Effect of Direct current stimulation on walking and movement in people with Multiple Sclerosis: an experimental study of immediate and carry-over effects

Intervention (Neubie DC Stimulation) Pulsed direct current (DC) stimulation will be delivered via the Neubie (Neuro-Bio-Electric Stimulator), applied bilaterally to the tibialis anterior, gastrocnemius, quadriceps (rectus femoris and vastus medialis), and hamstrings. The single intervention session will last approximately 60 minutes in total. Stimulation will be individualised to each participant's tolerance. Frequency will be set at 100–160 pps, consistent with the neuromuscular re-education application of the device. In accordance with NeuFit device guidelines, stimulation at this frequency range is limited to a maximum of 12 minutes per body area; stimulation will therefore be structured as 3 blocks of 12 minutes, each targeting a different lower-limb muscle group (Block 1: tibialis anterior and gastrocnemius; Block 2: quadriceps; Block 3: hamstrings), giving a total active stimulation time of approximately 36 minutes. As the Neubie delivers a proprietary pulsed DC waveform, pulse width is not an independently adjustable parameter — it is determined by the device's fixed internal waveform architecture and the selected frequency setting, and therefore no conventional pulse width range (e.g., in µs) can be specified. Similarly, intensity is not expressed in mA on this device; it is titrated individually using the NeuFit six-level power scale, targeting Level 3 (First Contraction) to Level 5 (Uncomfortable and Challenging), with intensity increased incrementally until each participant reaches a subjective intensity of 7/10 on a verbal rating scale. Intensity will not exceed a VAS-Pain ceiling of =4/10. The Neubie does not have an automated ramp function; intensity is manually titrated by incremental dial increases with verbal rating checks at each step. Stimulation will be delivered continuously within each 12-minute block, with brief pauses between blocks for electrode repositioning to the next muscle group. Functional assessments completed during stimulation include the Five Times Sit-to-Stand Test (5×STS), Timed Up and Go (TUG), 10-Metre Walk Test (10MWT), 2-Minute Walk Test (2MWT), handheld dynamometry, distributed across the three stimulation blocks according to the muscle groups being targeted. Stimulation will be administered by a trained researcher in a face-to-face clinical/laboratory setting.