The impact of social support on exercise persistence in adolescents: the mediating effect of exercise self-efficacy and autonomic motivation

Abstract

Objective

This study aims to explore the relationship between social support and exercise persistence among junior high school students. Furthermore, it introduces exercise self-efficacy and autonomous motivation as mediating variables to analyze the pathway through which social support influences exercise persistence in this population.

Methods

A total of 4,294 junior high school students from 13 prefecture-level cities in Jiangsu Province were surveyed using the Social Support Scale, Exercise Self-Efficacy Scale, Autonomous Motivation Scale, and Exercise Persistence Scale. After data cleaning, 3,776 valid responses were retained, yielding a valid response rate of 83%. Mediation analysis and bootstrapping methods were employed to test the hypothesized mediation model.

Results

(1) Social support was significantly positively correlated with exercise persistence (r = 0.275), exercise self-efficacy (r = 0.045), and autonomous motivation (r = 0.245). A small but significant positive correlation was also found between exercise self-efficacy and autonomous motivation (r = 0.044). (2) Mediation analysis indicated that social support not only had a direct positive effect on exercise persistence among junior high school students but also exerted indirect effects via exercise self-efficacy and autonomous motivation. The total effect was 0.368, with a direct effect of 0.239 and an indirect effect of 0.129.

Conclusion

(1) Social support plays a significant and direct role in promoting exercise persistence among junior high school students. (2) Exercise self-efficacy and autonomous motivation serve as important mediators in the relationship between social support and exercise persistence, with autonomous motivation exerting a stronger mediating effect. (3) A complete mediation pathway was identified, progressing from social support to exercise self-efficacy, then to autonomous motivation, and ultimately to exercise persistence, although the effect size of this pathway was relatively small.

Introduction

With the transformation of modern lifestyles and the widespread use of electronic devices, declining levels of physical activity among adolescents have emerged as a global public health concern. According to the World Health Organization, approximately 81% of adolescents aged 11 to 17 fail to meet the recommended guideline of at least 60 min of moderate-to-vigorous physical activity per day [1]. However, within the unique socio-cultural context of China, this issue presents a more complex facet, particularly for junior high school students. On the one hand, Chinese adolescents face global challenges, such as the proliferation of electronic devices leading to a sharp increase in screen time, which significantly encroaches upon time for physical activity [2]. On the other hand, they are subjected to immense and distinctive academic pressure stemming from the “exam-oriented education” system [3]. In an educational environment centered on the primary goal of securing progression to the next academic stage through competitive examinations, the value of subjects like physical education is often marginalized. Schools and families commonly allocate more time and resources to academic subjects, frequently resulting in the reduction of physical education class hours and a severe lack of extracurricular exercise time. This prevailing mindset of “prioritizing intellectual development over physical education” often leaves adolescents unable to act on their awareness of the importance of exercise due to their heavy academic workload. Consequently, under the cumulative weight of these multiple pressures, the state of their physical health has become a cause for significant concern. The junior high school stage is not only a critical period for physical development but also a crucial “window of opportunity” for the formation of healthy habits—especially exercise habits—that can extend into adulthood, profoundly influencing an individual’s lifelong health. Exercise persistence, as a key indicator of an individual’s ability to engage in physical activity consistently, is directly linked to the realization of exercise benefits and the achievement of health goals. In reality, the level of exercise persistence among adolescents is generally low, with high dropout rates [4]. Therefore, given the dual challenges of academic pressure and the allure of electronic devices faced by Chinese junior high school students, investigating the factors that can effectively enhance their “exercise persistence”—defined as the willingness and ability to consistently engage in physical activity—is not only of general health significance but also of urgent and practical relevance.

Among the numerous influencing factors, social support stands out as a core resource within an individual’s social environment, playing a pivotal role in the initiation and maintenance of exercise behavior among adolescents [5]. Typically originating from sources such as parents and peers, social support encompasses emotional encouragement, informational guidance, and tangible instrumental assistance, thereby fostering the adoption and continuation of positive behaviors [6]. Systematic reviews and empirical studies have consistently confirmed that overall support from family, peers, and society is significantly and positively associated with adolescent physical activity levels [7]. However, social support is not directly or mechanically translated into exercise persistence. Its influence must be mediated by an individual’s internal psychological processes. This implies that for a supportive external environment to effectively drive long-term behavioral adherence, it must first be converted into internal beliefs and motivation. Consequently, researchers have recently begun to focus on the internal mechanisms linking social support to exercise behavior, exploring the mediating roles of psychological variables such as exercise self-efficacy and autonomous motivation. This line of inquiry provides a novel perspective for a deeper understanding of exercise behavior in adolescents. To elucidate this pathway, the present study integrates two prominent health behavior theories—Social Cognitive Theory (SCT) and Self-Determination Theory (SDT)—to analyze how social support can overcome these practical barriers by activating individuals’ internal psychological resources, and ultimately, enhance exercise persistence among Chinese junior high school students.

SCT offers a theoretical framework for understanding the formation of beliefs regarding personal capability. The theory’s core concept is self-efficacy, defined as an individual’s belief in their ability to successfully execute specific behaviors [8]. In the context of physical activity, exercise self-efficacy has been established as a key psychological predictor of exercise participation and persistence among adolescents [9]. Adolescents with high self-efficacy are more inclined to set challenging goals and demonstrate greater resilience in the face of difficulties. Among adolescents, numerous studies have confirmed a strong positive correlation between exercise self-efficacy and exercise participation and persistence [10, 11]. Adolescents with high self-efficacy tend to set more challenging exercise goals, exhibit greater persistence when facing difficulties, and recover quickly from setbacks. According to Bandura’s theory, self-efficacy is constructed from four principal sources of information: mastery experiences, vicarious experiences, verbal persuasion, and physiological and emotional states [8]. Social support serves to bolster the development of self-efficacy precisely through these avenues. For instance, instrumental support from parents, such as providing transportation and equipment, creates opportunities for adolescents to achieve success and thereby build mastery experiences [12]. Similarly, exercising with peers directly offers a source of vicarious experience through social modeling [11, 13]. Furthermore, encouragement from significant others, including parents and teachers, functions as an effective form of verbal persuasion [14]. Therefore, by shaping an individual’s beliefs about their capabilities, social support constructs a critical first psychological pathway toward exercise persistence.

