The effects of physical activity extend beyond the immediate period of movement, according to a new study published in the Proceedings of the National Academy of Sciences. Researchers from Virginia Tech, in collaboration with the University of Aberdeen and Shenzhen University, have discovered that engaging in physical activity contributes to the total energy expenditure each day without prompting the body to conserve energy in other areas.
This finding is significant because while the health benefits of increased physical activity are well-documented, there is less understanding of how exercise impacts an individual’s “energy budget,” or the allocation of energy to various bodily functions. The study aimed to explore whether the energy budget functions like a fixed salary, where energy is redistributed to cover the cost of movement, or like a flexible, commission-based system that allows for increased energy expenditure.
Understanding the Energy Budget
To investigate this, researchers assessed the total energy expenditure, or the total calories burned in a day, among participants with varying levels of physical activity. The study involved 75 participants aged 19 to 63, whose physical activity levels ranged from sedentary to ultra-endurance running.
Participants consumed isotopes of oxygen and hydrogen, and their urine samples were collected over two weeks. The isotopes allowed researchers to measure the difference in carbon dioxide production, which correlates with energy expenditure. Physical activity was tracked using a small sensor worn at the waist, capturing motion in multiple directions.
“Our study found that more physical activity is associated with higher calorie burn, regardless of body composition, and that this increase is not balanced out by the body reducing energy spent elsewhere,” said Kevin Davy, professor in the Department of Human Nutrition, Foods, and Exercise and the principal investigator of the study.
Key Findings and Implications
The study revealed that instead of conserving energy in one area to compensate for calories burned through physical activity, the body continues to function at its usual rate. This means overall energy use rises in direct response to increased movement. For instance, the energy used for basic functions like breathing, blood circulation, and temperature regulation remains stable, indicating that the body does not “cancel out” the extra calories burned through activity.
“Energy balance was a key piece of the study,” said Kristen Howard, senior research associate at Virginia Tech and the article’s lead author. “We looked at folks who were adequately fueled. It could be that apparent compensation under extreme conditions may reflect under-fueling.”
The research also established a clear link between higher activity levels and reduced sedentary time. In essence, more physically active individuals are less likely to spend prolonged periods being inactive. This supports the notion that increased movement correlates with higher energy expenditure, challenging previous uncertainties among experts.
Future Research Directions
While the study supports the additive model of energy expenditure, the researchers acknowledge the need for further investigation. “We need more research to understand in who and under what conditions energy compensation might occur,” added Davy. This highlights the complexity of the human energy budget and the potential for varied responses among different individuals and conditions.
As the scientific community continues to explore the intricate dynamics of energy expenditure, this study provides a pivotal step in understanding how physical activity influences daily energy use. It underscores the importance of maintaining an active lifestyle for optimal health and challenges previous assumptions about the body’s energy conservation mechanisms.
