UNIVERSITY PARK, Pa. — Physical activity in adulthood may depend on exercise conducted while growing, according to a new study led by Penn State researchers. The study, conducted in birds, is the first to demonstrate directly that experiences during development influence how efficiently adults use energy during movement.
Moving efficiently may influence how animals evolve, explained Jonas Rubenson , professor of kinesiology at Penn State. The hypothesis is that animals who use less energy for movement have more energy available for mating, foraging, hunting or other activities needed for survival. In a paper published in Proceedings of the Royal Society B, Biological Sciences , Rubenson and his team found that the energy used for movement may be more plastic than previously thought.
In the study, researchers added small weights to one leg of developing guinea hens — a close relative of chickens and bipedal like humans — to understand whether bearing weight would affect movement efficiency once the animals reached maturity. Birds who carried weight throughout development were able to move with the same amount of energy with or without the weight, while birds who did not carry a weight throughout development used 23% more energy when the same weight was strapped to their ankles.
“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.”
This finding could have significant implications for human health, Rubenson explained, as a widely accepted scientific hypothesis suggests that adult humans avoid movement if it requires a lot of energy or feels effortful. This could mean that adults who were not physically active as children may need to expend even more energy for the same movement — leading them to be less active as adults.
“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."
The researchers studied 12 guinea fowl from the age of two weeks until the age of 16 weeks, which is close to the age they reach full size. Six of the fowl wore lead bands that weighed 4% of the birds’ body weight on one leg, while the other six did not carry extra weight. All 12 birds were raised and exercised in the same manner, and at nine weeks of age, all the birds were trained to walk on a treadmill.
At 16 weeks of age, a flow-through metabolic chamber was placed on the treadmill, which captured how much carbon dioxide and water vapor each bird expelled and how much oxygen they consumed. These chambers are the gold standard for measuring how much energy an animal is expending on a task, according to the research team.
The 12 birds’ energy outputs were measured standing still, walking on the treadmill unweighted, and walking on the treadmill with the weight band on their leg. The researchers compared the oxygen consumption and carbon dioxide production of birds in each condition.
While standing still, all the birds used the same amount of energy. There were substantial differences, however, when the guinea fowl wore leg weights. Birds unaccustomed to carrying weight during the experiment expended 23% more energy with a leg weight compared to when they walked unloaded. Birds who had been carrying weight throughout the experiment adapted to carrying an additional load. They expended slightly less energy with a leg weight than when they walked unloaded, which Rubenson said 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. The researchers were also surprised that, on average, animals that chronically carried the limb weight did not use any more energy when wearing their bands compared to typical fowl moving without the extra weight. “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.”
Stephen Piazza , professor of kinesiology, contributed to this research, as did several of Piazza and Rubenson’s current and former graduate students.
Talayah Johnson, co-first author of this study, earned her master’s degree from Penn State and is currently a doctoral student at University of Pennsylvania. Kavya Katugam-Dechene, co-first author, earned her doctorate from Penn State and is currently a research assistant professor of biomedical and rehabilitation engineering at University of North Carolina at Chapel Hill. Ian Dechene, research staff on the project, is currently a software engineer. Roberto Castro is a current doctoral student at Penn State, advised by both Piazza and Rubenson.
This research was funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under award numbers R21AR071588 and R01AR080711 . The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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Proceedings of the Royal Society B Biological Sciences
Experimental study
Animals
Chronic limb loading results in remarkable load carriage economy in growing fowl
1-Jul-2026