This section introduces the components of Flow Theory, the GameFlow model, adherence, the connection between adherence and Flow Theory in the context of physical exercise, and UCD.

Flow Theory, a concept within positive psychology [18], was developed by Csikszentmihalyi through interviews and questionnaires with various individuals, including chess players, rock climbers, dancers, and amateur athletes. These individuals exhibited deep engagement and devotion to their activities, reporting feelings of exhilaration, intense focus, and effortlessness. They did not perceive their experiences as time wasted. Flow, as outlined by Csikszentmihalyi, is considered a fundamental element of enjoyment [18]. He identified 8 common elements in the flow experience, as detailed in Textbox 1.

GameFlow [19] is a model that offers criteria for making video games enjoyable and fun. This model is based on Csikszentmihalyi’s Flow Theory [20] and integrates usability and user experience criteria. The GameFlow model consists of 8 elements. The first 7 elements correspond to the Flow Theory: concentration, challenge, player skill, control, clear goals, feedback, and immersion. Concentration is essential to stay focused on video game tasks. Challenges must be included according to the player’s abilities. Player skills encourage the development of skills. The player must perceive control over the activities and clear goals must be described. Further, adequate feedback must be received at the appropriate time. Immersion helps the player feel attracted to the game by forgetting their surroundings. Social interaction includes communication between players. The latter element does not correspond to the Flow Theory, but the authors consider it fundamental to enjoy the games.

Video games developed with the Flow Theory aim to keep players engaged by providing a fun challenge, clear objectives, and continuous progress feedback. This approach creates a sense of control and immersion, enabling players to escape from the worries of everyday life and, as a result, lose track of time while playing.

Adherence is defined as “the extent to which a patient’s behavior matches the recommendations of the health service provider” [21]. The medical term instructions encompasses a range of activities, including taking medication, exercising, and following other recommendations from health care providers [22]. It is crucial to identify adherence factors in patients as this plays a vital role in successfully completing an exercise program.

Some randomized trials of exercise interventions have provided evidence suggesting that exercise can offer mortality benefits similar to various pharmacological interventions in the context of secondary prevention of coronary heart disease, stroke rehabilitation, and diabetes prevention [23]. The adherence to exercise regimens serves as a predictor of long-term efficacy in exercise therapy, leading to reduced pain and improved physical function [24], and it is a central component of injury rehabilitation [25].

Promoting treatment adherence presents a challenge across various health domains [26]. Elbe et al [27] demonstrated that individuals participating in a randomized exercise intervention reported a high level of flow, an intrinsically motivating state that can positively impact long-term adherence. Petosa and Holtz [28] aimed to test the Flow Theory of exercise adherence and discovered that intrinsic motivation plays a crucial role in sustaining adherence to physical activities. Schüler and Brunner [29] proposed that experiencing flow during physical activities can enhance long-term adherence, as individuals find the activity rewarding and enjoyable, increasing the likelihood of regular participation.

Csikszentmihalyi et al [30] contended that individuals experience a highly intrinsically motivated state of flow when they are appropriately challenged by their tasks, and their skills are well-balanced. Maintaining individuals in a state of flow during physical rehabilitation promotes better long-term adherence to treatment [31].

UCD takes various definitions, but all share a common emphasis on addressing user needs throughout the design process, ultimately aiming to create products that are usable and understandable [32]. A UCD approach typically involves 3 key phases: analysis, design, and evaluation [33]. Integrating UCD into software development processes ensures that user experience is a core consideration from the project’s inception, leading to a highly usable end product.

A conceptual framework is a network of interconnected concepts designed to provide a comprehensive understanding of the phenomenon of interest [34]. Our development process for the conceptual framework is based on iterative analysis techniques, encompassing 8 phases as outlined by Jabareen [35], which is illustrated in Figure 1.

In this study, the development of the conceptual framework will be condensed into 6 stages. The phases of “Validating the Conceptual Framework” and “Rethinking the Conceptual Framework” are aspects that we anticipate exploring in future research. The following sections will provide a detailed description of the implementation of each of the aforementioned phases.

