Cognitive fatigue (CF) is the result of sustained mental effort and is characterized by subjective feelings of exhaustion and declines in cognitive performance. Interestingly, CF is also associated with slowed simple reaction time (RT); however, it is not known what stage of motor processing (perception, preparation, or response initiation) underlies this effect. This study aimed to partially resolve this question by examining whether CF is associated with a decline in motor preparation. Preparation level was indexed using simple RT and the StartReact effect, wherein a prepared movement is involuntarily triggered by a 120dB startling acoustic stimulus (SAS). It was predicted that if decreased motor preparatory activation underlies slower RTs associated with CF, then a diminished StartReact effect would also be observed following cognitive task completion. CF was induced through a 60min dual-task, wherein participants (n=8) were repeatedly required to remember a series of letters whilst responding to sequential mathematical operations. Pre- and post-tests consisted of subjective fatigue measurements using a short questionnaire and a simple RT task, involving a targeted wrist extension in response to an auditory GO-signal. On 25% of trials, a SAS replaced the normal GO-signal. Analysis revealed a significant speeding effect of the SAS on RT (p<.001) as well as significantly slower RT performance from the pre- to post-test (p<.050), but no interaction between the factors (p=.268). Although additional data will be collected to confirm this hypothesis, this study indicates that slowed RT in response to CF is at least partially attributable to decreased motor preparation.