Vol.3, No.1, 42-50 (2013) Open Journal of Preventive Medicine http://dx.doi.org/10.4236/ojpm.2013.31006 Mediation effects of social support on relationships of perceived environment and self-efficacy with school-based physical activity: A structural equation model tailored for Japanese adolescent girls Li He1*, Kaori Ishii2, Ai Shibata2, Minoru Adachi3, Keiko Nonoue4,5, Koichiro Oka2 1Graduate School of Sport Sciences, Waseda University, Tokorozawa, Japan; *Corresponding Author: meethl@moegi.waseda.jp 2Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan 3Graduate School of Education, Okayama University, Okayama, Japan 4Sonan Junior High School, Okayama, Japan 5Waseda Institute for Sport Sciences, Tokorozawa, Japan Received 5 December 2012; revised 7 January 2013; accepted 15 January 2013 ABSTRACT Background: Identifying correlates of physical activity that can be targeted as potential me- diators is important for developing interven- tions to promote physical activity in adolescent girls. However, the mediated effects of multi- level correlates of ph ysical activit y remain p oor ly understood. Therefore, the present study aimed to examine direct and mediated effects of per- sonal, social and perceived school physical en- vironmental factors on school-based physical activity of Japanese adolescent girls. Methods: In this cross-sectional survey of the Japanese adolescent lifestyles, 344 junior high school girls were invited to complete self-report meas- ures of age, grade, weight, height, self-efficacy, social support (family, friends and teachers), perceived school physical environment (equip- ment, facilities and safety) and physical activity at school (min per week during lunch time and after-school hours). Structural equation model- ing analysis controlling for age was performed to examine the effects of body mass index (BMI), self-efficacy, social support and school physical environmental variables on lunchtime and af- ter-hours physical activity. Results: The final structural model demonstrated an acceptable fit for each context-specific physical activity. During lunch recess, perceived equipment and friend support exhibited direct effects on physi- cal activity; perceived facilities, safety, and self- efficacy were indirectly associated with physical activity through friend support. During after- school hours, both family and friend support directly affected physical activity at school; perceived safety, facilities and self-efficacy ex- hibited indire ct effect s on physical acti vity through family or friend support. How ever, there were no significant associations between equipment and after-school-hours physical activity. Regardless of contexts, BMI had neither direct nor indirect effects on physical activity. Conclusion: Social support from family and friends was identified as factors mediating the effects of perceived environment and self-efficacy on school-based physical activity among Japanese adolescent girls. This finding encourages the future devel- opment of effective interventions to promote physical activity through family and friend sup- port in the fut ur e. Keywords: Public Health; Physical Activity; Adolescents; Correlates; Ecological Model; Mediator 1. INTRODUCTION Regular physical activity during adolescence has been well demonstrated to have short- and long-term benefits for health [1,2]. However, the majority of adolescents are not physically active. Throughout the world, participa- tion in physical activity declines dramatically from ado- lescence, particularly in girls [3]. In Japan, girls are less active than boys at all ages. According to the latest na- tional investigation, about 39% of adolescent girls (vs. 16% of adolescent boys) do not engage in 60 min of physical activity daily [4]. Considering that physical ac- tivity interventions should be designed for specific at- risk groups, adolescent girls are one such group, which Copyright © 2013 SciRes. OPEN ACCE SS
L. He et al. / Open Journal of Preventive Medicine 3 (2013) 42-50 43 underscores the interest in developing successful inter- ventions to promote their physical activity. Such interventions require identifying modifiable cor- relates of physical activity that can be targeted as poten- tial mediators [5]. However, most previous studies fo- cused on the direct effects of correlates. There is little research investigating indirect effects of factors on physical activity. From the social ecological perspective, physical ac- tivity behavior is determined by an interaction of multi- level influences across personal, social and environ- mental factors, although previous studies mainly exam- ine psychological and/or social environmental factors [6-12]. Few studies have examined physical environ- mental influences on physical activity, which are recog- nized as having long-term effects on population-based health behaviors. Even fewer studies have examined both the direct and indirect effects of multilevel factors on physical activity