Factors Involved in Higher Knee Extension Torque Induced by Repetitive Peripheral Magnetic Stimulation

Abstract

Objective The study aimed to determine the relationship between knee extension torque induced by repetitive peripheral magnetic stimulation (rPMS) and the characteristics of the participants. Design This was a basic study with non-invasive intervention. Knee extension torque induced by rPMS (rPMS-induced torque) and maximum voluntary contraction (MVC) were measured. Stepwise method of multiple regression was performed to determine the factors affecting rPMS-induced torque at 100% intensity and rPMS-induced torque divided by MVC (%MVC). Subcutaneous fat thickness, VL muscle thickness measured by ultrasound, MVC, and mean power frequency of electromyography (EMG) during MVC were selected as independent variables. Results rPMS was applied to the right vastus lateralis (VL) of 30 young healthy adults (average age, 21.1 ± 0.3 years). In the multiple regression analysis, rPMS-induced torque (p < 0.001) was shown to be independently and significantly associated with MVC (β = 0.510), subcutaneous fat thickness (β = -0.358), and VL muscle thickness (β = 0.208), while %MVC value (p < 0.05) was independently and significantly associated with VL muscle thickness (β = 1.059). Conclusion rPMS-induced torque decreases with thicker subcutaneous fat and increases with stronger MVC or with thicker muscle.