IntroductionEpidural electrical stimulation (EES) has been shown to improve motor dysfunction after spinal cord injury (SCI) by activating residual locomotor neural networks. However, the stimulation current often spreads excessively, leading to activation of non-target muscles and reducing the accuracy of stimulation regulation.ObjectivesNear-infrared nerve stimulation (nINS) was combined with EES to explore its regulatory effect on lower limb muscle activity in spinal-cord-transected rats.MethodsIn this study, stimulation electrodes were implanted into the rats’ L3–L6 spinal cord segment with T8 cord transected. Firstly, a series of EES parameters (0.2–0.6 mA and 20–60 Hz) were tested to determine those that specifically regulate the tibialis anterior (TA) and medial gastrocnemius (MG). Subsequently, to determine the effect of combined optical and electrical stimulation, near-infrared laser with a wavelength of 808 nm was used to irradiate the L3–L6 spinal cord segment while EES was performed. The amplitude of electromyography (EMG), the specific activation intensity of the target muscle, and the minimum stimulus current intensity to induce joint movement (motor threshold) under a series of optical stimulation parameters (power: 0.0–2.0 W; pulse width: 0–10 ms) were investigated and analyzed.ResultsEES stimulation with 40 Hz at the L3 and L6 spinal cord segments specifically activated TA and MG, respectively. High stimulation intensity (>2 × motor threshold) activated non-target muscles, while low stimulation frequency (
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