Synchronizing hand and foot movements under reactive versus predictive control results in differential timing structures between the responses. Under reactive control, where the movement is externally triggered, the electromyographic (EMG) responses are synchronized, resulting in the hand displacement preceding the foot. Under predictive control, where the movement is self-paced, the motor commands are organized such that the displacement onset occurs relatively synchronously, requiring the EMG onset of the foot to precede that of the hand. The current study used a startling acoustic stimulus (SAS), which is known to involuntarily trigger a prepared response, to investigate whether these results are due to differences in the pre-programmed timing initiation structure of the responses. Participants (n=17) performed isolated and synchronous movements of the right heel and right hand under both reactive and predictive modes of control. The reactive condition involved a simple reaction time (RT) task where participants performed the required movement in response to a visual go-signal. The predictive condition involved an anticipation-timing task where participants initiated the required movement coincidently with a sweeping clock hand reaching a target. On a subset of trials, a SAS (114 dB) was presented 150 ms prior to the imperative stimulus. Results from the SAS trials revealed that while the differential timing structures between the responses was maintained under both reactive and predictive control, the EMG onset asynchrony under predictive control was significantly smaller following the SAS. Additionally, there was no difference in the effect of the SAS when the movements were performed in isolation versus synchronously. Together, these results suggest that the timing between the responses, which differs between the two control modes, is pre-programmed; however, under predictive control, an increase in cortical activation from the SAS may have shortened the between-limb delay.