“Making the world a fitter place” is the modest motto of one of the world’s largest fitness chains, Fitness First. Indeed, in Germany, the number of fitness club members has increased from 4.7 million people in 2004 to 8.5 million people in 2013. Social consciousness in relation to health and fitness seems to be growing and this is important given our culturally ‘advanced’ educational, occupational, and leisure settings where sitting for most of the day has tended to replace active movement and active physical work. Despite valiant efforts to make the world a fitter place, Fitness First and other club managers, sporting organisations, and government officials are no doubt aware that only 34% of European young people aged 11 – 15 years old meet the recommended physical activity level guidelines (WHO, 2014).  Considering the decrease in physical activity levels in children (YRBS, 2010) and the fact that patterns of reduced physical activity established in childhood can be difficult to change as children develop throughout adulthood (Telama et al., 2005), we believe it is particularly important to study the effects physical fitness and acute bouts of exercise on the physical health and well-being of children.

Children need at least 1 hour of physical activity each day and, ideally, muscle strengthening activity (e.g., sit ups, push ups, and resistance exercises) at least 3 days a week.  In our efforts to make the world a fitter place we recently conducted a fascinating study with a group of teenagers. We were interested in the effect of physical fitness and acute bouts of exercise on cognitive performance and brain activity. Extensive research has highlighted the benefits of regular exercise for cognitive performance (Colcombe and Kramer 2003, Royall et al. 2002). Higher fitness levels in pre-adolescent children have been linked with superior cognitive performance (Hillman et al., 2005, 2009). In addition to fitness level, acute bouts of exercise (e.g., 20 minutes cycling or running) and exercise programmes across several weeks have been found to increase cognitive performance, regardless of prior exercise regimes (Zervas et al. 1991, Tuckman and Hinkle 1986, Hinkle et al. 1993, Davis et al. 2007).

However, less is known about the underlying biological and electrophysiological mechanisms associated with the beneficial effects of exercise on cognition. Animal models suggest that an increase in regional blood flow (Endres et al. 2003), promotion of brain vascularization (Pereira et al. 2007), an increase in levels of brain-derived neurotrophic factor (BDNF), as well as up-regulation of genes associated with cellular plasticity (Vaynman and Gomez-Pinilla 2006) may in part explain the beneficial effects of exercise on cognitive performance. We were particularly interested in the brain electrical signature associated with the effects of both physical fitness and acute bouts of exercise. Specifically, we examined the idea that physical fitness and acute bouts of exercise may increase the coherence of electrical brain dynamics, and this in turn may help to explain why physical fitness and acute bouts of exercise support better cognitive performance.

Notably, it is thought that neurons that ‘fire together wire together’ and that synchronous firing of neurons mediate the interaction between different neuronal assemblies (Schnitzler and Gross 2005). We used electrophysiological methods to measure EEG coherence. EEG coherence measures can be interpreted as the degree of synchronization of EEG oscillations across brain regions (Nunez, 1981). Changes in EEG coherence as a function of acute exercise and fitness may be an important mechanism underlying the beneficial effects of exercise on cognitive performance.

Our study used the following method. During a regularly scheduled physical education class, the physical fitness level of 30 students was assessed via individual maximal exercise performance on a stationary bike. The students (aged between 13 and 14) were then categorised into two groups – “fit” and “unfit”. Over the following two weeks each student came to the lab twice to perform a cognitive test while their EEG was measured. One EEG measurement session followed a 20-min bout of moderate intensity exercise and one followed a 20-min period of rest.

The cognitive performance task used in our study was a modified version of the Erikson flanker task (Eriksen and Eriksen 1974, Ruchsow et al. 2005). In the Go/NoGo version of the task, participants respond to specific target letters presented on a computer screen (B and U), but withhold the response to other letters (D and V). The flanking letters are either congruent and indicate a compatible response to the target letter, or are different and indicate an incompatible response.

We observed that both fitness levels and acute physical exercise had an effect on how quickly the teenagers responded to the Erikson flanker task, and the number of errors they made. More specifically, the fitter teenagers were significantly faster following 20 minutes of exercise, relative to 20 minutes of rest. Furthermore, unfit teenagers made more errors during the NoGo trials relative to the Go trials, following 20 minutes of rest. Finally, relative to their fitter peers, unfit participants had higher levels of lower alpha, upper alpha and beta coherence in the resting condition for no-go trials, possibly indicating a greater allocation of cognitive resources to the task demands. The higher levels of alpha coherence are of particular interest in light of its reported role in inhibition and effortful attention.

One interpretation of our results is that the unfit group was exerting a greater amount of effort than the fit group. Higher fitness levels may have facilitated greater cortical efficiency, particularly when the flanker task was performed after the resting condition, with fewer cognitive resources needed to maintain performance in comparison with unfit individuals. Interestingly, we found that group differences were less pronounced after a bout of exercise, which suggests that acute exercise might improve cognitive performance efficiency in less fit individuals. This interpretation is consistent with the finding that unfit, but not fit, adolescents had higher error rates for NoGo relative to Go trials following a rest period, whereas following acute exercise, there were no differences in error rates between groups.

Overall, unfit adolescents may perform cognitive tasks at the same level as fit participants in certain conditions (exercise condition, Go trials). However, in situations where attentional demands are high, relatively higher levels of coherence were coupled with higher error rates in the unfit group. The results suggest that physical fitness and acute exercise may enhance cognition by increasing functionality of the attentional system in adolescence. The present study therefore highlights the importance of intervention programs providing physical exercise for adolescents, which may improve attention and cognitive performance at school and in everyday life.

Let’s get out and play and make the world a fitter place!

Michael Hogan, Méadhbh Brosnan (LinkedIn) and Nicola Hohensen (somewhere between Berlin, Germany and Galway, Ireland!).

Originally published Oct 18, 2014 in ‘In One Lifespan’ @ PsychologyToday.com

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