## 2 Literature Review  
According to the reports from the Office of Disease Prevention and Health Promotion (ODPHP), 31 million adults age 50 or older were inactive with physical activities in 2014, the data from 2018 indicated that 37.3% of the population aged 65 and over engaged in no leisure-time physical activity (National Health Interview Survey) [13]. The slow increase of the data from 2008 to 2018 indicated that the awareness of healthy aging and the value of physical activities in leisure time is growing for the older population. However, after the COVID-19 pandemic, the unconfident and fear of the exercise environment and my own health conditions lead to a loss of trust to do exercise [14]. To support exercise intervention for older people, IEGs have been developed to reduce limits of distance, space, human resources, and entertainment, and many studies have reported the effectiveness of these IEGs [5; 7; 15; 16]. Immersive technology and exergames have been developing rapidly over the past decade, and their benefits have been launched [17; 18; 19; 20; 21]. Many different types of IEG are designed and tested for older people, usually to address a specific need in the context of disease management (e.g., Parkinson's disease and stroke), safety, presence, or access. Most of the studies used a specific solution to address the needs of patients or older users, such as chronic disease management, rehabilitation training, fall prevention, and balance challenges [22; 23; 24]. For example, [PERSON] and his team developed Canoe VR, an immersive exergame to support older adults' physical exercises, which has been well-received as an additional fitness tool [25]. [PERSON]'s findings indicate that using a VR exergame to exercise could improve both cognition and functional mobility among older adults [15]. Regarding the acceptance and usability of IEG, for instance, studies have reported positive experiences and perceived the technology as useful and easy to use, with little heightened gaming-related anxiety among older adults [26; 27]. Some studies have compared different factors of immersive exergames. The results from [PERSON]'s team's work indicate that usability and acceptance are not related to the type of training when using MR exergames with older adults [28]. Additionally, the physical environment in this study was designed to match the environment in the game developed by the team. [PERSON]'s team found that older adults preferred direct hand manipulation for interaction with virtual objects in immersive exergames, finding it more engaging and less cumbersome [8]. Although IEG for older adults shows a promising future, relevant perceptual factors are rarely discussed. The factors influencing the performance and effort expectation of playing exergames through immersive technologies such as virtual reality technology, remain less explored. A negative or passive attitude of perceived effort and performance would hamper the application of the immersive technology and experience benefits. Thus, it is necessary to understand the factors that specifically influence and how they can predict the perceived effort and performance of doing exercise through immersive exergames among the older population. There have been studies that examined the acceptance of health technologies among older adults using the unified UTAUT model [12] as the theoretical foundation and further extended contextual-specific predictors in various types of health technologies [29; 30; 31; 32]. These studies determined and examined several focal constructs including performance expectancy (PE), effort expectance (EE), social influence (SI), and facilitating conditions (FC). Self-efficiency, computer anxiety, perceived security, and doctors' opinions have been investigated in these studies. However, factors related to safety (e.g., perceived safety and physical posture through IEG should be considered, because these factors are widely associated with older adults' acceptance, choice, and use of a certain health-related technology [33, 34, 35, 36].