After answering the question of ‘Can I do it?‘, the self-determination theory (SDT) further elucidates the core question of the motivation ‘Why should I do it?‘. Autonomous motivation is a core concept of SDT, reflecting a motivational state in which an individual engages in a specific behavior based on intrinsic interest, value identification, or self-integration [15]. SDT posits that humans have an innate tendency toward growth and integration, the fulfillment of which depends on the satisfaction of three Basic Psychological Needs: the need for autonomy (to feel one’s behavior is voluntary and self-endorsed), the need for competence (to feel effective and capable), and the need for relatedness (to feel connected to and cared for by others) [16, 17]. When the social environment supports the satisfaction of these needs, an individual’s motivation is more likely to shift from being externally controlled to being internally driven, resulting in a higher quality of autonomous motivation. Previous research has established a positive association between social support and autonomous motivation. For instance, a study by McDonough and Crocker on adolescent athletes found that supportive coaching behaviors significantly predicted the athletes’ levels of autonomous motivation [18]. Similarly, research by Mageau and Vallerand has demonstrated that parental autonomy support is closely associated with adolescents’ autonomous motivation in physical activity [19]. And autonomous motivation has been proven to be one of the most important factors in predicting exercise persistence [16]. Individuals with high autonomous motivation are more likely to experience positive affect during exercise, exhibit greater persistence in the face of difficulties, and successfully integrate physical activity into their daily lives [20]. Research by Owen et al. on adolescents found that those with higher levels of autonomous motivation demonstrated superior exercise adherence over a 12-month follow-up period [21]. In this process, social support acts as a critical catalyst. In an exercise context, support from significant others satisfies the need for autonomy by enhancing an adolescent’s sense of volition (by respecting their choices and decisions). Positive feedback on performance fulfills the need for competence, while care and joint participation from peers and family address the need for relatedness [17]– [22]. Consequently, by satisfying an individual’s basic psychological needs, social support cultivates the intrinsic motivation required for long-term exercise adherence, thus constituting the second critical psychological pathway to exercise persistence.

Although both exercise self-efficacy and autonomous motivation have been identified as mediators in the relationship between social support and exercise persistence, their interrelationship and sequential role within this mediational process remain underexplored. From an integrated perspective of Social Cognitive Theory and Self-Determination Theory, these two psychological variables may operate in a serial mediation pathway. Theoretically, exercise self-efficacy is likely to precede autonomous motivation. When individuals receive support from significant others, the primary enhancement is in their confidence in their own exercise capabilities, leading to an increase in exercise self-efficacy. This heightened sense of efficacy, in turn, facilitates a greater identification with the value of exercise and the development of intrinsic interest, thereby fostering stronger autonomous motivation [23]. This sequence of relationships may reflect different stages of behavioral change. In the initiation stage of behavior, the main psychological barrier is often doubt about one’s own abilities, and self-efficacy is the key to determining whether an individual starts taking action. However, to sustain behavior in the long term, confidence alone is not enough. Behavior must be integrated into an individual’s values and self-identity, becoming a conscious and voluntary choice, at which point autonomous motivation becomes the dominant factor [24]. Specifically, when adolescents have successful exercise experiences within a socially supportive environment, their exercise self-efficacy is enhanced. This heightened sense of capability makes it easier for them to appreciate the inherent enjoyment and value of exercise, which in turn fosters the development of autonomous motivation grounded in intrinsic interest and personal value. A study by Williams and Deci found that enhanced feelings of competence, a construct closely related to self-efficacy, promoted the development of intrinsic motivation [25]. Furthermore, research by Standage et al. demonstrated a significant positive relationship between self-efficacy and autonomous motivation for exercise among adolescents, with autonomous motivation subsequently predicting actual exercise behavior [26]. Therefore, this study proposes a theoretical integration model of SCT and SDT, grounded in an integrated “Environment–Cognition–Motivation–Behavior” perspective(Figure 1). This model not only logically bridges the pivotal dimensions of “Can do” (from the SCT perspective) and “Want to do” (from the SDT perspective) but also elucidates the underlying psychological transformation mechanisms. Drawing on SCT, social support serves as a critical environmental resource that directly enhances adolescents’ confidence in specific exercise tasks—specifically, exercise self-efficacy—by providing mastery experiences and verbal persuasion. Furthermore, exercise self-efficacy within SCT is logically posited as the proximal antecedent for the satisfaction of the need for competence in SDT [27]. When individuals are convinced of their capability to complete exercise tasks, this elevated sense of efficacy directly satisfies their psychological need for competence. According to SDT, the satisfaction of basic psychological needs—particularly the need for competence—is a prerequisite for the internalization of external motivation into autonomous regulation [15, 28]. Consequently, social support not only empowers “capability beliefs” but, more crucially, ignites high-autonomy internal drive through the subsequent “competence satisfaction,” ultimately driving more sustained exercise persistence. In summary, the present study posits that the serial mediation model (Social Support → Self-Efficacy → Autonomous Motivation → exercise persistence) more likely delineates the dynamic psychological process of transition from behavior initiation to long-term maintenance. Although previous studies have separately confirmed the pairwise relationships between variables, few studies have systematically tested these three core concepts in a unified chain mediation model, and there is still insufficient systematic exploration of how multiple variables form a ‘mediation chain’ to work together [29]. This study aims to explore this core issue in depth.

Fig. 1.

Model diagram of chain mediation theory

In summary, the present study aims to construct a serial mediation model to systematically examine the association between social support and exercise persistence among Chinese junior high school students, and to investigate the sequential mediating pathway of exercise self-efficacy and autonomous motivation in this relationship, thereby offering scientific guidance for promoting sustained physical activity among Chinese adolescents. Based on the theoretical analysis and empirical research review above, this study proposes the following hypotheses, with the hypothesized model presented in Fig. 2:

Fig. 2.

Hypothesis model diagram of the chain mediation between social support and exercise persistence

H1: Social support will have a significant positive predictive effect on adolescent exercise persistence.

H2: Exercise self-efficacy will mediate the relationship between social support and exercise persistence.

H3: Autonomous motivation will mediate the relationship between social support and exercise persistence.

H4: Exercise self-efficacy and autonomous motivation will jointly mediate the relationship between social support and exercise persistence in a, such that social support influences autonomous motivation through exercise self-efficacy, which in turn influences exercise persistence.

