Strength-Duration Curve Outcomes, Profiles and Evidence in Spinal Cord Injury: Protocol for a Scoping Review (SCOPE-SCI Study)

IntroductionNeuromuscular and functional electrical stimulation (NMES/FES) are widely used in spinal cord injury (SCI) rehabilitation to preserve muscle health, manage spasticity, and support functional recovery. However, stimulation protocols typically use fixed parameters with limited individualisation. The strength-duration (SD) curve, reflecting the relationship between pulse duration and stimulus intensity required for muscle contraction, captures excitability changes due to denervation, reinnervation, and training. While historically used in neurophysiology, its translational role in guiding NMES/FES programming in SCI rehabilitation remains unclear. This scoping review aims to map current evidence on SD-curve measurement, outcomes, and clinical applications in SCI. Methods and analysisThis protocol follows PRISMA-ScR guidelines. We will search MEDLINE, EMBASE, CINAHL, and grey literature sources from inception to present. Eligible studies will include adults with traumatic or non-traumatic SCI, reporting SD curves or related excitability measures (rheobase, chronaxie, accommodation index). Data extraction will capture study characteristics, methods of SD-curve measurement, rheobase/chronaxie values, clinical applications (diagnostic, prognostic, therapeutic), and outcomes of SD-guided NMES/FES interventions. Results will be presented descriptively and thematically, with tables and figures mapping measurement approaches, reported values, and translational applications. Methodological and reporting gaps will be highlighted. Ethics and disseminationEthical approval is not required. Findings will be disseminated through peer-reviewed publication, international conferences, and to inform future pilot studies on SD-curve-guided rehabilitation in SCI.