Because of the different exercise modes, the exercise intensity of the different groups as measured by HR differed (Table 2; F(2,64) = 4.926, P < 0.010, η2 = 0.133). The CE (t(45) = 27.270, P < 0.001, r = 0.98) and ME (t(35) = 17.750, P < 0.001, r = 0.95) significantly differed regarding average HR during the intervention when compared with the CON. Moreover, the average HR in the CE was significantly higher than that in the ME (t(43) = 4.696, P < 0.001, r = 0.58). We conducted both ANCOVA including participants’ average HR as covariates and ANOVA without this covariate. Both analyses yielded similar results regarding the effects on WM and fitness. For the Results section, we report the ANOVA without average HR as covariates. To compare the efficiency of the intervention programs, we analyzed the effects on cardiovascular and motor performance for all three groups.
Motor fitness had no significant effect on the cardiovascular fitness performance; therefore, we abstained from including covariates. With an average HR of 139 ± 9.1 bpm (Table 2), children of the CE group remained in the range of 60%–70% of HRmax (128–149 bpm).
For cardiovascular performance, we found a significant main effect for time (F(1,68) = 10.030, P = 0.002, η2 = 0.129) as well as a time–group interaction effect (F(2,68) = 4.432, P = 0.016, η2 = 0.115). There was no effect for the group (F(1,68) = 0.638, P = 0.531, η2 = 0.018). Only participants in the CE significantly improved their cardiovascular performance with a large effect (F(1,25) = 12.535, P = 0.002, r = 0.58) (Table 1 and Fig. 1). No significant changes could be observed in the ME (F(1,22) = 1.570, P = 0.223, r = 0.26) or the CON (F(1,20) = 0.002, P = 0.963, r = 0.01). The cardiovascular performance at the posttest did not differ between any of the groups: CE compared with CON (t(67) = −0.330, P = 0.743, r = 0.04), ME compared with CON (t(67) = −0.827, P = 0.411, r = 0.10), or CE compared with ME (t(67) = −0.534, P = 0.595, r = 0.07). Confirming the efficacy of the cardiovascular exercise intervention, children in the CE benefited significantly through their participation in the additional cardiovascular exercise regarding their cardiovascular fitness. This was not the case in the ME or the CON.
Cardiovascular fitness had no significant effect on the motor fitness performance; therefore, we abstained from including covariates. With an average HR of 125 ± 10.8 bpm, children of the ME remained in the range of 55%–65% of HRmax (117–139 bpm).
For the overall change in motor performance, we found a main effect for time (F(1,68) = 64.662, P < 0.001, η2 = 0.487) and a significant time–group interaction (F(2,68) = 4.786, P = 0.011, η2 = 0.123) (Table 1 and Fig. 2). There was no group effect (F(1,68) = 1.893, P = 0.159, η2 = 0.053). After the intervention, participants in all three groups showed significantly improved motor performance (CE: F(1,26) = 32.726, P < 0.001, r = 0.75; ME: F(1,22) = 40.571, P < 0.001, r = 0.81; CON: F(1,20) = 4.448, P = 0.048, r = 0.43), which can be partly attributed to developmental processes. However, the motor performance score of the ME was significantly higher than that of the CON at posttest (t(68) = 2.515, P = 0.014, r = 0.29), which was not the case for CE compared with CON (t(68) = 0.912, P = 0.365, r = 0.11). The difference between motor performance of CE and ME failed to reach significance (t(68) = 1.740, P = 0.086, r = 0.21).
Effects of Different Exercise Programs on WMP
For WMP, we found a significant effect of time (F(1,68) = 60.131, P < 0.001, η2 = 0.469) (Fig. 3). The interaction effect of group–time was also significant (F(2,68) = 12.377, P < 0.001, η2 = 0.267). There was no GROUP effect (F(2,68) = 0.221, P = 0.803, η2 = 0.006). Planned contrasts identified improvements in WMP from pre- to posttest in the two exercise groups with large effect sizes (CE: F(1,26) = 19.709, P < 0.001, r = 0.66; ME: F(1,22) = 62.718, P < 0.001, r = 0.86), but not in the CON (F(1,20) = 0.769, P = 0.391, r = 0.19).
In the postmeasurement, only the ME differed significantly from the CON (t(68) = 2.521, P = 0.014, r = 0.29), but not from the CE (t(68) = 0.746, P = 0.458, r = 0.09), nor did the CE differ significantly from the CON (t(68) = 1.887, P = 0.063, r = 0.22).
