Design and setting

This study is a double-blind randomized controlled pilot feasibility trial with participant- and assessor-blinding. Participants will be assessed at baseline, mid-point (three weeks post-randomization), after completing the intervention (six weeks post-randomization), and two weeks following intervention completion. As shown in Fig 1, the SPIRIT timeline outlines the full schedule of enrollment, assessments, and intervention sessions across the eight-week study period. The study will take place at the Gray Centre for Mobility and Activity in Parkwood Institute, St. Joseph’s Health Care London, Ontario, Canada and has been approved by the Western University Research Ethics Board (REB #122650) and Lawson Health Research Institute Ethics Board (Approval #R-23-245) in accordance with the Declaration of Helsinki (1964). These boards will be notified on any trial amendments, deviations, or adverse events.

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Fig 1. SPIRIT [27] participant timeline.

https://doi.org/10.1371/journal.pone.0345100.g001

Participants and recruitment

Participants will be recruited from Parkwood Institute and will first undergo study screening to determine eligibility according to inclusion and exclusion criteria (Table 1). Once determined eligible, all participants will be provided with a letter of information containing all relevant information about study procedures and will provide written informed consent to a study team member prior to initiating any study procedures. Demographic information including age, level and severity of injury, time since injury, sex, and gender will be collected and stored separately from study data. Medication usage will also be documented, and participants will be asked to report any changes in medication over the course of their participation to the research team.

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Table 1. Inclusion and exclusion criteria.

https://doi.org/10.1371/journal.pone.0345100.t001

Randomization and blinding

Participants will be randomized to either the active rTMS intervention group or the sham rTMS control group using a 1:1 allocation ratio; all participants will receive active FES cycling. Randomization will be blocked by four and stratified by the American Spinal Injury Association Impairment Score (AIS) of C or D. An individual who is not a member of the research team will perform draws for the group assignment. Participant blinding in this protocol will be achieved using a sham rTMS coil, which functions through distribution of the electrical field so there is no focal stimulation over the cortex. As a result, the magnetic field generated is insufficient to induce an electrical response in the underlying tissue. The sham coil is identical in shape, color, and weight to the active coil and produces the same auditory and somatosensory sensations on the scalp associated with active stimulation. The study assessor will also be blinded to group assignment until data analyses are complete. Only the rTMS technician will be aware of group allocation; unblinding will be allowed if an adverse or unexpected event occurs.

Study procedures

This study will consist of 12 intervention sessions (two per week for six weeks) lasting approximately two hours. Each session will begin with the rTMS procedures immediately followed by FES cycling with changes in health status and side effects monitored throughout each session. Participants will be free to participate in any other exercise or rehabilitation program while in the study.

rTMS protocol

The rTMS protocol will be conducted using the Magstim Rapid² stimulator (Welcony, Roseville, MN, USA) fitted with a 70 mm figure-of-eight coil, targeting the first dorsal interosseous (FDI) muscle of the right hand. We selected the FDI muscle rather than a muscle in the lower extremity as cortical reorganization following SCI can result in decreased excitability in the lower extremity motor areas [33,34] and the hand area of the motor cortex contributes to lower extremity activation [35]. Additionally, there is substantial evidence for interlimb neural coupling, where activation of hand or arm motor circuits can modulate corticospinal drive to leg muscles. For example, active rhythmic arm cycling has been shown to facilitate MEPs in leg muscles in people with iSCI, indicating functional cross limb interactions [36]. Furthermore, rTMS over the primary motor cortex (M1) has been shown to restore spinal reciprocal inhibition and reduce lower limb spasticity in SCI patients, suggesting that cortical stimulation can influence lower limb function through descending pathways [37]. Consequently, these findings support the rationale for targeting the hand motor cortex to potentially influence lower limb function via interlimb interactions. Targeting the upper extremity also allows for a lower stimulation intensity due to the superficiality of the motor area for the hand, increasing the safety of the protocol. This protocol has been used by other studies evaluating gait in iSCI [15–17]. Several prior gait related rTMS trials in iSCI have also stimulated the FDI representation and still reported meaningful improvements in lower limb function. Nogueira et al. and Benito et al. delivered rTMS over the FDI region and reported enhancements in lower extremity strength, independent walking, and functional gait outcomes [17,18]. These studies demonstrate that stimulation of the hand representation in the motor cortex can facilitate lower limb recovery, supporting the rationale for targeting the FDI in the present protocol. Coil calibration is done to ensure accuracy in TMS delivery over M1 using stereotactic neuronavigation with a curvilinear reconstruction of an averaged brain using Brainsight (Rogue Research, Montreal, QC, Canada). First, single TMS pulses will be used to identify the FDI hotspot and determine the resting motor threshold (RMT). The hotspot is defined as the location within M1 that produces the largest MEPs in the FDI muscle for a given stimulus [38]. The RMT is defined as the minimum stimulation intensity that elicits a peak-to-peak MEP of at least 50μV in at least five consecutive trials [39]. After the hotspot and RMT have been identified, either the active or sham rTMS coil will be attached to the machine by the rTMS technician. rTMS will be administered using either the active or sham coil at 90% of the RMT (20 Hz, 15 trains of 120 stimuli, 28 second intertrain interval), following the protocol used by Benito et al. [18]. The total duration of rTMS delivery will be approximately 17 minutes and include 1800 pulses. The rTMS technician will monitor participants continuously throughout the session.

