Reduction in corticospinal inhibition in the trained and untrained limb following unilateral leg strength training

Abstract

This study used transcranial magnetic stimulation to measure the corticospinal responses following 8weeks of unilateral leg strength training. Eighteen healthy, non-strength trained participants (14 male, 4 female; 18-35years of age) were matched for age, gender, and pre-training strength; and assigned to a training or control group. The trained group participated in unilateral horizontal leg press strength training, progressively overloaded and wave periodised, thrice per week for 8weeks. Testing occurred prior to the intervention, at the end of 4weeks and at the completion of training at 8weeks. Participants were tested in both legs for one repetition maximum strength, muscle thickness, maximal electromyography (EMG) activity, and corticospinal excitability and inhibition. No changes were observed in muscle thickness in either leg. The trained leg showed an increase in strength of 21.2% (P=0.001) and 29.0% (P=0.007, compared to pre-testing) whilst the untrained contralateral leg showed 17.4% (P=0.01) and 20.4% (P=0.004, compared to pre-testing) increases in strength at 4 and 8weeks, respectively. EMG and corticospinal excitability did not change; however, corticospinal inhibition was significantly reduced by 17.7ms (P=0.003) and 17.3ms (P=0.001) at 4 and 8weeks, respectively, in the trained leg, and 25.1ms (P=0.001) and 20.8ms (P=0.001) at 4 and 8weeks, respectively, in the contralateral untrained leg. This data support the theory of corticospinal adaptations underpinning cross-education gains in the lower limbs following unilateral strength training.