The recommendations for participating in physical activity for children is 60 minutes per day, or more. Physical education is insufficient for children nowadays (Carlson, et. al., 2008). Children can benefit a great deal from physical activity; the beneficial effect comes in many forms. For example, physical activity is considered good for cardiovascular health, musculoskeletal health, blood pressure, among other forms (Strong, et. al., 2005). Depression is a common disease, and gets more serious with adolescents. A research by Turner, Thompson, Huber, and Arif (2012) where depression symptoms score was divided into quartiles for analyses, showed that nearly three fourth of the students were in the third or fourth quartiles, which is too many students. Depression is the most common problem of psychological problems (Davey, 2008). The beneficial effect of physical activity for both psychological and physical well-being is well established. Accumulative evidence also suggests that physical activity improves cognitive performance (Singh, Uijtdewilligen, Twisk, Mechelen, & Chinapaw, 2012). This review will critically examine the effect of physical activity on academic performance and further more whether the effect is mediated by depression. The review is divided into four sections where in the first one the relationship between physical activity and academic performance will be discussed, in the second section the relationship between physical activity and depression will be discussed. In the third section the relationship between depression and academic performance will be discussed and the fourth and final section will be about future directions.
Physical activity and academic performance
Several reviews have indicated that physical activity is related to improved academic performance but the strength of the relationship varies between studies (Singh, Uijtdewilligen, Twisk, Mechelen, & Chinapaw, 2012; Trudeau, & Shephard, 2008; Biddle, & Asare, 2011). For example a review made by Biddle and Asare (2011) showed that physical activity can have a positive effect on cognitive functions, the behaviour in the classroom and academic achievement in children but the association is often weak and not entirely consistant. Harrison and Narayan (2003) did a cross-sectional research about adolescent?s participation in sports and other activities. Their results were that if adolescents participated in sports or other extracurricular activities they were more likely to do their homework and have a positive attitude towards school and teachers. However, Tremblay, Inman and Willms (2000) also did a cross-sectional research on 12 year old children to see whether physical activity did increase academic achievement in mathematics and reading. The participants answered a questionnaire about their physical activity and academic climate. The results showed a very weak but significant association between physical activity and academic achievement in both mathematics and reading. Similar results were in a research by Carlson et. al. (2008), but they did a longitudinal and cross-sectional research on children in kindergarten until they were in 5th grade and weak but significant association was also found in the result of this research. The only association between time spent on physical education and academic performance was with the group of girls who spent the most time in physical education (70 – 300 minutes per week) and the girls who spent the lowest time in physical education (0 – 35 minutes per week). No association was found in boys. The differences in gender could be because boys have higher levels of fitness than girls at baseline and that boys need to have more stimulus than is provided in physical education. Cross-sectional studies give an example that there is a relationship between two variables but their weaknesses is that it can?t say which variable causes the other. Intervention studies can say much more about the relationship between the variables. By using an intervention, Davis et. al. (2011) found out that the more exercise obesity children performed the better cognitive function they had. They put 171 obese children into three randomized groups, low dose exercise, high dose and control group. Low dose group had 20 minutes of exercise each day after school and 20 minutes of sedentary activities such as board games for 3 months. High dose group had two 20 minutes bout of exercise each school day. The children?s academic achievement was measured by using Woodcock-Johnson Tests of Achievement III. The results showed that the high dose exercise group had more improved cognitive performance than the other two groups and low dose exercise group had better cognitive performance than the control group. These results show?s that the more exercise obese children have the better cognitive function they will have.
All these research find a positive relationship between physical activity and academic performance but the association is sometimes week and sometimes strong. But the researches are different and that could cause the different results. The strength of the relationship between these two variables could differ because of the different age of the participants. Increased physical activity could have much more effect on academic performance in adolescent than in children. Also the self-described physical activity and grades from participants could not be true so the association could differ because of that. Cross-sectional data is a limitation because it says only that there is a relationship between the variables but not what variable causes the other variable, but it can indicate that there is a relationship. Intervention studies provide stronger evidence that physical activity may lead to improved academic performance. But because there was only one intervention study then that is a limitation. More intervention studies need to be done to provide a stronger evidence of the relationship between those two variables. There need to be more intervention studies for more than just obese children. In spite of these limitations the results indicate that there is a relationship between these two variables. Other, little is known about the re mechanism whereby physical activity affects academic performance. Independent line of researches raises the possibility that the impact of physical activity on academic performance may be mediated by other variables, for example depression.
