In this study, we investigated corticospinal excitability during mental sim
ulation of a leg extension movement with the technique of transcranial magn
etic stimulation. Motor evoked potentials were recorded in both knee extens
ors (quadriceps) and flexors (biceps femoris) in 19 trained participants (h
ealthy volunteers). The amplitude and latency of motor evoked potentials we
re compared in three conditions: (1) at rest, (2) during motor imagery, and
(3) at rest, immediately after motor imagery. The results showed a signifi
cant effect (p < 0.001) of conditions on motor evoked potentials amplitude
in the quadriceps but not in the biceps femoris. During motor imagery, the
size of motor evoked potentials in the quadriceps increased significantly (
p < 0.001) compared with rest and post-imagery conditions. Changes in motor
evoked potentials latency across conditions were not significant, however.
These results are consistent with previous studies in the upper limb and s
uggest that corticospinal excitability can be enhanced during motor imagery
to facilitate responses in specific lower limb muscles.