This study explores the relationship between physical exercise and social anxiety of college students, as well as the mediating effect between mobile phone addiction tendency and self-control. The results show that physical exercise can not only directly and negatively predict social anxiety, but also indirectly predict social anxiety of college students through the independent mediating effect of mobile phone addiction tendency and self-control, as well as the chain mediating effect of both. This paper further explains the reason of the effect of physical exercise on college students' social anxiety, and has certain implications for the prevention and intervention of college students' social anxiety.
4.1. Physical exercise and social anxiety
The results of this study showed that physical exercise was negatively correlated with social anxiety (β=-0.044), but after the inclusion of mediating variables, physical exercise had a significant predictive effect on social anxiety. It is important for today's college students to maintain proper physical exercise and socializing. Previous relevant studies have pointed out that physical exercise can effectively alleviate the level of social anxiety of college students. Whether it is the intervention study using physical exercise methods on social anxiety or the intervention study of college students' physical exercise behavior on social anxiety, it can be found that physical exercise can have a positive impact on college students' social anxiety. Different intensity of physical exercise intervention has different effects on college students' social anxiety. Low intensity physical exercise intervention and medium intensity physical exercise intervention have significant improvement effects on college students' social anxiety, social avoidance and social distress 5. Duan et al. (2014) used moderate-intensity physical exercise (sports dance, basketball and badminton) to intervene college students, and the results showed that moderate-intensity physical exercise had a significant effect on inhibiting the anxiety of college students44. Stubbs et al. (2017) analyzed community-based cross-sectional data from the World Health Survey, estimating that 237,964 people in 47 countries had anxiety disorders, of which only 38 had physical activity data, and found a significant positive association between low levels of physical activity and anxiety in 17 of these countries45. Ye (2015) took college students with high levels of social anxiety as experimental subjects and conducted sports option course intervention on them, and found that sports dance, yoga, martial arts and three big ball events could significantly alleviate social anxiety46. Wang and Xie (2016) pointed out that college students with anxiety and depression tendency were interfered with by holding racket singles practice, holding racket doubles practice and volleyball practice47. Through comparative analysis of the data, they found that different practice methods had different degrees of improvement in anxiety level, and holding racket singles had the best improvement effect. Yang (2015) selected 387 community rehabilitation drug addicts and screened out the exercise and sedentary groups48. After analyzing the data of the two groups, he found that the anxiety level of the exercise group was lower than that of the sedentary group, and there was a very significant difference, indicating that physical exercise can reduce the anxiety level. Therefore, encouraging this special group of college students to participate in physical exercise can improve social anxiety to some extent. However, the existing relevant studies on the impact of physical exercise on college students' social anxiety vary in the degree of significance of the impact on college students' social anxiety under the different intensity of different projects and different physical exercise behaviors 7. However, the prediction effect of physical exercise on college students' social anxiety is more obvious after the intervention of adding intermediary variables.
4.2. Independent mediating effect of mobile phone addiction tendency
We found that mobile phone addiction tendency plays a mediating role between physical exercise and social anxiety of college students. This is consistent with previous research evidence that physical exercise is negatively correlated with mobile phone addiction tendency 49,50, mobile phone addiction tendency is positively correlated with social anxiety 17. The study found that from the point of view of exercise physiology, physical exercise is a kind of pressure stimulation, the stimulation of high-intensity intermittent exercise will quickly stimulate the right hemisphere of the brain, and enter a pleasant atmosphere, physical exercise will increase blood flow and oxygen intake, stimulate the central nervous system, at the same time, it also stimulates the human body to release endorphins, can stimulate people to form positive emotions, Improve achievement motivation, correct psychological disorders, improve immunity and prevent certain physical and mental diseases. Physical exercise can produce a feeling of happiness in the individual body, which can instinctively reject the Internet, which makes college students physically wean themselves from the tendency of mobile phone addiction tendency 51. Some studies have shown that regular physical activity can reduce phone addiction. Bu (2014) conducted sports intervention on mobile phone addiction tendency and found that the total score and subordinate dimension levels of mobile phone addiction tendency decreased significantly, indicating that physical exercise can effectively improve mobile phone addiction tendency49. Xu (2019) concluded that physical exercise can negatively predict mobile phone addiction tendency, and ball games have the greatest effect on mobile phone addiction tendency50. According to the study of Yang et al. (2020), maintaining a certain amount of physical exercise is a feasible plan to reduce the mobile phone addiction tendency of college students24. Through the comparison of the total score of mobile phone addiction tendency among different levels of exercise, it is found that moderate exercise can maximize the benefit of such reduction. Relevant studies have pointed out that the influence of mobile phone addiction tendency on social anxiety is multi-channel. In the process of excessive use of mobile phones, individuals gradually lose their social communication ability, which is more likely to lead to social anxiety 17. Chen and Sun (2011) pointed out that if people are addicted to online dating, they will be more solitary in reality and unwilling to communicate with others, and the interpersonal relationship will be worse, and they will be unable to face the real society and even have interpersonal communication barriers54. The longer the addiction to mobile phones, the deeper the social loneliness and anxiety, and mobile phone addiction tendency may lead to the reduction of social involvement and social contact, which has a further deepening of social anxiety 58.
