**4. Potential mechanisms for the association between PA, CRF and AA**

students; and between CRF and mathematics for socioeconomic disadvantage students. This finding is important to understand the importance of CRF on students' learning, regardless of their socioeconomic status. In Spain, it was observed that CRF was associated with AA, and the significant association remains even after adjustment for fitness and body composition indicators [69]. In Portugal, the relationship between CRF and body weight status on AA was investigated among seventh-grade students from different cohorts [70]. CRF and weight status were independently and synergistically related to AA, independent of the different cohorts. This finding provides further support that CRF and healthy weight students

Although the evidence of the positive relationship between CRF and AA seems to be overwhelming, results from the presented studies need to be interpreted with caution, since the cross-sectional design can only suggest an association between the variables, rather than provide causal inference. Thus, longitudinal studies are needed to clarify the association. So far,

However, recent research assessed potential differences in AA based on CRF over a 2-year period, and found that students who maintained a healthy CRF had the highest mean scores in AA tests [71]. Those who had the lowest scores were not in the healthy zone for CRF in grades 5 and 7. These suggest that attaining and maintaining a healthy CRF could be successful in terms of one's AA. A more recent investigation also examined the relationship between changes in CRF and changes in mathematics and reading achievement between grades 6 and 8 [72]. Improvements between grades 6 and 8 in CRF were positively correlated with AA. The results from this study support and corroborate previous studies, suggesting that students who are more cardiorespiratory fit are more likely to perform better on AA tests. This highlights the long-term role of improving fitness and increasing AA. Thus, it seems that develop-

there are not many longitudinal studies that analyzed the effect of CRF on AA.

mental changes in CRF are important to consider when examining changes in AA.

onstrate that improvements in CRF are prospectively associated with better AA.

positive effect of PA, CRF and consequently cognition and AA.

Further, in Taiwan, the association between change in fitness and subsequent change in AA from grade 7 to grade 9 was examined [73]. The regression analyses in this study confirmed that improvement in CRF was significantly associated with better AA. Interestingly, CRF exhibits stronger longitudinal associations with AA than other forms of fitness or body mass index for students. More recently, in Portugal, Sardinha et al. [74] examined the prospective associations between CRF and AA in students from grade 5 to grade 7. Results corroborated those observed previously, indicating that being persistently fit, compared with those classified as persistently unfit, increased the odds of having high levels of AA at follow-up. Students, who were unfit at baseline but improved their CRF and became fit, also had higher odds of achieving better marks than those persistently unfit. These longitudinal studies dem-

**Summary:** Numerous cross-sectional studies demonstrate that CRF is consistently associated with AA. Results from these studies are confirmed by recent longitudinal studies, indicating that low levels of CRF can jeopardized students' academic future. An investment in PA promotion and PE is important because it might play a role in the

are more likely to have better performance at school.

244 Health and Academic Achievement

The association between PA, CRF and AA is not yet clearly understood. However, there are several potential mechanisms that may explain the association [75]. Animal and human research have been helpful in understanding the neurobiological mechanisms by which PA and CRF affect brain structure and function [76], cognition, [3, 4] and consequently AA [4]. Although understanding molecular and cellular changes in brain is currently limited in humans, larger scale neuronal changes can be assessed using neuroimaging tools. Advances in neuroimaging techniques have enabled the field of neuroscience to bridge the gap between animal and human studies. Changes in brain structure and function as a result of PA and CRF can now be addressed through an understanding of changes in the volume and thickness of neuronal tissue, via alterations in functional changes such as blood flow across brain regions, and through the understanding of how neural networks influence one another [76]. Furthermore, with a cross-talk mechanistic approach between organs, exercise may induce systemic factors released from peripheral organs such as muscle (myokines), liver (hepatokines) and adipose tissue (adipokines) that may contribute to neurotrophin and neurogenesis, as well as cognition and memory function [77]. Even though some uncertainties about the exact mechanisms remain, this is an evolving and promising field of research that further emphasizes the systemic and integrated effects of exercise on mechanisms that link biology to selected behaviors.

