Ipsilateral corticospinal responses to ballistic training are similar for various intensities and timings of TMS

Aim: In previous studies, unilateral ballistic training either increased or decreased corticospinal excitability for the untrained opposite limb. The objective here was to investigate whether these discrepancies can be explained by methodological differences such as the intensity of stimulation assessing excitability or the timing of excitability testing after training. Methods: Motor evoked potentials (MEP) were elicited by stimulating the ipsilateral cortex at high intensity (70% MEPmax) and low intensity (20% MEPmax) at specific time-points after performance of 300 ballistic movements of the index finger. Results: Ballistic practice significantly facilitated MEP size for high-intensity stimuli, whereas responses to low-intensity stimulation were variable. MEP sizes at individual time-points were not significantly facilitated until 4 min after training, although there was no difference between early and late responses when grouped over multiple time-points. Conclusions: The data indicate that previous discrepancies in ipsilateral responses to ballistic training cannot be attributed to specific procedures used to assess corticospinal excitability as there was no tendency towards depression of MEP amplitude at any point post-exercise for both testing intensities. This suggests that other experimental factors such as locus of attention or availability of visual feedback are more likely to account for the discrepancies.