This study investigated the test-retest reliability of measures of the central and peripheral nervous systems in healthy adults and individuals with chronic cervical spinal cord injury (SCI). Neuroexcitability measures of the upper limbs were obtained using threshold-tracking methods, which offer fast assessments, but whose reliability has not been established.

Twenty-seven healthy controls (HC) and ten individuals with chronic cervical SCI underwent a test-retest assessment with roughly seven days in between tests. Transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) and nerve excitability tests (NET) of the median nerve were performed. Motor evoked potentials were measured at the abductor pollicis brevis (APB) of the dominant hand in healthy controls and the APB or extensor carpi radialis longus in individuals with SCI.

For all outcome measures, absolute and relative reliability were determined. No significant differences were observed between the measurement days. TMS measures exhibited excellent reliability for resting motor threshold and intermediate-to-good reliability for stimulus-response function. The majority of NET outcome variables showed at least moderate reliability estimates in both the HC and SCI groups.

Threshold-tracking-based measures of the central and peripheral nervous systems provide reliable measures of neuroexcitability, both in healthy adults and individuals with SCI. The use of neurophysiological measures in research and clinical settings warrants a consideration of each variable’s reliability.