Research methodology

Data source

This study targeted junior high school students in Jiangsu Province, China. A stratified random sampling method was employed, selecting two classes from each grade level in secondary schools across all 13 prefecture-level cities in Jiangsu. From September to December 2024, questionnaires were primarily distributed on-site. A total of 4,500 questionnaires were distributed, and 4,294 were collected. After excluding invalid responses (e.g., missing answers, inattentive responses), 3,776 valid questionnaires remained, yielding a response rate of 83%, which meets the standards for survey research. The basic information collected in the questionnaire is shown in Table 1.

Table 1.

Basic information of the test subject (N = 3,776)

Variable	Category	N	%
Gender	Male	1931	51.1
	Female	1845	48.8
Grade Level	Grade 7 (Junior One)	1447	38.3
	Grade 8 (Junior Two)	1266	33.5
	Grade 9 (Junior Three)	1063	28.1
Only Child	Yes	1325	35.1
	No	2451	64.9
Age	12	492	13.030
	13	883	23.385
	14	1254	33.210
	15	795	21.054
	16	352	9.322

Quality control

This study implemented several quality control measures to ensure data reliability and validity. First, questionnaires were administered by students’ academic advisors, who served as trained survey administrators. Before the formal data collection, all administrators received standardized training, including instruction on the survey protocol, explanation of questionnaire content, and guidance on important considerations for accurate completion. Second, a data cleaning protocol was established to ensure the external validity of the dataset. During data preprocessing, responses with logical inconsistencies, omissions, obvious errors, or unidentifiable information were either rechecked or excluded to ensure the authenticity and integrity of the data. Third, tests for common method bias were conducted before data analysis. To minimize such bias, participants were assured of the anonymity and confidentiality of their responses and were informed that the data would be used solely for academic research purposes. The research plan was approved by the Ethics Committee of Nantong University (2022 [70]). The informed consent was obtained from all the participant’s and their legal guardians or parent involved in the study. All methods of this study were performed following Helsinki Declaration guidelines and regulations.

Inclusion and exclusion criteria for participants

Inclusion criteria

Participants were required to meet the following criteria:

1. Currently enrolled in a junior high school in China.

2. Capable of independently understanding and completing the questionnaire.

Exclusion criteria

Participants were excluded if they met any of the following conditions:

1. Self-reported or medically diagnosed with neurological or psychiatric disorders, such as major depressive disorder, generalized anxiety disorder, bipolar disorder, or schizophrenia.

2. Currently taking medications that affect mood or cognition, including antidepressants, anxiolytics, sedatives, or other central nervous system drugs.

3. Possessed severe memory or cognitive impairment.

Measurement instruments

General information questionnaire

This section collected demographic data, including gender, age, grade level, ethnicity, and whether or not the child is an only child.

Social support scale

The Social Support Scale used in this study was developed by Ye Yuemei et al. based on Xiao Shuiyuan’s Social Support Rating Scale, an instrument commonly used in China, to assess individuals’ levels of social support in the context of physical exercise [30]. The scale comprises 17 items across three dimensions: Subjective Support (Including 5 items such as caring for classmates and taking care of classmates), Objective Support (Including 6 items such as seeking help from others and actively confiding in family and friends), and Support Utilization (Including 6 items such as receiving financial support and care from family and friends), which collectively measure the extent to which an individual perceives, receives, and utilizes social support within their social network. A sample item is, “When I encounter difficulties, I often seek help from my family and friends.” Responses are recorded on a 5-point Likert scale, ranging from 1 (Strongly Disagree) to 5 (Strongly Agree), where higher scores indicate a greater level of perceived social support. The scale’s original validation, conducted on a sample of middle school students, demonstrated good psychometric properties. To further confirm its suitability for the present study, we assessed its internal consistency (Cronbach’s α coefficient) and construct validity using Confirmatory Factor Analysis (CFA). The results indicated excellent internal consistency, with Cronbach’s α coefficients of 0.891 for Subjective Support, 0.852 for Objective Support, 0.836 for Support Utilization, and 0.920 for the total scale. The CFA results suggested a good model fit to the data: χ²/df = 2.024, RMSEA = 0.071, CFI = 0.958, NNFI = 0.913, and TLI = 0.947. These findings confirm that the scale possesses good reliability and validity for the sample used in this research.

Self-determined motivation scale

To measure the autonomous motivation of middle school students, this study utilized the Behavioural Regulation in Exercise Questionnaire-2 (BREQ-2), developed by Mullan, Markland, and Ingledew based on Self-Determination Theory [31]. The scale consists of 18 items distributed across five dimensions that reflect the continuum of internalization: Amotivation (4 items), External Regulation (4 items), Introjected Regulation (3 items), Identified Regulation (3 items), and Intrinsic Motivation (4 items). All items are rated on a 5-point scale from 1 (“Not at all true for me”) to 5 (“Very true for me”). The questionnaire assesses the reasons underlying an individual’s engagement in exercise, with sample concepts such as, “I often feel positive after exercising.” The scale demonstrated good reliability and validity in the present study. Reliability analysis revealed excellent internal consistency for the five subscales, with Cronbach’s α coefficients of 0.902 for Amotivation, 0.857 for External Regulation, 0.868 for Introjected Regulation, 0.898 for Identified Regulation, and 0.956 for Intrinsic Motivation. The Cronbach’s α for the total scale was 0.935. Confirmatory Factor Analysis (CFA) results indicated good construct validity, with the following fit indices: χ²/df = 2.564, CFI = 0.928, TLI/NNFI = 0.933, and RMSEA = 0.062.

Physical activity self-efficacy scale

The Physical Activity Self Efficacy Scale (PASS) developed by Jiang Ying et al. is used to evaluate participants’ self-efficacy in physical exercise [32]. PASS includes two dimensions: situational motivation (6 items) and subjective support (4 items), with a total of 10 items. The scale uses Likert 5-point scoring, ranging from “1 = strongly disagree” to “5 = strongly agree”. The higher the item score, the stronger the exercise self-efficacy. The scale describes a person’s confidence in overcoming obstacles and completing tasks, such as: I will stick to my exercise plan even without anyone to accompany me. The cumulative variance contribution rate of the two factors is 67.782%. The results of confirmatory factor analysis showed that the twofactor model fitted well (x²/df = 2.688, GFI = 0.958, NFI = 0.970, CFI = 0.981, IFI = 0.975, RMSEA = 0.066, RMR = 0.023), and the Cronbach’s alpha coefficient, split half reliability, and test-retest reliability of the scale were 0.908, 0.819, and 0.531, respectively.

