There have been plenty of studies regarding the effect of physical exercise and learning, and we also know that having a fit and healthy body can help with resilience – we mention this in our psychology book, too. This new study adds to this knowledge base based on the analysis of… saliva.
From the press release:
“Get some exercise!” It’s one suggestion adults frequently hear when they complain about stress in their lives. Exercise helps relieve stress. But does this also apply to children? Does exercise help them manage the pressures to achieve at school? A research team led by Dr. Manuel Hanke and Dr. Sebastian Ludyga from the Department of Sport, Exercise and Health recently examined the effect of physical activity on children’s stress levels. Their findings appear in the Journal of Science and Medicine in Sport.
For their study, they had 110 children between the ages of 10 and 13 wear a sensor tracking their daily movement over the course of a week. They then brought the participants into the lab on two separate occasions to complete a stressful task and a non-stressful control task (see the box). The researchers tested the children’s physical stress reaction via the concentration of the stress hormone cortisol in their saliva.
Less cortisol in active children
“We wanted to determine whether physical activity makes children more resilient under laboratory-controlled circumstances,” explains project director Sebastian Ludyga. The results showed that the participants who got more than an hour of exercise per day, as the World Health Organization (WHO) recommends, did in fact produce less cortisol in the stress task than the children who were less active.
“Regularly active children seem to have a reduced physiological stress reaction in general,” notes Manuel Hanke, lead author of the study. Even in the control task, which involved an unfamiliar situation, making it still somewhat unsettling for the participants, there was a difference in cortisol levels between more and less active children — though overall cortisol levels were lower than in the stress task.
Stress hormone levels increase during exercise
One possible explanation for this finding could be that cortisol levels also increase during exercise, says Sebastian Ludyga. “When children regularly run, swim, climb, etc., the brain learns to associate a rise in cortisol with something positive. The body’s reaction always has a cognitive component as well: this positive association helps to prevent the concentration of cortisol from rising to too high a level in exam situations as well.”
Besides their analysis of the saliva samples, the researchers also examined cognitive reactions to the stress task by recording participants’ brainwaves via electroencephalogram (EEG). The team plans to analyze these data next. “Stress can interfere with thinking. Some of us are familiar with this in its most extreme form — a blackout,” Hanke explains. The team now aims to determine whether physical activity also has an influence on these cognitive effects of stress.
Methodology
For their study, the researchers used the Trier Social Stress Test for Children: the participants had to read a story with an open ending, then had five minutes to prepare before using their notes to tell the rest of the story for a jury. What they didn’t know in advance was that the preparation time was intentionally kept so short so that it would not be sufficient. After about a minute, their notes were mostly exhausted but they still had to fill five minutes and think something up on the spur of the moment. This task was followed by a seemingly simple arithmetic task in which participants were asked to repeatedly reduce a number in the high three digits by a certain value over the course of five minutes. The stress in this task is primarily caused by errors, which require the participant to restart the task from the beginning. In the control task, which was conducted on a separate occasion, the children also had to read a story, but they then discussed general questions about the story with a researcher without any pressure to perform. In both sessions, the researchers took saliva samples at regular intervals before and after the tasks in order to measure cortisol levels.
Abstract of the study:
Objectives
High reactivity to psychosocial stress during childhood increases the risk of future psychological and physiological disorders. The main objective of this study was to investigate associations between children’s moderate-to-vigorous physical activity (MVPA) and physiological and psychological reactions to acute psychosocial stress.
Design
Randomized cross-over study comparing two groups.
Methods
After a 7-day accelerometer-based measurement of MVPA, 110 children aged 10–13 years (48 female) were categorized into a low (<30 min/d) or a high MVPA group (>60 min/d). On separate laboratory appointments, participants completed the Trier Social Stress Test for Children (TSST-C) and a non-stressful control task in randomized order. Stress reactivity was assessed from saliva cortisol, heart rate variability and self-reported anxiety.
Results
In repeated measures analyses of variance, main effects of condition indicated higher stress reactivity in the TSST-C compared to control for cortisol and anxiety, with more pronounced effects in girls compared to boys. Differences in heart rate variability disappeared after controlling for confounding variables. No interactions with MVPA were found. A main effect of MVPA indicated generally lower cortisol reactivity in the high compared to the low MVPA group.
Conclusions
The TSST-C is suitable for induction of psychosocial stress in the laboratory, but sex-specific differences have to be considered. Children who met the WHO recommendations for MVPA exhibited generally lower endocrine reactivity to both laboratory tasks combined, underlining the potential role of regular physical activity in the regulation of the stress response in early developmental stages. Further studies are necessary to ascertain causal associations.