Acute neural adaptations to resistance training performed with low and high rates of muscle activation

Understanding neural adaptations to training, and their relation to functional improvements, plays an important role in designing and evaluating training programs. Neural adaptations to strength training have yet to be completely characterized, with disagreement regarding the role of motor cortex (M1). Unlike skill training, which is consistently associated with an increase in excitability and a decrease in inhibition within M1, adaptations to strength training are equivocal. There is evidence that rate of muscleactivation (ROA) used during a training protocol may influence M1 plasticity. In the present study, the role of ROA on acute, neural adaptations to a single session of strength training was evaluated. Thirty subjects participated in a single session of maximal, isometric knee extension testing and training. Subjects were randomized into groups that were tested with high ROA and trained with high ROA (Ballistic), low ROA (Ramp), or did not train (Control). Changes in performance (maximal torque, maximal rate of torque development, muscle activation) were assessed during training and 24 hours after. Transcranial magnetic stimulation, femoral nerve stimulation, and short-interval intracortical inhibition were used to assess changes in corticospinal tract (CST) excitability, spinal reflex excitability, and M1 inhibition for rectus femoris during training and 24 hours after. All three groups improved rate of torque development, with Control apparently due to training effects of the test contractions. Neural adaptations were also similar among groups. Training/testing resulted in an immediate depression of resting M1 excitability, which recovered within ten minutes, and no change in CST excitability during voluntary muscle activation. Training/testing was also associated with increased spinal reflex excitability during voluntary muscle activation, but not rest. M1 inhibition