Longitudinal estimation of intramuscular tibialis anterior coherence during subacute spinal cord injury: Relationship with neurophysiological, clinical and functional measures

Tibialis Anterior (TA) electromyographic coherence estimation is assumed to reflect common supraspinal descending input spinal motoneurons, related to corticospinal tract activity. This study documented residual voluntary motor recovery at 2 week intervals during subacute spinal cord injury (SCI) with intramuscular TA EMG coherence estimation within the 10-60Hz bandwidth, assessed during controlled maximal isometric and isokinetic dorsiflexion. Several clinical and functional lower limb measures (muscular testing, dorsiflexion maximal voluntary torque and gait function measured with the WISCI II) and neurophysiological measures (TA motor evoked potentials, MEPs) were also recorded. Total and TA muscle strength, voluntary torque generation and gait function improved during subacute SCI, in addition to 40-60Hz, but not 15-30Hz intramuscular TA coherence. TA MEPs failed to reflect significant recovery of function. The SCI spasticity syndrome non-specifically reduced 15-30Hz TA coherence and was detected as high TA coherence values during fast isokinetic movement in all frequency bands. To conclude, longitudinal assessment of adaptive and maladaptive motor plasticity during subacute SCI can be detected with TA EMG coherence estimation during controlled movement, providing orientative diagnostic information during neurorehabilitation.