behavior [13-15]. Moreover, such ecological approach suggests that examined behaviors should be specific to the relevant environment (i.e., the school physical environment is relevant to school-based physical activity). However, existing studies of environmental influences on adoles- cent physical activity behavior have focused on overall physical activity level without distinguishing physical activity in different contexts (i.e., in certain places and at certain times) [16]. Currently, no studies have reported direct and indirect effects of correlates on context-spe- cific physical activity among adolescents, although a comprehensive understanding of how environmental and personal factors interact to influence individuals’ con- text-specific physical activity behavior is necessary for the development of effective interventions and health po- licies. For children and adolescents, schools are important settings for physical activity. Students spend much of their day at school and have many potential opportunities for daily activity there, such as physical education classes, break times (including lunch recess) and af- ter-school hours. Physical education classes alone do not provide them with enough opportunity to meet recom- mended amounts of physical activity [17]. One review suggested that involvement in physical activity during non-curricular school time contributes 5% - 40% of the recommended daily 60 minutes of physical activity [18]. It is therefore important to explore the direct and indirect effects of personal, social and school environmental fac- tors that may influence such non-curricular physical ac- tivity at school. As a particularity of social context among Japanese adolescent girls, the strong desire to thinness or under- weight can be listed. Contrary to other developed coun- tries in which increase of obesity are major problems, the prevalence of underweight increased among them [19- 22]. Society’s equating thinness with beauty and attract- tiveness in women can be one of reason for this [23]. Thus, contribution of body weight on the relationship between multilevel factors and physical activity may be different between Japanese adolescents and those in other western countries. On the other hand, increase in autonomy and peer in- fluence is one of relatively common characteristics in adolescence regardless of nationality. Especially, gender influences on these become more pronounced [24]. Compared with boys, adolescent girls, with the earlier development of puberty and self-concept, has been found to be more concerned about the self-appearance, popu- larity in the class, the evaluation from other classmates and teachers [25]. Thus, even in same school environ- ments, the pattern and direction in relationship between factors and physical activity would be difference be- tween genders. Therefore, further understanding how the multilevel factors interact with each other to develop the tailored intervention strategies to promote physical ac- tivity among adolescent girls. In sum, the present study expanded current literature by examining not only the direct but also the indirect effects of all the selected individual, social and environ- mental factors with school-based physical activity at dif- ferent times of days in Japanese adolescent girls. 2. METHODS 2.1. Participants and Data Collection Data for the present study were collected from a cross- sectional survey of the Japanese adolescent lifestyle. Data collection was conducted between Oct. and Dec. 2010. A total of 761 public junior high school students (aged 12 - 15 years old) in Japan participated in this sur- vey, including 344 girls. All participants were invited to complete a self-report questionnaire individually during class time. Information on demographic such as age, gender and grade were collected with this questionnaire. Informed consent was obtained from all participants, their guardian and the school. Participation was volun- tary, and confidentiality was ensured. The study protocol was approved by the Research Ethics Committee of Wa- seda University. 2.2. Measures Measures of weight and height were collected through a height and weight measuring scale. Body mass index (BMI) was calculated. Participants were grouped into underweight, normal weight, overweight and obesity by BMI ranges specific for age and gender using Centers for Disease Control and Prevention criteria [26,27]. Copyright © 2013 SciRes. OPEN ACCE SS