Physical activity and depression
Physical activity has often been associated with depression, in other words depression has shown to decrease with more physical activity (Mata, Thompson, Jaeggi, Buschkuehl, Jonides, & Gotlib, 2012; Toker, & Biron, 2012). A review of reviews was conducted to find out the relationship between physical activity and depression in children and adolescents (Biddle, & Asare, 2011). There were 5 reviews which were reviewed concerning physical activity and depression. The results showed that physical activity seems to have a negative effect on depression, but the intervention designs do not have enough quality and many of the reviews have cross-sectional researches which can deviate the relationship or it will not show whether physical activity affect depression or the other way around. A cross-sectional research that was conducted to find risk factors for depression in adolescents showed that the adolescents who were depressed were less likely to engage in physical activity than the adolescents who was not depressed (Diego, Sanders, & Field, 2001). But cross-sectional studies do not show the cause of the variables so it does not say whether depression causes less physical activity or physical activity causes less depression symptoms. Gallegos-Carrillo et. al. (2012) did a longitudinal research of 1047 Mexican adults, both male and female, who were free of depression between the years of 1998 – 2000. The participant?s lifestyle and health were assessed, that is how much physical activity they had. The participants were divided into 3 groups after how much physical activity they performed each week, that is light, moderate or vigorous. After 6 years the participants was assessed again to see whether physical activity would prevent depressive symptoms. The results showed that the vigorous physical activity participants performed they had lower risks of developing depressive symptoms. The limitations in this research were that there was only one follow up after 6 years and that the participants had to fill out a questionnaire about how much physical activity they had. Another longitudinal research showed that leisure-time physical activity reduced depression symptoms only in women after both two and four years follow up but this was not found in men (Wang, DesMeules, Luo, Dai, Lagace, & Morrison, 2011). But the long term effect on leisure-time physical activity and the changes of physical activity and marital status on the risk of evolving depression was the reason for this research. No participant had a depression at the baseline of the research. Similar results were also in a longitudinal research about adolescent girls because the sexes have found to be different in depression and physical activity (Jerstad, Boutelle, Ness, & Stice, 2010). In that research, girls aged 11-15 years old reviewed a list of physical activity and crossed in a box for an activity that they had done more than 10 times for the past year and they answered a questionnaire for depression symptoms. This was done once a year for a 6 years period. The results showed that there was a relationship between regular basis of physical activity and depression. If the girls were involved in physical activity it reduced the likelihood of having depression symptoms in the future. Because the research was only about adolescents girls the results can?t be generalized to other groups. A research by Alosco et. al. (2012) points out that there is a relationship between depression and physical activity in older adults with heart failure. They did their longitudinal research on older people with heart failure. For baseline measure the older adults wore an accelerometer for 7 days and did an assessment to measure their fitness and answered a questionnaire concerning depression.
All of those researches show that there is a relationship between physical activity and depression. There is a limitation is that there is no intervention study, because intervention studies provide stronger evidence than cross-sectional and longitudinal for the relationship between physical activity and depression. Cross-sectional studies is not good enough because they can?t indicate the affect, which variable predicts what. The self-report of depressive symptoms and physical activity is a limitation in the longitudinal study?s because it is not reliable; the participants could for example exaggerate how much time they spent in physical activity and decrease the depressive symptoms.
