Physical activity (PA) has largely been studied via reflective social cognitive approaches. Emerging correlational findings have shown the independent prediction of habit, which represents automatic behaviour from stimulus-response bonds (cued and repetitive action) with PA. Preliminary research suggests that habit during the preparation of exercise may be the most important predictor to enactment. An opposing view to habit is exercise variety which proposes that flexibility increases autonomy. Currently no experimental research has tested the effectiveness of incorporating habit or variety to promote PA. The purpose of this study was to conduct a randomized-controlled trial to examine the promotion of preparation habit formation compared with control and variety groups on PA behavior. New gym members (n=141) were recruited across Victoria, BC for this eight week, three-arm randomized-controlled trial. Participants in the habit and variety groups attended their respective workshops and received a phone call booster follow-up at week four. An ANCOVA controlling for baseline PA found the habit group to increase MVPA compared to the control and variety group for both accelerometry (control p<.05; d=.40; variety p=.07; d =.36) and self-report (control p<.05; d=.51; variety p<.05; d =.50). Manipulation checks showed that the habit group engaged in significantly more exercise consistency, cue use and demonstrated greater automaticity during preparation (?2=.07 to .16; p<.05). The findings support the utility of a habit building workshop on short-term PA change. Future research is needed to replicate these findings and extend the duration of assessment times to evaluate whether PA changes are sustained across time.