Changes in agonist neural drive, hypertrophy and pre-training strength all contribute to the individual strength gains after resistance training.

Purpose: Whilst neural and morphological adaptations following resistance training (RT) have been investigated extensively at a group level, relatively little is known about the contribution of specific physiological mechanisms, or pre-training strength, to the individual changes in strength following training. This study investigated the contribution of multiple underpinning neural [agonist EMG (QEMG _MVT ), antagonist EMG (HEMG _ANTAG )] and morphological variables [total quadriceps volume (QUADS _VOL ), and muscle fascicle pennation angle (QUADSθ _p )], as well as pre-training strength, to the individual changes in strength after 12 weeks of knee extensor RT.
Methods: Twenty-eight healthy young men completed 12 weeks of isometric knee extensor RT (3/week). Isometric maximum voluntary torque (MVT) was assessed pre- and post-RT, as were simultaneous neural drive to the agonist (QEMG _MVT ) and antagonist (HEMG _ANTAG ). In addition QUADS _VOL was determined with MRI and QUADSθ _p with B-mode ultrasound.
Results: Percentage changes (∆) in MVT were correlated to ∆QEMG _MVT (r = 0.576, P = 0.001), ∆QUADS _VOL (r = 0.461, P = 0.014), and pre-training MVT (r = -0.429, P = 0.023), but not ∆HEMG _ANTAG (r = 0.298, P = 0.123) or ∆QUADSθ _p (r = -0.207, P = 0.291). Multiple regression analysis revealed 59.9% of the total variance in ∆MVT after RT to be explained by ∆QEMG _MVT (30.6%), ∆QUADS _VOL (18.7%), and pre-training MVT (10.6%).
Conclusions: Changes in agonist neural drive, quadriceps muscle volume and pre-training strength combined to explain the majority of the variance in strength changes after knee extensor RT (~60%) and adaptations in agonist neural drive were the most important single predictor during this short-term intervention.