Bilateral activation of the abdominal muscles induces longer reaction time

Bilateral deficit is the increase in reaction time during bilateral activation compared to unilateral activation. This has been reported extensively for the limb muscles and is argued to be due to concurrent inhibition through transcallosal pathways. Unlike the limb muscles, the axial muscles are commonly activated bilaterally during functional tasks and have bilateral projections to their motoneurones. Thus it is reasonable to hypothesise that there will be no bilateral deficit for these muscles.

Recordings of electromyographic (EMG) activity were made using surface electrodes placed bilaterally over the abdominal muscles in eight healthy right-handed subjects. Subjects performed either right or left pelvic elevation (unilateral abdominal activation), or posterior pelvic tilt (bilateral abdominal activation) "as fast as possible" in response to an auditory tone. Movements were performed as either a simple or choice reaction time task.

Bilateral activation induced significantly longer reaction time than unilateral activation, and was observed during both simple and choice reaction time tasks.

The results demonstrate that reaction time is delayed during bilateral activation of the abdominal muscles.

These findings suggest that bilateral deficit is present for the axial muscles. This could be mediated through inhibition at various levels of the nervous system or variations in postural demand.