TMS will be performed to investigate the mechanisms of this training on cortical plasticity as indexed by cortical excitability changes. For the MEP study, we will initially adjust TMS intensity to achieve a baseline MEP in the tibialis anterior muscle of the leg to about 1 mV peak-to-peak amplitude before intervention. Stimulation intensity will be kept constant for each subject throughout the study. The MEPs will be recorded in a computer for off-line analysis. We will record 10 MEPs for each time and average their peak-to-peak amplitude. For the paired pulse stimulation, a first subthreshold conditioning stimulus will be applied, followed at a variable interstimulus interval (ISI), by a second suprathreshold stimulus. We will use the following ISIs - 2, 3, 4, 6, 9, 10, 12, 15 ms. The percentage of change for each ISI before and after treatment will be calculated from the MEPs and will therefore important to measure changes in intracortical facilitation and inhibition. Each session will last approximate 1 hour including set-up time.