Exercise persistence scale

This study used the “Amateur Sports Exercise Persistence Questionnaire” developed by Wang Shen et al. to measure students’ exercise persistence [33]. The questionnaire consists of 14 items, divided into three dimensions: effort investment (5 items), emotional experience (5 items), and behavioral habits (4 items). All items are scored using a 5-point scoring method, such as “I participate in sports activities for at least 30 minutes each time” in the behavioral habit dimension. The questionnaire showed good reliability and validity in this study. The reliability test results showed that the internal consistency reliability (Cronbach’s alpha coefficient) of the three dimensions of effort investment, emotional experience, and behavioral habits were 0.791, 0.860, and 0.882, respectively. The Cronbach’s alpha coefficient of the entire scale was 0.923; The results of confirmatory factor analysis indicate that the scale has good construct validity, and the fitting indices are as follows: χ²/df = 2.896, CFI = 0.945, GFI = 0.901, RMSEA = 0.069。.

Statistical analysis

This study utilized SPSS 26.0 and AMOS 29.0 to conduct data analysis.

1. Common method bias test, using Harman single factor test.

2. Descriptive statistics and Pearson correlation analysis were performed using IBM SPSS 26.0 to evaluate the preliminary characteristics and interrelationships among the study variables.

3. Then, AMOS 29.0 software to perform the serial mediation role of exercise self-efficacy and Autonomous motivation on the association of Social support and exercise persistence relationship using structural equation model (SEM). All continuous variables run in the models were standardized and employed bootstrapping test mediation models to estimate bias-corrected confidence interval with 5000 bootstraps sample for the models' direct, indirect, and total effect. Thus, the 95% confidence interval, which consists of zero considered as an insignificant effect and vice versa.

Results and analysis

Control and test for common method bias

Given that the data were collected through self-reported questionnaires, which are inherently subjective, steps were taken to minimize common method bias. Harman’s single-factor test, the inclusion of control variables, and statistical correction methods were applied to the key variables—social support, self-determined motivation, peer relationships, and exercise persistence. The exploratory factor analysis extracted 12 principal components with eigenvalues greater than 1. The first factor accounted for 24.57% of the total variance, which is below the critical threshold of 40%. Therefore, it can be concluded that common method bias was not a significant concern in this study.

Correlation analysis of adolescents’ social support, exercise self-efficacy, autonomous motivation, and exercise persistence

Social support, exercise self-efficacy, autonomous motivation, and exercise persistence were all significantly positively correlated, with correlation coefficients ranging from 0.044 to 0.275. Specifically, social support showed a significant positive correlation with the sub-dimensions of exercise persistence, with correlation coefficients between 0.209 and 0.249. This finding supports Hypothesis 1 (H1). Furthermore, social support was significantly positively correlated with exercise self-efficacy and its sub-dimensions, with correlation coefficients ranging from 0.144 to 0.308. A significant positive correlation also existed between social support and autonomous motivation and its sub-dimensions, with correlation coefficients between 0.044 and 0.046. Exercise self-efficacy demonstrated a significant positive correlation with autonomous motivation and its sub-dimensions, with coefficients ranging from 0.041 to 0.044. Additionally, exercise self-efficacy was significantly positively correlated with exercise persistence and its sub-dimensions, with correlation coefficients between 0.188 and 0.229. Finally, autonomous motivation showed a significant positive correlation with the sub-dimensions of exercise persistence, with correlation coefficients ranging from 0.169 to 0.211 (Table 2).

Table 2.

Analysis of the mean, standard deviation, and correlation between variables n = 3776

	M	SD	A_1	A_2	A_3	A	B_1	B_2	B_3	B_4	B_5	B	C_1	C_2	C	D_1	D_2	D_3	D
A_1: Subjective Support	19.788	4.741	1
A_2: Support Utilization	23.243	5.801	0.771**	1
A_3: Objective Support	24.694	5.190	0.741**	0.766**	1
A: Total Social Support	67.726	14.424	0.905**	0.931**	0.911**	1
B_1: External Regulation	9.913	4.561	−0.020	0.006	−0.019	−0.011	1
B_2: Introjected Regulation	8.230	3.680	0.144**	0.175**	0.133**	0.165**	0.476**	1
B_3: Identified Regulation	5.952	1.721	−0.032*	−0.026	−0.040*	−0.036*	0.639**	0.233**	1
B_4: Intrinsic Motivation	14.779	6.947	−0.016	0.011	−0.018	−0.007	0.986**	0.491**	0.565**	1
B_5: Amotivation	17.127	3.528	0.308**	0.314**	0.294**	0.333**	0.356**	0.480**	0.439**	0.331**	1
B: Total Self-Determined Motivation	54.273	13.561	0.213**	0.250**	0.207**	0.245**	0.730**	0.785**	0.377**	0.741**	0.722**	1
C_1: Situational Motivation	22.092	5.680	0.044**	0.051**	0.024	0.044**	0.016	0.026	−0.026	0.018	0.043**	0.048**	1
C_2: Perceived Social Support	15.415	3.698	0.046**	0.046**	0.026	0.043**	0.014	0.013	−0.000	0.014	0.034*	0.034*	0.872**	1
C: Total Self-Efficacy	37.507	9.086	0.046**	0.051**	0.026	0.045**	0.016	0.022	−0.017	0.017	0.041*	0.044**	0.980**	0.952**	1
D_1: Habit	15.162	4.269	0.209**	0.212**	0.206**	0.228**	−0.0257	0.120**	−0.053**	−0.021	0.242**	0.169**	0.194**	0.165**	0.188**	1
D_2: Effort	19.547	5.102	0.236**	0.247**	0.247**	0.266**	−0.036*	0.156**	−0.065**	−0.029	0.298**	0.206**	0.228**	0.197**	0.223**	0.769**	1
D_3: Experience	19.754	5.268	0.236**	0.238**	0.230**	0.256**	−0.044**	0.144**	−0.082**	−0.035*	0.287**	0.200**	0.221**	0.190**	0.215**	0.672**	0.814**	1
D: Total Exercise Persistence	54.464	13.398	0.249**	0.255**	0.250**	0.275**	−0.039*	0.154**	−0.074**	−0.032	0.303**	0.211**	0.235**	0.202**	0.229**	0.876**	0.946**	0.917**	1

