Changes in agonist neural drive, hypertrophy and pretraining 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 (QUADS0(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 (HEMGANTAG). In addition QUADS(VOL) was determined with MRI and QUADS0(p) with B-mode ultrasound. Results Percentage changes (Delta) in MVT were correlated to Delta QEMG(MVT) (r = 0.576, P = 0.001), Delta QUADS(VOL) (r = 0.461, P = 0.014), and pre-training MVT (r = -0.429, P = 0.023), but not Delta HEMGANTAG (r = 0.298, P = 0.123) or Delta QUADS0(p) (r = -0.207, P = 0.291). Multiple regression analysis revealed 59.9% of the total variance in Delta MVT after RT to be explained by Delta QEMG(MVT) (30.6%), Delta 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 (similar to 60%) and adaptations in agonist neural drive were the most important single predictor during this short-term intervention.