en Cellular and molecular Neuroscience Cellular and molecular Neuroscience Original Original <p><strong>Introduction:</strong> In this study we compared transcranial magnetic stimulation (TMS) elicited motor evoked potentials (MEPs) in a postural (bilateral low back extension: BLBE) and a respiratory (forced expiration during breath holding: FEBH) task.</p><p><strong>Methods:</strong> Using TMS of the left motor cortex, simultaneous patterns of corticospinal facilitation of the contralateral erector spinae (ES) and rectus abdominis (RA) muscles during graded voluntary activation were compared in seven healthy subjects. </p><p><strong>Result:</strong> The facilitation pattern demonstrated task dependency by showing that MEP amplitudes in the ES muscle tended to be smaller at any given contraction level in the FEBH task than in the BLBE task. </p><p><strong>Discussion:</strong> The results suggested a linear-type relationship between the size of MEPs with increasing background contraction of ES and RA in the BLBE task. However, both muscles showed a plateau effect with higher background contractions (>50% of maximum) during the FEBH task. The varied response of ES and RA across these two tasks reinforces the importance of task speci.c training in clinical settings.</p> Corticospinal Facilitation, Transcranial Magnetic Stimulation, Erector Spinae, Rectus Abdominis. 209 216 http://bcn.iums.ac.ir/browse.php?a_code=A-10-1-165&slc_lang=en&sid=1 Shapour Jaberzadeh 1370031947532846003916 1370031947532846003916 Yes Maryam Zoghi 1370031947532846003917 1370031947532846003917 No Prue Morgan 1370031947532846003918 1370031947532846003918 No Michael Storr 1370031947532846003919 1370031947532846003919 No