Motivation toward Physical Activity and Healthy Habits of Adolescents: A Systematic Review

Adolescence is a transformative period in which rapid physical, cognitive and psychosocial growth takes place. Laying the foundation for healthy behaviors is paramount during these formative years. The aim of this review is to determine which countries are leading in research on adolescents’ motivation towards physical activity and healthy habits and their main findings. A systematic review was conducted following the PRISMA statement using the Web of Science and Scopus databases during the months of September to December 2022. The search terms used were: “Physical activity”, “Motivation” and “Adolescents”, in the following research areas: Education, Educational Research and Sport Sciences. A total of 5594 articles were identified, but only those that met the established criteria were included (32 articles). It is concluded that most of the research is led in Spain with 16 articles, followed by 3 in Chile, 2 in Portugal, 2 in Norway and the rest of the countries with 1. Likewise, most of the works include very similar aspects regarding the incidence of motivation towards the adherence to the practice of Physical Activity and healthy habits.


Introduction
Adolescence is a period in which young people face the difficult task of developing their personality and identity, as well as establishing their relational network [1]. It is the stage of development located between childhood and adulthood, in which a growing process of physical, psychological and social maturation takes place, leading the human being to become an adult. Very important rapid changes occur, with which the individual becomes biologically, psychologically and socially mature and capable of trying to live independently [2]. These changes affect the quality of life, both in terms of healthy habits and the practice of Physical Activity (PA), in which diet and nutrition play an important role in maintaining health and preventing diseases. These are times when adolescents should have tools that allow them to make a good decision on health and nutrition habits [3]. Added to that is the importance of PA that is associated with improved health outcomes and reduced cognitive impairment; many of these benefits are seen with only 60 min of moderate-to-vigorous intensity of PA per day [4].
Unfortunately, as indicated by the World Health Organization (WHO) [5], 1 in 4 adults and 3 in 4 adolescents (aged 11 to 17 years) worldwide are obese. As the economic development of countries increases, inactivity increases. There are countries where levels of physical inactivity can reach 70%, which added to the fact that adolescents are more prone to unhealthy behaviors due to globalization; unhealthy nutritional behaviors have been adopted, such as nutrient-poor food, insufficient intake of all food groups, high sugar content, fast food and little PA [3], as well as convenience foods. According to the WHO [5], new threats to the health of children and adolescents, as major health risks, include the rapid increase in childhood obesity, of which has become one of As a result of these reviews, the following questions arise: how can motivation promoted by PE teachers, a young person's family, context and their personal characteristics affect and influence the attitude of adolescents towards the practice of PA and healthy habits? In view of the above, it is very necessary to investigate with greater precision and different variables in order to have more background on the incidence of motivation towards physical practice and healthy habits in adolescents, given the importance of acquiring good behaviors in this line for their development throughout their lives.
The aim of this study is to determine which countries lead the main research findings on motivation towards PA and healthy habits in adolescents.

Materials and Methods
The method used for this study was the elaboration of a systematic review. For this purpose, the PRISMA 2020 statement [21] was followed in order to achieve an adequate and organized structure of the manuscript. It is a qualitative review that presents the evidence in "descriptive" form and without statistical analysis (systematic review without meta-analysis). Quantitative reviews can also present the evidence in descriptive form, but using statistical techniques to "numerically" combine the results against a point estimator called "meta-analysis" [22].

Search Procedure and Strategy
The search was carried out during the last weeks of September to December 2022 in the "Web of Science (WOS)" and "Scopus (SJR)" databases. The main topic of this research revolves around the impact on the motivation of adolescents to practice PA and healthy habits. The search terms used were: "Physical activity", "Motivation" and "Adolescents". These terms have been selected as they are considered to be the most appropriate to focus the search on research that responds to the central theme.
The search initially produced a result of 5594 papers. A time range was delimited, selecting only papers published between 2015 and 2022; a total of 3274 studies remained. The search was refined by selecting those works that were only "articles", obtaining a count of 3099. This number was reduced to 3031 when we selected all the articles that were written in English or Spanish, and finally, 1319 studies were selected after applying the criteria of the following research areas: "Sport science", "Education educational research".

