The relationship between quality of sports friendships and mental health in Chinese junior high school students: the bidirectional chain mediating effects of sport motivation and exercise adherence

Abstract

Background

The purpose of this study was to investigate the effects of quality of sport friendships on mental health and the mediating role of sport motivation and exercise adherence in middle school students.

Methods

A total of 1,083 middle school students were selected using a combination of cluster sampling and stratified sampling methods. The participants were assessed using the Sport Friendship Quality Scale, Mental Health Scale, Exercise Motivation Scale, and Physical Exercise Adherence Scale. Structural equation modeling was employed to examine the relationships among the four variables.

Results

(1) The quality of sport friendships positively predicted mental health (β = 0.192, p < 0.01); (2) Sport motivation and exercise adherence act as independent mediators between the quality of sport friendships and mental health respectively; (3) Sport motivation and exercise adherence act as bi-directional chain mediators between the quality of sport friendships and mental health.

Conclusion

(1) The quality of sports friendships can positively predict mental health, sport motivation, and exercise adherence. (2) The quality of sports friendships not only directly predicts mental health but also indirectly affects mental health through the mediating roles of sport motivation and exercise adherence, as well as the bidirectional chain mediation between the two. This further explains how the quality of sports friendships impacts the mental health of junior high school students, providing significant insights into improving their mental health levels.

Introduction

Junior high school students are at the stage of adolescence, their physiological and psychological development is at a rapid stage, which is called the “stormy period”. In terms of psychological development, although junior high school students are more mature than primary school students, their sound personality has not yet been formed, and they are still prone to some mental health problems when facing stressful events in their lives [1]. In 2019, China’s National Health and Health Commission issued the “Healthy China Action - Action Programme on Mental Health of Children and Adolescents”, which clearly states that it is necessary to further strengthen the mental health of children and adolescents, and promote the mental health and overall development of children and adolescents. With the introduction of the above-mentioned document, the state has paid sufficient attention to the mental health problems of children and adolescents, and has also taken many concrete measures [2]. However, the mental health problems of Chinese children and adolescents continue to worsen, and relevant studies have shown that the mental health problems of adolescents in junior high school show a worsening trend over time, with anxiety and suicide attempts being the most obvious [1]. Junior high school students are in an important period of growth and development, and their physiological functions are rapidly approaching maturity, but their psychological development is lagging behind, leading to the phenomenon of unbalanced physical and mental development of junior high school students [3]. It can be seen that mental health problems have become one of the main problems of contemporary junior high school students. Therefore, it is of great practical significance to conduct systematic and in-depth research on the mental health of junior high school students.

Mental health has consistently been a research focus in academic fields. It is defined as not only the absence of mental illness or disorders but also the maintenance of a good state in terms of physical well-being, psychological functioning, and social behavior [4]. Existing studies on the mental health of middle school students primarily focus on four aspects: family environment, school education, personal characteristics, and social culture. First, the family environment. A good family environment is the foundation of a healthy adolescent psychology. Parenting styles and whether parents are divorced or not can have a significant impact on the mental health of secondary school students [5]. Second, schooling. School is an important place for junior high school students to learn and live, and related studies have shown that in the Chinese context, there are significant differences in the mental health level of junior high school students in different types of schools, and the detection rate of mental health problems in private schools is higher than that in public schools [6]. In addition to study pressure [7], the classroom environment [8] and teachers’ different behaviours [9] may also influence the mental health level of junior high school students. Third, self-characteristics. Gender [10], obesity [11], poor learning [12], and physical activity [13] can significantly influence the mental health level of junior high school students. Fourth, social factors. Among the social factors, internet addiction and heterosexual interactions can significantly affect the mental health level of junior high school students. The detection rate of mental health problems of junior high school students with Internet addiction is higher than that of junior high school students without Internet addiction [14], while heterosexual relationships can help students’ physical and mental health development [15].

Accordingly, previous researchers have conducted in-depth investigations on the important topic of mental health, but the following reaserch gap exist. In previous studies, while some research has focused on the impact of peer relationships on individuals’ mental health, relatively little attention has been paid to whether sport friendship quality—friendships developed within the context of physical activities affects individuals’ mental health. Second, although many explanatory variables for mental health have been identified in previous studies, few studies have included the four variables of sport friendship quality, sport motivation, exercise adherence, and mental health in the same model, especially the mediating roles of sport motivation and exercise adherence, which have yet to be tested.