In order to deepen the understanding of the changes in WMP between the groups and to test the second hypothesis, a supplementary analysis was conducted. Therefore, the change of WMP (difference between post- and preperformance) was compared between the groups. There was a significant between-groups effect (F(2,65) = 11.873, P < 0.001, η2 = 0.268), which turned out to be significantly larger in the ME compared with CE (t(68) = 2.345, P = 0.022, r = 0.27), meaning that children in the ME benefited more strongly regarding their WMP from the exercise intervention than children in the CE. Furthermore, the difference of the ME turned out to be significantly larger compared with the CON (t(68) = 4.971, P < 0.001, r = 0.52), and the difference between CE and CON also gained significantly, meaning that children of the CE improved more regarding their WMP when compared with the CON (t(68) = 2.869, P = 0.005, r = 0.33).
We investigated the effects of a 10-wk cardiovascular versus motor exercise intervention program on cognitive performance in children age 9–10 yr using a WM task (LDS). The children performed the intervention in addition to their regular physical education regimen, which includes three lessons per week in Germany. Interventions took place three times a week for 45 min, avoiding uncontrollable holiday time. The main finding indicated that WMP of the 9- to 10-yr-old children benefited from both the cardiovascular and the motor afterschool exercise programs. Second, the results illustrate that WMP improved to a larger degree in response to the motor exercise intervention when compared with the cardiovascular intervention.
Effects of motor exercise on WM
The motor performance of the CE, ME, and CON showed significant increases from pre- to posttest, but to a different extent (effect size r: CE = 0.75, ME = 0.81, CON = 0.43). Despite the changes in the CON, which seems to reflect a possible developmental influence (17), the motor intervention seemed to be the most efficient. At postmeasurement, only the ME showed a significantly better motor performance compared with the CON.
The motor exercise intervention increased WMP by 49.2% (CON 3.8%), which turned out to be a large effect (r = 0.86). Our longitudinal results support a directional relationship between motor and cognitive domains and add evidence to initial cross-sectional and acute intervention results. This is similar to the findings by Rigoli et al. (33) showing that motor coordination (specifically aiming and catching skills) has an indirect effect on academic outcomes via WM.
Our results are also in line with an uncontrolled 8-wk longitudinal study of kindergarten children, which examined the causal link between motor-demanding exercise training and cognitive functioning (7). Their findings support a beneficial effect of coordinative exercise on inhibition in kindergarten children. However, Chang et al. (7) did not include a control group; thus, it is not clear whether the observed improvements in cognitive functions after coordinative exercise can be clearly attributed to the intervention.
The positive link between motor exercise and WM in our study may be explained from a neuroscientific and behavioral learning perspective. The motor exercise intervention was composed of both fine and gross motor body coordination exercises, for example, bimanual coordination tasks, in which the hands performed complex temporal and/or spatial tasks. Such motor tasks were shown to activate neural networks in frontal and parietal areas (34). Training of WM through motor tasks induced positive changes in WM, which similarly could be associated with increases in prefrontal and parietal activity (29). As previously shown in the findings by Serrien et al. (34) and Olesen et al. (29), similar brain regions seem to be involved in both complex motor tasks as well as WM tasks. Furthermore, an increased activation of the cerebellum during the execution of motor-demanding tasks is accompanied by an activation of the prefrontal cortex (for review, see ). Such an additional use of this brain region might also facilitate cognitive task processes in the prefrontal cortex (e.g., WMP) as suggested by Budde et al. (5).
Effects of cardiovascular exercise on WM
The 10-wk cardiovascular exercise intervention was designed to enhance cardiovascular fitness through running activities with low demand on complex motor functions. A cardiovascular fitness increase of 11.2% in the CE confirms the efficacy of our cardiovascular exercise intervention. Statistically, this increase represents a large effect (r = 0.58).
We found a large positive effect of the cardiovascular exercise intervention on WMP (r = 0.66). This is in line with our assumptions from the results of previous cross-sectional studies in children, which have demonstrated that cardiovascular fitness is positively related to cognitive functions in this age group (for review, see ). However, the reviewed studies are only cross-sectional in nature or the interventions include exercise types beyond cardiovascular exercise; thus, a causal relationship between cardiovascular fitness and cognitive functions cannot be assumed from these findings (e.g., [20,32]). Although longitudinal studies with adults across the lifespan revealed no consistent positive effect of cardiovascular exercise on cognitive functions like WM (35), we found a positive effect for preadolescent children. It is reasonable to assume that children’s cognitive functions might benefit from or mature faster through certain experiences like exercise because these can affect the ongoing cognitive and neural development at this immature stage (e.g., ).
