The secret to easier exercise as an adult may start in childhood

A surprising new study suggests that staying active while growing up could make exercise easier and less exhausting for the rest of your life.

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."

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."

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.