Relationship between sports friendship quality and mental health

The quality of sport friendships refers to the close relationships that adolescents develop in sport situations both in and out of school, where adolescents gain a sense of intimacy and trust through mutual interactions in sport, receive comfort, companionship, support and help from friends, and achieve acceptance and recognition by their peer groups [16]. The quality of sport friendships is an important factor affecting the mental health of junior high school students [17]. Sports friendships can have a positive contribution to adolescents’ mental health and social development, and adolescents tend to show higher motivation and greater willingness to fully present their true selves when playing sports with peers with whom they have a closer relationship during sports [18]. The level of friendship quality is an important factor influencing the development of psychological health of individuals in adolescence [19]. Friendship quality is mainly divided into two dimensions: positive and negative. Negative friendship quality can directly affect the level of mental health, the higher the quality of negative friendships, the lower the level of mental health, while friendships with more positive characteristics are high-quality friendships, which can have a positive effect on the level of mental health [20]. In summary, the study proposes Hypothesis 1: The quality of junior high school students’ sports friendships can positively predict mental health. Accordingly, this study builds on existing research to further investigate the relationship between sports friendship quality and mental health and its underlying mechanisms.

Mediating effects of sport motivation

Sport motivation refers to the psychological drive of people to participate in and maintain sport and exercise activities [21]. Participation in sports can promote the development of friendships, and friendships can also motivate adolescents to participate in the same or similar sports activities, making and consolidating friendships is one of the basic motivations for adolescents to participate in sports [22]. A study conducted on 345 primary and secondary school students investigated the relationship between sport friendship quality and sport motivation. Using structural equation modeling to analyze the collected data, the study found that sport friendship quality can directly predict sport motivation. High-quality sport friendships significantly enhance individuals’ intrinsic drive, fostering their motivation and enthusiasm to participate in physical activities [23]. And along with the continuous growth of adolescents, the influence of the quality of sports friendships on sports motivation also shows a gradual increase [24]. Self-determination theory suggests that there are three different forms of motivation and that the motives that drive an individual’s behaviour are classified from strong to weak: internal motivation, external motivation and no motivation. One study used psychometrics to test secondary school students and showed that increasing students‘ internal motivation for sport and physical activity improved students’ psychological well-being, while increasing external motivation for sport led to a decrease in students’ psychological well-being [25]. Another study, using a questionnaire survey of 243 students, found that sport motivation serves as a mediating factor in the relationship between physical activity and mental health. Specifically, under the influence of sport motivation, students participating in physical activities exhibited improved mental health levels [26]. In summary, there is a close and intrinsic relationship between the quality of sport friendship, sport motivation and mental health. Then, can sport friendship quality have an indirect effect on mental health through sport motivation? Accordingly, the study proposed Hypothesis 2: Sports motivation mediates the relationship between sports friendship quality and mental health.

The mediating effect of exercise adherence

Exercise adherence refers to the long-term participation in regular physical activity [27]. Sport friendship is a special kind of peer relationship, which is closely related to the frequency of exercise [28]. Synergy theory suggests that synergism occurs when an exogenous action or aggregation state reaches a critical level, and this synergism can qualitatively turn into a synergistic effect that changes system disorder into order and produces a stable structure from chaos [29]. Adolescents will produce a cluster effect under the synergy of peers, and this cluster effect can make the originally disordered exercise behaviour become orderly, and can also make the individual get a higher level of emotional experience and sense of belonging to the group, and motivate adolescents to be willing to repeatedly engage in physical exercise [30]. Related studies have shown that the higher the quality of sports friendships has a greater impact on the degree of participation in sports and the degree of adherence to sports among adolescents, and the quality of sports friendships and exercise adherence are highly positively correlated [31]. It has been pointed out that the psychological benefits of physical activity only become apparent when physical activity is sustained over a period of time [32]. As the duration of exercise increases and the number of exercises increases, the psychological effects of physical activity increase [33]. Related studies have shown that individuals with high levels of exercise adherence have higher levels of mental health compared to individuals with low levels of physical activity adherence [34]. In summary, the quality of sports friendship and exercise adherence showed a significant positive relationship, and the level of exercise adherence can have a certain impact on the level of mental health. It can be found that exercise adherence has a close relationship with both sports friendship quality and mental health. So, can exercise adherence have an indirect effect between sports friendship quality and mental health? Accordingly, the study proposes Hypothesis 3: Exercise adherence mediates the relationship between sports friendship quality and mental health.