In school-aged children, a growing body of literature suggests differential brain structure related to CRF [75]. Specifically, an association has been shown among CRF, greater hippocampal volume, cognition and memory [78]. Such findings are interesting because the hippocampus is intricately involved in learning and memory, aspects of cognition important to AA, and these data suggest that CRF is beneficial to this subcortical region of the brain as well as the cognitive processes supported by it. Chaddock et al. [79] further observed differences in the basal ganglia, a subcortical structure involved in the interplay of cognition and willed action, between children with lower and higher CRF. Children with higher CRF exhibited greater volume in the dorsal striatum when compared to lower fit children. Such findings indicate that higher CRF is associated with better control of attention, memory and cognition. Children with better CRF exhibited increased inhibitory control and response resolution, and further higher basal ganglia volume was related to better task performance. These findings point to the dorsal striatum's involvement in higher order cognition and that CRF might influence cognitive control during children development.

Functional neuroimaging data have indicated that higher CRF is associated with increased cerebral blood flow in the microvasculature of the hippocampus in children, independent of sex, age and hippocampal volume [80]. Increased hippocampal blood flow is also linked to higher task performance on a spatial memory task. Thus, CRF might influence how the brain regulates its metabolic demands via blood flow to a particular region important for learning and memory.

To characterize PA-related differences in brain function, Davis et al. [81] used functional magnetic resonance imaging (fMRI) to investigate changes in the blood oxygen level dependent (BOLD) signal following PA intervention. Twenty sedentary, overweight children were randomized into an after-school PA intervention or a non-PA control group that lasted 14 weeks. Following the PA intervention, increased bilateral activation of the prefrontal cortex and decreased bilateral activation of the posterior parietal cortex was observed in the PA group relative to the non-PA control group. These differences in brain were elicited during tasks that tap inhibition, one aspect of executive control, indicating that the PA intervention affect brains function. A study, using fMRI, observed increased activation in prefrontal and parietal brain regions during early task blocks, and decreased activation during later task blocks in children with higher CRF relative to children with lower CRF [82]. As higher CRF children outperformed lower CRF children on aspects of the task requiring the greatest amount of executive control, higher CRF children appear more capable of adapting neural activity to meet the demands imposed by tasks that tapped higher order cognitive processes such as inhibition and goal maintenance. These two presented studies [81, 82] suggest that higher CRF children are more efficient in the allocation of resources in support of cognitive control operations.

Additional evidence may be derived from other investigations that have examined the neuroelectric system to investigate which cognitive processes occurring between stimulus engagement and response execution are influenced by CRF. Studies that examined the P3 component, a stimulus-elicited neuroelectric component involved in the allocation of attentional resources, have shown that higher CRF children have larger amplitude and shorter latency P3 response relative to their lower cardiorespiratory fit peers [21, 83]. Such findings indicate that higher CRF children allocate greater attentional resources and have faster cognitive processing speed relative lower cardiorespiratory fit children [21, 83]. Additional research also suggests that higher CRF children are related to greater flexibility in the allocation of attentional resources [81, 82].

At the biochemical level, investigations have shown that PA augments the synthesis of brainderived neurotrophic factor (BDNF), which enhances brain plasticity by changing the structure of the neuron and strengthening its signaling capability [84]. An increase in BDNF is associated with increases in the volume of the hippocampus as well as improved memory performance [85]. Induced by PA (among other factors), BDNF activation is also related with increased long-term potentiation and neurogenesis [84]. Long-term potentiation is shown to improve learning and memory by strengthening the communication between specific neurons [86]. Based on animal studies, the increase in neurogenesis is hypothesized to increase learning [76, 84].

Besides these physiological and psychological effects described above, PA practice and CRF improve students' behavior in the learning context, consequently increasing the odds of better

**Figure 1.** Simplified model of the relationship between physical activity, cardiorespiratory fitness and academic achievement. BDNF, brain-derived neurotrophic factor; FGF-2, fibroblast growth factor 2; VEGF, vascular endothelial

Physical Activity, Aerobic Fitness and Academic Achievement

http://dx.doi.org/10.5772/intechopen.71284

247

**Summary:** The mechanisms underlying the relationship between PA, CRF and AA are not yet clearly understood. There is evidence that PA and CRF can affect brain structure and function using a variety of neuroimaging tools. At a biochemical level, CRF enhances the synthesis of brain-derived neurotrophic factor (among other molecular and cellular processes). Increasing BDNF is associated with increases in the volume of the hippocampus and improved

concentration and achievement [56], which is directly related to AA.

memory.

growth factor.

