How much energy your body needs to move as an adult could be influenced by how active you were during childhood. A new study led by researchers at Penn State suggests that physical activity early in life may have lasting effects on movement efficiency. Using birds as a model, the scientists provided the first direct evidence that experiences during development can change how much energy animals expend when moving as adults.
According to Jonas Rubenson, a professor of kinesiology at Penn State, the ability to move efficiently could play an important role in animal evolution. Animals that spend less energy getting around may have more resources available for essential activities such as finding food, hunting, and reproducing. The findings, published in Proceedings of the Royal Society B, Biological Sciences, suggest that the energy demands of movement are more adaptable than scientists previously believed.
To investigate, the researchers attached small weights to one leg of young guinea fowl, birds closely related to chickens that walk on two legs like humans. They wanted to determine whether carrying extra weight during development would change how efficiently the birds moved once they matured.
The results revealed a striking difference. Birds that grew up carrying the weights could walk with the added load without expending additional energy. By comparison, birds raised without weights required 23% more energy when the same load was attached to their legs.
“This study showed how limb loading — the application of mechanical stress on arms or legs, typically through weights or exercise — during development can help an animal save energy during movement throughout its lifespan,” said Rubenson, senior author of the study. “This is one of the first studies to indicate that animals’ behaviors and environments in youth can affect how effortful moving is as adults.”
Why Childhood Exercise Could Matter for Lifelong Health
Although the experiment involved birds, the findings raise important questions about human physical activity. One widely accepted scientific hypothesis proposes that people tend to avoid movement when it feels physically demanding or requires substantial energy.
If early activity influences movement efficiency in humans as it does in these birds, people who were less active during childhood might need to expend more energy to perform the same movements as adults. That additional effort could make them less inclined to exercise, potentially reinforcing a pattern of inactivity.
Rubenson believes the discovery could have broad implications for public health, particularly as children today are generally less physically active than those in earlier generations.
“Overall, children in the U.S. today are much less active than previous generations,” Rubenson said. “This study suggests that more exercise through play and exercise during childhood could make it easier for people to remain or become more active as adults. If people do not need to exert as much energy to move as adults, then exercise — and all its health benefits — will be more accessible to them. This could have implications for many aspects of our nation’s well-being, from heart health to mental health.”
How Researchers Tested the Effects of Early Exercise
The experiment followed 12 guinea fowl from two weeks of age until they reached 16 weeks, when the birds were approaching their full adult size.
Half of the birds wore lead bands on one leg, with each band weighing 4% of the bird’s body weight. The remaining six birds developed without any added weight. Apart from this difference, all 12 animals experienced the same living conditions and exercise routines.
When the birds reached nine weeks of age, the researchers began training them to walk on a treadmill.
At 16 weeks, the team assessed their energy expenditure using a flow-through metabolic chamber fitted to the treadmill. This equipment measured the oxygen each bird consumed, along with the carbon dioxide and water vapor it released. According to the researchers, this approach is considered the gold standard for determining how much energy an animal uses during a particular activity.
Each bird was tested under three conditions: standing still, walking on the treadmill without added weight, and walking while wearing a weight band on one leg. By comparing oxygen consumption and carbon dioxide production across these conditions, the scientists could determine how the additional load affected energy use.
Early Training Produced a Surprising Energy-Saving Effect
The researchers found no differences in energy consumption when the birds were standing still. However, their responses changed considerably once they began walking with weights.
Birds that had not carried weights while growing up experienced a 23% increase in energy expenditure when walking with the added load compared with walking without it.
The birds that had worn weights throughout development showed a remarkably different response. Their bodies had adapted so effectively that walking with the extra load required slightly less energy than walking without it. This unexpected result surprised the research team.
“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,” Rubenson said.
Another unexpected finding emerged when the researchers compared the two groups. On average, birds accustomed to carrying weights throughout development used no more energy while walking with their bands than ordinary birds used when walking without any added weight.
Together, these observations suggest that experiences early in life can substantially influence how efficiently animals move as adults.
“This shows that animals — and this probably includes humans — can become more efficient based on their life experiences. So, when humans exercise regularly throughout our childhood and adolescence, it could build our capacity for exercise throughout our lives.”
The findings provide new evidence that physical activity during development can have lasting effects on the energy required for movement. Whether the same adaptations occur in humans remains to be established, but the research suggests a potential mechanism through which childhood exercise could help support physical activity later in life.
Research Team and Funding
Stephen Piazza, a professor of kinesiology at Penn State, also participated in the research, along with several current and former graduate students working with Piazza and Rubenson.
The study’s two co-first authors were Talayah Johnson and Kavya Katugam-Dechene. Johnson completed her master’s degree at Penn State and is now pursuing a doctorate at the University of Pennsylvania. Katugam-Dechene received her doctorate from Penn State and currently serves as a research assistant professor of biomedical and rehabilitation engineering at the University of North Carolina at Chapel Hill.
Other contributors included Ian Dechene, who worked as research staff on the project and is now a software engineer, and Roberto Castro, a Penn State doctoral student jointly advised by Piazza and Rubenson.
Funding was provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, part of the National Institutes of Health, through awards R21AR071588 and R01AR080711. The researchers are solely responsible for the study’s content, which does not necessarily reflect the official positions of the National Institutes of Health.
