Recovery time of motor evoked potentials following lengthening and shortening muscle action in the tibialis anterior

Motor evoked potentials (MEP) at rest remain facilitated following an isometric muscle contraction. Because the pre-synaptic and post-synaptic control of shortening (SHO) and lengthening (LEN) contractions differs, the possibility exists that the recovery of the MEP is also task specific. The time course of MEP recovery was assessed in the tibialis anterior following SHO and LEN (0.26 rad/s) at 25% and 80% of maximal voluntary contraction. Following LEN and SHO contractions, the MEP recovered to baseline levels within 10 s. Despite task-specific differences between SHO and LEN contractions, the MEP facilitation from the augmented neurotransmitter release appears to be short lasting and not influenced by contraction type.