Most parents hear the same advice on repeat. Get the kids outside, let them run, limit the screen time.
The reminders are familiar; the proof of what active childhoods actually buy them, years down the road, has been harder to come by.
A new study by Penn State kinesiology researchers, published in Proceedings of the Royal Society B, suggests that exercise during growth may permanently lower the energy cost of adult movement.
The work was done in guinea fowl, two-legged birds often used as a model for human walking.
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Trained birds carried an added load as adults without using any more energy than they did unloaded.
Birds raised without the weight burned 23 percent more energy with the same weight strapped to the ankle, according to the Penn State announcement.
Researchers tested the idea
The team followed 12 guinea fowl from the age of two weeks until 16 weeks, when they reach adult size. Six wore a lead band on one leg weighing about 4 percent of their body weight; the other six carried nothing.
All birds were raised and exercised the same way. From week nine, every bird trained on a treadmill. At 16 weeks, each bird walked inside a metabolic chamber that measured oxygen use.
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The chamber is a gold-standard way to work out how much energy a body is actually spending during movement.
"The birds became so efficient that they were not using any more energy to carry the weight than they needed to walk without the weight," said Jonas Rubenson.
He is a professor of kinesiology at Penn State and senior author of the paper.
The finding is the first direct experimental test of a longstanding question. Does a growing body learn to move more cheaply, and does that economy carry into adulthood? In these birds, the answer looked like yes.
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Why this may matter for children
The study is in animals, not people, and the sample is small. Human confirmation will take time and much larger work. But the biology is close enough that researchers are paying attention.
If a developing body sets its fuel economy partly through what it has to carry and how often it moves, inactive childhoods could leave adults paying a higher energy price for everyday activity.
Rubenson sees that price as a possible driver of a loop. If moving feels harder, adults do less of it, and the health benefits of activity slip further out of reach.
Regular exercise throughout childhood and adolescence may build the body's capacity for exercise later in life, he said in the Penn State release.
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The gap between what children should be doing and what they are doing is wide.
The World Health Organization estimates that about 80 percent of adolescents worldwide do not meet its physical activity recommendations, with girls less active than boys.
For children aged 6 to 17, the Centers for Disease Control and Prevention recommends at least 60 minutes of moderate-to-vigorous activity every day.
The guidelines call for vigorous aerobic activity, muscle-strengthening work and bone-loading moves such as running or jumping on at least three days a week.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.