L. He et al. / Open Journal of Preventive Medicine 3 (2013) 42-50 44 Participants were required to report the frequency (day/week) and duration (min/day) of physical activity at school during lunch recess and after hours in a usual week. For analysis, minutes per week were calculated for each setting (lunchtime physical activity and after-school physical activity) [28]. Based on a previous instrument [29], 10 items were used to assess three factors of school physical environ- ment. The three factors were 1) “equipment” (3 items), examining the accessibility or usability of physical equip- ment (e.g., There is enough equipment for activities at school); 2) “facilities” (4 items), measuring the accessi- bility or usability of physical activity facilities (e.g., The school grounds are big enough for activities); and 3) “safety” (3 items), investigating perceived safety of phy- sical activity equipment and facilities (e.g., It is safe to engage in physical activity on the grounds and in the gym at school). All items were rated on a four-point scale from 1) strongly disagree to 4) strongly agree. The factorial reliability (equipment: Cronbach α = 0.71; fa- cilities: Cronbach α = 0.75; and safety: Cronbach α = 0.83) of this scale was confirmed by respondents. In terms of social support for physical activity, par- ticipants were asked to rate support from three sources on a four-point scale from 1) not supportive at all to 4) strongly supportive for the following question: “How do you rate support for engaging in physical activity from 1) family; 2) teachers at school and 3) friends at school?”. The measure of self-efficacy related to physical activ- ity (i.e., belief in one’s ability to be active relative to peers [30]) contained 1 item with responses ranging from 1) strongly disagree to 4) strongly agree. The statement was “I am able to do physical activities/exercises/sports better than my friends.” 2.3. Data Analysis Only girls with complete data (N = 280) were included in the analyses. Means and standard deviations (SD) were then calculated through descriptive statistics using SPSS18.0 software. The size of the final sample was adequate to estimate the models [31]. Finally, structural equation modeling (SEM) analysis with maximum like- lihood estimation in Amos 17.0 was performed to test the fit of proposed models. The original proposed model that led to a good model fit of the final model is described below. The measure- ment model included (a) three latent variables of physi- cal environment: equipment (3 indicators), facilities (4 indicators) and safety (3 indicators); (b) relations be- tween latent variables and their indicators and (c) corre- lations between the three latent environmental factors. The structural model included (a) paths from perceived physical equipment, facilities and safety and BMI to perceived self-efficacy and self-reported physical activity; (b) path from self-efficacy to each source of social sup- port and (c) paths from self-efficacy and three sources of social support to physical activity. Model fit was assessed using the goodness-of-fit index (GFI), adjusted goodness-of-fit index (AGFI), root mean square error of approximation (RMSEA) and Akaike information criterion (AIC). GFI and AGFI are used to measure how well the model fits the data, which varies from 0 to 1, with .90 indicating an acceptable model fit and 0.95 indicating a good model fit [32,33]. RMSEA is a measure of the discrepancy between a population-based model and a hypothesized model assessed per degree of freedom. There is good model fit if the RMSEA is less than or equal to 0.05, with the upper limit of confidence interval less than 0.08 and the lower 90% confidence limit including or close to 0 [33]. A lower AIC value for a model reflects a better-fitting model compared with competing models [34]. A model was considered to fit the data when the following criteria were met: GFI > 0.90, AGFI > 0.90 (AGFI < GFI), RMSEA< 0.05 and a lower AIC value than competing models. A p value less than 0.05 was considered statistically significant. To adjust the original specified model, new free pa- rameters were added based on the modified indices be- fore the Wald test that deleted all non-significant free parameters to increase model fitness. Then only signifi- cant causal paths with corresponding standardized re- gression coefficients (β) were shown in the figures of final structural models that demonstrated a good model fit. With the standardized regression coefficients, the magnitude of each factor could be directly compared with other factors in the model. 3. RESULTS 3.1. Participant Characteristics Adolescent girls (mean age = 13.44, SD = 0.93) with complete data comprised the final sample. Mean height and weight were 155.37 cm (SD = 5.32) and 46.98 kg (SD = 8.72), respectively. The majority of adolescents had normal weight (5 ≤ BMI < 85 percentile, n = 236, 84.3%). More information about characteristics of the studied variables is provided in Table 1. 3.2. Structural Equation Model for Lunch-Time Physical Activity The final structural model for lunchtime physical ac- tivity in Figure 1 demonstrated a good model fit (GFI = 0.95, AGFI = 0.93, RMSEA = 0.02 [90% confidence interval = 0.00 - 0.04]). The recalculation of the model after addition and deletion of free parameters reduced the AIC value from 780.95 to 215.56. During lunch recess, perceived friend support (β = 0.11) was found to have a direct positive effect on girls’ physical activity. Self- Copyright © 2013 SciRes. OPEN ACCE SS