**The correlation is significant at the 0.01 level (two-tailed)

The chain-mediation analyses

Based on the correlation analysis, Structural Equation Modeling (SEM) was conducted using AMOS to examine the mediating effects of exercise self-efficacy and autonomous motivation on the relationship between social support and exercise persistence. Given the large sample size (N = 3776), the Chi-square statistic is known to be sensitive and may be inflated, leading to a higher χ2/df ratio. Therefore, following the recommendations of Hu and Kline, we prioritized other fit indices such as CFI, RMSEA, and SRMR to evaluate model fit [34–36]. The results (CFI > 0.95, RMSEA < 0.08, TLI > 0.90) demonstrate an excellent fit despite the sensitivity of the Chi-square test(χ²/df = 21.05, CFI = 0.962, TLI = 0.947, RMSEA = 0.073, SRMR = 0.097). Social support positively predicted exercise self-efficacy (β = 0.046, P < 0.05), autonomous motivation (β = 0.465, P < 0.05), and exercise persistence (β = 0.239, P < 0.001). Exercise self-efficacy positively predicted autonomous motivation (β = 0.056, P < 0.05) and exercise persistence (β = 0.209, P < 0.001). Autonomous motivation positively predicted exercise persistence (β = 0.256, P < 0.005 (Table 3). From this model it can be seen that all path coefficients reached the significance level (p < 0.01). The mediating effects of this study are shown in Fig. 3; Table 3.

Table 3.

Path parameters of chain mediation model

Route	β	SE	P
Social support →Exercise self-efficacy	0.046	0.017	0.007
Social support →Autonomous motivation	0.465	0.167	0.005
Social support →Exercise persistence	0.239	0.019	0.001
Exercise self-efficacy →Autonomous motivation	0.056	0.025	0.027
Exercise self-efficacy →Exercise persistence	0.209	0.017	0.001
Autonomous motivation →Exercise persistence	0.256	0.093	0.006

Fig. 3.

Path analysis diagram

Test of mediating effects

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 results are presented in Table 4. The direct effect of social support on exercise persistence was significant, with an effect size of 0.239 (Bootstrap CI [0.192, 0.289]), accounting for 64.93% of the total effect, thus supporting Hypothesis H1. The first indirect effect—through exercise self-efficacy (social support → exercise self-efficacy → exercise persistence)—was significant, with an effect size of 0.010 (Bootstrap CI [0.002, 0.002]), representing 2.59% of the total effect. The second indirect effect—through autonomous motivation (social support → autonomous motivation → exercise persistence)—was also significant, with an effect size of 0.119 (Bootstrap CI [0.012, 0.096]), accounting for 32.30% of the total effect. The third indirect effect—via both mediators in sequence (social support → exercise self-efficacy → autonomous motivation → exercise persistence)—was significant as well, with an effect size of 0.001 (Bootstrap CI [0.001, 0.002]), representing 0.18% of the total effect. These findings support Hypotheses H2 and H3. The total indirect effect was 0.0403, accounting for 35.07% of the total effect, thereby supporting Hypothesis H4 (Table 4).

Table 4.

Analysis of the mediating effects

	Effect	BootSE	LLCI	ULCI	Proportion of Effect
Total effect	0.368	0.020	0.331	0.407
Direct effect	0.239	0.003	0.192	0.289	64.93%
Social support →Exercise self-efficacy→Exercise persistence	0.010	0.002	0.003	0.016	2.59%
Social support →Autonomous motivation→ Exercise persistence	0.119	0.012	0.096	0.144	32.30%
Social support →Exercise self-efficacy→Autonomous motivation→ Exercise persistence	0.001	0.004	0.001	0.002	0.18%

Discussion

This study aims to explore the underlying mechanisms through which adolescent social support influences exercise persistence, with a particular focus on the sequential mediating role of exercise self-efficacy and autonomous motivation in this relationship. The healthy development of adolescents plays a pivotal role in promoting high-quality population development, and physical exercise, as a key factor in promoting their physical and mental health, is influenced by various factors [37]. This study constructs a mediation model to comprehensively elucidate how social support influences adolescents’ exercise persistence through psychological mechanisms. The results indicate that social support significantly influences adolescents’ exercise persistence, with a total effect of 0.368. This finding aligns with the general consensus in the field of health promotion that social support has a positive impact on exercise persistence, laying the foundation for further exploration of its underlying mechanisms [7]. This study further found that social support exhibits a significant direct effect (0.239) on exercise persistence, while also exerting an indirect effect through exercise self-efficacy and autonomous motivation, with a total indirect effect of 0.129. In the indirect pathways, the effect of social support → autonomous motivation → exercise persistence (0.119) was significantly larger than the effect of social support → exercise self-efficacy → exercise persistence (0.010). While the chained mediating effect of social support → exercise self-efficacy → autonomous motivation → exercise persistence (0.001) existed, its effect size was extremely small. Therefore, this discussion section will focus on these core findings and provide detailed explanations in conjunction with relevant theories and existing literature.

The direct effect of social support on exercise persistence

This study revealed multiple pathways through which social support influences adolescents’ exercise persistence. The findings demonstrated a total effect size of 0.368, with a substantial direct effect of 0.239, accounting for 64.93% of the total effect. This result indicates that even after considering the mediating pathways through exercise self-efficacy and autonomous motivation, a significant direct association between social support and exercise persistence remains. This finding strongly challenges health behavior intervention models that place an overemphasis on psychological-cognitive transformation and instead highlights the primacy of structural enablement for this specific cohort of junior high school students in Jiangsu Province [2]. These findings are highly consistent with previous research. For example, Zhang et al. found that among college students, peer support directly promoted physical activity, while family and school support exerted an indirect effect via self-efficacy [38]. Similarly, this study confirms that social support directly affects adolescents’ exercise persistence, suggesting that support from peers, families, or schools can effectively enhance their persistence in physical activity.

