Adaptations of cortical-spinal excitatory and inhibitory pathways in strength changes caused by resistance training in untrained individualsBased on Transcranial Magnetic Stimulation

Due to the role of neural adaptations in the primary stages of resistance training, this study aimed to determine the adaptations of cortical-spinal excitatory and inhibitory pathways in strength changes in agonist and antagonist muscles after 4 weeks of resistance training using TMS. 10 healthy untrained individuals participated in this study voluntarily. The training protocol included 4-week of seated one-arm dumbbell curl training with 80% of a one-repetition maximum. To assess MEP and CSP, the area under the curve (AURC) was used, which was obtained based on different intensities of the TMS. Repeated-measures ANOVA and Bonferroni were used to analyze the data. The results showed a 21% and 31% increase in agonist muscle strength in weeks 2 and 4 respectively. In contrast, the antagonist muscle just showed a 15% increase in strength in the fourth week. The area under the MEP curve showed a significant increase after 4 weeks of training (p <0.001) in biceps but not in triceps. In addition, CSP showed a significant decrease in biceps and triceps after 4-week (p> 0.05). However, the changes in corticospinal function were not associated with increased muscle strength. The results of this study showed that cortical-spinal responses to resistance training in the upper body are not limited to trained muscles and the nervous system to increase strength by modulating the cortical areas creates different adaptations for both agonist and antagonist muscles.