The intention-behavior gap is a well-known phenomenon in health behavior research. Individuals often intend to engage in healthy behaviors but fail to act. Fitness apps have emerged as a promising tool to bridge this gap and promote physical activity. This study aimed to understand the acceptance factors relevant to intending to use fitness apps (UTAUT2) and factors that prevent people from using fitness apps. By shedding light on behavioral-related factors such as organizational and motivational challenges, social inclusion, and volitional factors, this study contributes to explaining and bridging the intention-behavior gap. An online survey was conducted with a sample size of n = 100. Participants were asked about their fitness app usage, motivation for using fitness apps, and barriers preventing them from using them. The results showed that while hedonic motivation and habit influence users’ intention to use fitness apps, performance expectancy influences the intention to use a fitness app for non-users. Further, the results showed no influence of behavioral-related factors on the intention to use fitness apps but on sport behavior. The study’s findings offer implications for research and actionable guidelines for promoting physical activity and overcoming the intention-behavior gap.