Fig. 5.

Surface electromyography (sEMG) properties following spinal cord injury (SCI). Left: Changes in sEMG properties may be related to weak cortical control (hashed blue lines) but also to aberrant plasticity within the intrinsic spinal cord circuitry (green lines). For example, the lack of UMN control may be reflected in reduced muscle strength and coordination to control volitional muscle activity, reflected in amplitude- and frequency-based sEMG properties [e.g., amplitude: root mean square (RMS), peak; frequency: median frequency (MDF), power spectrum density (PSD), intra- or intermuscular coherence at the β-band]. Right: The lack of UMN efferents to the spinal cord induces sprouting within the spinal cord circuitry. Given the intact afferents arriving from the periphery and/or pathways within the spinal cord, the intrinsic spinal cord circuitry is prone to hyperexcitability. This is reflected in the amplitude-based sEMG properties as an involuntary activation, many times propagating to several muscle groups in the form of tonic, clonic, or unit spams. These forms of spontaneous activity, thought to involve intrinsic spinal cord circuitry, are detected at rest and present unique frequency-based sEMG features such as low-frequency muscular coherence. SCI spinal cord injury, sEMG superficial electromyography, UMN upper motor neuron, F flexors, E extensors, Hz hertz, LMN lower motor neuron