Bidirectional chain-mediated effects of sport motivation and exercise adherence

This study proposed two independent mediating pathways—sport motivation and exercise adherence—when exploring the relationship between sport friendship quality and mental health. At the same time, related studies have shown that individuals’ motivation to participate in physical activity can effectively predict exercise adherence [35], and the richer the motivation to exercise and the more regular the exercise, the more stable their exercise adherence [36]. Another study found that sport motivation has a positive contribution to exercise adherence [37]. Combined with hypotheses 1–3, it is believed that there may be a chain mediation path of sports friendship quality → sports motivation → exercise adherence → mental health, and the internal mechanism by which the quality of junior high school students‘ sports friendships affects their mental health may be as follows: High-quality sports friendships enhance junior high school students’ motivation to play sports, and along with the enhancement of their motivation, their exercise adherence becomes more stable, and the frequency of their participation in sports is higher, which in turn leads to their more stable exercise adherence. The quality of sports friendships may have a positive effect on mental health. On the other hand, it is possible that there is a chain mediation path of sports friendship quality → exercise adherence → sport motivation → mental health, and the improvement of sports friendship quality has a greater impact on the degree of participation in adolescent sports and adherence to sports [31]. Physical activity habits formed through long-term adherence to physical activity can also significantly affect individual sport motivation [38]. It can be found that sport motivation and exercise adherence may be able to predict each other. Accordingly, the study proposed Hypothesis 4: sport motivation and exercise adherence have a bidirectional chain mediating role between the quality of sports friendships and psychological well-being.

The current study

• In summary, this study examines the relationship between the four variable of quality of sports friendship, mental health, sport motivation and exercise adherence based on previous research. We outline the proposed model in Fig. 1. In total, the study proposed the following hypotheses:

Fig. 1.

Conceptual model. Note: Quality of Sports Friendship = QSF; Sports Motivation = SM; Exercise Adherence = EA; Mental Health = MH (same below)

1. H1: The quality of junior high school students’ sports friendships can positively predict mental health.

2. H2: Sports motivation mediates the relationship between sports friendship quality and mental health.

3. H3: Exercise adherence mediates the relationship between sports friendship quality and mental health.

4. H4: Sport motivation and exercise adherence have a bidirectional chain mediating role between the quality of sports friendships and psychological well-being.

Materials and methods

Participants

This study employed a combination of cluster sampling and stratified sampling to select one urban and one rural junior high school from the northern, central, and southern regions of Jiangsu Province, China, for data collection. Prior to the survey, researchers distributed an Informed Consent Form to all participants, which provided a detailed explanation of the study’s purpose, procedures, potential risks and benefits, as well as the voluntary nature of participation. Written consent was also obtained from the legal guardians of minor students.During the survey, special emphasis was placed on protecting participants’ privacy and ensuring data confidentiality. All questionnaires were completed anonymously, and no personal information was recorded or disclosed, guaranteeing the privacy and safety of all participants. Participants were also informed that they could withdraw from the study at any stage without providing a reason and without facing any negative consequences. Data collection was conducted using paper-based questionnaires, administered in a classroom setting under the guidance of trained researchers. The researchers provided detailed instructions on how to complete the questionnaire and ensured that participants worked in a quiet and distraction-free environment to complete their responses independently. Regarding the determination of sample size, this study adhered to the principle of setting the sample size to be 5–10 times the number of measurement items, with the minimum sample size determined to be no less than 460 [39]. A total of 1,083 people agreed to fill out the questionnaire and completed it. Excluding 83 invalid questionnaires due to unanimous responses and missing data, 1,000 valid samples were collected, with a recovery rate of 92.34%. Additionally, using Monte-Carlo simulation, we calculated the required sample size for our model. The effective sample size collected in this study was 1,000, and the results indicated that with a sample size of 1,000, the power value exceeded 0.95, demonstrating sufficient statistical power [40]. Of these, respondents ranged in age from 12 to 15, 562 were boys and 438 were girls; 452 students served as class officers and 548 did not; 385 in the first year, 254 in the second year and 361 in the third year.

Measures

Quality of sports friendship

This study utilized the Adolescent Sport Friendship Quality Scale, a version of the Sport Friendship Quality Scale developed by Weiss and Smith [41] and revised by Zhu et al. [23] to better suit the cultural context of China. The scale consists of 25 items across six dimensions: Common Interests and Communication, Conflict Resolution, Positive Personal Qualities, Companionship and Enjoyment, Self-Esteem Enhancement, and Sport Support. It uses a 5-point Likert scale ranging from 1 (“completely disagree”) to 5 (“completely agree”), with no reverse-scored items. Higher mean scores indicate higher levels of sport friendship quality. A previous study showed that the scale has good applicability in the student population [42]. As shown in Table 1, in this study, the Cronbach’s alpha for the scale was 0.935, indicating excellent internal consistency. Confirmatory factor analysis yielded the following model fit indices: χ²/df = 3.034, CFI = 0.919, GFI = 0.911, AGFI = 0.946, NFI = 0.902, IFI = 0.920, TLI = 0.952, and RMSEA = 0.064. All indices met the acceptable standards for model fit.