Inclusion and Exclusion Criteria
The following inclusion and exclusion criteria were established: (1) research that was only applied in the school system; (2) the sample only consisted of adolescents between 10 and 19 years of age, belonging to an educational center; (3) non-experimental cross-sectional research; (4) application of validated instruments with complementary items.
For the application of these criteria, an initial preliminary reading of the title and abstract of each article was carried out, which made it possible to discard the works that did not meet these criteria. Subsequently, a more exhaustive reading of the selected articles was carried out, leaving a final sample of 32 scientific papers, where 22 of them were in English writing journals and 11 in Spanish ( Figure 1).  Table 1 shows a summary of some significant data of the selected sample. The data collected include the following aspects: year of publication, authors, country, objective, conclusion, recommendations and limitations. In some of the studies, not all items are specifically detailed, and therefore, some specific data are not reflected in the table, as well as the titles of the works and journals in which they have been published and other information found in the bibliographic references.   [24] To examine the interrelationships between the quality of motivation, self-regulation techniques and PA behavior and to explore the possible mediating role of self-regulation techniques in the relationship between autonomous motivation and PA behavior.

Results
Youth who were autonomously motivated were more likely to engage in strategic efforts to pursue those behaviors, such as planning and monitoring their progress, compared to youth who exercise for controlled reasons.
The development of interventions that support autonomous motivation for PA may encourage greater engagement in self-regulation techniques and positively affect PA behavior.
1. Reliance on self-report measures and correlational design, which limits causal inference.

2017 Spain
Sánchez-Miguel et al. U. Extremadura [25] To test the possible relationships between variables related to PA levels, as well as differences in gender and educational level, motivation, self-identity, body dissatisfaction and daily sitting time in a sample of Spanish high school adolescents.
Gender differences in the variables evaluated. Male participants showed higher intrinsic motivation and lower demotivation than females. In addition, males showed higher levels of PA than females.
The importance of promoting the intrinsic reasons for PA to encourage positive consequences in high school students.  To analyze the relationship between the motivations generated by the PE teacher and the gender and level of PA practice of the adolescents.
Correlational analysis revealed that intrinsic motivation variables are the most related. Males were more motivated than females, except for external introductory motivation and motivation. More active adolescents were more motivated than sedentary adolescents.
It was shown that the instrument analyzed is valid and reliable. It was recommended that the seven-factor structure should be respected. The positive correlation between high levels of motivation and active boys and adolescents was observed. Future studies should analyze in depth the results obtained using intervention studies that better clarify the relationship between the different study variables. In addition, it would also be useful to determine the influence of motivation and shame, given the variability of how they are perceived as adolescents grow older and progressively make their own independent decisions.  To establish the influence of the NPB on the physical sports practice habits of 8th grade (13 years old) elementary school students.
The data found suggest that the NPB could be factors that positively influence the promotion of physical sports practice habits in the school context.
"The proposal of a healthy physical-sports activity should be initiated from the school stage, not only as a preventive means but also as an educational-cultural phenomenon, since it has been observed that PA practiced during school hours is not enough to promote optimal health benefits".
Does not indicate any limitation.

2020 Spain
Vargas and Herrera U. Valencia [37] To find out the motivation of adolescents towards PE and regular PA practice as a function of gender.
Boys showed greater intrinsic motivation and a higher level of habitual PA than girls. Likewise, students who habitually perform a higher level of PA have a higher level of intrinsic motivation.   To identify the motivational profiles of secondary school students and relate them to their teaching style and way of life.
The results revealed the existence of two motivational profiles in the students: "self-determined" with higher scores in intrinsic motivation and identified regulation and a "non-self-determined" profile with higher levels of demotivation, introjected regulation and external regulation. It was found that students with a more self-determined profile presented higher levels of perceived autonomy support, higher levels of intrinsic motivation and a healthier lifestyle, with a positive relationship between the autonomy support perceived by the student, their level of self-determined motivation towards sport and a healthy lifestyle.
The importance of the teacher's performance in the classroom through autonomy support, in order to contribute to higher levels of motivation and a more active lifestyle. Intervention programs should take these aspects into account, offering activities that are compatible with school schedules, generating motivating contexts and adapted to the stage of the subject.
1. Expand to a larger and representative sample of young people of these ages.

