercially available HD-EMG amplifiers are expensive and cumbersome and reduce the ability of the subject to move freely and lack the possibility to record locally or display visual feedback. Hence, the existence of such devices could promote its use across clinical, rehabilitative, and recreational and sport structures
We have identified and combined together highly specialised components to build the prototype of a novel wireless, portable high-density EMG system. The prototype is working and we named it WiHDE. WiHDE can securely transfer (via LAN or Wi-Fi transmission) or store data from long-term recordings locally. Furthermore, we have worked on methods to provide instant visual spatial feedback based on time or frequency characteristics of muscular activity. The system is compatible with commercially available electrode grids and is currently controlled through Matlab code for immediate compatibility with existing research environments.
In its initial stage, WiHDE is thought to join or replace the bench instrumentation in research laboratories whilst further improvements in its usability and design will allow to expand towards rehabilitation and sport-oriented applications.
