A Systematic Review of Stimulation Parameters Used in Transcutaneous Spinal Cord Stimulation for Upper Body Rehabilitation in People with Cervical Spinal Cord Injury.

BACKGROUND: Transcutaneous spinal cord stimulation (tSCS) has been shown to be an effective enhancement for upper extremity (UE) motor recovery when paired with upper extremity activity-based rehabilitation training (UE ABRT) for those with cervical spinal cord injury (cSCI). Factors suggested to contribute to the effectiveness tSCS include parameters of stimulation and participant characteristics. This review aimed to identify stimulation parameters linked to enhanced neurophysiological engagement and functional recovery. Additionally, this review also considered how participant characteristics influenced the effectiveness of tSCS-based rehabilitation. MATERIALS AND METHODS: A systematic search was conducted for studies up to September 2025 in the following databases: Ovid MEDLINE, Ovid Embase, Web of Science, Cochrane Library, and CINAHL. Two reviewers independently screened the studies and evaluated the quality of the studies using the Modified Downs and Black Checklist. Participant characteristics, injury profile, stimulation parameters, and study design were extracted. RESULTS: A total of 3619 articles were initially screened, of which 38 met the inclusion criteria. Fourteen studies included only an able-bodied (AB) population, 19 studies included people with cSCI only, and five studies investigated the effects of tSCS in both AB and SCI participants. The mean quality of the studies was poor (11.82 ± 2.18: Modified Downs and Black Checklist score; scores <15 classified as poor quality). Although some stimulation parameters remained consistent among most studies (frequency: 30 Hz, pulse width: 1 ms, carrier frequency: 5-10 kHz), many of these parameters had no neurophysiological justification. Additionally, parameters such as electrode configuration and intensity of stimulation were highly variable. The studies included participants across a wide age range, and the articles focused on individuals with traumatic and chronic injuries. CONCLUSIONS: There is a lack of mechanistic understanding of how tSCS parameters can influence neurophysiological engagement. There are notable gaps in the literature regarding how participant characteristics, such as age or injury chronicity, affect the efficacy of tSCS and the selection of optimal stimulation parameters. Many studies failed to provide adequate justification for their chosen parameters, limiting the ability to assess their effectiveness.