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For many, New Year’s resolutions included exercising more often. Exercise can help improve the body’s function and feeling and has been proven to reduce health risks, like heart disease.

There may be a catch to that premise that exercise is inherently good: A surprising finding by Michigan State University researchers may impact some growth restricted individuals when they are physically active.

“We used a mouse model for growth restriction to determine if exercise improved cardiac function,” said David Ferguson, assistant professor in the MSU Department of Kinesiology. “We found growth-restricted mice didn’t respond to exercise. In fact, it worsened the mice’s health outcomes.”

The findings, published in the Medicine & Science in Sports & Exercise journal, could have impacts for millions around the world.

Growth restriction is most common for those who were born prematurely, with low birth weight (under five pounds), steadily trend lower than the 25th percentile on growth charts in early life or consistently receive poor nutrition. The World Health Organization estimated 149.2 million children under the age of 5 were “stunted” in growth due to malnutrition in 2020. Growth restrictions, such as this, can have a detrimental and long-lasting effect later in life, such as with increased likelihood of developing Type 2 diabetes, hypertension and other health challenges.

Research has also proven physical activity, or exercise, can improve cardiovascular functions and improve muscle strength.

So, when MSU researchers in the Neonatal Nutrition and Exercise Research Lab began studying growth-restricted mice, they expected to find similar results: Exercise is good.

Surprisingly, they found the opposite.

While the control group of mice expanded exercise capacity, the test groups consistently saw negative impacts to body function. For example, postnatal female mice that were growth restricted and that exercised had 11.45% lower ventricular volume and an 18% lower left ventricle area. The blood flow velocities in growth-restricted gestational and postnatal female mice were indicative of cardiac fibrosis. Cardiac fibrosis is the process by which the muscle of the heart becomes stiff, thick or scarred as a result of injury or disease and is often associated with heart failure.

“As adverse outcomes to physical activity are rare,” the August 2021 publication states, “it was not expected to occur.”

The researchers—which includes Kinesiology graduate students and alumni Eric Leszcynski, Ashley McPeek, Logan Pendergast, Joseph Visker and Ashley Triplett—are eager to conduct follow-up work.

Why did this happen?

It comes down to molecules and biological programming, says Ferguson.

“Protein is made up of amino acids, which are the building blocks for everything. They make your muscles, organs, skin. You need a certain amount of it in your diet; if you don’t get it, those tissues don’t grow,” he explained. “The body then responds to those lack of nutrients by slowing down. To survive, you need to not waste the precious calories you do have. Your body will be more inclined to be still, not move as much. With that, it hinders your heart’s ability to respond to exercise, so that when you do exercise, your body will respond negatively.”

The heart responds best when its pumping mechanism is flexible. The more individuals exercise, the more the organ gets stretched and increases capacity for more (and more strenuous) activities. For growth-restricted mice—and humans—when they can’t or don’t exercise, the heart doesn’t stretch and therefore becomes stiff, which can lead to cardiac fibrosis.

What can I do?

The results are not a one-size-fits-all finding. Physical activity is still beneficial—the key is being attuned to the body’s response.

Not everyone who was born prematurely or with low birth weight will experience the same effects, Ferguson says, but it is important for every individual to listen to how their own body is responding to exercise with blood pressure and heart rate.

It is also key to focus on health in early life. For caregivers of young children, Ferguson recommends a steady and increased amount of protein in diets and encourages children to exercise and move often.

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Related news: The power of movement

• DIABETES AND PHYSICAL ACTIVITY: In his work in the Motorsport Performance Lab, Ferguson is pioneering research to fuel athletic excellence—and drive change for diabetes in sport (2017, New Educator). The work is making a difference on the racetrack: With help from findings at Ferguson’s lab, motorsport driver Charlie Kimball, a Type 1 diabetic, was able to go four seconds faster on the track; a critical competitive-edge in sport racing (2018).
• HOW WE LEARN TO MOVE: A decades-long study at MSU examined questions such as: How do we grow and learn motor skills, such as jumping, throwing and running? What changes in our body, brain and environment influence our physical maturation and skills? (2021, New Educator)
• GETTING A BETTER WORKOUT—IN ISOLATION: Research from MSU Kinesiology Professor Emerita Deb Feltz has the answer for those who want to stay fit (and stay motivated to stay fit!), but are isolated from physical activity centers due to COVID-19 (2021, New Educator)
• STEREOTYPES & EXERCISE: Kinesiology alum Tayo Moss explored how perceived stereotypes impacted performance. The findings could impact the way we view teamwork. (2021, New Educator)
• MEET ASHLEY TRIPLETT: Triplett, one of the authors of the study, joined the MSU Kinesiology faculty in fall 2021 as an assistant professor. Her research focuses on the impact of anterior cruciate ligament (ACL) reconstruction on health-related factors—including physical activity participation. Learn more about Ashley and other new faculty who joined the College of Education.