Table 1.

Fit indices for each of the validated factor analyses

	χ²/df	CFI	TLI	GFI	AGFI	NFI	IFI	RMSEA
QSF	3.034	0.919	0.952	0.911	0.946	0.902	0.920	0.064
SM	3.249	0.956	0.952	0.939	0.928	0.937	0.956	0.047
EA	3.774	0.973	0.967	0.963	0.947	0.964	0.973	0.053
MH	2.180	0.976	0.973	0.960	0.951	0.957	0.976	0.034

Sports motivation

This study utilized the Sport Motivation Scale (SMS), developed by French scholar Briere [43] based on Deci and Ryan’s Cognitive Evaluation Theory of motivation, and translated into Chinese by Peng, where it has been widely applied [44]. The scale consists of 28 items divided into three dimensions: intrinsic motivation, extrinsic motivation, and amotivation. It employs a 5-point Likert scale ranging from 1 (“completely disagree”) to 5 (“completely agree”), with no reverse-scored items. The mean score of all items reflects the strength of exercise motivation. Previous studies have demonstrated the scale’s strong applicability in student populations [45]. As shown in Table 1, in the present study, the Cronbach’s alpha for the scale was 0.951, indicating excellent internal consistency. Confirmatory factor analysis of the scale produced the following fit indices: χ²/df = 3.249, CFI = 0.956, GFI = 0.939, AGFI = 0.928, NFI = 0.937, IFI = 0.956, TLI = 0.952, RMSEA = 0.047, all meeting the acceptable standards for model fit.

Exercise adherence

This study employed the Exercise Adherence Scale, developed by Wang et al. [46], to assess the exercise adherence of middle school students. The scale consists of 14 items divided into three dimensions: effort investment, emotional experience, and behavioral habits. It uses a 5-point Likert scale, ranging from 1 (“strongly disagree”) to 5 (“strongly agree”), with no reverse-scored items. Higher mean scores across all items indicate higher levels of exercise adherence. Previous research has demonstrated that this scale has strong applicability in student populations [47]. As shown in Table 1, in the present study, the Cronbach’s alpha for the scale was 0.917, indicating excellent internal consistency. Confirmatory factor analysis produced the following fit indices: χ²/df = 3.774, CFI = 0.973, GFI = 0.963, AGFI = 0.947, NFI = 0.964, IFI = 0.973, TLI = 0.967, and RMSEA = 0.053, all meeting the acceptable standards for model fit.

Mental health

This study utilized the Mental Health Scale for Middle School Students, developed by Su and Huang [4], to assess the mental health levels of junior high school students. The scale comprises 25 items divided into five dimensions: life satisfaction, enjoyment of learning, interpersonal harmony, calmness during exams, and emotional stability. A 5-point Likert scale is employed, ranging from 1 (“completely disagree”) to 5 (“completely agree”), where higher mean scores indicate higher levels of mental health. Previous research has demonstrated the strong applicability of this scale in student populations [48]. As shown in Table 1, in the present study, the Cronbach’s alpha for the scale was 0.938, indicating excellent internal consistency. Confirmatory factor analysis yielded the following model fit indices: χ²/df = 2.180, CFI = 0.976, GFI = 0.960, AGFI = 0.951, NFI = 0.957, IFI = 0.976, TLI = 0.973, and RMSEA = 0.034, all of which met the acceptable standards for model fit.

Control variables

In the process of data analysis, gender, grade level, and whether the student held a class leadership position were included as control variables in the analytical model. Specifically, Yu research indicated significant gender and grade-level differences in the mental health levels of middle school students [49]. Similarly, Song study found that middle school students who held class leadership positions exhibited significantly higher mental health levels than those who did not [50]. Based on these findings, this study included gender, grade level, and class leadership experience as control variables to ensure that the results more accurately reflect the relationships among the variables under investigation.

Data analysis

In this study, IBM SPSS23.0 with AMOS24.0 statistical software was used for data analysis of all data collected. After the questionnaires were collected, all data were processed as follows: (1) Internal consistency test was performed on all questionnaires using SPSS23.0. (2) Validated factor analysis was performed on all questionnaires using AMOS 24.0. (3) A common method bias test was conducted using the ‘Harman’ one-way method. (4) Pearson’s correlation analysis was performed using SPSS23.0 to calculate the relationship between the quality of sports friendship, sport motivation, exercise adherence and mental health. (5) Structural equation modelling test using Amos24.0 to verify the separate mediating roles of exercise motivation and exercise adherence between sports friendship quality and mental health. As well as the bidirectional chain mediating role of exercise motivation and exercise adherence between sports friendship quality and mental health.

