## 2 Theoretical Model and Hypotheses
### A Research Model for Evaluating User Experience Factors  
Based on the theoretical intersection of TAM and DOI, this section outlines how these frameworks are integrated into a research model designed to assess the user experience factors influencing older adults' adoption of fitness apps. A review of the IT adoption literature reveals that many of the characteristics attributed to an innovation are inherent in the process of adopting new technologies ([PERSON] et al., 2015). Both TAM and DOI share a common premise: adopters evaluate innovations based on their perceptions of the embedded characteristics. Consequently, this study is analyzed from the perspectives of both DOI and TAM, which are often regarded as highly similar due to their complementary constructs ([PERSON] et al., 2015). Furthermore, it has been demonstrated that the constructs in TAM form integral components of the perceptual innovation profile ([PERSON] et al., 2015), highlighting how the integration of these two theories can lead to the development of more robust models ([PERSON] et al., 2015).  
The innovation attributes outlined in the DOI theory help explain the continued use of fitness applications. Considering that seniors vary in their ease of adoption and learning of new technologies, this study considered as exploratory factors the DOI's relative advantages (RA), compatibility (CO), trialability (TR), and observability (OB), and the TAM's perceived ease of use (PEU) and perceived usefulness (PU) of TAM. Also, the study identified behavioral intention of use (BIU) and behavior of use (BU) as objects to be validated. Furthermore, considering the distinctive design characteristics of fitness apps, this study adapted the DOI by incorporating gamification (GA) as a perceptual assessment variable.  
Gamification has received considerable attention ([PERSON] et al., 2015) because it is a means to support user engagement and enhance positive service use patterns. This can be achieved by enhancing the quality and productivity of user activities, social interactions, and behaviors ([PERSON] et al., 2015). The desired usage patterns are thought to emerge from the positive, intrinsically motivating experiences ([PERSON] et al., 2015) that gamification fosters through elements of play and motivation within services ([PERSON] et al., 2015). While gamification has been shown to yield positive outcomes,these effects are highly context-dependent, varying with the environment in which it is applied and the characteristics of the users engaging with it [28]. Therefore, the gamification experiences provided by the specific population and fitness apps in this study offer a unique opportunity for a targeted evaluation.  
Building on the theoretical foundations discussed earlier, the adapted technology acceptance model (TAM) and Decomposed Innovation (DOI) theory serve as the theoretical frameworks for this study. Based on the findings, a model has been developed to explain how older adults accept and use fitness apps. For a visual representation of this model, please refer to Figure 1.  
Having established a combined theoretical model, the next step is to formulate specific hypotheses that emerge from these integrated constructs, thereby guiding the empirical investigation into seniors' acceptance behaviors.