In the first phase, the process commenced with a comprehensive review of multidisciplinary texts. To conduct this research, we adhered to the recommendations outlined by Templier and Paré [36] and Cant et al [37]. The literature review is presented in Multimedia Appendix 1 (also see [38-52]).

During these phases, key adherence factors were extracted from the “Results” and “Discussion” sections of each paper in the reviews. Subsequently, the information obtained through data extraction underwent a comparative analysis by 2 reviewers (JFAA and MPB-C). In instances of disagreement, the reviewers engaged in discussions until a consensus was reached. The identified key adherence factors can be found in Multimedia Appendix 2 (also see [38-52]).

In the fourth phase, the goal was to organize and categorize the concepts based on their characteristics or attributes. As many concepts serve similar purposes, this phase involved categorizing them accordingly.

The objective of the fifth phase was to significantly reduce the number of concepts, making it manageable for manipulation. The concept integration is presented in Multimedia Appendix 3.

In the sixth phase, the objective was to create a diagram or model illustrating the relationships between the identified concepts. Following this, the team proceeded to integrate these concepts into the serious game development process. This involved conducting a series of analyses on existing theories related to product/software development. After careful analysis, the team identified 2 cross-cutting themes: UCD [33] and the GameFlow Model. UCD principles focus on the development of engaging products that encourage user adoption, taking into account user characteristics and needs right from the beginning of the development. Another model, the GameFlow model [19], was used to infuse more enjoyment into video games and to integrate the principles of Flow Theory into the development process. This theory has been found to enhance treatment adherence [31].

The first phase consisted of 3 interlinked steps aimed at identifying the characteristics of target users, as well as differences related to age and video game genre preferences.

In the first step, it is essential to consider the diverse characteristics of the population when creating a product or service. Individuals vary in terms of physical, social, psychological, and technical conditions. Understanding and considering these differences in a system offer numerous advantages, including broader adoption, cost savings, and the development of safer and more efficient systems [54]. It is vital to involve users’ perspectives from the outset, as this is crucial for accurately identifying and categorizing their needs and expectations, ultimately transforming them into achievable and specific requirements. In the second step, developing serious games necessitates the recognition of age-related preferences for different types of video games. In the third step, the video game genre should be taken into account to enhance patient acceptance of the game. Figure 3 illustrates this process.

Identifying patient requirements and characteristics is a crucial step before commencing treatment and designing a serious game. In our review of papers [38-40,46-49], we found that the initial exploration and exercise history were described in 47% (7/15) of the papers. To enhance adherence, it is important to consider elements such as the patient’s health status, prior therapies, and habits. In health care, a multidisciplinary team must assess patients’ physical and mental characteristics as these factors can significantly impact adherence. For instance, a patient with a chronic condition that causes pain may have reduced adherence to rehabilitation exercises [55]. It is the responsibility of health care professionals to prescribe treatments that alleviate or eliminate such pain. Additionally, evaluating the patient’s history of previous therapies and identifying habits, such as smoking, alcohol consumption, and exercise routines, can help determine the most effective approach to enhance adherence to new exercises.

An initial examination by health care professionals is essential. This examination allows for a thorough assessment of the patient’s health status, aiming to identify potential barriers or facilitators to treatment adherence. Consequently, it enables the establishment of personalized treatments and exercise regimens with appropriate intensity, duration, frequency, and exercise types, ultimately improving adherence.

Age often influences an individual’s preference for specific types of games. When patients feel comfortable using a video game, they are more likely to enter a state of flow, which, in turn, promotes usage and enhances adherence. Several studies have explored how age can impact motivation and overall experience [56]. Hence, it is essential to consider age during the planning and development of a serious game. Children tend to be more motivated by games featuring elements of fantasy, socialization, and a balance of fun and challenge [57]. Conversely, teenagers and adults generally prefer games with competitive elements, aiming to become the top player and overcome challenging levels. Additionally, as children mature into teenagers, their interest often shifts toward social interaction through online games, including e-sports and massively multiplayer online role-playing games [58]. Lastly, it is important to note that many older adults may experience a decline in processing speed, cognitive functions, and reflexes [59]. Consequently, it is advisable to recommend puzzles or casual video games [60] as they are characterized by simple rules and do not require special skills to play.

