1.1 The Theory of Planned Behavior
The Theory of Planned Behavior (TPB) is an extension of the theory of rational action (TRA) [25–26]. The TRA mentioned that intention is the best predictor of actual behavior, and intention can produce an individual's attitude towards behavior, that is, to view behavior with subjective norms, and subjective norms can produce beliefs about the opinions of others, as well as an individual's motivation to agree with the opinions of others [27]. When applied to fitness, if an individual is not a sportsman, but believes in his position in the life of other important people (such as spouse, children, friends), and these people think he should participate in fitness, he will participate in fitness.
The difference between TBP and TRA is that intention is not the only predictor of behavior. Especially in some situations, individuals may lack some control to respond to behavior, or there is a long interval between intention and behavior. In addition to subjective norms and attitudes, TPB also mentions perceptual behavior control, that is, personal perception can express behavior, which will also affect performance results. Understanding behavioral intention can improve fitness exercise behavior and there is a difference between intention and maintaining fitness behavior. Therefore, when developing fitness intervention, it is necessary to understand that fitness exercise may be phased. For example, when using TPB for research, e-mail information is more able to control the situation and effectively improve fitness exercise intention and actual fitness exercise behavior. Banting et al. (2009) also mentioned [28] that only intention, that is, as predicted by theory, will not affect behavior, but the quality and attitude of intention are the key. Research on TPB and TRA shows that TPB is significantly better than TRA in predicting fitness behavior, and the main difference is in perceptual behavior control [29]. Moreover, some researchers have focused their research on fitness behavior and continuous participation, and the results show that perceptual behavior control and subjective norms are the beginning of personal fitness [30]. Therefore, in practical application, the instructor should encourage the important others of the participants, let them help the participants increase their fitness activities, and at the same time, should improve the participants' attitude towards fitness activities and the intention of actual fitness activities, to achieve the goal of transferring the participants from possible fitness activities to actual fitness activities.
1.2 The Social Cognitive Theory
The social cognitive theory (SCT) framework shows that individuals, behavior, and environment interact with each other, and individual factors are the determinants of other factors. In fact, not only the environment affects behavior, but also behavior affects the environment. All three factors together affect our thoughts, behaviors, and feelings. In addition to the interaction between different factors, the biggest criterion of this orientation is the belief that individuals can successfully perform their behavior (self-efficacy), that is, self-efficacy is related to efficacy beliefs and efficacy expectations [31]. In short, it is "Can I?". Self-efficacy can affect many behaviors, especially those that challenge us. For example, if an individual has more physical activities or has maintained fitness for many years, once he believes that he can adopt and maintain the behavior of the above problems, he will tend to do it [31]. Self-efficacy is a predictor of good behavior in different health situations, such as smoking cessation, weight management, and heart disease rehabilitation [32]. In the field of fitness, self-efficacy has produced many consistent findings: self-efficacy can improve fitness participation, and vice versa [33]. Self-efficacy plays a very important role when fitness exercises pose great challenges. For example, research shows that the theory of self-efficacy can predict the fitness exercise behavior of patients with stage I and stage II diabetes and patients with circulatory system diseases. Moreover, when individuals resume their fitness activities, fitness activities will restore their self-efficacy [34]. In short, a social cognitive theory has been unanimously supported by researchers, and self-efficacy plays a role in improving fitness behavior.
Since the interaction between individual factors was mentioned in the social cognitive theory, researchers not only investigated the prediction behavior of self-efficacy, but also investigated the impact of fitness on self-efficacy. In particular, in chronic diseases and fitness exercise tests, fitness exercise can be the source or catalyst of self-efficacy. Many researchers have studied different fitness behaviors, such as walking, strength training, volleyball, aerobic dance, and fitness courses, and the results show support [35]. A study of applying self-efficacy courses to change fitness exercise behavior found that after the intervention of a 10-week high school physical education curriculum, the measured indicators and self-efficacy level were significantly correlated, especially for girls [36]. Ashford, et al. (2010) conducted a comprehensive analysis to investigate which intervention strategy is the most effective determinant for improving self-efficacy in physical activities. The results showed that there are 27 unique strategies to improve self-efficacy, among which, providing feedback for better performance and alternative experience provides the most effective impact on the change of self-efficacy in physical activities[37].
