Effects of neuromuscular priming with spinal cord transcutaneous stimulation on lower limb motor performance in young active males

This study investigated the effects of non-invasive spinal cord transcutaneous stimulation (scTS) applied during an exercise-based priming protocol on the neuromuscular performance of lower limbs in young active males. Twelve volunteers (age: 22.7±2.1 years) participated in this randomized crossover, sham-controlled study. Maximal voluntary contraction and low-level torque steadiness of knee extensors as well as maximal explosive extension of lower limbs were assessed before and after the priming protocol with scTS or sham stimulation over a total of four experimental sessions. Further, characteristics of evoked potentials to scTS related to spinal circuitry excitability were assessed in supine position before and after the scTS priming protocol. The exercise component of the ∼25-minute priming protocol consisted of low-volume, low- and high-intensity lower limb motor tasks. scTS priming protocol tended to increase or maintain maximum isometric torque during knee extension (4.7%) as well as peak force (0.2%) and rate of force development (6.0%) during explosive lower limb extensions, whereas Sham priming protocol tended to decrease them (-4.3%, -3.3% and -15.1% respectively). This resulted in significant interactions (p=0.001 to 0.018) and medium-large differences between scTS and Sham protocols. These findings were associated with meaningful trends of some neurophysiological variables. Conversely, priming protocols did not affect low-level torque steadiness. Overall, the application of scTS during the proposed priming protocol enhanced lower limb maximal performance compared to Sham priming protocol. Future studies are warranted to assess the implementation of optimized scTS and exercise-based priming protocols during training and rehabilitation programs that include high-intensity neuromuscular efforts.