From Brain to Muscle: Central and Peripheral Neural Adaptations Underlying Strength Gains Following Resistance Training

Abstract

Objective: This study was conducted to evaluate the difference between the two resistance training methods in developing maximal strength in the upper extremity of healthy adults and investigate differences between training groups, sex and alterations in A/G ratio, CRP, EEG and NCS parameters.

Methods: The study was conducted as a parallel group randomized controlled trial in Shifa Neuro Clinic and Laboratory from August 2023 to September 2024, involving 100 healthy adults between the ages of 18-35 years. The participants were divided into two groups: an 8-12 repetitions resistance-training group and an 8 RM (1 repetition max) training group. Both groups exercised 2 times per week for 8 weeks. 1RM was used as an assessment of muscle strength and before/after training assessment for EEG, NCS, A/G ratio and CRP.

Results: 1RM strength increased significantly over time, F(1,98)=301.758, p<0.001. The group effect and time×group interaction were not significant (p=0.479 and p=0.307, respectively). The A/G ratio changed significantly over time (p=0.002) but its change did not differ between groups (p=0.928) and was not associated with strength gain (ρ=0.043, p=0.668). There were no significant differences found in EEG measures. For most NCS parameters, there was no change either, except for right median sensory onset latency (p=0.014) and left median motor elbow latency (p=0.008) which showed significant time×group interaction. Strength gain was not significantly affected by sex (p=0.081) nor was there significant interaction between group and sex (p=0.631). Throughout the study, the CRP was found to be negative.

Conclusion: In healthy adults, eight weeks of resistance training led to a significant increase in maximal strength of the upper extremities. The extent of improvement was similar in the hypertrophy-oriented and 1RM training groups with no significant difference between the two approaches. The A/G ratio varied throughout the time period but not in relation to strength gain. Overall, the results suggest that strength gains can be achieved without a significant change in most of the EEG and NCS parameters, indicating that early strength gain might involve a combination of interacting muscular, neural, motor-learning and task-specific mechanisms.