Exertion games are digital games that encourage physical activity. Understanding how to make these games engaging is therefore important for promoting physical activity. Game balancing to mitigate wide differences in ability can help provide the right level of challenge and enhance engagement in social exertion games where players compete against each other. However, there is a lack of understanding of exertion game balancing design in non-parallel exertion games, where one player's actions in uence the other's performance. Game balancing in non-parallel games should be able to moderate the influence each player has over the other, but current knowledge of exertion game balancing provides little guidance on how to achieve this. This thesis aims to address gaps in exertion game balancing design by investigating the interrelationship between game adjustments, game balancing and player engagement. The thesis presents the different game adjustments that can be applied in exertion games, which I applied to the traditional table tennis game, a digital table tennis game and a digitally augmented table tennis game to study this interrelationship. It also explores differences in balancing between different game worlds and investigates how digital tech- nology could be used as a resource for exertion game balancing design. I designed four experiments to understand (i) balancing in different game worlds, (ii) static and dynamic sport equipment (i.e. bat and table) adjustments, (iii) the effects of altering players' performances such as their styles of play, and (iv) the relationship between the restriction on players' performance and player engagement. With (i) I found that game adjustments impact differently in different game worlds because the level of skill required to play the game (e.g. degree of accuracy of players' actions required to play) is different. However, in (i) I did not enhance player engagement, which is why I carried out a study (ii) to investigate game adjustments that could alter players' skills and players' performance in a more controllable way. This resulted in more effective adjustments for enhancing player engagement. With (iii) I investigated game balancing through altering the players' performances differently, and identified two ways that the restriction on players' performance can contribute in balancing the game: through the degree of challenge imposed by the restriction in place, and through the style of play the restriction encouraged from the more skilled players. To further investigate these study results I conducted another study (iv) to get deeper insight into the relationship between the restriction on players' performance and player engagement. The results of the case studies including the game design considerations derived in (i), game design strategies derived in (ii) and (iii), and the understanding about the relationship between the restriction on players' performance and player engagement (iv), can help in making exertion games more engaging. Although the findings and contributions were derived from the study of the table tennis game, I discuss how the findings can be applied to other exertion games. I hope the insights and contributions provided in this research can be generalised to inspire the design of future exertion games with the ultimate goal of encouraging people to engage in physical activity.