Social cognitive theory posits that behavior is shaped not only by personal factors but also by environmental influences. Social support, as a critical environmental resource, can provide individuals with essential informational, emotional, and instrumental support [39]. For the junior high school students in Jiangsu Province in this study, who commonly face intense competition for academic progression, immense academic pressure significantly encroaches upon their extracurricular time and energy [37]. In such a high-pressure environment, autonomously scheduling exercise becomes a “luxury,” and the barriers to participating in physical activity are considerable. At this juncture, instrumental support—such as parents providing transportation and covering costs, or peers extending explicit invitations to exercise together—plays a role that transcends mere encouragement. It fundamentally lowers the barriers to behavioral initiation and the associated time costs at their very source [12]. This form of support transforms exercise from a “psychological task” that demands complex self-regulation and planning into a simple and immediate physical activity, thereby bypassing the psychological barriers that arise from academic fatigue.

The direct effect of social support manifests at various levels. For instance, encouragement from parents, invitations from friends for joint exercise, and guidance from coaches can directly furnish opportunities and facilitate convenience, thereby enhancing exercise persistence; furthermore, family, peer, and social support have a significant positive association with adolescent physical activity [5]. At the family level, support can be expressed through the provision of exercise equipment, the scheduling of time for physical activity, or joint family participation in sports [3]. Parents’ positive attitudes toward physical activity and their own active participation are significant predictors of their children’s engagement levels [12]. When parents demonstrate the importance they place on exercise by actively creating opportunities for their children or participating alongside them, adolescents are more inclined to perceive physical activity as an important and valuable endeavor, which in turn strengthens their persistence. At the peer level, support primarily provides social incentives through joint participation. Adolescence is a critical stage for socialization, during which peer support can offer crucial emotional backing and a sense of belonging. When adolescents feel accepted and encouraged by their peers, they are more willing to sustain their involvement in physical activity. Concurrently, mutual monitoring and encouragement among peers also contribute to maintaining the continuity of exercise behavior, a finding substantiated by the research of Zou et al. [13]. In their research, Zou et al. found that adolescents more readily attain a sense of belonging and acceptance within peer groups, and this sense of social integration is a key reason for their participation in and enjoyment of physical exercise. Second, this social support can also directly enhance adolescents’ positive attitudes and behavioral intentions toward exercise through the provision of emotional encouragement and validation. When adolescents feel cared for, understood, and supported by their peers, they are more likely to actively participate in and persist with exercise [13]. Moreover, this direct social influence, without the need for complex psychological processes, can facilitate the formation and maintenance of exercise habits in adolescents. When adolescents receive guidance and support from their social circles during physical activity, their motivation and drive to participate are significantly enhanced.

Notably, in the present study, the value of the direct effect of social support on exercise persistence (0.239) was substantially larger than the value of the total indirect effect (0.129). This indicates that the association of social support with exercise persistence is not merely limited to its pathway through an individual’s exercise self-efficacy and autonomous motivation; more importantly, it directly facilitates the occurrence and maintenance of exercise behavior by providing tangible environmental resources and behavioral conveniences. This implies that the mere receipt of support itself is a powerful driver of exercise persistence, independent of an individual’s perceptions of their own capability or motivation. This underscores the fundamental role of structural social support systems and interpersonal interactions in promoting exercise persistence, a role that transcends purely psychological mechanisms. Therefore, promoting adolescent exercise should adopt a comprehensive, multifaceted strategy that not only focuses on cultivating individual psychological factors but also emphasizes strengthening the direct social and environmental support for their exercise behavior. This can include active parental involvement, mutual peer support, and encouragement from teachers. For instance, schools can organize more group-based physical activities, families can schedule joint parent-child exercise sessions, and communities can provide more accessible sports facilities. All of these measures can directly provide adolescents with the opportunities and motivation for exercise, thereby enhancing their exercise persistence.

The mediating role of exercise self-efficacy

This study found that the mediating effect of exercise self-efficacy in the relationship between social support and exercise persistence was 0.010. Although the effect size is relatively small, it remains statistically significant. A high level of self-efficacy is typically associated with stronger outcome expectations, more concrete action goals, and higher levels of physical activity participation. According to Bandura’s theory of self-efficacy, individuals’ beliefs in their capabilities are critical determinants of behavioral choices and persistence. Self-efficacy, in turn, positively influences physical activity behaviors and engagement [8].

Social support can enhance adolescents’ exercise self-efficacy through various mechanisms such as verbal encouragement, substitution of experiences, and control of experiences [40]. First, verbal encouragement and positive feedback from significant others can directly boost an individual’s confidence in their ability to exercise. When adolescents receive affirming comments about their exercise performance from parents, teachers, or peers, they are more likely to believe they can persist in physical activity. The belief that others genuinely trust in their abilities significantly enhances their self-efficacy [41]. Second, vicarious experiences—observing peers similar to oneself succeed in physical activity—can serve as role models and foster the belief that “if they can do it, so can I,” thereby enhancing self-efficacy [40]. Third, mastery experiences gained through participation in sports—such as improving skills, developing strategies, or achieving team goals—offer direct experiences of success, which are particularly effective in reinforcing competence perceptions [8]. Finally, social support can help adolescents cope with fatigue and avoid misinterpreting normal tiredness or discomfort as signs of inadequacy, thereby strengthening exercise self-efficacy [40]. However, findings from this study suggest that adolescents’ exercise decisions may be more strongly driven by intrinsic interest or social incentives than by their perceptions of personal ability. The relatively small mediating effect of exercise self-efficacy could be attributed to cognitive developmental characteristics specific to adolescence. This developmental stage is marked by the formation of self-concept but also by heightened self-doubt. Adolescents tend to be more influenced by external evaluations, and their perceptions of internal competence may be relatively unstable [42].

While social support can indeed enhance self-efficacy and self-efficacy can promote exercise persistence, the small effect size (0.010) of this mediating path suggests that it may not be the primary mechanism through which social support influences exercise persistence. This implies that, within the complex network by which social support affects exercise persistence, the indirect pathway via self-efficacy may be less crucial than others. Considering the educational pressure in Jiangsu Province and the background of the physical education entrance examination, the standardization and mandatory nature of physical education exams may narrow students’ exercise self-efficacy to a belief in test taking ability for specific exam items (such as long-distance running and standing long jump), rather than a generalized perception of comprehensive ability to enjoy sports. This may also be one of the reasons for the low mediating effect value of exercise self-efficacy. Therefore, allocating substantial resources to reinforce this specific pathway may not be the most efficient strategy. This does not negate the importance of self-efficacy; rather, it indicates that within the “social support–exercise persistence” linkage, the mediating role of self-efficacy may not be the top priority intervention point. Enhancing exercise self-efficacy through social support may require longer timeframes and more sustained interventions. Effective strategies should adopt a more comprehensive approach, emphasizing stronger direct effects and motivational pathways, particularly those that target autonomous motivation, to achieve more significant improvements.

