A new study finds that general activity levels among children and teens is lower than previously thought and that 19-year-olds are essentially as inactive as 60-year-olds. In fact, the only activity increases found throughout the lifespan are in young adults after the age of 20. Then, starting at age 35, activity levels tend to decline through midlife and older adulthood.
For the study, conducted by Johns Hopkins Bloomberg School of Public Health, 12,529 participants wore tracking devices for seven straight days, allowing researchers to identify different times throughout the day when activity levels were highest and lowest, across age groups and between males and females.
The findings come amid growing concern that exercise deficits are contributing to the growing obesity epidemic, particularly among children and teens.
“Activity levels at the end of adolescence were alarmingly low, and by age 19, they were comparable to 60-year-olds,” said the study’s senior author, Dr. Vadim Zipunnikov, assistant professor in the Bloomberg School’s Department of Biostatistics.
“For school-age children, the primary window for activity was the afternoon between two and six P.M. So the big question is how do we modify daily schedules, in schools for example, to be more conducive to increasing physical activity?”
The researchers used data from the National Health and Nutrition Examination Survey from the 2003-2004 and 2005-2006 survey cycles. Participants (51 percent female, 49 percent male) wore tracking devices for seven straight days, removing them for only bathing and at bedtime. The devices measured how much time participants were sedentary or engaged in light or moderate-to-vigorous physical activity.
The findings were divided into five age groups: children (ages six to 11); adolescents (ages 12 to 19); young adults (ages 20 to 29); adults at midlife (ages 31 to 59); and older adults (age 60 through age 84).
Activity among participants in their 20s — the only age group that saw an increase in activity levels — was spread out throughout the day, with an increase in physical activity in the early morning. This rise in activity may be due to starting full-time work and other life transitions.
For all age groups, men generally had higher activity levels than women, particularly high-intensity activity, but after midlife, these levels dropped off sharply compared to women. Among adults 60 years and older, males were more sedentary and had lower light-intensity activity levels than females.
The findings confirm that recommended guidelines for activity levels are not being met. For example, the World Health Organization (WHO) recommends at least 60 minutes of moderate-to-vigorous physical activity a day for children ages five to 17 years. The researchers found that more than 25 percent of boys and 50 percent of girls ages six to 11 and more than 50 percent of male and 75 percent of female adolescents ages 12 to 19 had not met the WHO recommendation.
The researchers say there is a growing consensus for the benefits of reducing sedentary behavior and increasing even low-intensity levels of physical activity.
“The goal of campaigns aimed at increasing physical activity has focused on increasing higher-intensity exercise,” Zipunnikov said. “Our study suggests that these efforts should consider time of day and also focus on increasing lower-intensity physical activity and reducing inactivity.”
The findings are published online in the journal Preventive Medicine.