The new study shows that many teens fail to maintain adequate amounts of exercise and many adolescents continue this trend into adulthood.
Tracking exercise patterns over time among ethnic groups in the U.S. is rare, says Penny Gordon-Larsen, PhD, and colleagues. They tracked exercise and TV/computer habits among more than 13,000 adolescents of various ethnic groups in grades 7-12, following up to see if their habits changed as young adults (ages 18-26).
The results showed that too many teens skimp on exercise and that the trend worsens with age.
Since physical inactivity is a risk for later weight problems, understanding these behavioral trends, and promoting child and adolescent exercise, is important for achieving optimal adult health, they write.
"The vast majority of adolescents do not achieve five or more bouts of moderate physical activity per week, and continue to fail to achieve this amount of activity into adulthood," write the researchers in the November issue of the American Journal of Preventive Medicine.
Thirty minutes of moderate exercise on most, if not all, days of the week, is the recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine.
No more than two hours per day should be spent on TV, videos, or computer games, notes the study, referring to recommendations from the American Academy of Pediatrics.
Of the teens who worked out five or more times per week and had 14 or less hours of screen time, only 4% maintained this level of exercise as young adults. Thirty seven percent of these teens also continued to maintain less than 14 hours of screen time when they became adults.
Almost a third of these teens failed to maintain favorable levels of exercise as adults.
The study also showed a decline in the number of people who watched less than 14 hours of screen time per week from adolescence to adulthood, although they say that the decline was less dramatic.
"Across the teenage and adult years, close to half of the respondents spent more time watching TV or playing computer games than recommended," says Gordon-Larsen, in a news release.
Black and Hispanic teen girls particularly need to increase their activity levels, say the researchers.
"Significantly greater percentages of Hispanic (78%) and black females (79%) failed to achieve five or more bouts per week across both time periods [as teens and adults], compared with whites (68%)," they write.
Applying the study's findings to the general population, an average of more than 12 million teens failed to get at least five moderate exercise sessions per week and continued that poor activity level as adults.