This work is part of a larger project exploring how affective computing can support the design of player-adaptive video games. We investigate how controlling some of the game mechanics using biofeedback affects physiological reactions, performance, and the experience of the player. More specifically, we assess how different game speeds affect player physiological responses and game performance. We developed a game prototype with Unity1 which includes a biofeedback loop system based on the level of physiological activation through skin resistance (SKR) measured with a smart wristband. In two conditions, the player moving speed was driven by SKR, to increase (respectively decrease) speed when the player is less activated (SKR decreases). A control condition was also used where player speed is not affected by SKR. We collected and synchronized biosignals (heart rate [HR], skin temperature [SKT] and SKR), and game information, such as the total time to complete a level, the number of ennemy collisions, and their timestamps. Additionally, emotional profiling (TIPI, I-Panas-SF), measured using a Likert scale in a post-task questionnaire, and semi-open questions about the game experience were used. The results show that SKR was significantly higher in the speed down condition, and game performance improved in the speed up condition. Study collected data involved 13 participants (10 males, 3 females) aged from 18 to 50 (M = 24.30, SD = 9.00). Most of the participants felt engaged with the game (M = 6.46, SD = 0.96) and their level of immersion was not affected by wearing the prototype smartband. Thematic analysis (TA) revealed that the game speed impacted the participants stress levels such as high speed was more stressful than hypothesized; many participants described game level-specific effects in which they felt that their speed of movement reflected their level of stress or relaxation. Slowing down the participants indeed increased the participant stress levels, but counter intuitively, more stress was detected in high speed situations.