Early physical activity may shape lifelong movement efficiency

Jonas Rubenson, a professor of kinesiology at Pennsylvania State University, said the ability to move efficiently may play an important role in animal evolution. Animals that use less energy to move may have more resources available for essential activities such as finding food, hunting and breeding.

The study, published in Proceedings of the Royal Society B: Biological Sciences, suggests that the energy required for movement may be more adaptable than scientists previously believed.

To investigate, researchers attached a small weight to one leg of each of six young guinea fowl. The bird is related to the chicken and, like humans, walks on two legs. The team wanted to determine whether carrying extra weight during development would affect how efficiently the birds moved after reaching adulthood.

The results revealed significant differences. Birds that grew up carrying weights were able to walk with an additional load without using more energy. By comparison, birds raised without weights required 23% more energy when walking with the same load attached to their legs.

“This study showed how limb loading—applying mechanical stress to the arms and legs, usually through weights or exercise—during development helps conserve kinetic energy throughout an animal’s life,” said Rubenson, the study’s senior author. “This is one of the first studies to show that an animal’s behavior and environment when young can influence the difficulty of locomotion as an adult.”

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 is that people may avoid movement when it feels physically demanding or requires a great deal of energy.

If early-life activity affects locomotor efficiency in humans as it did in these birds, people who were less active during childhood may need to expend more energy to perform the same movements as adults. That additional effort could reduce the desire to exercise and reinforce patterns of inactivity.

Rubenson said the findings could have far-reaching public health implications, particularly because children today are generally less physically active than previous generations.

“Overall, American children today are much less active than previous generations,” Rubenson said. “This study suggests that getting more physical activity through play and exercise during childhood may make it easier for people to stay active or become more active as adults. If people didn’t have to expend as much energy exercising as adults, exercise and all its health benefits would be more accessible. This could impact many aspects of our nation’s well-being, from heart health to mental health.”

How researchers tested the effects of early exercise

The researchers followed 12 guinea fowl from two weeks of age until they reached adult size at 16 weeks.

Six birds wore a lead band on one leg. Each band weighed 4% of the bird’s body weight. The other six birds grew without the added weight. Aside from this difference, all 12 birds experienced the same living conditions and exercise habits.

When the birds reached nine weeks of age, researchers began training them to walk on a treadmill.

At 16 weeks, the team measured energy expenditure using a flow-through metabolic chamber attached to a treadmill. The device measured the oxygen consumed by each bird, along with the carbon dioxide and water vapor it released. According to the researchers, this method is considered the gold standard for determining how much energy animals use during specific activities.

Each bird was tested under three conditions: standing still, walking on a treadmill without additional weight and walking with a weight band attached to one leg. By comparing oxygen consumption and carbon dioxide production across the conditions, the researchers could determine how the added load affected energy use.

Early training produced unexpected energy savings

The researchers found no difference in energy expenditure when the birds were stationary. However, the two groups responded very differently once they began walking with added weight.

Birds that had not carried weights while growing up showed a 23% increase in energy expenditure when walking with added weight compared with walking without it.

Birds that carried weight throughout development adapted much more effectively. Walking with the extra load required slightly less energy than walking without the load. The research team said this unexpected result surprised them.

“Birds have become so efficient that they no longer expend more energy carrying their weight than it would take to walk without weight,” Rubenson said.

Another unexpected finding emerged when the researchers compared the two groups. On average, birds accustomed to carrying weight during development did not use more energy while walking with a band than normal birds that had grown up without additional weight.

Taken together, the observations suggest that experiences early in life can significantly affect how efficiently an animal moves as an adult.

“This shows that animals, and this probably includes humans, can become more efficient based on their life experiences. Therefore, if humans exercise regularly throughout childhood and adolescence, they may be able to increase their athletic performance throughout their lives.”

What the findings could mean for human exercise

The study provides new evidence that physical activity during development can have a lasting effect on the energy required for movement. It remains unknown whether humans develop the same adaptations, but the findings suggest a possible mechanism through which early-life exercise could support physical activity later in life.

Research team and funding

Stephen Piazza, a professor of kinesiology at Penn State, also participated in the study, along with several current and former graduate students who work with Piazza and Rubenson.

The study’s co-lead authors were Talayah Johnson and Kavya Katugam-Dechene. Johnson earned a master’s degree from Pennsylvania State University and is currently pursuing a doctoral degree at the University of Pennsylvania. Katugam-Dechene received a PhD from Pennsylvania State University and is currently a research assistant professor of biomedical and rehabilitation engineering at the University of North Carolina at Chapel Hill.

Other contributors included Ian Deschene, who served on the project’s research staff and is now a software engineer, and Roberto Castro, a doctoral student at Penn State who was co-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 content of their research, which does not necessarily reflect the official views of the National Institutes of Health.