2021 Spain
Moral-García et al. U. Pontificia de Salamanca [42] To determine the relationships between the motivation towards PA practice of a group of adolescents in secondary education (taking into account task or ego orientation) and the variables sex, age, PA level, BMI and morphotype.
It was observed that girls and younger students are more task-oriented in PA practice, as well as obese and overweight subjects and those who consider themselves to be of the ectomorph morphotype. Boys show greater ego orientation in PA practice.
The multiple factors involved in PA practice in adolescence should be studied. It seems advisable to promote task orientation in the practice of PA in secondary education (more markedly so among boys and older adolescents), both at the school and out-of-school level, as this can lead adolescents to a higher level of practice or the maintenance of this practice in the future.  To investigate associations between task-and ego-involving motivational climates, perceived physical competence, physical performance, enjoyment and anxiety during two different types of EF fitness testing lessons.
The results indicated that the task-involving climate and perceived competence increased students' enjoyment and decreased their anxiety levels, whereas the ego-involving climate had no effect on students' enjoyment and increased their anxiety levels.
Strategies that promote motivational climate involving tasks and students' perceived competence should be employed to increase enjoyment and decrease anxiety during EF fitness testing lessons. To analyze the association between the specific dimension (physical fitness, appearance, physical competence, physical strength and self-esteem) of students' physical self-concept (PSC) and their PA levels (intentions to be physically active and students' perceived levels of extracurricular PA) and sedentary behavior (SB). They also test the role of students' motivation (intrinsic) and motivation toward PA in these relationships.
The majority of students' PSC dimension positively predicted students' PA scores and were negatively associated with SB. In addition, the majority of students' PSC dimension was positively associated with intrinsic motivation and negatively predicted motivation.
Sex differences should be considered in the relationship of these variables. These differences may lead teachers to promote specific strategies to optimize the specific dimension of PSC, especially in girls, and their motivational processes with the aim of increasing their PA levels and reducing sitting time.
1. As this is a cross-sectional design, future longitudinal or experimental studies would allow for us to examine changes in the identified relationships over time and provide more solid evidence in this type of research. 2. The data in this research were collected with self-reported questionnaires by students, which may imply a social desirability bias; it would be important to analyze the association of these variables using objective measures (e.g., accelerometers). To analyze and compare the motivational indicators of adolescents in face-to-face PE classes during COVID-19, according to gender, educational level and PA.
Differences were found in achievement goals, motivational climate and levels of motivational regulation in different groups by gender, PA and educational level, favoring older and more active participants. A more positive motivational profile was found for girls in general and, in particular, for active boys, in terms of more self-determined motivations and mastery goal orientations.
This study suggests that restrictions related to face-to-face FE classes during the COVID-19 pandemic had a negative impact on student motivation.
It is important to keep in mind that this study was primarily intended to analyze the differences between the different groups with a convenience sample, which represents an inherent limitation of the study.

2022 Lithuania
Jankauskiene et al. U. Lithuanian Sports [49] It aims to test associations between support for teacher autonomy, self-determined motivation for PE, PA habits and non-participation in PE in a sample of adolescents in a cross-sectional study.
The results show that perceived teacher autonomy support was directly positively associated with PA habits and negatively associated with non-participation in PE classes.