The positive effects of cardiovascular exercise on WMP may be explained through general physiological and metabolic mechanisms related to improved cardiovascular function. Human data further reveal the possibility of changed steroid hormones (3) as well as changes in gray matter structures of 9- to 10-yr-old children (6) responsible for the observed positive effects of CE on WMP. The authors of the recently published cross-sectional study revealed that individual differences in cardiovascular fitness play a role in the childhood cortical gray matter structure, which is important for scholastic success.
Differential effects of cardiovascular exercise and motor exercise on WM
To our knowledge, this is the first report of a controlled longitudinal study that compared the effects of cardiovascular and complex motor exercises on children’s WM. WMP in both experimental groups improved after the intervention, suggesting that both exercise regimens are capable of improving WM. Indeed, both ME and CE demonstrated large effects in WMP with the ME having larger increases compared with the CE as was assumed in our second hypothesis. Additionally, the ME was the sole group whose WMP at postmeasurement was significantly larger compared with the control condition.
The ME exercised with a lower intensity (55%–65% of HRmax) compared with the CE (60%–70% of HRmax), which supports the assumption of differential brain mechanisms for the link of cardiovascular versus motor-demanding exercises and cognition seen in older adults (28). In the ME, the effects were achieved with a minor stimulation of the cardiovascular system. Because of the lower cardiovascular demands, the motor exercise intervention did not cause a significant increase in cardiovascular fitness in participants of the ME (3.6%). With an exercise intensity of 55%–65% HRmax, the lack of fitness gains observed in the ME may be due to a threshold phenomenon. According to Stratton (37), an exercise intensity equal to or greater than 60% of HRmax reserve is necessary for promoting fitness in young children.
Research with older adults provides possible explanations for these different mechanisms, e.g., different brain activation patterns after training of cardiovascular or motor exercise (42). Furthermore, with regard to brain volume of subcortical structures, motor exercise showed superior effects on volume of the hippocampus and the basal ganglia compared with cardiovascular exercise (28). These brain changes may be partly responsible for changed cognitive processes. On the behavioral level, these results provide some support for the argument that motor and cognitive development (particularly executive functions) are fundamentally interrelated (10,23). Motor training requires perceptual and higher level cognitive processes that are essential for action and ensuring anticipatory and adaptive aspects of postural control or coordination. Thus, motor training might facilitate the handling of information (41), which is important for cognitive processes.
The present study is subject to some limitations. First, it has to be mentioned that only WM was emphasized, which limits the scope of this study and allows for little generalization to other aspects of cognition. Consequently, future research should expand on these results by further examining other cognitive functions like attention or inhibitory control, which have previously shown to be linked to motor skills in cross-sectional studies (31). Furthermore, regarding our second hypothesis, we would have expected the ME to more clearly exhibit a WMP benefit in comparison with CE. This result was not clearly evidenced. However, we observed significantly higher WMP improvements in the ME compared with the CE. Moreover, only the ME showed significantly larger posttest scores in WM than the CON. Although academic performance has not been evaluated in this study, several studies have demonstrated a relationship between chronic exercise (for review, see ) as well as performance on WM tasks (33) and academic achievement in the areas of reading, mathematics, or language. An additional limitation is that no follow-up data have been collected to demonstrate the extent to which the effects of cardiovascular and motor exercise regimens were maintained over longer periods. Future research may gain additional insight into the underlying mechanisms contributing to the observed differences of cardiovascular and motor exercise intervention effects on cognition, beyond behavioral outcomes.
In conclusion, both cardiovascular and motor exercises improved WM in preadolescent children. Yet, WM seems to benefit more from motor exercise than cardiovascular exercise. To the best of our knowledge, this is the first controlled longitudinal study reported to reveal the directional nature of the relationship between cardiovascular and motor exercise regimens and cognitive functioning in school children. These findings carry significant implications for PA in schools, given the strong predictive ability of WM for academic achievement. Our results underline the need for additional exercise regimens in schools rather than reductions considering the dual advantages of academic achievement and physical health. Cardiovascular as well as motor exercise regimens should be equally addressed in schools because of the different underlying brain mechanisms, which might benefit more from a variety of activities. By establishing a causal link between exercise and cognition in children, educators and policy makers should carefully consider additional PA programs in schools. More interventional research that focuses on a possible neurobiological explanation for the exercise–cognition link is needed.
The authors thank the participating schools and all children involved in the study. In addition, the authors thank Dallas Hemphill for his native speaker corrections. The study was conducted as part of the Deutsche Forschungsgemeinschaft project BU1837/5-1.
The authors have no conflict of interest to declare. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:© 2016 American College of Sports Medicine
EXERCISE TYPES; BILATERAL COORDINATION; EXECUTIVE FUNCTIONS; COGNITION; PHYSICAL ACTIVITY; LONGITUDINAL INTERVENTION