Introduction: Despite the well-known benefits of physical activity, inactivity remains a challenge. Current technologies, through motivational messages, attempt to address this but often overlook individual differences. Objective: To assess the influence of a user's motivational profile on the effectiveness of messages from a virtual coach during exercise. Method: 67 participants completed two stepping sessions. A virtual coach provided them with motivational messages, tailored or not to their profile, using vocal and facial expressions. Results: The coach's presence did not change overall activity. However, prevention-oriented participants were more responsive to a tailored coach, increasing their activity, and less efficient with a mismatched coach. Intrinsic motivation was pivotal, especially with a promotion agent. Conclusion: Personalizing multimodal feedback from a virtual agent proves beneficial. The effect hinges on the user's profile and personality, key elements for physical activity support tools.