Anticipatory Postural Adjustments of Trunk Muscles during Unilateral Arm Flexion

Controversy regarding feedforward activation of transversus abdominis and limited studies regarding bilateral activation of trunk muscles during unilateral arm movement lead us to perform a study to evaluate bilateral anticipatory activity of trunk muscles during unilateral arm flexion. Eighteen healthy subjects participated in this study. The electromyographic activity of the right Anterior Deltoid (AD) and bilateral trunk muscles including the Transversus Abdominis/Obliquus Internus (TA/OI), Superficial Lumbar Multifidus (SLM) and Lumbar Erector Spinae (LES) during rapid flexion of the right upper limb in response to a visual stimulus was recorded and the onset latency and anticipatory activity of the recorded trunk muscles were calculated. The cotralateral TA/OI was the first muscle activated in anticipation of the right arm flexion. The ipsilateral TA/OI activated significantly later than all other trunk muscles (P<0.0005). In addition, anticipatory activity of the ipsilateral TA/OI was significantly lower than all other trunk muscles (P<0.0005). There was no significant difference in either onset latency or anticipatory activity among other trunk muscles (P>0.05). Normal anticipatory activity during unilateral arm flexion was not bilateral anticipatory co-activation of TA/OI. Further surveys are required to detect normal muscle activation pattern in healthy subjects prior to prescribing bilateral activation training of Transversus Abdominis for subjects with chronic low back pain.