sEMG

Surface electromyography (sEMG) is a non-invasive method for recording the electrical activity produced by skeletal muscles. It uses electrodes placed on the skin over or near the target muscle to detect the summed electrical potentials generated by active motor units during contraction.

Electrodes can be single pairs or high-density arrays. Common types include Ag/AgCl surface electrodes. Proper placement and skin preparation affect signal quality, and standardized guidelines such as SENIAM are used to optimize electrode location and referencing.

Signals are typically filtered to remove noise, rectified, and smoothed for analysis. Features include time-domain measures such as root mean square (RMS) and peak amplitude, as well as frequency-domain metrics like mean and median frequency, which can reflect muscle fiber conduction and fatigue. High-density sEMG (HD-sEMG) uses dense grids to map the spatial distribution of activity, enabling analysis of motor unit recruitment patterns and muscle synergistic behavior.

Applications span clinical, research, and practical domains. sEMG is used in neuromuscular assessment and rehabilitation after stroke or injury, in sports science and ergonomics to study muscle function and loading, and in the control of prosthetics and human–computer interfaces.

Limitations include susceptibility to skin impedance, hair, sweat, and motion artifacts. Crosstalk from neighboring muscles reduces spatial specificity, and normalization against maximal or submaximal contractions is often needed for comparisons across conditions or sessions.

Compared with intramuscular EMG, sEMG is non-invasive and safer but generally provides lower spatial resolution and less direct measurement of individual motor units.