Serious games should align with individuals’ gaming preferences and expectations. Everyone has their own affinity for specific video game genres, which can lead to enjoyment and, subsequently, bring about behavioral changes that foster game adherence with increased enthusiasm and frequency. Video games are classified into various genres based on their gameplay and style. Lucas and Sherry [61], drawing from sources such as video game manufacturers, gaming websites, and gaming magazines, outlined a classification that includes genres such as Strategy, Fantasy/Role-Playing Games, Adventure, First-Person Shooter, Fighting, Simulation, Classic Arcade Games, Card/Dice Games, Quiz/Trivia, Board Games, Kids Games, Sports, Racing/Speed, and Puzzles. Research has indicated that genre preferences may also be influenced by an individual’s gender [62]. Typically, men tend to gravitate toward genres such as Sports, Role-Playing Games, First-Person Shooter, and Adventure games, while women often favor Racing/Speed, Puzzles, and Adventure games. Interestingly, studies have demonstrated that both men and women share a common preference for Adventure games.

Building upon the groundwork laid in the “understand context” phase, which involves identifying the patient’s requirements, characteristics, and selecting an appropriate game type through initial exploration, the phase of constructing the serious game commences. The development phase is focused on integrating elements derived from key adherence factors and the GameFlow model into the video game.

Incorporating elements from the original GameFlow model, this framework utilizes elements such as concentration, feedback, immersion, and social interaction. As for challenge/player skill and control, some authors argue against separating these elements [63,64], so they have been integrated into the concept of adaptivity. Within this framework, adaptivity is intertwined with maintaining a delicate equilibrium between the patient’s challenge and skill levels, which is especially crucial for those with physical limitations. A gradual progression of challenge is essential, allowing the patient to maintain a sense of control and receive personalized exercises tailored to their specific limitations.

From the key adherence factors, accessibility is integrated with usability. This combination is based on studies that have emphasized the interdependence of these 2 concepts when implementing an interactive system, rather than treating them as isolated elements [65].

By combining the principles of the GameFlow model with key adherence factors in the development of the serious game, we establish a foundation for crafting an enjoyable video game that not only motivates patients to sustain its use but also bolsters treatment adherence. Figure 4 illustrates the key components of this phase.

Developing adaptive games offers the opportunity to tailor exercise programs to better align with patients’ limitations. Personalized exercise programs, encompassing aspects such as exercise type, duration, frequency, and intensity, play a crucial role in promoting adherence. Such personalization enhances the patient’s perception of progress in their rehabilitation treatment. It is noteworthy that in 60% (9/15) of the papers in our review, the concept of a personalized exercise program was discussed [39,41-44,48,49,51,52]. Maintaining a balance between challenge and skill, while adjusting difficulty based on the player’s needs, is essential to ensure a positive gaming experience, prolong usage, and sustain motivation.

Research has indicated that an appropriate level of challenge relative to the player’s skills fosters improved acceptance, commitment, motivation, and learning, ultimately leading to prolonged use [66].

Achieving an optimal immersion experience, deep enjoyment, and heightened engagement relies on maintaining a balance between an individual’s abilities and the challenges they face. When the challenge is not sufficiently difficult, it can lead to feelings of boredom or detachment. Conversely, when the challenge surpasses an individual’s ability, it can lead to anxiety, stress, and ultimately, resignation. People’s abilities and affective states evolve over time as they become proficient in the game. If a serious game system for physical rehabilitation does not incorporate adaptability in its challenge levels, patients are at a higher risk of becoming disengaged, experiencing boredom, and ultimately discontinuing their treatment [67].

An adaptive game can effectively manage challenge levels for each individual, preventing players from becoming stuck, tailoring the game to their preferences and requirements, and even identifying when the game is no longer providing an adequate level of challenge.

Incorporating adaptability into a game involves increasing the difficulty level in line with the player’s skill. A common approach to achieving this is by including an option to manually adjust the difficulty, which clinicians can use to tailor the game’s challenge to the patient’s abilities. Various techniques are utilized, such as those based on scoring systems [67], procedural content generation and semantic modeling [68], genetic algorithms [69], and artificial intelligence [70]. An effective adaptive system should possess the capability to analyze the patient’s skill information and draw inferences from the data collected. This allows the patient to adjust the game’s challenge level, providing the player with a sense of control.