The mediating role of autonomous motivation

The study revealed that the mediating effect of autonomous motivation on the relationship between social support and exercise persistence was 0.0341—the largest effect among the three examined mediating paths. These findings indicate that social support indirectly promotes adolescents’ exercise persistence by enhancing their autonomous motivation, consistent with the core tenets of Self-Determination Theory. According to this theory, autonomous motivation is a key driver of sustained behavior. A systematic review by Teixeira et al. further highlighted that autonomous motivation is positively associated with exercise persistence, with intrinsic motivation being particularly important for long-term maintenance [43].

Self-Determination Theory posits that when the three basic psychological needs—autonomy, competence, and relatedness—are met, individuals are more likely to develop intrinsic motivation, which in turn fosters the self-regulation of exercise behaviors [44]. When an individual possesses a higher level of autonomous motivation, this predicts an increase in positive outcomes for adolescents, which in the present study is manifested as greater exercise persistence [45]. Research by Zhang et al. supports this conclusion, showing that autonomous motivation correlates with increased levels of moderate-to-vigorous physical activity among adolescents [46]. Qi et al. found in their study on children that autonomous motivation not only facilitates engagement in moderate-to-vigorous physical activity but also mediates the relationship between social support and physical exercise [47]. One possible reason for the stronger mediating effect of autonomous motivation is that adolescence is a period of rapid development of self-awareness and a heightened need for autonomy. Adolescents increasingly seek independence and a sense of control over their choices, and intrinsic motivation directly fulfills these developmental needs. Therefore, cultivating autonomous motivation may be particularly effective for promoting exercise persistence during this life stage.

Social support facilitates autonomous motivation by fulfilling the three basic psychological needs. First, concerning autonomy, social support—especially autonomy-supportive parenting—encourages adolescents to make their own choices about exercise activities, respecting their preferences and emotions. This fosters intrinsic decision-making and self-regulation [3, 48]. When adolescents feel that their exercise behaviors are self-endorsed rather than imposed, their levels of autonomous motivation increase significantly [49]. Parental self-directed support is a correct parenting approach and an important external driving force for exercising one’s initiative. It can help teenagers bravely express their true selves and constantly change, develop, and pursue themselves through exercise practice. Second, regarding the need for competence, social support can provide adolescents with opportunities for success in exercise through positive feedback, guidance, and access to resources, thereby reinforcing their sense of capability [37]. When adolescents recognize that participating in physical activity improves their abilities and self-confidence, their interest and intrinsic motivation to exercise are enhanced. Third, physical activity is often social in nature, and social support can satisfy adolescents’ need for relatedness. Through teamwork, cooperation, and healthy competition, adolescents establish positive peer relationships, gaining a sense of social belonging. These positive interactions reduce psychological tension and foster autonomous motivation [50]. Peer support can serve as a source of motivation. Once autonomous motivation is activated, it directly influences exercise persistence [51, 52]. Adolescents with high levels of autonomous motivation are more likely to view exercise as enjoyable and self-expressive. Even in the face of difficulties, they are more likely to persist, thereby demonstrating stronger persistence to exercise routines.

The relatively large effect size of this pathway suggests that fostering adolescents’ autonomous motivation through social support is more effective than the self-efficacy pathway. Comparing the effect values of the two paths, it was found that the value of the autonomous motivation effect was greater than the value of the exercise self-efficacy effect, which to some extent indicates that social support is more effective in helping teenagers “want” to exercise (autonomous motivation) than just helping them “feel capable” of exercising (self-efficacy). This strongly indicates that social support is more effective in helping adolescents want to exercise (autonomous motivation) than in merely helping them believe they can exercise (self-efficacy). Therefore, when social support activates adolescents’ intrinsic interest and sense of value in exercise, it leads to more substantial and lasting improvements in exercise persistence. Given the prominent mediating role of autonomous motivation, future intervention strategies should focus on creating environments that support adolescents’ basic psychological needs—autonomy, competence, and relatedness—in order to cultivate intrinsic motivation for exercise. This approach may be a more effective pathway for promoting long-term exercise persistence in adolescents. It aligns closely with the practical applications of Self-Determination Theory, such as offering greater choice during physical education classes, encouraging personal goal-setting, and promoting teamwork and social interaction.

Integrated mechanism of the mediation effect

By integrating the results of effect analysis and the underlying mechanisms, this study found that the influence of social support on adolescents’ exercise persistence is a multifaceted and complex process. The pathway analysis revealed a hierarchy of effects: the direct effect (0.239) was the most prominent, followed by the indirect effect via autonomous motivation (0.119), then the indirect effect via exercise self-efficacy (0.010), and finally, the mediation effect through both exercise self-efficacy and autonomous motivation (0.001), which contributed the least. Although the mediation effect was relatively small, it reveals an important psychological sequence: social support first enhances individuals’ exercise self-efficacy, which in turn fosters the development of autonomous motivation, ultimately leading to improved exercise persistence. This pathway exemplifies a cognitive–motivational–behavioral sequence.

According to social cognitive theory, behavioral change typically follows a sequential psychological process [39]. In the context of physical activity, individuals must first develop a positive sense of efficacy regarding their exercise capabilities. On this basis, they are more likely to develop intrinsic, autonomous motivation, which then manifests as persistent engagement in physical activity. From the perspective of developmental psychology, this mechanism also aligns with the characteristics of adolescent psychological development. Adolescence is a critical period in which self-concept evolves from concrete to abstract, and individuals become increasingly attuned to their internal qualities and abilities. During this period, support from others helps adolescents build confidence in their capabilities, which in turn strengthens intrinsic autonomous motivation, eventually translating into sustained exercise behaviors. At the theoretical level, there is also a conceptual linkage between exercise self-efficacy and autonomous motivation. Social cognitive theory posits that individuals with high self-efficacy are more likely to set challenging goals and pursue them with persistence, thereby enhancing their levels of autonomous motivation [53, 54]. From the perspective of self-determination theory, exercise self-efficacy is regarded as a core psychological need that facilitates the formation of autonomous motivation [48]. When individuals feel competent in a given activity, their intrinsic drive to engage in that activity is strengthened. Therefore, social support may initially enhance adolescents’ exercise self-efficacy, which subsequently fosters their autonomous motivation, ultimately promoting exercise persistence.

