Effects of spinal cord transcutaneous stimulation priming on single-leg balance control

Background: Balance control relies on proprioceptive, visual and vestibular inputs, contributing to functional performance and injury prevention. Neuromodulation strategies targeting the spinal circuitry controlling lower limbs are emerging as potential approaches to enhance lower limb neuromuscular performance. For example, non-invasive lumbosacral spinal cord transcutaneous stimulation (scTS) applied to prime the nervous system can improve lower limb performance during repeated, high-level efforts. However, it is unclear whether such neural priming approach can influence low-level motor outcomes and balance control. Aim: To assess the effects of scTS priming on single-leg stance balance control with and without visual input. Methods: Twelve young active males (age: 22.7 ± 2.1 years) participated in this randomized crossover, sham-controlled study. Single-leg stance balance control with eyes open and eyes closed was assessed before and after the priming protocol with scTS or sham stimulation for approximately 25 minutes over a total of two different experimental sessions. Anterior-posterior, medio-lateral and a composite of the two directions were assessed on the force platform as well as electromyography of tibialis anterior (TA) and medial gastrocnemius muscles. Results: Priming protocols with scTS or sham application did not influence single-leg stance performance, as reflected by trial duration, kinetic and electromyography outcomes (priming effect: P-values ranging from 0.343 to 0.759). A significant effect of vision emerged, with shorter trial duration (P = 0.018), larger anterior-posterior (P = 0.004), medio-lateral (P < 0.001) and total displacement (P < 0.001), as well as longer co-contraction between TA and medial gastrocnemius (P < 0.001) with eyes closed compared to eyes open. Also, a time × priming × eyes interaction was found for the TA muscle activation (P = 0.046), indicating increased TA activation at the end vs beginning of eyes open trials following scTS priming. Conclusion: The scTS priming did not affect single-leg stance balance performance under both eyes closed and open conditions. Also, as expected, impaired balance control was found with eyes closed.