Results

Common method bias test

All data for this study were obtained through self-reporting by junior high school students. Therefore, a common method bias test was required. Common method bias was procedurally controlled through anonymous measurement and some questions were reverse-ended. Using spss23.0, the data collected were tested for common method bias using the ‘Harman one-factor method’ [51], and the results showed that there were 17 factors with an eigenroot greater than 1, and the maximum factor variance explained was 29.83% (< 40%), which was inferred to mean that there was no serious common method bias in the data of the study. common method bias.

Descriptive statistics and correlation analysis of variables

Table 2 presents in detail the mean and standard deviation of the variables and the correlation coefficients between the variables. The quality of sports friendships showed significant positive correlations with sport motivation (r = 0.423, p < 0.01), exercise adherence (r = 0.506, p < 0.01), and mental health (r = 0.497, p < 0.01). Sport motivation (r = 0.529, p < 0.01), exercise adherence (r = 0.604, p < 0.01) and mental health showed significant positive correlations. Sport motivation and exercise adherence (r = 0.477, p < 0.01) showed a significant positive correlation.

Table 2.

Mean, standard deviation and correlation coefficients of the variables

	Mean	SD	1	2	3	4
1.QSM	3.582	0.721	1
2.SM	4.644	1.218	0.423**	1
3.EA	3.502	0.804	0.506**	0.477**	1
4.MH	3.632	0.725	0.497**	0.529**	0.604**	1

Note: * Significant at the 0.05 level (two-tailed). ** Significant correlation at the 0.01 level (two-tailed). (same below)

Testing the mediating effects of sport motivation and exercise adherence

In this study, structural equation modelling was used to analyse the chain mediating effects of sports motivation and exercise adherence between sports friendship quality and mental health for testing. Structural equation modelling was constructed for the four latent variables of sports friendship quality, sports motivation, exercise adherence, and mental health.

First, the chain-mediated effects of sport motivation and exercise adherence between sport friendship quality and mental health were tested first. Using Amos24.0 for structural equation modelling test, each fitting index is: χ²/df = 3.43, CFI = 0.960, GFI = 0.960, AGFI = 0.945, NFI = 0.945, IFI = 0.960, TLI = 0.952, RMSEA = 0.049, which shows that each fitting index meets the standard, indicating the model is fits well. From Fig. 2; Table 3, it can be seen that the quality of sports friendship significantly and positively predicted mental health (β = 0.192, p < 0.01), sport motivation (β = 0.715, p < 0.01) and exercise adherence (β = 0.415, p < 0.01), hypothesis H1 was verified. Sport motivation can positively predict exercise adherence (β = 0.211, p < 0.01) and mental health (β = 0.160, p < 0.01). Exercise adherence positively predicted mental health (β = 0.342, p < 0.01). From this model it can be seen that all path coefficients reached the significance level (p < 0.01).

Fig. 2.

Chain-mediated model of sport motivation and exercise adherence in the relationship between sport friendship quality and mental health

Table 3.

Path test

	SM			EA			MH			MH
	β	SE	t	β	SE	t	β	SE	t	β	SE	t
Gender	-0.023	0.07	-0.32	0.044	0.04	1.06	0.043	0.04	1.06	0.033	0.03	0.97
Grade	-0.023	0.04	-0.58	-0.017	0.02	-0.69	0.007	0.02	0.28	0.018	0.02	0.91
CL	-0.023	0.07	-0.33	-0.001	0.04	-0.03	0.044	0.04	1.10	0.05	0.03	1.47
QSF	0.715**	0.05	14.69	0.415**	0.03	13.08	0.500**	0.03	18.07	0.192**	0.03	6.92
SM				0.211**	0.02	11.27				0.160**	0.02	9.93
EA										0.342**	0.03	13.23

Note: Class Leder = CL

A bias-corrected nonparametric percentage Bootstrap test was used, and samples were repeated 5000 times for the mediation effect test as well as for the estimation of confidence intervals, which indicated a significant mediation effect if the confidence interval did not contain zero. The mediation model consisted of three paths: the independent mediating effect of sport motivation, the independent mediating effect of exercise adherence, and the chain mediating effect of sport motivation and exercise adherence. The test results are shown in Table 4, the confidence intervals of sport motivation (95% CI: 0.088, 0.142) and exercise adherence (95% CI: 0.113, 0.170) did not contain 0 and played a partial mediating role, respectively, and the hypotheses H2 and H3 were verified. The confidence intervals for the chain mediated effect of sport motivation → exercise adherence (95% CI: 0.039, 0.065) also did not contain 0, and the chain mediated effect was present.

Table 4.