Discussion
The aim of this study was to determine which countries are the leaders in research and their main findings on motivation for PA and healthy habits among adolescents. In the studies analyzed in the systematization of the two highest level databases, WoS and SJR, it was found that Spain leads the research conducted in this area, with 50% of the same in 16 articles. Analyzed by continent, this research is led by Europe with a total of 24 publications, equivalent to 75%, and is distributed as follows: A total of 16 in Spain, 2 in Finland, 2 in Portugal, 1 in Norway, 1 in Estonia, 1 in Belgium and 1 Lithuania. The second continent is America with six articles, corresponding to 19% of the total published: a total of three in Chile, one in the United States, one in Mexico and one in Brazil; finally, in Asia, there are two articles, representing 6% of the total published: one in China and one in Pakistan.
In the case of Spain, the research is carried out in different Autonomous Communities and their universities. Selected by the institution to which the first author belongs are: In the Autonomous Community of Andalusia, three articles: one at the University of Granada [28] and three at the University of Almeria [18,30,35]. In the Community of Castilla-León, there are two articles at the Universidad Pontificia de Salamanca [31,42]. In the Community of Catalonia, there is one article at the University of Lleida [41]. In the Community of Extremadura, there are four articles in the University of Extremadura [23,25,29,47]. In the Community of Madrid, there is one article in the Universidad Antonio de Nebrija [32]. In the Community of Murcia, there is one article in the University of Murcia [17]. In the Community of Valencia, there are two articles at the University of Valencia [37,39] and one article at the "Miguel Hernández" University of Elche [27].
In the case of the second country, Chile, two of the publications are led by Chilean authors and carried out in the Araucanía region: one article in the Catholic University of Temuco [15] and one article in the University of Playa Ancha (Valparaíso, Chile) [36]. The third article is led by the University of Jaén (Jaén, Spain), followed by other authors from the Universidad of Los Lagos (Osorno, Chile) [26].
It is relevant to highlight that in three of the articles of the systematic review, researchers who did not correspond to the country from which the sample was studied appeared as the main authors, as was the case of Hagger et al. [24], which, with the first researcher from an Australian university, developed the work in the context of students from Finland. This was additionally the case for Mayorga-Vega et al. [26], with Spanish and Chilean researchers carrying out the aforementioned study in Chile, and for the research developed with Pakistani schoolchildren, led by authors from a Chinese university working with others from Pakistan (Kiyani et al.) [44].
In relation to the objective, the collection was analyzed and the main findings of the incidences in the motivation of adolescents towards PA and healthy habits were synthesized. The articles revised mostly coincide with the influence of motivational factors in the adherence to PA and in the life satisfaction of adolescents, particularly the motivation of their self-determination to perform PA. Similarly, students with a higher level of regular PA practice registered more intrinsic motivation and identified regulation towards PE and lower motivation in those who do not practice DFA. Other personal factors, such as sport self-concept, physical self-concept or perceived competence, are also key predictors of future PA [51][52][53]. It is also observed how factors related to self-perception and those that were most frequently associated with enjoyment and potential health benefits become motivational factors that influence self-determination to perform PA among adolescents. Likewise, several results show that male adolescents have a higher level of intrinsic motivation and PA than girls. Finally, intrinsic motivation means that a person's actions are consistent with self-approved reasons for the action (e.g., for pleasure, fun or personal interest). Men present higher values of PA practice than women in terms of self-determined demotivation toward physical exercise [54,55].
Regarding psychological predictors of PA, adolescent boys reported higher levels of self-determined motivation towards physical exercise and intention to be physically active than girls. In addition, boys show greater ego-orientation in PA practice [56][57][58]; in turn, females are more inclined to less sporty activities, whereas males tend to be more predisposed to competition [57,59,60]. However, in the systematic investigation by Hopkins et al. [53], the importance of adolescent girls' attitudes or behavioral beliefs is highlighted when considering their motivation to participate in or continue with sports over time.
Additionally, research results show that PE has an impact on motivation towards adherence to PA practice, showing that generating strategies towards teacher autonomy support positively predicted students' enjoyment, confidence and motivation, while a controlling teacher style negatively affected confidence, enjoyment and motivation, being associated with students' overall intrinsic motivation, which would impact the predictability of the context of the PE class towards the adoption of healthy lifestyle habits such as proper eating and regular PA practice [61].
