This study presents a user research evaluating the effectiveness of a dynamic difficulty adjustment (DDA) algorithm in a VR exergame, where game difficulty adapts in real time based on players’ heart rate and in-game score. Through a within-subject experiment involving 28 university students, we compared adaptive gameplay against a fixed-difficulty baseline using both objective performance metrics and subjective questionnaires. Results indicate that the DDA system is indeed effective in improving managing the player's physical and gameplay experience. The findings support the integration of adaptive difficulty to sustain engagement, optimize exertion levels, and enhance overall user experience in VR fitness applications.