In our review, progress information was found in only 33% (5/15) of the papers [39,43,45,48,49]. One of the initial steps in enhancing adherence is to determine whether the treatment is being correctly followed. Often, physicians may have limited information regarding treatment adherence. In many cases, physicians rely solely on the information provided by the patient [26]. However, this approach can be problematic, especially in situations where rehabilitation is slow and gradual. It is crucial for patients to receive objective data that keep them informed about their progress and help them understand the changes and improvements they are experiencing. Recognizing the benefits attained through exercise is vital for sustaining engagement and enhancing adherence. To facilitate this, serious games can offer accessible and comprehensible reports on the rehabilitation process. These reports may include graphical representations and statistics, as the inclusion of objective measures serves to motivate both patients and medical professionals to persist with the treatment.

The games should engender intense concentration or complete absorption. As Csikszentmihalyi [20] has highlighted, concentration is a fundamental element for achieving a state of flow. Prior research has demonstrated that maintaining the patient’s concentration on the game can redirect their focus away from their medical treatment, the ailment they are contending with, and in certain instances, their pain. This diversion contributes to improved adherence to rehabilitation exercises [38,71]. The game should capture attention from the outset and sustain it throughout the gaming experience. High concentration helps in diverting attention away from external stimuli, ensuring a consistent focus [72]. To foster concentration in a video game, it is important to avoid overloading the game scene with distractions. For instance, this could involve limiting the number of nonplayer characters, moving objects, vehicles, obstacles, and other elements [73]. Additionally, clear task objectives are essential to reduce negative emotions and foster positive ones.

A common element found in all 15 of the papers in our review [38-52] was feedback. Feedback is crucial for learning, and as noted by Pritchard et al [74], it has a positive impact on performance. Feedback serves as a valuable guide to help individuals achieve specific goals. It plays an essential role in instructional design, enhancing and sustaining cognitive engagement, and ultimately contributing to treatment adherence. Feedback constitutes a fundamental interaction between the game and the user, distinguishing between the expected and actual performance. It can be implemented through various modalities, including visual, auditory, haptic, or thermal options. Visual feedback can be delivered through messages or avatars that assist in correcting improper movements. Additionally, visual feedback may take the form of scoring, rewards, achievements, and experience points [75]. Auditory feedback is conveyed through elements such as voices, sound effects, and variations in background music [76]. Haptic feedback is typically integrated through an interactive interface, utilizing servomotors with varying intensity levels to inform the patient about the correctness of their exercise performance [77]. By contrast, while less commonly used, thermal feedback has the potential to convey emotions to individuals [78].

The utilization of technology, particularly through wearable systems, proves instrumental in monitoring exercises, collecting posture information, and tracking limb movements, thereby bolstering treatment adherence [79]. Wang et al [79] conducted a systematic review to identify and categorize interactive wearable systems designed for monitoring movement and posture during upper-body rehabilitation. Commonly, accelerometers and inertial measurement units were used to monitor and offer feedback on movement performance during rehabilitation. Furthermore, the use of smartphones for monitoring physical activity and providing feedback is on the rise. As noted by Collado-Mateo et al [39], technology offers precise control over physical activity, allowing for the customization of exercise plans in terms of frequency, duration, and timing. It also enables real-time feedback, reminders, communication between patients and health care professionals, and the sharing of activities with colleagues, among other advantages.

Lastly, gathering user feedback on the visual and operational aspects of the video game is crucial for enhancing the interactive system. This feedback can be collected in written formats, including questionnaires and comments, as well as through verbal formats, such as interviews.

Immersion involves a state of being unaware of time and the real world, providing a distraction from daily concerns. This state is also considered crucial for truly enjoying the game [80]. A pleasurable experience when using a video game lies in its capacity to induce immersive experiences. Therefore, the incorporation of immersion is key to creating an environment where the player feels immersed in the video game. Research suggests that video games featuring immersive elements lead to heightened enjoyment and improved adherence to the intervention regimen [81].

