Look at a group of kids, and you’re going to see many different shapes and sizes.
Does it make a difference in their impulse control or ability to concentrate? What if they are the same weight, but one has more fat than the other? Does their fitness level make a difference in such abilities?
New research from Northeastern University suggests that both body composition and fitness level relate to inhibitory controls, but do so independently and uniquely
“We found that greater aerobic fitness was associated with better inhibitory control,” said Kellyn Carlson, a Ph.D. student at Northeastern’s Institute for Cognitive and Brain Health who led the study. Inhibitory control is the ability to suppress a response or actively ignore irrelevant distractions
“Body fat relates differently,” Carlson continued, “with more impulsive, but not more accurate, responses in tests.”
The study, which involved roughly 100 pre-adolescent children, was published in July in the journal Scientific Reports.
Researchers first measured participants’ body composition using a Dual-Energy X-ray Absorptiometry, or DEXA scanner, a medical imaging device. Unlike the more typical measure of body mass index, a measure of weight relative to height, the DEXA scanner measures and is able to categorize the body’s mass in terms of lean tissue such as muscle tissue and organs, as well as fat, bone, and water. This enables the researchers to isolate body fat and lean tissue as variables and measure their individual impacts on inhibitory control.
It is the “gold standard measure,” Charles Hillman, Michele and Anthony Manganaro distinguished professor and director of the institute, said of the DEXA.
Hillman noted that measuring body composition with the scanner rather than using BMI is particularly useful for analyzing children who are still growing.
“Some kids have spurts where they grow really tall over a certain amount of time, or they put on a lot of weight before they grow,” Hillman said. “There’s not a set trajectory, they’re moving targets.”
Researchers including Lauren Raine, assistant professor of physical therapy, movement, and rehabilitation sciences and medical sciences, then evaluated each child’s aerobic fitness, or how well the body uses oxygen to produce energy, through a graded exercise test. This test evaluates how efficient the participant is at using oxygen during exercise, calculating the amount of oxygen a participant inhales and how much carbon dioxide they exhale over the course of an increasingly strenuous session on a treadmill. Because the researchers were able to isolate each child’s lean body mass, they were able to focus on the lean tissue and its ability to use oxygen and contribute to aerobic fitness rather than the whole body’s use of oxygen.
“The idea is that fat-free mass, muscle, is what is metabolically consuming the oxygen,” when under maximum stress, Hillman explained. Fat, while a metabolically demanding tissue, is not consuming the oxygen in such a situation, he added
On the second day, the researchers evaluated the participants’ inhibitory control
To test this, participants were given what researchers called a “Go” task and then a “No-Go” task. The participants wore electroencephalogram headsets on their heads so that researchers could measure their brain activity during the tests
In the “Go” test, participants were shown either a picture of a tiger (80% of the time) or a lion (20% of the time) and asked to press a button when they saw the lion.
“Where we’re using 9- and 10-year-olds, we’re looking for something that’s not going to give them any emotional response,” Carlson said, laughing, while explaining the lion-and-tiger choice. “If you see the images of them, they’re very friendly looking lions and tigers.”
The test was repeated over 100 times, effectively training the children to respond more automatically when shown a lion.
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For the “No-Go” test, the researchers switched the instructions, asking the participants to press a button when they saw the tiger.
“Withholding that button press when they see a lion is very hard because we both make it 80% of the time that they’re pressing the button, and they had previously seen the lion and want to press the button for the lion,” Hillman said.
The researchers found that children who had higher fitness levels, meaning their bodies used oxygen during heavy exercise more efficiently, were also more accurate in the No-Go test, demonstrating better inhibitory control. Children with increased fitness levels also dedicated more brain activity to both the Go and No-Go tests than children who were less fit, the researchers found
In contrast, children who had more body fat reacted more impulsively to the No-Go test but did not improve their accuracy compared with leaner children, according to the research
The results demonstrate that fitness and body composition each relate to inhibitory control uniquely and independently, Carlson said
“We know being fit and being lean is important for all kids and it’s good for your health and all those things, but we really don’t know what that means for brain health in kids in terms of how they operate together or independent of one another,” Hillman added. “This gets us closer to answering that question.”
