Adaptive interfaces offer new opportunities to enhance motivation and intensity of physical exercise. We developed VeRitas, a physiologically controlled exergame in which the player's exertion influences their avatar's performance. Three adaptive interventions are identified, varying display immersion, the level of physical resistance, and the accuracy of physiological data. A study examined players’ heart rates, rate of perceived exertion, physical power and workload. Our work reveals that enhanced immersion clearly increases physical exertion, and that complex interactions between adaptive physical resistance and falsified physiological data occur during gameplay. New directions for adaptive interfaces are proposed that enhance training and gaming performance. We suggest that users may benefit from delegating control and precision to exergaming systems, but this requires careful consideration around the design of awareness mechanisms to communicate performance.