Mediating effects and effect sizes

Path	Effect	Percentage of total effect	Bootstrap	95%CI
			Lower	Upper
QSF→SM→MH	0.114	22.80%	0.088	0.142
QSF→EA→MH	0.142	28.40%	0.113	0.170
QSF→SM→EA→MH	0.052	10.40%	0.039	0.065
Total indirect effects	0.308	61.60%	0.269	0.343
Total effect	0.500		0.446	0.554

Second, the chain-mediated effects of exercise adherence and sport motivation on the relationship between sports friendship quality and mental health were then tested. The model fitted well, with each fit index being χ²/df = 3.240, CFI = 0.945, GFI = 0.937, AGFI = 0.926, NFI = 0.931, IFI = 0.945, TLI = 0.936, and RMSEA = 0.048. As shown in Fig. 3; Table 5, the results of the mediation effect test indicate that the quality of sports friendships not only affects mental health through the independent mediating effects of exercise adherence and sport motivation, but also through the chain mediating effects of exercise adherence and sport motivation to influence mental health. The specific paths of (1) quality of sport friendship → exercise adherence → mental health (95% CI: 0.160, 0.226) (2) quality of sport friendship → sport motivation → mental health (95% CI: 0.046, 0.088) (3) quality of sport friendship → exercise adherence → sport motivation → mental health (95% CI: 0.036, 0.061), the None of the confidence intervals contained 0.

Fig. 3.

Chain-mediated model of exercise adherence and sport motivation between quality of sport friendships and mental health

Table 5.

Mediating effects and effect sizes

Path	Effect	Percentage of total effect	Bootstrap	95%CI
			Lower	Upper
QSF→EA→MH	0.194	38.80%	0.160	0.226
QSF→SM→MH	0.066	13.20%	0.046	0.088
QSF→EA→SM→MH	0.048	9.6%	0.036	0.061
Total indirect effects	0.308	61.60%	0.269	0.343
Total effect	0.500		0.446	0.554

The examination of the two aforementioned chained mediation models revealed that sport motivation and exercise adherence play bidirectional mediating roles between the quality of sports friendships and mental health, thereby confirming Hypothesis 4. Further analysis showed that the total indirect effect values and total effect values of the two chained mediation models are equal, indicating that both models have the same explanatory power. However, the chained mediation effect of the path “sport motivation → exercise adherence” accounts for a larger proportion of the total effect compared to the path “exercise adherence → sport motivation”.

Discussion

The relationship between quality of sports friendships and mental health

The results of the study show that the quality of junior high school students’ sports friendship can positively predict mental health, and hypothesis H1 is verified. That is, the higher the quality of junior high school students’ sports friendship, the higher their mental health. The ecological theory of development states that the peer microenvironmental system in early adolescence has a significant contributing role in adolescents’ individual development [52]. Compared to parents and teachers, the evaluation of individuals by their friends and the quality of their friendships can have a significant impact on adolescents’ cognition, emotion and behaviour [53]. Adolescents are in an important period of growth and development, and their sense of independence is beginning to be awakened, and the quality of friendship at different levels will be an important factor in judging their mental health [54]. Therefore, for junior high school students, the level of friendship quality is very important for the development of mental health. The improvement of the quality of junior high school students’ sports friendships becomes an important intervention to improve their mental health. In the sports context, sports friendship is a very special kind of peer relationship, which can help junior high school students to enhance the sense of exercise experience, reduce the sense of isolation, and improve the ability of social interaction [55]. In summary, an in-depth exploration of the relationship between the quality of junior high school students‘ sports friendships and their mental health and its underlying mechanisms is of great significance to the improvement of junior high school students’ mental health as well as the prevention and treatment of mental health problems.

The mediating effect of sports motivation

Sport motivation is a mediating variable between sports friendship quality and mental health, and the results of the study show that sports motivation has a partial mediating effect between sports friendship quality and mental health, which verifies the hypothesis H2. The quality of junior high school students’ sports friendship not only affects their mental health directly, but also affects their mental health indirectly through sports motivation. It is evident that improving the mental health of middle school students requires not only enhancing the quality of sport friendships but also focusing on the development of sport motivation. Differences in the behaviours shown by adolescents during sports often stem from differences in their autonomous tendencies. Motivation plays an important role in the formation of intrinsic goals and the enhancement of an individual’s subjective well-being [56]. Adolescents with higher quality of sport friendships tend to have higher motivation and behaviour for sport participation [57]. The stronger the sport motivation, the stronger the inhibitory effect it has on negative emotions that affect the level of mental health of adolescents [58]. The quality of sport friendships is one of the most basic motives for adolescents to participate in sports [59], and the enhancement of sport motivation deepens the quality of sport friendships [60]. Relevant studies have shown that improving students‘ sport motivation has an important role in promoting the development of students’ mental health level [25]. In summary, the quality of sports friendship can significantly enhance the sports motivation of junior high school students, which in turn affects the promotion effect on their mental health level.