L. He et al. / Open Journal of Preventive Medicine 3 (2013) 42-50 45 Table 1. Characteristics of participants and outcome physical activity variables. Participants (Na = 280) Mean SDa Age 13.44 0.93 Height 155.37 5.32 Weight 46.98 8.72 BMI 19.40 3.14 Lunch-time Physical Activity 8.46 26.74 After-school Physical Activity 138.89 259.05 Grade (N, %) Grade 1 99 35.4% Grade 2 96 34.3% Grade 3 85 30.4% Weight status (N, %) Underweight 12 4.3% Normalweight 236 84.3% Overweight 22 7.9% Obesity 10 3.6% aN: number; SD: standard deviation. Figure 1. Effects of personal, social and environmental factors on lunch-time physical activity. Only statistically significant paths are shown in the figure. The significance level was set at p < 0.05. BMI: body mass index; Family: family support; Teacher: teacher support; Friend: friend support. efficacy (β = 0.04) indirectly influenced physical activity through friend support. With respect to the influences of school environmental factors, perceived equipment ex- hibited a direct negative effect (β = − 0.15) on physical activity. The total effects of perceived facilities (β = 0.01) and safety (β = −0.01) on physical activity were fully mediated by self-efficacy and friend support. Equipment was identified as the most influential environmental fac- tor related to physical activity. There were no significant associations of BMI, family support or teacher support with physical activity. 3.3. Structural Equation Model for After-School Physical Activity The final structural equation model for after-school physical activity in Figure 2 also demonstrated a good model fit (GFI = 0.95, AGFI = 0.93, RMSEA = 0.03 [90% confidence interval = 0.00 - 0.04]). The AIC value was reduced from 842.24 to 219.74 after the model modifications. In the final structural model, perceived equipment, teacher support and BMI failed to exhibit direct or indirect effects on physical activity. Perceived facilities (β = 0.02) and safety (β = −0.02) were found to indirectly affect physical activity through self-efficacy and family support or friend support. Their effect sizes on physical activity were generally low. The standard- ized indirect effect of self-efficacy on physical activity through family and friend support was 0.09. Support from friends (β = 0.16) and family (β = 0.13) were found to directly affect physical activity. The final model iden- tified friend support as the most influential factor directly affecting physical activity during after-school hours. 4. DISCUSSION The present cross-sectional study examined effects of perceived school physical environment, social support, self-efficacy and BMI on school-based physical activity in adolescent girls. Figure 2. Effects of personal, social and environmental factors on after-school physical activity. Only statistically significant paths are shown in the figure. The significance level was set at p < 0.05. BMI: body mass index; Family: family support; Teacher: teacher support; Friend: friend support. Copyright © 2013 SciRes. OPEN ACCE SS
L. He et al. / Open Journal of Preventive Medicine 3 (2013) 42-50 46 The primary finding of this study was that social sup- port directly affected school-based physical activity as a possible mediator. Specifically, friend support was found to be the source of support most highly related to physi- cal activity in both lunchtime and after-school settings. Previous studies have demonstrated similar findings on moderate-to-vigorous physical activity during non- school-time and mean daily physical activity in adoles- cent girls [11,35-38]. Collectively, findings suggest that developing strategies to encourage or assist with friends’ physical activity behaviors can be beneficial in promot- ing physical activity in adolescent girls, regardless of contexts. Compared with friend support, support from family and teachers for physical activity were found to be less important in both contexts. This finding is under- standable because adolescent girls are becoming inde- pendent from family and strengthening their identifica- tion with peers [11,37]. Interestingly, the effect of family support on physical activity was significant in the af- ter-school context but not at lunch time. This suggests that parents mainly act as a “gate keeper” by providing instrumental support (e.g., transportation and providing access to equipment) so that children can engage in or- ganized physical activity during after-school hours [39, 40]. Similarly, the non-significant association of teacher support with physical activity was understandable be- cause physical activity becomes a free choice in leisure time. Teachers’ influence may be more significant in physical education courses rather than in free time be- havioral choices. In Japan, approximately 71.2% of jun- ior high school girls join in their school’s extracurricular sports clubs during after-school hours. Only 0.7% of girls are motivated by teachers. However, 26.4% of re- port that they take