The research explores the influence of performance expectancy, social influence, hedonic motivation, habit, and user engagement in continued usage. Data was collected from 438 fitness app users in China through an online survey. Performance expectancy (β = -0.008, p = 0.874), social influence (β = 0.026, p = 0.557), hedonic motivation (β = 0.104, p = 0.064), and habit (β = 0.084, p = 0.165); none of these has a direct effect on continued user intention. However, each determinant significantly influenced gamified features (p < 0.05), which in turn had a strong and significant effect on continued app use (β = 0.593, p < 0.001). Mediation analysis confirmed that gamified features significantly mediated the relationships between the four antecedents and continued usage. The results show that gamification is crucial to improve user experience and promote long-term use of a fitness app.