These findings suggest a clear hierarchy of influence: direct social support exerts the strongest effect, followed by the cultivation of autonomous motivation, while self-efficacy contributes to a lesser extent, and the mediation path has minimal practical impact. By ranking the magnitudes of these effects, we are able to identify the primary and secondary pathways through which social support affects exercise persistence. This finding integrates both social cognitive theory and self-determination theory, revealing the multiple mechanisms through which social support promotes adolescent exercise persistence. Social support not only directly provides opportunities and environments conducive to physical activity but also indirectly influences exercise behavior by enhancing self-efficacy and autonomous motivation. Specifically, the direct effects of social support may reflect environmental-level influences within the social-ecological model, such as the supportive home environment or peer invitations to exercise [5]. The path of autonomous motivation highlights the importance of meeting the internal psychological needs of adolescents, that is, when adolescents feel that exercise is autonomous, capable, and able to establish connections with others, they are more likely to persist in exercising.

Although exercise self-efficacy is widely recognized as a key predictor of behavioral change, its role as a mediator in the current study was relatively limited. This may suggest that, within the complex mechanisms by which social support influences exercise persistence, stimulating intrinsic autonomous motivation may be more critical than simply enhancing self-efficacy. Although the effect of the exercise self-efficacy pathway is relatively weak, this does not imply that exercise self-efficacy is unimportant. A more plausible explanation is that self-efficacy may play a “gatekeeper” or “threshold” role. Individuals require a minimum level of self-efficacy to even consider participating in an activity; below this threshold, the behavior will not occur at all. However, once this threshold is surpassed, the marginal contribution of the level of self-efficacy to exercise persistence may be less than the contribution of autonomous motivation [24].Thus, effective interventions to promote adolescent exercise persistence should adopt a comprehensive approach, prioritizing direct social support and the development of autonomous motivation, while carefully evaluating the utility of investing in more complex mediation paths that demonstrate minimal actual impact. If direct effects and the mediation via autonomous motivation are indeed the primary drivers, then interventions should focus on these areas—for example, by providing tangible support through families and schools or designing exercise programs that tap into adolescents’ intrinsic interests and sense of autonomy. For the relatively minor mediation pathway, unless further evidence suggests that it holds greater importance for specific subgroups or contexts, dedicated interventions may not be the most efficient use of resources.

Notably, while the mediation effect of exercise self-efficacy and autonomous motivation (0.001) was statistically significant, its explanatory power for exercise persistence is minimal. This finding partially challenges the simple linear assumption that social support must first enhance self-efficacy to foster autonomous motivation. It also suggests that, within this academically high-pressure cohort of junior high school students in Jiangsu, self-efficacy and autonomous motivation might play parallel or moderating roles in the relationship between social support and exercise persistence [29]. This indicates that, among Chinese junior high school students, social support may more directly cultivate autonomous motivation, or that the contribution of self-efficacy’s influence on autonomous motivation to exercise persistence is not pronounced within this specific mediational chain. This weak serial mediation effect may imply that theirs is not a strictly linear or sequential relationship, and that social support may instead be linked more directly to exercise self-efficacy and autonomous motivation through independent pathways. For example, social support can directly provide opportunities for autonomous choice (fostering autonomous motivation) and can also directly provide successful experiences (enhancing exercise self-efficacy), or these two processes may occur in parallel. Furthermore, there may be other mediating variables not included in the present model—such as psychological resilience or emotion regulation—that play a more significant role in the relationships among social support, self-efficacy, autonomous motivation, and exercise persistence. Concurrently, this may also reflect the statistical dilution effect in long mediational chains, wherein the multiplication of path coefficients at each step results in a final effect that becomes trivial [55]. These factors could all be reasons for the small value of the serial mediation effect observed between exercise self-efficacy and autonomous motivation.

Limitations and future directions

While this study offered meaningful insights into adolescent exercise persistence, it has key limitations that suggest directions for future research.

First, the cross-sectional design identifies associations but precludes causal conclusions, as relationships may be bidirectional. The study relied on correlational, self-report data lacking experimental verification. Future research must validate these findings, ideally by testing targeted interventions using experimental methodologies like randomized controlled trials (RCTs) to confirm the model’s practical applicability and provide direct evidence for practice.

Second, the reliance on self-report measures may introduce bias from factors like social desirability or recall inaccuracy, affecting data precision. Future studies should incorporate multiple data collection methods, such as behavioral observation, objective activity monitoring, and third-party evaluations, to enhance objectivity and validity.

Third, the study had a narrow focus on social support, self-efficacy, and autonomous motivation. Adolescent exercise is influenced by a wider range of factors, including personality traits, health status, time availability, and environmental accessibility. Future research should construct more comprehensive theoretical models that integrate these additional relevant variables to better capture the behavior’s complexity, exploring their potential interactions and relative importance.

Conclusion

Using a mediation model, this study examined the mechanisms through which social support influences exercise persistence in adolescents. The key findings are as follows:

1. Social support exerts a significant direct positive effect on exercise persistence among junior high school students.

2. Exercise self-efficacy and autonomous motivation serve as important mediators in the relationship between social support and exercise persistence, with the mediating role of autonomous motivation being particularly pronounced.

3. A complete mediation pathway exists in which social support influences exercise self-efficacy, which in turn enhances autonomous motivation, ultimately leading to improved exercise persistence. However, the magnitude of this mediation effect is relatively small.

Authors’ contributions

Qingchang Wu: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.Weidong Zhu: Data curation, Investigation.Yuan Zhang: Data curation, Investigation.Hu Lou: Data curation, Investigation.Siyan Liu: Data curation, Investigation.Changli Wu: Data curation, Investigation.Jun Xiang: Data curation, Investigation.Ning Ren: Data curation, Investigation.Rong Cao: Data curation, Investigation, software, Supervision, Writing – review & editing.

Funding

No Funding.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study has been approved by the Ethics Committee of Nantong University. The informed consent was obtained from all the participant’s and their legal guardians or parent involved in the study. All methods of this study were performed following Helsinki Declaration guidelines and regulations.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.