part in extracurricular sports clubs because of their friends and family [41]. Considering that no comparable previous studies exist, to better under- stand the context-specific difference in social support related to physical activity, more in-depth research is needed to examine preferred types of physical activity in different contexts, and to identify types of support (e.g., encouragement or tangible assistance) in association with context-specific physical activity. Findings in thepresent study suggest considering family and friend support as possible mediators in future longitudinal or intervention studies to observe changes of physical activity in specific contexts. Based on available evidence [35,42], when test- ing the interventional effects of social support on direct promotion of physical activity at school, the following should be considered: increasing the frequency of parents or friends watching or talking about physical activity, parents or friends increasing their encouragement of girls joining in extracurricular sport clubs started at school and parental assistance with fees for equipment needed for these clubs. Self-efficacy has been demonstrated as a consistent correlate and mediator of adolescents’ physical activity [10,11,14,16,43,44]. However, in the current study, self- efficacy did not directly affect physical activity of ado- lescent girls. The inconsistency between previous studies and the current study might be attributed to aspects of self-efficacy measured. The present study focused on the self-efficacy in performance of activities; previous stud- ies primarily examined barriers self-efficacy. Ryan et al. found that the impacts of different types of self-efficacy (e.g., barriers self-efficacy, performance self-efficacy and asking self-efficacy) on physical activity were dif- ferent [30]. Additionally, our finding might further con- firm the study of Dishman et al. suggesting that physical activity interventions designed to enhance self-efficacy might be especially needed during preadolescence [7]. Therefore, to gain a complete understanding of the re- lationship between self-efficacy and context- specific physical activity, future studies should include more as- pects of self-efficacy that may directly account for the variance in physical activity, and should follow changes in self-efficacy throughout primary and junior high school. This study provided additional evidence of associa- tions between different features of school physical envi- ronment and physical activity by context [45-48]. First, perceived equipment had a direct negative effect on girls’ lunchtime physical activity. It is possible that girls who actually used equipment reported a lower score for available equipment than girls who did not use it because the latter were less aware of the real equip- ment situation. Second, the negative effect of perceived safety on school-based physical activity might be ac- counted for by inaccurate measures of the physical envi- ronment. Some previous studies have shown that the agreement between perceived and objectively measured environment is often poor, and the relationship between objective and self-report measures of physical environ- ment and physical activity is inconsistent among adoles- cents [49,50]. Therefore, future research is needed to test whether perceptions of equipment and safety match ob- jective measurements to clarify the influences of equip- ment and safety on physical activity. In addition, this study indicated that increasing perceptions of accessible facilities at school might promote physical activity par- ticipation among adolescent girls through increasing self-efficacy and social support. This information high- lights the importance of increasing information channels regarding available or accessible facilities at school among students or parents. There are various ways to accomplish this. For instance, school officials could re- port to students and parents in timely manner updated news about regular maintenance of facilities, or install a sign on school grounds informing students about the Copyright © 2013 SciRes. OPEN ACCE SS
L. He et al. / Open Journal of Preventive Medicine 3 (2013) 42-50 47 available facilities and policies about using them. One more finding of this study was that BMI had no significant influence on girls’ physical activity. BMI is one of the most studied biological markers of body weight and shape. Evidence from systematic reviews have shown that there is no consistent association be- tween BMI and adolescent girls’ physical activity level, with the majority of studies reporting either a small negative or no correlation [43,51,52]. The small or non- significant effects of BMI may suggest that other poten- tially body weight-and shape-related factors like body image need to be assessed in future behavioral models for girls. Different from BMI, the construct of body im- age measured physical appearance attitudinally, consist- ing of subjective