By manipulation of movement reaction time we investigated the co-ordination between the motor command for arm movement and the associated 'anticipatory' postural response of the abdominal muscles. Limb movement reaction time was varied by changing the expectation of limb movement direction required in a choice-reaction-time task. Timing of the 'anticipatory' postural contraction of transversus abdominis (TrA) was invariant while the limb movement reaction time varied with changes in expectation of required response. In contrast, the timing of 'anticipatory' postural activity of the other abdominal muscles co-varied with limb movement reaction time. Dissociation of the behaviour of TrA and the other abdominal muscles suggests that TrA may be controlled independently of the motor command for limb movement in contrast to the other abdominal muscles.