Popularity and pervasiveness of mobile apps have great potential to motivate healthy behavioural modifications. Considering the increased prevalence of obesity, overweight and sedentary lifestyle in modern societies, this study takes an important step in proposing design elements for fitness apps that can stimulate enhanced physical activity behaviour. We posit that persuasive technology principles infused into social cognitive theory elements will lead to the design of successful fitness apps. We empirically validated our conceptualization using app descriptions and lifecycle data of mobile apps. Implications for practice and future research are discussed.