FES cycling protocol

An FES bike (Restorative Therapies RT300 – New Hampshire, USA) will be used to deliver sequenced electrical currents to the following muscles bilaterally to perform the cycling motion: gluteus maximii, quadriceps, hamstrings, tibialis anterior, and gastrocnemii. During FES cycling, the stimulation sequence will follow a fixed pattern that is based on pedal position to activate lower limb muscle groups in synchrony with the cycling motion. FES parameters will follow guidance from previous studies in this population with pulse width of 200–400 µs and amplitude of 125–150 mA [12]. The intensity of the electrical currents will be set to a level that elicits a visible muscle contraction but remains tolerable for the participant; intensity will be set during the first intervention session and kept the same in the subsequent sessions unless adjustments are warranted during each intervention session based on participant tolerance. Thereafter, all individual cycling parameters, including any adjustments to stimulation intensity, will be saved under the participant’s profile, ensuring reproducibility across sessions. Duration of FES cycling sessions will be 60 minutes with approximately 15 minutes of equipment set-up and 45 minutes of cycling time and the target cycling speed will be set to 30–35 revolutions per minute (RPM), with resistance ranging from 5–15 N [12]. Although there is a short delay between rTMS and FES cycling, prior studies demonstrate that high-frequency rTMS increases corticospinal excitability for at least 60 minutes after stimulation in individuals with incomplete SCI, suggesting that facilitatory effects on cortical excitability are likely to persist through the FES setup period [40]. The FES bike automatically adjusts based on the participant’s applied force to maintain the target speed. For example, if the participant generates insufficient force, the bike will provide graded assistance to achieve the target RPM; conversely, if the participant exerts greater force, the bike will increase resistance to stabilize the cycling speed. Participants will be instructed to actively contribute to pedaling throughout the session by pushing into the pedals and matching the target cadence with verbal encouragement provide to promote continuous voluntary effort rather than passive movement while emphasizing consistency of speed rather than maximal cadence.

Outcome measures

Primary outcomes include feasibility, acceptability, and safety of the protocol. To assess feasibility the: 1) time taken to complete the recruitment of all participants, 2) proportion of participants recruited from the total number screened, and 3) blinding success will be collected using a blinding questionnaire where participants will be asked to indicate which study group they believe they were assigned to and rate their confidence in their choice. To measure the acceptability of the protocol: 1) protocol adherence rate (target ≥ 80%), 2) number of dropouts in each of the treatment and sham groups (target ≤ 20%), and 3) the willingness of participants to undergo therapy (in the form of an 11-point scale (0–10) completed during the baseline assessment session, target: at least 7/10 in ≥80% of participants), will be collected. This questionnaire was included based on prior evidence that individuals with SCI are generally interested in participating in physiotherapy based clinical trials but may be less certain when interventions involve electrical stimulation [41]. Safety will be monitored throughout the trial using a standardized adverse event case report form. At each session, participants will be asked about any new or ongoing adverse events, and any event identified will be documented with its onset date, resolution date, detailed description, and severity, classified according to the Common Terminology Criteria for Adverse Events (CTCAE) [42]. Events will also be categorized as serious or non-serious, expected or unexpected, and their relationship to the study procedures will be recorded. For serious adverse events, information on the nature of the event (e.g., hospitalization, life-threatening occurrence, disability) will be captured. The outcome of each event and its impact on study participation will also be documented. All safety data will be reviewed descriptively to inform the feasibility and safety profile of the protocol for a future definitive trial.