1.3 The Self-Determination Theory
Self-Determination Theory (SDT) mainly focuses on three basic psychological needs: competence, relationship, and self-decision. Moreover, self-determined behavior also focuses on the continuum of external motivation and internal motivation. In particular, spontaneous planning represents self-determining motivation. In other words, self-determining is not controlled by external incentives or pressure. This process can trigger internal motivation behavior. Relevant research believes that [38–39]: the above three different psychological needs are an inherent motivation. After connecting with other social environments (sense of relationship), they affect the other environment (ability) and the individual's initial participation (spontaneous) consciousness. Hagger & Chatzisarantis (2007) [40] used SDT to predict fitness exercise behavior. The results showed that: in fitness exercise behavior, spontaneous participants had a stronger social support system, and showed a stronger motivation and improved fitness attachment. When the three psychological needs of relationship, self -determination, and competence were met, the degree of attachment was significantly improved, and the level of internal motivation was increased.
The research on the relationship between the self-determined theory and the intrinsic motivation of physical activities shows that participants can distinguish the difference between internal and external goals in the field of physical activities [41], and more spontaneous planned fitness exercises can produce a higher level of attachment than controlled planned fitness exercises [42–43]. SDT let us know that participants with high intrinsic motivation (such as getting fun and fun from fitness) have a higher attachment to fitness courses than participants with external motivation (such as improving appearance to attract the opposite sex). To enable participants to participate continuously, build a spontaneous supportive climate in the physical activity situation and cultivate self-determined formal motivation, some external motivation (such as social support and reward) is allowed in this process. The fitness instructor can make the participants feel more competent and spontaneous in the class, which can trigger a higher level of attachment, and provide a positive social environment to help meet the need for a sense of relationship, to build a longer period of attachment.
1.4 The transtheoretical model (TTM)
In the past decade, the theories, models, and courses on behavior change have focused on eliminating or controlling negative behaviors (such as drinking, smoking, drug abuse, and overeating) rather than improving positive behaviors (such as fitness and exercise). In essence, the models and theories mentioned above, such as classical restriction, demonstration, and the relationship between stimulus and response, have been used to intervene or reduce different negative behaviors. These research results show that the habits formed over a long time are particularly difficult to change. Although behavioral changes (such as abstinence from alcohol, smoking, drugs, or overeating) are often considered urgent events, recurrent events are still common.
From the above events, the TTM of behavior change is thus generated [44]. Although previous models understand why people engage in (or do not engage in) fitness activities, these models tend to focus on a short time. However, TTM mentions that the process of individual progress from one stage to another is cyclical, not linear. Because many people have not succeeded in trying to establish and maintain the desired career pattern, TTM believes that different interventions and information need to be tailored for individuals at special stages and times, and according to this model, change is considered a long-term process, involving different cognition and behavior at different stages. Interventional research has tested the principles of TTM, which mainly focus on the matching stage to special personal needs. The results show that there is a close relationship between the stage changes and the level of physical activity [45]. It is noteworthy that the concept of stage mentioned above includes some personality traits and states. In particular, traits are generally considered stable and not easy to change. On the other hand, states are easy to change and lack stability. In the cross-domain mode, both are dynamic and stable. In other words, although the stages can last for a some time, they are easy to change. Six stages are mentioned in TTM:
Preconcentration stage: In this stage, the individual has no activity in the next six months and has no intention of starting fitness activities. For instructors, it is important to find out why individuals do not participate in fitness activities.
Contemplation stage: In this stage, the individual has the intention to start fitness exercise in the next six months, but not now. Leaving aside their intentions, individuals may stay in Phase 2 for more than two years.
Preparation stage: At this stage, individuals have some fitness exercises, perhaps less than three times a week, but not enough to generate major benefits. During the preparation period, individuals have planned behaviors and actual activities (in the past year) to make behavioral changes, such as some fitness exercises.
Action stage: In this stage, individuals have regular fitness exercises (three or more times a week, each lasting for more than 20 minutes or more), but the time has not yet reached 6 months. This is the lowest stable state and the highest dangerous period of the tendency to relapse into the past life. This stage is also the busiest period. In this stage, most of the change processes will be used, because relapse often occurs at this stage, many different behaviors (such as enhancement) and cognitive processes (such as self-assessment and environmental reassessment) are often used to intervene in relapse.
Maintenance stage: In this stage, individuals have been exercising regularly for more than 6 months. Although they have tended to maintain regular exercise throughout their lives, in addition to injury suspension or other health problems, boredom and loss of focus may cause problems. One noteworthy problem is that it may be tiring and difficult to maintain a new habit initially. Although most of the studies that test the cross-theoretical model mainly focus on the early stage, the results of the research in the later stage show that improving self-efficacy to cope with the hindrance of physical exercise is a good guideline for men and women to maintain physical changes.