In the development of the serious game, the quest for enhanced immersion necessitates an environment devoid of external distractions or an overabundance of environmental elements [82]. Both the story (the events within the virtual world) and the narrative (how these events are structured and sequenced) are vital elements in achieving this immersion. These elements, when used effectively, evoke empathy and foster emotional engagement among users [83]. Audio is another crucial aspect to consider in achieving immersion; sound effects and music are also used in occupational therapy to assist patients in exercising joints and muscles [84]. Music, in particular, stimulates the brain areas related to emotional processing and motor control [85]. Research has demonstrated that background music and sound effects in video games contribute to immersion and have the potential to alleviate tension [86]. However, it is important that background music is not chosen randomly in a serious game. It should be thoughtfully integrated to establish a connection with other elements, such as the environment and the storyline, to resonate with the user. Furthermore, audio elements such as sound effects, ambient sounds, and nonplayer character voices enhance emotional engagement and stimulate the player’s imagination [87]. Therefore, the way sound is perceived can significantly influence the player’s attention and their unconscious emotional state.

The perception of therapy was discussed in 67% (10/15) of the papers included in our review [38-41,44,46-49,52]. It is crucial to inform and remind the patient about the advantages of adhering to the rehabilitation plan and make them aware of the expected exercise outcomes. This approach can significantly boost exercise adherence.

Participants are more likely to engage in and sustain their prescribed exercises when they observe improvements in their health as a direct result of their treatment adherence. Communicating the benefits, objectives, expectations, and even the sensations associated with these exercises is a responsibility shared by health care professionals both in their clinical practice and within the serious game. Health care professionals should exercise caution when discussing gradual changes during therapy to ensure that patients maintain realistic expectations and avoid overly optimistic beliefs [39]. In the serious game, patients should receive information through on-screen messages, images, audio, or video about each exercise they perform in the virtual game and the expected benefits.

Self-efficacy, defined as an individual’s confidence in their ability to successfully perform a behavior or achieve an objective [94], is widely recognized as a pivotal element for enhancing adherence. In fact, self-efficacy was a key focus in 73% (11/15) of the papers within our review [38,39,42-47,49,51,52]. This concept holds the power to instigate behavioral change, particularly in individuals undergoing treatment. Self-efficacy has found application in various health domains, including weight loss, nutrition, and physical activity. In the serious game being developed, several elements can be incorporated to boost self-efficacy, such as promoting familiarity with other participants through social support, facilitating communication with staff, optimizing the environment, and providing constructive feedback. Fostering familiarity with other participants in the program connects patients with individuals who share similar experiences, promoting social interaction [39-42,44-49,51]. Establishing familiarity with the staff involves health care professionals providing formal social support, support, and motivation [38-52]. Creating a familiar and supportive environment, which encompasses the facilities, home settings, and materials used, is essential for enabling autonomy and a sense of relatedness. This boosts individuals’ confidence as they perform exercises, especially when supported by devices and in a secure environment [40,41,43-46,48,49]. Finally, offering feedback on the progress toward goals achieved after each rehabilitation session significantly contributes to enhancing patients’ perceived self-efficacy [39].

Usability and accessibility should be fundamental components of an interactive system [65] and are crucial elements to incorporate into the serious game. Individuals engaged in an intervention regimen using a serious game should have access to user interfaces and data-acquisition devices that are user-friendly and easy to use. Research has suggested that proper interaction with software applications in a rehabilitation treatment leads to improved adherence to the intervention, as individuals feel more confident using the interactive system [103]. Usability pertains to how users use the system to accomplish specific goals with effectiveness, efficiency, satisfaction, and ease [104]. Accessibility encompasses considerations related to designing systems that are accessible to individuals with various physical, sensory, and cognitive abilities [105]. In our review, accessibility was addressed in 60% (9/15) of the papers [40,41,43-49]. If systems prioritize accessibility without considering usability, individuals with disabilities may be able to use the software, but they might not have an enjoyable user experience due to usability errors (eg, a saturation of elements, incorrect placement of text or images, and difficulty to use). Conversely, if a system focuses on usability without considering accessibility, it means that the needs of individuals with disabilities are not taken into account. Methods of usability engineering can be applied to ensure a user-friendly experience [106]. Additionally, established strategies and guidelines are available to incorporate accessibility features into video games [107,108], web-based systems [109], and mobile apps [110].