Strength training reduces intracortical inhibition.
OBJECTIVE
Paired-pulse transcranial magnetic stimulation was used to investigate the influence of 4 weeks of heavy load squat strength training on corticospinal excitability and short-interval intracortical inhibition (rectus femoris muscle).


METHODS
Participants (n = 12) were randomly allocated to a strength training or control group. The strength training group completed 4 weeks of heavy load squat strength training. Recruitment curves were constructed to determine values for the slope of the curve, V50 and peak height. Short-interval intracortical inhibition was assessed using a subthreshold (0.7 × active motor threshold) conditioning stimulus, followed 3 ms later by a supra-threshold (1.2 × active motor threshold) test stimulus. All motor evoked responses were taken during 10% of maximal voluntary isometric contraction (MVC) torque and normalized to the maximal M-wave.


RESULTS
The strength training group attained 87% increases in 1RM squat strength (P < 0.01), significant increases in measures of corticospinal excitability (1.2 × Motor threshold: 116%, P = 0.016; peak height of recruitment curve = 105%, P < 0.001), and a 32% reduction in short-interval intracortical inhibition (P < 0.01) following the 4-week intervention compared with control. There were no changes in any dependent variable (P > 0.05) detected in the control group.


CONCLUSIONS
Repeated high force voluntary muscle activation in the form of short-term strength training reduces short-interval intracortical inhibition. This is consistent with studies involving skilled/complex tasks or novel movement patterns and acute studies investigating acute voluntary contractions.
Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Vic., Australia.
A T
AT
Weier
A J
AJ
Pearce
D J
DJ
Kidgell
D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D002540:Cerebral Cortex / Q000502:physiology*; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D053580:Muscle Strength; D009433:Neural Inhibition; D011712:Pyramidal Tracts / Q000502:physiology; D052097:Quadriceps Muscle / Q000294:innervation*; D011999:Recruitment, Neurophysiological; D055070:Resistance Training; D012684:Sensory Thresholds; D013997:Time Factors; D019415:Torque; D050781:Transcranial Magnetic Stimulation; D014739:Victoria; D014836:Volition; D055815:Young Adult