**Figure 1** shows a simplify model of potential mechanisms for the relationship between PA, CRF and AA. PA may influence CRF. CRF, in turn, along with PA, are related with changes in brain structure, brain function and cognition. These changes may affect AA.

regulates its metabolic demands via blood flow to a particular region important for learning

To characterize PA-related differences in brain function, Davis et al. [81] used functional magnetic resonance imaging (fMRI) to investigate changes in the blood oxygen level dependent (BOLD) signal following PA intervention. Twenty sedentary, overweight children were randomized into an after-school PA intervention or a non-PA control group that lasted 14 weeks. Following the PA intervention, increased bilateral activation of the prefrontal cortex and decreased bilateral activation of the posterior parietal cortex was observed in the PA group relative to the non-PA control group. These differences in brain were elicited during tasks that tap inhibition, one aspect of executive control, indicating that the PA intervention affect brains function. A study, using fMRI, observed increased activation in prefrontal and parietal brain regions during early task blocks, and decreased activation during later task blocks in children with higher CRF relative to children with lower CRF [82]. As higher CRF children outperformed lower CRF children on aspects of the task requiring the greatest amount of executive control, higher CRF children appear more capable of adapting neural activity to meet the demands imposed by tasks that tapped higher order cognitive processes such as inhibition and goal maintenance. These two presented studies [81, 82] suggest that higher CRF children are more efficient in the allocation of resources in support of cognitive control operations.

Additional evidence may be derived from other investigations that have examined the neuroelectric system to investigate which cognitive processes occurring between stimulus engagement and response execution are influenced by CRF. Studies that examined the P3 component, a stimulus-elicited neuroelectric component involved in the allocation of attentional resources, have shown that higher CRF children have larger amplitude and shorter latency P3 response relative to their lower cardiorespiratory fit peers [21, 83]. Such findings indicate that higher CRF children allocate greater attentional resources and have faster cognitive processing speed relative lower cardiorespiratory fit children [21, 83]. Additional research also suggests that higher CRF children are related to greater flexibility in the alloca-

At the biochemical level, investigations have shown that PA augments the synthesis of brainderived neurotrophic factor (BDNF), which enhances brain plasticity by changing the structure of the neuron and strengthening its signaling capability [84]. An increase in BDNF is associated with increases in the volume of the hippocampus as well as improved memory performance [85]. Induced by PA (among other factors), BDNF activation is also related with increased long-term potentiation and neurogenesis [84]. Long-term potentiation is shown to improve learning and memory by strengthening the communication between specific neurons [86]. Based on animal studies, the increase in neurogenesis is hypothesized to increase

**Figure 1** shows a simplify model of potential mechanisms for the relationship between PA, CRF and AA. PA may influence CRF. CRF, in turn, along with PA, are related with changes in

brain structure, brain function and cognition. These changes may affect AA.

and memory.

246 Health and Academic Achievement

tion of attentional resources [81, 82].

learning [76, 84].

**Figure 1.** Simplified model of the relationship between physical activity, cardiorespiratory fitness and academic achievement. BDNF, brain-derived neurotrophic factor; FGF-2, fibroblast growth factor 2; VEGF, vascular endothelial growth factor.

Besides these physiological and psychological effects described above, PA practice and CRF improve students' behavior in the learning context, consequently increasing the odds of better concentration and achievement [56], which is directly related to AA.

**Summary:** The mechanisms underlying the relationship between PA, CRF and AA are not yet clearly understood. There is evidence that PA and CRF can affect brain structure and function using a variety of neuroimaging tools. At a biochemical level, CRF enhances the synthesis of brain-derived neurotrophic factor (among other molecular and cellular processes). Increasing BDNF is associated with increases in the volume of the hippocampus and improved memory.
