The general view of physicians and other experts has been that the spike in obesity among teenagers had to do with too little exercise and too much TV-watching.

This new study says the opposite is true.

Kids have been at least as active in the last 10 years as they were earlier while TV viewing has decreased. The obesity epidemic began 10 years ago and continues—causing alarm about the immediate and long-term damage obesity causes among adolescents.  They face grim medical futures if this problem is not addressed. But, how? No one knows yet. The key will be in what’s new? What’s never happened before to this age group? Somewhere in those zones of their lives, there are clues.

Even though only one-third of this age group did the recommended amount of exercise, there is “no clear evidence” that they have become less active. (Emphasis added)

Daily attendance rates in physical education classes improved, classes which provided physical activity. (Emphasis added)

The study says, however, there are “considerable” differences in patterns by age, sex and ethnicity. (Emphasis added)

This study shows how complex this disease is.

A decade has gone by, and yet this may be one of the only studies which examines the question of what the activity level of teenagers is now as compared to the time before this obesity crisis began.

It is time to throw away all assumptions and begin again to find the root causes of this life-changing diagnosis.

Johns Hopkins Bloomberg School of Public Health

“Decreased physical activity may have little to do with the recent spike in obesity rates among U.S. adolescents, according to researchers at the Johns Hopkins Bloomberg School of Public Health. Prompted by growing concern that the increase was due to decreased physical activity associated with increased TV viewing time and other sedentary behaviors, researchers examined the patterns and time trends in physical activity and sedentary behaviors among U.S. adolescents based on nationally representative data collected since 1991. The review found signs indicating that the physical activity among adolescents increased while TV viewing decreased in recent years. The results are featured in the October 30 online issue of Obesity Reviews.

“Although only one third of U.S. adolescents met the recommended levels of physical activity, there is no clear evidence they had become less active over the past decade while the prevalence of obesity continued to rise,” said Youfa Wang, MD, PhD, MS, senior author of the study and an associate professor with the Bloomberg School’s Center for Human Nutrition and the Department of International Health. “During the recent decade, U.S. adolescents had greater access to TV, but significantly fewer of them watched TV for three or more hours per day. In addition, daily physical education attendance rates improved along with the use of physical education class in engaging in physical activity. However, there are considerable differences in the patterns by age, sex and ethnicity.” (Emphasis added)

Source: Johns Hopkins Bloomberg School of Public Health News Release, November 2, 2009

Primary Source: Obesity Reviews, Online edition, October 30, 2009