Depression and academic performance
In a cross-sectional research that conducted a stepwise regression on risk factors for depression in adolescents, how much time the adolescents spent on their homework and their report of their grades explained 13% of the variance of depression symptoms (Diego, Sanders, & Field, 2001). They were explaining the relationship between academic performance and depression. A cross-sectional research was done with data from student responses National college health assessment from 2008 to study the relation between depressive symptoms and academic performance (Turner, Thompson, Huber, & Arif, 2012). The depressive symptoms were divided into a quartile. The results showed that students who had the lowest level of depressive symptoms were least likely to report having C, D, or F for grades but the students who fell into the second quartile were most likely to report having an average grades of C, D or F. For better explanation, the students who had moderate symptoms of depression were more likely than those who had milder or more severe to have worse academic performance. Pelkonen, Marttunen, & Aro (2003) were also researching the risk for depression by a longitudinal study in Finland and their results indicated the relationship between poor academic performance and depressive symptoms. The data was collected when the participants were 16 years old and researched the risk factors for depression at the age of 22. Chen, Rubin and Li (1995) showed in a 2 year longitudinal research that depression has been related to academic performance, according to them depressed children in China had more academic achievement problems than children that were not depressed. Another longitudinal analysis research which was performed in Los Angeles, which 243 adolescents participated in, showed that if the adolescent perceived themselves as a victim it caused psychological adjustment such as depression and loneliness which caused lower grades in school (Juvonen, Nishina, & Graham, 2000). That is similar to the findings of Schwartz, Gorman, Nakamoto, & Toblin (2005) which did a longitudinal investigation which focused on the relationship between victimization of 9 year old children and academic achievement over a 1 year period. The participants were 240 from 12 classrooms. The results showed that the children who perceived themselves as a victim in the peer group, they had lower academic achievement than the children who did not perceive themselves as a victim, but the results showed evidence that this relation was mediated by depressive symptoms. Shahar, Henrich, Winokur, Blatt, Kuperminc, & Leadbeater (2006) did a research about the relation between personality factor, self-criticism and depression on academic achievement in adolescents. This was a one year longitudinal study where 460 students in sixth and seventh grade participated in. They answered a questionnaire to measure their self-criticism and depression and their grades were obtained from their report cards. Their findings were the first to certificate relation between depression and a personality aspect of defencelessness in predicting academic achievement. The results showed that interaction between adolescent self-criticism and depression predicted a decrease in one?s average grade. A longitudinal research was done by Lehtinen, Raikkonen, Heinonen, Raitakari, & Keltikangas-Jarvinen (2006) where the purpose was to find out whether the grades in school at the age of 9, 12 and 15 was associated with depressive symptoms 12 to 21 years later or at the ages of 21 to 37. Because there had been found difference between sexes both in depression and grades, the sexes were measured separately. The results were that lower grades in 12 and 15 year old girls was associated with depression 12 and/or 17 years later, grades seemed not to have any other association with later depression. Because it seems that some researches will mean that depression has an effect on academic performance while other point out that academic performance has an effect on depression Hishinuma, Chang, McArdle, and Hamagami (2012) did a longitudinal research to put in a model called Longitudinal bivariate dynamic latent change model, which can be used to transmit the hidden scores from one variable to another over time. The results indicate that depression causes lower grades in adolescents but not that lower grades cause depression.
There is a relationship between depression and academic performance according to previous researches. The cross-sectional researches do not have much reliability because they only indicate that there is a relationship between depression and academic performance but they can?t say much more about the relationship. Longitudinal researches are better than cross-sectional but intervention researches are the best of describing the relationship but there is no intervention research so that is a major limitation.
Summary and future directions
As reviewed above there is a relationship between physical activity and academic performance but this evidence is not strong and most of the studies have been correlational. But as also reviewed above there is a relationship between physical activity and depression and also between depression and academic performance but this evidence is also not strong because there are only correlational study?s.
Future studies should examine if interventions if aimed at increasing physical activity also improve academic performance. They should also examine potential mechanism whereby physical activity affects academic performance. The literature review above suggests that physical activity is associated with less depression and that depression is associated with worse academic performance. These findings raise the possibility that the relationship between physical activity and academic performance may be mediated by the beneficial effects of physical activity on depression.
The model below will explain that there is a relationship between physical activity and academic performance, but if depression in the individual is taken into account there will not be a relationship between these two variables because it is mediated by depression.
Figure : Depression as a mediator between physical activity and academic performance.
If this model is right, then it will suggest that for adolescents to get higher grades they can increase the physical activity and by doing so decreasing depression and finally get higher grades in school.