The Influence of Transcranial Magnetic Stimulation Interpulse Interval Duration on Knee Extensor Corticospinal Excitability.

To examine the influence of interpulse interval duration on knee extensor corticospinal excitability. Seventeen college-aged males and females participated in a single laboratory visit, during which 25 single transcranial magnetic stimulation pulses were delivered to the motor cortex with interpulse intervals of 5, 10, 15, and 20 sec. Surface electromyographic signals were detected from the dominant vastus lateralis and rectus femoris. Motor evoked potential amplitude was compared across the four conditions. For the vastus lateralis, the Friedman test indicated significant differences among conditions (chi-squared [3] = 7.80,  = 0.050); however, there were no pairwise differences ( ≥ 0.094) and small effect sizes ( ≤ 0.269). For the rectus femoris, the Friedman test results showed no significant differences among conditions (chi-squared [3] = 2.44,  = 0.487). Across all muscles and conditions, low intraclass correlation coefficients and high standard errors of measurement were suggestive of poor reliability. Unlike resting hand muscles, interpulse interval duration has little influence on corticospinal excitability for the knee extensors during active contractions.