PE is an important subject that could help improve participation in general PA during the day; provide the possibility to develop physical exercise; improve self-concept and well-being based on eudaimonia; and acquire the knowledge, skills, motivation and habits to be active outside school hours and in later life [62]. PE is the only opportunity for some students to learn and practice sports, gymnastics, games, dance, exercise and healthy living habits [63,64]. According to the self-determination theory, the quality of motivation is a mediator that relates to behavioral, emotional and cognitive outcomes of EF [65][66][67][68]. EF teachers play a major role in the experiences of students' need for autonomy [69]. Additionally, teacher autonomy support is associated with higher students' autonomous motivation for leisure-time PA [70,71] and the perceived controlling behavior of EF teachers is associated with lower levels of intention to be physically active and lower out-of-school PA [72].
Regarding the second objective: to determine the main recommendations made, it can be identified in terms of the PE class that teachers should mainly consider fostering their students' satisfaction with the practice of PA and/or sports with strategies that favor the motivational climate which is focused on perceived task involvement. They should focus on strategies that incorporate elements such as personal development, progression and effort [73], which is positively associated with a number of adaptive outcomes such as perceived competence and enjoyment [74,75], given that a student's perceived egoinvolving climate has been found to be related to maladaptive outcomes such as boredom, anxiety and feelings of decreasing enjoyment [76].
Among the proposals presented in the 32 articles, there are some coincidences, for example, that the PE class (from the educators and researchers perspective) must know the context; incorporating a variety of variables such as gender, sociometric features and anthropometrics, among others, is useful in order to make adaptations in the teaching-learning process-knowing the students and the context in which they grow and develop will allow the teacher to design learning experiences that are adapted, relevant and challenging, and that promote the progressive advance in regard to each student and his/her previous knowledge [77][78][79][80][81].
Regarding the last objective of identifying the main limitations found and/or suggested by the authors in their research that could help to guide future studies in this area of research, the aspect that they point out most as a limitation is that their investigations were cross-sectional where cause-effect cannot be seen. It is worth mentioning that within the inclusion and exclusion criteria, one condition they had to meet was that they were of this type of methodology, although longitudinal research "compares data obtained at different times or moments from the same population, with the purpose of evaluating changes" [82]. However, cross-sectional research provides information on the object of study (population or sample) only once at a given time. This limitation could be analyzed in future systematic review studies that incorporate longitudinal studies in this area.
Likewise, research using aspects such as gender, context and family aspects, among others, is recommended in order to obtain a more complete view, although the greater the number of variables to be observed in a study, the more complex it is to carry out. In addition, a more representative sample could be used, since the sample studied is a subgroup of the population from which data are collected and should be representative of that population [83]. However, the sampling method is used to estimate the size of a sample depending on the type of research to be conducted, the objectives and/or hypotheses, and the defined research design [82].
Finally, another aspect mentioned in some research is the type of questionnaire applied, some of which can be interpreted differently by researchers. In certain topics, respondents answer according to their knowledge of them; in others, they may underestimate or overestimate their answers, generating erroneous information for the researcher, affecting the reliability, validity and objectivity [83]. It is also recommended that students should be supported in their participation, given that they could respond without taking into account the objectives of the study. Undoubtedly, analyzing the limitations of this or other types of research is very necessary and advisable to help improve future research.

Conclusions
It is concluded that Spain leads the publications on this subject with 16 articles analyzed, followed by Chile with 3, and Portugal and Norway with 2 articles each.
Teachers of PE should motivate adolescents towards physical practice through methodological intervention strategies that increase their satisfaction with learning and increase their commitment to PA and healthy habits in the long term.
Most research agrees that motivation is a relevant factor in terms of the importance of adherence to the practice of PA, and that in the PE class, satisfaction with physical sports practice should be encouraged in adolescents by means of methodological strategies that favor a motivational climate.

Limitations of the Study and Future Prospects
Since these were cross-sectional studies, it has not been possible to investigate more deeply into cause-effect situations or temporal characteristics.
It is recommended that future research should carry out a more in-depth analysis with the inclusion of demographic data, combining different variables to obtain information on the cause-effect of adherence to PA practice and healthy habits in adolescents.

Conflicts of Interest:
The authors declare no conflict of interest.