We often hear that Americans don’t get enough exercise and spend too much time in front of screens. Studies have shown that most kids in the U.S. get less than the recommended 60 minutes of physical activity each day, and that physical activity declines from childhood to young adulthood. However, do all children become less active as they age? What can we learn from adolescents who do maintain an active lifestyle?

Tracking kids’ activity levels, TV viewing

To find out more, a team of researchers applied an innovative analytic approach to identify distinct trajectory patterns of kids’ physical activity over time, and examined the association of physical activity with participation in organized sports and time spent watching television. The researchers, including Trudy Burns, professor of epidemiology in the University of Iowa College of Public Health, tracked 537 children who were part of the Iowa Bone Development Study, one of the largest, long-term studies of bone health ever conducted.

The children were about 5 years old when they entered the study and were followed for 14 years. Their activity levels were measured with monitors, while information about sports participation and TV viewing was gathered using surveys.

Their results, published online May 18, 2015, in the Journal of the American Medical Association Pediatrics, showed four trends for moderate- to vigorous-intensity physical activity (MVPA): consistently inactive, consistently active, decreasing activity, and substantially decreasing activity. The majority of participants (52.9%) followed the pattern that started out active and became less so as they entered adolescence; many fewer (18.1%) followed a consistently active pattern.

Sports help keep kids active 

Results showed that the developmental pathways of healthy behaviors (high physical activity and low TV viewing) were associated. However, while low TV viewing was associated with high activity, unhealthy TV viewing was not associated with inactivity, indicating the need for further study. What was clear was that sport participation could be a critical way to avoid a consistently inactive pattern even though it did not necessarily guarantee an active lifestyle.

According to lead researcher and CPH alumna Soyang Kwon (PhD ’10), research assistant professor at Northwestern University, “although it is true that the majority of kids’ physical activity levels decrease during adolescence, it is encouraging and exciting to identify kids who maintain an active lifestyle. These results will be the basis of our future studies to learn what helps kids stay active throughout childhood.”

Lifelong habits are often set during childhood. Studies like this one help us understand how we can encourage children to reap the benefits of physical activity during childhood, and potentially, into adulthood.

The study team also included UI researchers Kathleen Janz, professor in the Department of Health and Human Physiology; Elena Letuchy, statistician in the Department of Epidemiology; and Steven Levey, professor in the Department of Preventive and Community Dentistry.

The research was supported by grants from the National Institutes of Health, the Roy J. Carver Charitable Trust, and Delta Dental of Iowa Foundation.