Secondary outcome measures include the assessments related to lower extremity function. These outcomes will be collected by a registered physiotherapist who is blinded to group allocation. Outcome measures will be assessed in the same order for all participants. On all assessments after the baseline assessment participants will begin by completing the Global Rating of Change (GRC) scale, which asks participants to rate their perceived improvement in lower extremity function on a scale ranging from −7 (indicating “a very great deal worse”) to +7 (indicating “a very great deal better”) [43]. The 5x sit-to-stand test (5xSTS), the timed-up-and-go (TUG) test, and the tests of standing balance will be conducted using inertial measurement units (IMUs) (Clario – Oregon, USA).

1. Participants will be asked to walk on a 7-metre-long instrumented walkway (ProtoKinetics – Pennsylvania, USA) to collect gait parameters including gait speed, step length, step width, and cadence.
2. The Walking Index for Spinal Cord Injury (WISCI) II will be used to assess walking ability by evaluating the level of physical assistance and use of gait aids. The WISCI II is scored out of 20 with higher scores indicating more independence with walking and has been demonstrated to be a valid and reliable tool for use in the SCI population [44].
3. The 5xSTS test will ask participants to stand up from a seated position on chair with their arms by their sides, sit back with their back touching the chair, and repeat five times. The total time to complete the five repetitions will be recorded. This test has been validated for use in people with iSCI [45].
4. The TUG test will require participants to stand up from a seated position on a chair, walk 3 metres at a comfortable pace, turn 180 degrees, walk back to the chair, turn again, and sit down, with the total duration of time in seconds recorded. This test has been shown to be reliable and valid in the iSCI population [46,47].
5. In the standing balance assessment, participants will stand on a firm surface with their feet shoulder-width apart and their hands on their hips, if able, for 30 seconds with eyes open and then repeated with eyes closed. Mean sway velocity, measured in metres per second, will be measured during this assessment.
6. The Lower Extremity Motor Score (LEMS) will be measured to assess the strength of five key muscle groups in the lower limbs using a six-point grading scale [48]. Each muscle group will be scored separately on both sides of the body, with a maximum of 5 points per muscle. The scores for each lower extremity will be added together for a total out of 50, with higher values indicate better muscle strength.

Data analysis and management

This is a pilot study designed to inform the development of a protocol for a definitive randomized controlled trial. As this is a pilot trial, the sample size was not determined through a formal power calculation. Instead, the target of 14 participants (7 per group) reflects pragmatic considerations related to recruitment feasibility in individuals with iSCI, a population with known challenges in enrollment [49,50]. Methodological guidance indicates that feasibility focused pilot studies may appropriately include smaller sample sizes when the primary objectives are to assess recruitment, adherence, safety, and protocol procedures rather than to obtain precise estimates of treatment effects [30,51,52]. Pilot trials in SCI population frequently use similarly small samples due to the clinical characteristics and limited pool of eligible participants [49]. Outcomes related to demographics, feasibility, acceptability, and safety will be reported descriptively [53]. For the secondary outcomes, mean scores and mean changes over time will be summarized descriptively to explore preliminary trends in the effectiveness of the intervention. Reasons for any missing values will be categorized and reported, allowing for patterns to be analyzed to evaluate the acceptability of the intervention and the burden of the protocol. Consistent with the exploratory nature of this study, analyses will be interpreted descriptively rather than through formal hypothesis testing, with emphasis placed on patterns of change across time and between groups. Because the study includes repeated measurements, results will be organized by timepoint to reflect within group changes over the study period, and between group differences will be described accordingly. Effect sizes with confidence intervals will be calculated for each group using Cohen’s d to provide estimate of the magnitude of change and to support planning a future definitive trial [30,54]. Given the pilot nature and small sample size, effect sizes will be interpreted cautiously, recognizing their potential instability and risk of overestimation. Lastly, data will be used to inform the sample size calculation for the definitive randomized controlled trial based on the minimum clinically important difference (MCID) in walking speed [55]. In iSCI, the MCID for walking speed is 0.13m/s [56]; power will be set at 80%, alpha at 0.05 and a dropout rate based on the findings of the pilot trial. As this is a single site pilot trial a data safety and monitoring committee (DSMC) is not required.

Status and timeline

This study is ongoing with participant recruitment and data collection anticipated to be complete by January 2026 and results available in July 2026. Recruitment began on September 7, 2023 and will conclude on Nov 30, 2025. Data will be made available with publication of findings as appropriate.