The mediating effect of exercise aderence

Exercise adherence serves as another mediating variable in the relationship between sport friendship quality and mental health. The findings indicate that exercise adherence partially mediates this relationship, supporting hypothesis H3. This suggests that enhancing exercise adherence among middle school students is a crucial pathway for improving their mental health. Related studies have shown that interpersonal elements such as the quality of sports friendships can have a more important impact on exercise adherence compared to other environmental factors during exercise [61]. Sport friendships are an important factor in sound adolescent personality, guiding individuals to take on constant challenges in order to adapt to social co-operation and competition, resulting in a long-term, regular exercise cycle [62]. Physical activity can significantly affect the level of mental health [63], and exercise adherence is an important factor affecting mental health, and the longer one maintains long-term regular physical activity behaviours, the better one’s mental health will be [64]. In summary, sport friendship quality serves as an external resource that promotes exercise adherence among middle school students. High-quality sport friendships can be transformed into an intrinsic demand for exercise, enabling students to maintain a consistent and long-term exercise routine during their leisure time [65], thereby enhancing their mental health.

Bidirectional chain-mediated effects of sport motivation and exercise adherence

The results of this study indicate that there is a bidirectional chained mediating effect of sport motivation and exercise adherence between sport friendship quality and mental health. Exercise motivation and exercise adherence were found to be mutually predictive, thereby confirming hypothesis H4. The proportion of the chained mediating effect in the model from exercise adherence to sport motivation was smaller than that from exercise motivation to exercise adherence. This finding suggests that there may be certain differences between the two pathways through which sport friendship quality enhances middle school students’ mental health. Specifically, compared to the pathway of exercise adherence → sport motivation, the chained mediating effect of sport friendship quality through sport motivation → exercise adherence more effectively improves the mental health of middle school students.

First, in the chain mediation model of sports friendship quality → sports motivation →exercise adherence →mental health, the quality of sports friendships can affect exercise adherence through sports motivation, and finally act on mental health. The cognitive decision-making model of exercise adherence suggests that sports motivation is an important resource for long-term maintenance of regular exercise [66]. Individuals’ exercise motivation can effectively improve their exercise persistence [67]. Under normal circumstances, people with higher exercise motivation tend to be able to indulge in their exercise activities for a long period of time, which makes it easier for them to form long-term regular exercise habits. According to Self-Determination Theory, exercise motivation refers to the intrinsic drive of individuals to engage in physical activities according to their own will, reflecting the autonomous regulation of behavior. Individuals with high exercise motivation are more likely to participate in preferred physical activities based on their cognitive intentions and attentional preferences. This not only helps enhance adolescents’ positive emotions during exercise and enrich their subjective experiences but also facilitates the development of constructive cognitive and memory patterns related to exercise, thereby improving their adherence to physical activity [68]. Related studies have shown that maintaining regular exercise habits over time can have a positive effect on adolescents’ mental health [69], which is also consistent with the findings of the present study that the strength of exercise motivation can lead to changes in exercise adherence, which affects the frequency of participation in physical activity, and then affects the individual’s mental health.

Second, in the chain mediation model of sports friendship quality→ exercise adherence → exercise motivation → mental health, along with the improvement of sports friendship quality, it also enhances the individual’s adherence to physical exercise, while friendship reflects a special one-to-one emotional connection [70], and the formation of exercise adherence to a certain extent depends on the quality of junior high school students’ friendships with other individuals, and the peer relationship between individuals is always in the process of dynamic development [71], and it is because of this dynamic development that may cause the relationship between individuals to be in a fluctuating state. It can be observed that the formation of exercise adherence to some extent depends on external factors, while sustained participation in physical exercise activities relies on the continuous drive of sport motivation [72]. Therefore, the quality of sports friendships through exercise persistence has a more limited reinforcing effect on exercise motivation, which in turn has a relatively low effect on the subsequent improvement of junior high school students’ mental health.