feelings and beliefs on one’s own ap- pearance (e.g., body dissatisfaction) [53] and perceptions of how the body moves and functions, or what the body can “do” [54]. Considering cultural influences and norms on poor and ideal body image and that girls tend to be more concerned about their physical appearance than boys during adolescence, body image rather than BMI is often thought to be more likely to reflect variances of physical activity or other weight-related behavior in adolescent girls [43,55]. Therefore, it would be worth- while including the construct of body image in future models. The collective evidence is sufficient to encourage the use of support from friends and families as mediators in future intervention studies designed to increase physical activity among Japanese adolescent girls. Given that dif- ferences between school systems and environments may limit the generalizability of findings between coun- tries, and many previous studies were conducted in Western countries, research on Japanese adolescent girls is needed. There are several strengths of the present re- search worth noting. First, this study extended previous research by measuring both direct and indirect effects of multilevel contributing factors on context-specific physical activity rather than overall physical activity level. In addition, several sources of social support and various school physical environmental attributes were examined concurrently in the present study. Although previous studies have compared the effects of family and friend support on physical activity, there are no studies that simultaneously investigated the relative importance of family, friends and teachers on girls’ school-based physical activity. Second, the present study contributed to studies on adolescents by exploring the mechanisms underlying the physical activity behavior of Asian ado- lescent girls. Finally, the present study used SEM analy- sis which was helpful in exploring potential mediators that can possibly intervene and allowed examination of relative contributions of factors explaining physical ac- tivity. Despite the strengths, a number of limitations must be noted. One is the use of a self-report measure of physical activity, which is subject to error and bias. Further stud- ies should combine existing objective and subjective measures to investigate context-specific physical activity more accurately. Furthermore, lack of objective meas- urement of the physical environment characteristics may account for the inaccurate perceptions of the physical environment. Future research should use both self-report and objective measures to accurately evaluate the envi- ronment. Another limitation is the list-wise deletion adopted in the present study, which may lead to bias in data findings. A further limitation is that the generalize- bility of findings beyond the study location may be lim- ited by the data from a single school. However, the prevalence of overweight and obesity in the present study (11.5%) was slightly higher than the prevalence in a national survey (7.4%) [22]. This implies that the structural models in the present study might be reflective of counterparts across the country. Still another limita- tion is the cross-sectional data used in this study, which only permits estimates of between-person relations among variables. Therefore, a longitudinal or interventional de- sign that permits estimates of the effects of changes of mediators on the physical activity within participants is warranted in future research. In summary, the present study indicated that 1) social support mediated the cross-sectional effect of physical environment and self-efficacy on physical activity among adolescent girls and 2) associations between examined factors and school-based physical activity differed by context. Results imply that it is possible to develop a school-based intervention through collective supports from families and friends to increase girls’ school-based physical activity level. Furthermore, the mediated effect of perceptions of self-efficacy and physical environment that may be helpful for increasing perceptions of social support should be tested in future studies. 5. ACKNOWLEDGEMENTS The authors would like to thank the participating students and school in the present study. This investigation was supported by the Grants- in-Aid for Scientific Research (No. 22700680) from the Japan Society for the Promotion of Science, Waseda University Grant for Special Research Projects (2010A-095, 2011A-092), and the Global COE Pro- gram “Sport Sciences for the Promotion of Active Life” from the Japan Ministry of Education, Culture, Sports, Science, and Technology. REFERENCES [1] Hallal, P.C., Victora, C.G., Azevedo, M.R. and Wells, J.C. (2006) Adolescent physical activity and health: A system- atic review. Sports Medicine, 36, 1019-1030. doi:10.2165/00007256-200636120-00003 Copyright © 2013 SciRes. OPEN ACCE SS
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