Influence of stimulation parameters on torque development during the combined application of electrical nerve stimulation and muscle lengthening

• Published in: Journal of neurophysiology 2024-10, Vol.132 (4), p.1255-1264
• Main Authors: Pineau, Antoine, Martin, Alain, Lepers, Romuald, Papaiordanidou, Maria
• Format: Article
• Language: English
• ISSN: 0022-3077; 1522-1598; 1522-1598
• DOI: 10.1152/jn.00136.2024

This study investigated the influence of stimulation parameters on torque production when combining a brief muscle lengthening with electrical stimulation. Fifteen volunteers participated in one experimental session where two distinct stimulation modalities were compared: wide-pulse high-frequency ( , pulse duration: 1ms, frequency: 100Hz), favouring afferent pathways activation, and narrow-pulse low-frequency ( , pulse duration: 0.05ms, frequency: 20Hz), favouring activation of the efferent pathway. Both stimulation modalities, were applied to evoke 5-10% of maximal voluntary contraction either in isometric conditions ( ) or in combination with a muscle lengthening (lengthening condition: ). The torque-time integral (TTI) during the stimulation trains and the muscle activity after the cessation of the stimulation trains (sustained EMG activity, normalized to the maximal EMG activity) were assessed and compared between the stimulation modalities and the conditions (two-way ANOVA). An interaction effect was obtained, revealing significant differences in TTI and sustained EMG activity between the WPHF+LEN and the other tested conditions (P=0.048 and P=0.044, respectively). TTI and sustained EMG activity were higher for WPHF+LEN (228.4±105.3 Nm.s and 0.085±0.070, respectively) compared to WPHF (168.4±72.9 Nm.s; 0.052±0.026), NPLF+LEN (136.4±38.9 Nm.s; 0.031±0.016) and NPLF (125.2±36.1 Nm.s; 0.028±0.015). The increased TTI during the WPHF+LEN condition suggests that the contribution of afferent pathways to the evoked torque can be enhanced with the muscle lengthening superimposition. They highlight the importance of using WPHF stimulation that already solicits Ia afferents to benefit from the cumulative afferent activation induced by the muscle lengthening to further increase torque production.