In summary, this study examined the relationship between quality of sports friendship and mental health among middle school students, as well as the mediating roles of exercise motivation and exercise adherence. The total indirect effects through the three mediating pathways accounted for 61.60% of the total effect. This finding indicates that exercise motivation and exercise adherence not only significantly influence middle school students’ mental health but also play an important bridging role between sport friendship quality and mental health. In other words, the improvement in mental health driven by sport friendship quality is not solely direct but is largely mediated through enhanced exercise motivation and adherence. These results provide new insights into interventions aimed at improving mental health in middle school students. Specifically, the close relationships established with peers during physical activities can stimulate their exercise motivation, foster the development of regular exercise habits, and subsequently improve their mental health. This highlights the importance of integrating physical activities with social network development when designing mental health intervention programs. Group and cooperative sports activities, in particular, can help individuals release neurotransmitters such as endorphins and dopamine, which alleviate anxiety and stress, thereby enhancing mental health levels [73]. Additionally, these activities can provide students with more opportunities for social interaction, helping them establish stronger and more stable interpersonal relationships [74]. Such connections, in turn, further enhance exercise motivation and adherence, ultimately contributing to better mental health outcomes.

We also found a bidirectional pathway between sport friendship quality and mental health. Although the effect sizes of these two pathways differ only slightly, their cumulative impact in real-world contexts cannot be overlooked. Based on this finding, intervention practices should be tailored to specific circumstances. More specifically, the primary focus of interventions should be on stimulating students’ exercise motivation, as strong exercise motivation can promote sustained participation in physical activities. This, in turn, enhances exercise adherence and helps students develop long-term, consistent exercise habits. Such a virtuous cycle not only increases their engagement in physical activities but also continuously improves their mental health. Therefore, when designing intervention strategies, priority should be given to enhancing exercise motivation as a way to strengthen exercise adherence, thereby achieving more effective mental health outcomes. While exercise motivation plays a more prominent role, the bidirectional pathways identified in this study offer flexibility for intervention design. This flexibility enables more personalized interventions, allowing adjustments based on students’ varying levels of exercise motivation and adherence. For example, for students with low exercise motivation, interventions could focus on promoting participation through sports activities that emphasize social interaction and enjoyment. For students with stronger exercise motivation, setting long-term goals may help further enhance their adherence to physical activities. These findings provide a more refined and individualized approach to intervention design, offering valuable insights for practical implementation.

Research limitations and future prospects

In this study, we encountered several limitations and challenges. First, there may be biases in the sample selection. Although we made every effort to ensure the representativeness of the sample, due to time and resource constraints, we were unable to survey a broader population of middle school students. Future studies should aim to expand the sample size and scope to enhance the external validity of the findings and provide more accurate effect size estimates. Additionally, significant differences exist in psychological developmental stages [75] and physical activity behaviors [76] among different populations. While this study focused on middle school students, future research could extend the investigation to other groups, such as university students or older adults. Such efforts would provide a more comprehensive scientific basis for both practical applications in this field. Second, the questionnaires used in this study contained a relatively large number of items, which might have caused respondent fatigue. In future research, we plan to mitigate this issue by offering external incentives, such as monetary rewards or small gifts, to maintain participants’ engagement. Additionally, we will optimize the questionnaire items to minimize redundancy and ensure that the questionnaire remains concise and effective.

At the same time, we also plan to collecting data from multiple time points and sources to further mitigate the potential effects of common method bias. Third, although this study controlled for variables such as grade level, gender, and class leadership experience, it did not account for other potentially influential factors such as family history, socioeconomic status, and prior mental health history. These variables might play a role in shaping the model’s outcomes. Future research should aim to collect a broader range of data to more comprehensively capture relevant variables. Finally, this study employed a cross-sectional design, which limits the ability to infer causal relationships between variables. This constraint prevents us from examining the temporal dynamics and causal mechanisms underlying the relationships among sport friendship quality, mental health, sport motivation, and exercise adherence. Future research could adopt a longitudinal design to explore the dynamic interplay among these variables. For instance, it would be valuable to investigate whether improvements in mental health, in turn, enhance sport friendship quality, thereby creating a bidirectional feedback loop over time. Such a design would provide deeper insights into the causal and reciprocal relationships within this framework.

Conclusion

The following conclusions were drawn from this study: (1) The quality of sports friendships positively predicts mental health. (2) The mediating role of sport motivation and exercise adherence between quality of sport friendships and mental health is established, and the mediating role contains three paths: the separate mediating role of sport motivation, the separate mediating role of exercise adherence, and the bidirectional chain mediating role of sport motivation and exercise adherence. Through this paper, it can be found that the mental health level of junior high school students has a close relationship with sport motivation and exercise persistence. Therefore, in order to improve the mental health level of junior high school students, it is necessary to pay enough attention to sport motivation and exercise persistence.

Author contributions

LXY wrote the main manuscript text, and the corresponding modifications are made.

Funding

This research received no external funding.

Data availability

Data is provided within the manuscript.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the Declaration of Helsinki, and it has been approved by the Human Research Ethics Committee of Huaibei Normal University, and informed consent has been obtained from the parent or legal guardian of the participant under the age of 16.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.