4.3. Independent mediating effect of self-control
We found that self-control plays a mediating role between physical exercise and social anxiety of college students. This is consistent with previous research evidence, that is, physical exercise is positively correlated with self-control 27, while self-control is negatively correlated with social anxiety 52. This study further verified the complete mediating effect of self-control between physical exercise and social anxiety of college students, and this mediating effect was supported by previous theories and empirical studies. Relevant studies have pointed out that it takes a lot of willpower to complete the process of physical exercise, which will cause a temporary loss of self-control resources, with the increase of physiological load, near the physiological limit will produce discomfort, if the exercisher can endure and persist, self-control resources will increase, and ultimately improve the individual's self-control ability 53. Exercise psychology believes that physical exercise is an effective way to improve the self-control of college students 27. Through various ways such as aerobic exercise and endurance exercise, the toughness of the self-control ability of the sedentary subjects can be enhanced 54, and the self-control ability of college students can be improved to a certain extent after continuous running for a period of time 28. Through the self-control intervention course of moderate intensity physical exercise, it can effectively improve the emotional self-control of middle school students, improve the bad behavior, and cultivate the positive and stable thinking mode. In other words, the improvement of self-control ability of middle school students through physical exercise is effective 55 .
In addition, Li (2013) found in her study that students with good self-control performance had better academic performance and lower anxiety level32. Wang and Lu et al. (2004) showed that the self-control ability of middle school students has a direct effect on their emotional performance56. Gallagher et al. (2008) believe that people with improved self-control ability who can better cope with various problems are more able to exert individual subjective initiative and deal with social interaction problems more actively57.
4.4. The chain mediation effect between mobile phone addiction tendency and self-control
This study found that physical exercise is a complete mediator for college students' social anxiety, that is, physical exercise exerts an indirect effect on college students' social anxiety through the chain mediation of mobile phone addiction tendency and self-control. We found that there is a strong correlation between mobile phone addiction tendency and self-control.
We found that there was a significant correlation between mobile phone addiction tendency and self-control, and individuals with mobile phone addiction tendency lacked self-control over the duration and frequency of their use of mobile phones 58, that is, those with mobile phone addiction tendency had weak self-control ability. Jiang et al. (2019) found in their research on college students' mobile phone addiction tendency that college students' interpersonal skills would be weakened due to their addiction tendency to mobile phones, which may also lead to problems in college students' interpersonal relationships to a certain extent, such as interpersonal adaptation difficulties, social anxiety and interpersonal tension 59. Relevant studies have pointed out that individuals with severe mobile phone addiction tendency are addicted to the instant gratification brought by mobile phones, and have poor control over their behaviors, desires and emotions. They are not well aware of the consequences of their behaviors, or even though they are aware of the consequences of their behaviors, it is difficult to restrain their desires and adjust their thinking. It can be difficult to take the first step to change, so even recognizing your problem prevents you from making changes in your actions, leading to higher levels of social anxiety in real life. Therefore, the more severe the mobile phone addiction tendency, the worse the level of self-control, and therefore the higher the level of social anxiety 58. In a study on secondary vocational students, Wang (2020) pointed out that the mobile phone addiction tendency of secondary vocational students is significantly negatively correlated with self-control and its four dimensions (withdrawal, loss of control, inefficiency and avoidance)60. Specifically, the higher the mobile phone addiction tendency of secondary vocational students, the weaker their self-control ability. Long-term use of mobile phones seriously affects the physical and mental development of secondary vocational students. Affect their sleep, academic level, interpersonal relations and so on 60. College students are a group with significant social relationships and strong social needs. In the whole social process, mobile phone addiction tendency is an important factor affecting social anxiety. When college students improve their mobile phone addiction tendency through physical exercise, their self-control ability will be improved, which in turn can improve their social anxiety.
4.5. Limitations and prospects
First of all, this study is based on existing research and relevant theoretical basis, but limited by questionnaire method and cross-sectional research, it cannot infer causality. In the future, longitudinal research can be used to investigate the relationship between physical exercise and social anxiety of college students in stages.
Secondly, although this study examined the mediating effect of mobile phone addiction tendency and self-control, important variables related to college students' social anxiety, such as personality, self-esteem and psychological needs, should be further investigated to fully explain the model of physical exercise and college students' social anxiety.
Finally, this study only discusses the relationship mechanism of college students' social anxiety in the group of college students, which belongs to a small sample study. However, college students' social anxiety is affected by multiple factors including genetic factors, neurobiochemical factors, psychological factors and environmental factors, so it can be followed up in a large sample in the future.