In the last 30 years, technological advances have altered occupational and recreational activities that have resulted in decreased daily physical activity. The resultant increase in physical inactivity and sedentary behaviour has been reported to be an independent risk factor for a number of chronic diseases. Any modality or strategy that results in increased physical activity levels and energy expenditure merits further investigation. Aim: to determine if active video games promote health enhancing physical activity in an asymptomatic adult population (18- 45 years of age). A secondary aim of the thesis is to examine affect states and psychological states associated with the use of active video games in an adult population since these factors are likely to have an effect on medium and long term adherence rates. Three studies were carried out to answer the research questions. Methods: Study 1 assessed the physiological responses to a sedentary video game, an active video game (Nintendo Wii Sports) and a modified version of the same active video game. Study 2 compared physiological and affect responses to stationary cycling and active video game cycling (GameBike). Finally, Study 3 compared the acute physiological and affect responses to two different types of active video games (fitness-themed and entertainment-themed), and also to two bouts of conventional exercise, an acute bout of moderate exercise intensity and a bout of self-selected intensity treadmill exercise that allowed for greater autonomy to research participants. Results: Study 1 showed that Wii Sports resulted in very light-to-light intensity exercise. A simple modification to play rules was enough to bring it to moderate intensity. Study 2 showed that participants were working at a higher metabolic and cardiovascular intensity during the GameBike session than during a matched workload conventional stationary cycling session. Active video game resulted in higher enjoyment ratings. Study 3 showed that the entertainment-themed video game was the best option to exercise at moderate intensity and maintain positive affect states, enhanced state of well-being and higher ratings of the state of flow. Conclusion: The findings of this research suggests that active video game results in very light-to-vigorous intensity exercise and therefore is a valid strategy to increase physical activity levels in a healthy adult population. This level of exercise is well within the current recommendations for physical activity. Active video game leads to significantly more positive affect states that conventional exercise and this may have important implications for public health since lack of enjoyment is a correlate in physical activity participation. Active video games may also play a positive role in reducing sedentary behaviour by reducing sitting time and increasing light-to-moderate intensity activities.